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Part V

Department of LaborOccupational Safety and HealthAdministration

Dixie Divers, Inc.; Grant of PermanentVariance; Notice

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71242 Federal Register / Vol. 64, No. 243 / Monday, December 20, 1999 / Notices

1 The acronym for ‘‘self-contained underwaterbreathing apparatus’’ is ‘‘SCUBA.’’ The term‘‘SCUBA’’ refers to open-circuit diving equipmentalone, or to open-circuit, semi-closed-circuit, andclosed-circuit diving equipment combined. Theterm ‘‘rebreather’’ refers to semi-closed-circuit orclosed-circuit diving equipment alone or combined;this diving equipment recycles part or all of theexhaled breathing gas into the system that deliversthe breathing gas to the diver.

2 The abbreviation ‘‘O2’’ means ‘‘oxygen,’’ whilethe phrase ‘‘nitrox breathing-gas mixture’’ or theterm ‘‘nitrox’’ refers to a breathing-gas mixturecomposed of nitrogen and O2 in varyingproportions.

DEPARTMENT OF LABOR

Occupational Safety and HealthAdministration

[V–97–1]

Dixie Divers, Inc.; Grant of PermanentVariance

AGENCY: Occupational Safety and HealthAdministration, Department of Labor.ACTION: Grant of permanent variance.

SUMMARY: This notice announces thegrant of a permanent variance to DixieDivers, Inc. (Dixie). The permanentvariance is from the Occupational Safetyand Health Administration (OSHA)requirements for decompressionchambers during mixed-gas divingoperations, including paragraphs (b)(2)and (c)(3)(iii) of 29 CFR 1910.423 andparagraph (b)(1) of 29 CFR 1910.426.

The permanent variance coversrecreational diving instructors anddiving guides employed by Dixie. Usingboth classroom instruction and practicedives, recreational diving instructorstrain novice divers individually or insmall groups in recreational divingknowledge and skills, includingconventional diving procedures and thesafe operation of diving equipment.Dixie’s recreational diving instructorsaccompany students during practicedives, which vary in depth from a fewfeet of sea water (fsw) to 130 fsw, andlast between 30 minutes and one hour.Diving guides (who may also serve asrecreational diving instructors) leadsmall groups of trained sports divers tolocal undersea locations for recreationalpurposes; the guides select the divinglocations and provide the sports diverswith information regarding the dive site,including hazardous conditions and safediving practices. While leading divers toa dive site, the guides dive to amaximum depth of 130 fsw for periodsof 30 minutes to one hour.

The permanent variance specifies theconditions under which Dixie’srecreational diving instructors anddiving guides may conduct theirunderwater training and guiding tasksusing open-circuit, semi-closed-circuit,or closed-circuit self-containedunderwater breathing apparatus(SCUBA) supplied with a breathing gasconsisting of a high percentage ofoxygen (O2) mixed with nitrogen, andwithout a decompression chamber nearthe dive site. These conditions address:The requirements for SCUBAequipment, including carbon-dioxidecanisters, counterlungs, moisture traps,moisture sensors, carbon-dioxide and O2

sensors, and information modules;depth limits for diving operations; use

of nationally-recognized no-decompression limits and O2-exposurelimits; the O2 and nitrogen compositionof the breathing-gas mixture; proceduresand equipment for producing andanalyzing breathing-gas mixtures;emergency-egress procedures andsystems; management of diving-relatedmedical emergencies; procedures formaintaining diving logs; use ofdecompression tables and dive-decompression computers; and trainingrequirements for recreational divinginstructors and diving guides.DATES: The effective date of thepermanent variance is December 20,1999.FOR FURTHER INFORMATION CONTACT:Office of Information and ConsumerAffairs, Room N3647, U.S. Departmentof Labor, Occupational Safety andHealth Administration, 200 ConstitutionAvenue, NW, Washington, DC 20210,Telephone: (202) 693–1999.

Additional information also isavailable from the following Regionaland Area Offices:

Regional Office:

U.S. Department of Labor—OSHA, 61Forsyth St., SW., Atlanta, GA 30303,Telephone: (404) 562–2300

Area Offices:

U.S. Department of Labor—OSHA, 5807Breckenridge Parkway, Suite A,Tampa, FL 33610, Telephone: (813)626–1177

U.S. Department of Labor—OSHA, 8040Peters Road, Building H–100,Jacaranda Executive Court, FortLauderdale, FL 33324, Telephone:(954) 424–0242

U.S. Department of Labor—OSHA,Ribault Building, suite 227, 1851Executive Center Drive, Jacksonville,FL 32207, Telephone: (904) 232–2895

SUPPLEMENTARY INFORMATION:

I. Table of Contents

The following Table of Contentsidentifies the major sections under‘‘Supplementary Information.’’ Tounderstand fully the informationpresented in the following sections, werecommend reviewing the 40 conditionsof the permanent variance listed belowunder section VI.I. Table of ContentsII. BackgroundIII. Application for a Permanent VarianceIV. Comments to the Proposed Variance

Part 1. Comments to proposed section I(Background).

Part 2. Comments to proposed section II(Proposed Alternative).

Part 3. Comments to proposed section III(Rationale for the Proposed Alternative).

Part 4. Comments to proposed section VI(Issues).

Part 5. General comments to the proposedvariance.

Part 6. Our revisions to the proposedvariance.

V. DecisionVI. OrderVII. ReferencesVIII. Authority and Signature

II. BackgroundDixie Divers, Inc. (Dixie) applied for

a permanent variance from paragraphs(b)(2) and (c)(3)(iii) of 29 CFR 1910.423and paragraph (b)(1) of 29 CFR 1910.426under Section 6(d) of the OccupationalSafety and Health Act of 1970 (29 U.S.C.655) and 29 CFR 1905.11. Theseparagraphs address the availability anduse of decompression chambers duringmixed-gas diving operations.

Dixie operates six diving schools,either directly or as franchises. Theschools employ 18 skilled andexperienced recreational divinginstructors to train novice divers inrecreational diving knowledge andskills. The same 18 employees alsoserve as diving guides and lead groupsof sport divers to local diving sites forrecreational purposes. (We also refer torecreational diving instructors anddiving guides jointly as ‘‘employees’’ or,more generally, as ‘‘divers.’’)

As recreational diving instructors, theemployees train recreational divingstudents in conventional divingprocedures and the safe operation ofdiving equipment. The diving studentsmay use an open-circuit, semi-closed-circuit, or closed-circuit self-containedunderwater breathing apparatus(SCUBA) during these training dives. 1

SCUBAs supply divers with compressedair or a breathing gas consisting of ahigh percentage of oxygen mixed withnitrogen or another inert gas. 2

Dixie’s training program for divingstudents involves both classroominstruction and practice dives in whichthe employees accompany divingstudents to maximum depths of 130 feetof sea water (fsw). These dives lastbetween 30 minutes and one hour.During these dives, the recreationaldiving instructors provide underwater


71243Federal Register / Vol. 64, No. 243 / Monday, December 20, 1999 / Notices

3 ATA, as used here, is the partial pressure of aconstituent gas in the total pressure of a breathinggas. If the percentage of the constituent gas in thebreathing gas remains constant throughout a dive,its partial pressure or ATA, increases in proportionto increases in diving depth.

4 Filter-membrane systems produce nitroxbreathing-gas mixtures in two steps: First, theyroute air through filters to remove hydrocarbonsand other contaminants, then they pass thedecontaminated air through membranes thattransfer O2 across the membrane fibers at higherrates than nitrogen (hence, ‘‘de-nitrogenating air’’).As the rate of air flow across the membrane fibersincreases, the resulting ratio of O2 to nitrogen alsoincreases. Under the permanent variance, a filter-membrane system will reduce the hazardsassociated with producing high-O2 breathing-gasmixtures because the proportion of O2 in the systemwill never exceed 40 percent (40%).

instruction in, and allow the divingstudents to practice using, divingprocedures and equipment. Arecreational diving instructor may makeas many as three to four training divesa day while training diving studentseither individually or in small groups.

As diving guides, the employees leadsmall groups of trained sports divers tolocal undersea diving locations forrecreational purposes. The diving guideselects the diving location prior todeparture, and provides the sportsdivers with information regarding thedive site, including hazardousconditions and safe diving practices.The divers in the recreational divinggroups use open-circuit, semi-closed-circuit, or closed-circuit SCUBAs thatsupply compressed air or a nitroxbreathing-gas mixture during the dive.During these diving excursions, divingguides dive to a maximum depth of 130fsw for periods of 30 minutes to onehour. A diving guide may make as manyas five recreational diving excursions aday.

The places of employment affected bythis permanent variance are:Dixie Divers of Boca Raton, 8241 Glades

Road, Boca Raton, FL 33434Dixie Divers of Boynton Beach, 340

North Congress, Boynton Beach, FL33426

Dixie Divers of Deerfield, 1645Southeast 3rd Court, Deerfield Beach,FL 33441

Dixie Divers of Key Largo, 103400Overseas Highway, Key Largo, FL33037

Dixie Divers of Palm Bay, 4651 BabcockStreet, Northeast, Palm Bay, FL 32905

Dixie Divers of Panama City, 109B West23rd Street, Panama City, FL 32405

III. Application for a PermanentVariance

In its application for a permanentvariance (referred to as ‘‘varianceapplication,’’ ‘‘proposed variance,’’ or‘‘proposal’’), Dixie proposed analternative to the decompression-chamber requirements of paragraphs(b)(2) and (c)(3)(iii) of 29 CFR 1910.423and paragraph (b)(1) of 29 CFR1910.426. Paragraph (b)(2) of 29 CFR1910.423 requires that ‘‘[f]or any diveoutside the no-decompression limits,deeper than 100 fsw or using mixed gasas a breathing mixture, the employershall instruct the diver to remain awakeand in the vicinity of the decompressionchamber which is at the dive locationfor at least one hour after the dive(including decompression or treatmentas appropriate).’’ Paragraph (c)(3)(iii) of29 CFR 1910.423 requires that thedecompression chamber be ‘‘[l]ocatedwithin 5 minutes of the dive location,’’

while paragraph (b)(1) of 29 CFR1910.426 permits mixed-gas diving onlywhen a ‘‘decompression chamber isready for use at the dive location.’’ Thepurpose of having a decompressionchamber available and ready for use atthe dive site is to treat two conditions:(1) Decompression sickness (DCS),which may occur from breathing air ormixed gases at diving depths anddurations that require decompression;and (2) arterial-gas embolism (AGE),which may result from overpressurizingthe lungs, usually while ascendingrapidly to the surface during a dive.

In the variance application, Dixieproposed to implement alternativeprocedures that meet or exceed the levelof employee protection afforded byOSHA’s decompression-chamberrequirements. As an alternative to adecompression chamber, Dixieproposed to have its employees useopen-circuit, semi-closed-circuit, orclosed-circuit SCUBA supplied withbreathing-gas mixtures that contain afraction of O2 ranging from 22 to 40percent (22–40%) by volume, with theremaining breathing-gas mixtureconsisting of nitrogen. In addition, thepartial pressure of O2 in the nitroxbreathing-gas mixture would neverexceed 1.40 atmospheres absolute(ATA) 3 for any SCUBA. Dixie woulduse one of the following procedures toproduce nitrox breathing-gas mixtures:Mixing pure nitrogen with pure O2;removing O2 from air for mixing withpure nitrogen; adding pure O2 to air; orde-nitrogenating air (e.g., removingnitrogen from air using filter-membranesystems 4). According to the proposal,Dixie would: Analyze the O2 fraction inthe breathing-gas mixtures for accuracy;institute quality-assurance proceduresfor the analytic processes; and usebreathing-gas mixing systems rated forO2 service whenever the highest O2

fraction used in the mixing processexceeds 40 percent (40%). Dixie alsoproposed to restrict diving operations

under the variance to depths of 130 fswor less, and to use the nationally-recognized no-decompression limits andO2-exposure limits developed by theNational Oceanic and AtmosphericAdministration (NOAA) and DivingScience and Technology (DSAT).

By increasing the O2 partial pressureand decreasing the nitrogen partialpressure of the breathing-gas mixturecompared to air, and by restricting divesto no-decompression limits and depthsof 130 fsw or less, Dixie asserted thatboth the rate and the severity of DCSwould be no greater for its employeesthan for divers who operate according toparagraph (a)(2)(i) of 29 CFR 1910.401.In addition, Dixie contended that usingnationally-recognized O2-exposureprocedures would reduce the risk of O2

toxicity among its divers to the rateexpected among divers who usehyperbaric air.

Dixie proposed a number of otherrequirements to ensure that itsemployees remain within safe divingparameters, thereby avoiding DCS andAGE. These requirements includedlimiting the maximum carbon dioxide(CO2) level in the inhaled nitroxbreathing-gas mixture to 0.01 ATA.Dixie would control excessive CO2

levels as follows: By using pre-packedsorbent materials to absorb CO2 from theexhaled breathing gas prior torebreathing; by installing sensors fordetecting high CO2 levels or conditionsthat could result in high CO2 levels(such as moisture sensors to detectflooding in the breathing loop); and byusing counterlungs to serve as low-breathing-resistance reservoirs for thebreathing gas. In addition, Dixieproposed that its divers use aninformation module that provides themwith critical dive information (e.g., gaspressures, water-temperature); therequired information would vary withthe type of SCUBA. For rebreathers,visual or auditory warning deviceswould alert the diver to significantequipment problems (e.g., solenoidfailure, low battery levels) or deviationsfrom established diving parameters (e.g.,diverging from the planned O2 levels).Closed-circuit rebreathers would needto operate using a gas-controllerpackage, a manually-operated gas-supply bypass valve, and separate O2

and diluent-gas cylinders.Dixie proposed a number of other

conditions to safeguard its divers. Foremergencies involving SCUBAmalfunctions that could endanger diverhealth and safety (e.g., high CO2 levels),the proposed variance required thatDixie have a reliable ‘‘bail-out system’’available. The bail-out system wouldneed to provide a separate supply of



breathing gas to the second stage of theSCUBA regulator; when rebreathers areused, the bail-out system could delivera diluent supply of breathing gas to thesecond stage of the regulator. Otherprotective conditions, which refined oremphasized existing requirementscurrently specified in OSHA’sCommercial Diving Operations Standard(CDO Standard), included the following:Maintaining decompression tables anddiving logs at the dive site; assuring theavailability of personnel, facilities, andequipment to treat DCS and AGE; andproviding quality control of divertraining.

In summary, Dixie stated that theoccurrence and severity of DCS wouldbe minimal when its divers breathenitrox gas mixtures, while the risk ofAGE would be negligible when they usethe equipment and proceduralsafeguards specified in the varianceapplication. Consequently, divers whouse SCUBAs according to the proposedvariance would experience a level ofDCS and AGE that is equal to, or lowerthan, the level experienced byrecreational diving instructors who diveunder the conditions specified by theexemption to the CDO Standard at 29CFR 1910.401(a)(2)(i). These conditionsallow for the use of compressed airsupplied to open-circuit SCUBAs underno-decompression diving limits. Dixieasserted, therefore, that it should nothave to maintain a decompressionchamber at the dive location for itsrecreational diving instructors anddiving guides when it complies with theconditions specified in the varianceapplication.

In a Federal Register notice publishedon October 31, 1997, we provided the

public with a copy of Dixie’s varianceapplication (62 FR 58995). This noticeinvited interested parties, includingaffected employers and employees, tosubmit written comments, data, views,and arguments regarding the varianceapplication. In addition, the noticeinformed affected employers andemployees of their right to request ahearing on the variance application. Atthe request of several parties, weextended the comment period for thisnotice until March 2, 1998 in a FederalRegister announcement dated January 6,1998 (63 FR 579).

IV. Comments on the ProposedVariance

We received 123 comments inresponse to the two Federal Registernotices. Of this total, two comments(Exs. 2–98 and 2–115) wereduplications, and one comment (Ex. 2–112) consisted solely of a request toextend the comment period. (Exs. 6–1 to6–17 also were requests to extend thecomment period.) Two additionalcomments (Exs. 2–118 and 2–119)requested a hearing on the proposal. Wedenied these hearing requests becauseneither of the two requestors employedrecreational diving instructors, thesubject of this variance application.OSHA received 103 comments that weregeneral, non-specific endorsements ofthe variance application; the vastmajority of these comments varied onlyslightly in content. The remaining 15commenters submitted detailedcomments regarding the conditions andissues specified in the varianceapplication.

We have organized our discussion ofthe substantive comments to the

variance application into six parts.Comments concerning proposed sectionI (Background) are in Part 1, while Part2 consists of comments made about theconditions specified in proposed sectionII (Proposed Alternative). Part 3discusses comments made regardingproposed section III (Rationale for theProposed Alternative), and Part 4presents comments to the issues raisedin proposed section VI (Issues). Nocommenters addressed sections IV andV of the variance application, titled‘‘References’’ and ‘‘AdditionalInformation’’ respectively. Part 5consists of general and miscellaneouscomments. Throughout each of thesefive parts, we explain the actions we aretaking with regard to individualcomments or groups of comments. Thelast part, Part 6, describes refinements tothe proposed variance that we havemade in developing the permanentvariance; these refinements are basedupon our interpretation of the proposedconditions and our overall review of therecord.

We and other parties submittedadditional exhibits (Exs. 4, 4A, 5, and 7through 13) to the docket (see Table I).These exhibits, which contain scientificand technical information, providedadditional information we used inreplying to comments and discussingrevisions to the proposal. The principaltopics covered by the exhibits are: O2

toxicity; nitrogen narcosis;decompression procedures; theoperation and use of SCUBAs; andtreatment of diving-related medicalemergencies. Table I below providesspecific reference information on theseexhibits.

TABLE I.—REFERENCE INFORMATION ON EXHIBITS 4, 4A, AND 5 THROUGH 16

Ex.No. Reference information

4 D. J. Kenyon and R. W. Hamilton. ‘‘Managing Oxygen Exposure when Preparing Decompression Tables.’’ In: N. Bitterman and R. Lin-coln (eds.), Proceedings of the XVth Meeting of the European Undersea Biomedical Society, pages 72–77. European Undersea Bio-medical Society, September 1989.

R. W. Hamilton. ‘‘IV. Oxygen Physiology, Toxicity, and Tolerance.’’ In: R. W. Hamilton (author), Special Mix Diving: Part One, pages 25–38. Hamilton Research and Life Support Technologies, March 2, 1994.

4A R. W. Hamilton, R. E. Rogers, M. R. Powell, and R. D. Vann. The DSAT Recreational Dive Planner: Development and Validation of No-Stop Decompression Procedures for Recreational Diving. Diving Science and Technology, Inc., and Hamilton Research, Ltd., February28, 1994.

5 D. Richardson (ed.-in-chief). Proceedings of Rebreather Forum 2.0. Diving Science and Technology, Inc., 1996.7 R. W. Hamilton. ‘‘Tolerating Exposure to High Oxygen Levels: Repex and Other Methods.’’ Marine Technology Society Journal, volume

23, number 4, pages 19–25, December 1989.8 R. J. Kiessling and C. H. Maag. ‘‘Performance Impairment as a Function of Nitrogen Narcosis.’’ Journal of Applied Psychology, volume

46, number 2, pages 91–95, 1962.9 A. D. Baddeley. ‘‘Influence of Depth on the Manual Dexterity of Free Divers: A Comparison Between Open Sea and Pressure Chamber

Testing.’’ Journal of Applied Psychology, volume 50, number 1, pages 81–85, 1966.10 A. D. Baddeley, J. W. De Figueredo, J. W. Hawkswell Curtis, and A. N. Williams. ‘‘Nitrogen Narcosis and Performance Under Water.’’

Ergonomics, volume 11, number 2, pages 157–164, 1968.11 W. B. Wright. ‘‘Use of the University of Pennsylvania, Institute for Environmental Medicine Procedure for Calculation of Cumulative Pul-

monary Oxygen Toxicity.’’ U.S. Navy Experimental Diving Unit, Report 2–72, 1972.12 R. J. Biersner. ‘‘Request for Your Recommendation Regarding Acceptable Delay in Recompression Treatment of Diving-Related Medical

Emergencies.’’ Memorandum to Dr. Edward D. Thalmann, August 28, 1998.



TABLE I.—REFERENCE INFORMATION ON EXHIBITS 4, 4A, AND 5 THROUGH 16—Continued

Ex.No. Reference information

13 E. D. Thalmann. Letter to R. J. Biersner Responding to the Memorandum in Ex. 12, October 5, 1998.14 J. R. Clarke. CO2 Canister Test Parameters and Procedure at NEDU. Attachment to U.S. Navy Experimental Diving Unit E-mail Memo-

randum, November 22, 1999.15 J. R. Clarke. ‘‘Statistically Based CO2 Canister Duration Limits for Closed-Circuit Underwater Breathing Apparatus.’’ U.S. Navy Experi-

mental Diving Unit, Report 2–99, 1999.16 P. B. Bennett. ‘‘Nitrox?’’ Alert Diver, March/April, 1998.

Part 1. Comments to proposed section I(Background).

(a) The skills and experience of, andthe diving operations performed by, theapplicant’s divers (62 FR 58996, secondcolumn) received two comments. Bothcomments were primarily concernedabout Dixie’s recreational divinginstructors and diving guides engagingin diving activity beyond the scope ofthe proposed variance. The Associationof Diving Contractors, Inc. (Ex. 2–99)contended that recreational divinginstructors and diving guides ‘‘[engage]in services of a commercial nature,’’ andimplied that the conditions of thevariance application would allow themto extend their commercial divingactivities beyond the scope of theproposed variance.

The second commenter (Ex. 2–105)did not object to the proposed variancefor no-decompression dives to depths of130 fsw or less if they are ‘‘of aninstructional, training, or scientificnature and [do] not involve any form ofsalvage or underwater construction orrelated working tasks.’’ This commenterstated that the recreational diving must‘‘not encompass working dives (i.e.[,]salvage, construction). This is a very[important] distinction as thecommercial diving industry cannot bearthe financial burden imposed by theinsurance companies who would lumpprofessional recreational instructors inwith professional commercial divers.’’

In reply to these commenters, we notethat the permanent variance will notcover recreational diving instructors anddiving guides when they engage inactivities that do not involverecreational diving instruction anddiving guide activities. They mustcomply with our CDO Standard asappropriate, including thedecompression-chamber requirements,while engaged in these other activities.To ensure that Dixie understands underwhat conditions the permanent varianceapplies, we are specifying in Condition(1) (see below at section VI, titled‘‘Order’’) that the permanent variancecovers only recreational divinginstructors and diving guides who areemployees of Dixie Divers, Inc., and

then only while they are performing asdiving guides and recreational divinginstructors.

(b) The background information notedthat the applicant’s employees ‘‘maymake as many as three or four trainingdives a day while training divingstudents’’ and that ‘‘[a] guide may makeas many as five * * * excursions a day’’(62 FR 58996, second column). Thisbackground information elicited onecomment. This commenter (Ex. 2–109)stated that ‘‘[b]oth NAUI [NationalAssociation of Underwater Instructors]and PADI [Professional Association ofDiving Instructors], the two largestcertifying agencies in the U.S., limitinstructors teaching entry-level classesto no more than two dives per day witha single class.’’ The commenter alsonoted that ‘‘Dixie could hire moreinstructors, which would lessen theirtime in the water, decreasing [their]nitrogen exposure, lessening theirsusceptibility to DCS, thus obviating theneed for the variance.’’

The basis for the NAUI and PADIlimitations is unclear (e.g., do theselimits address diver safety or trainingeffectiveness). Nevertheless, we believethat adopting the no-decompressionprocedures for repetitive divingpublished in the 1991 NOAA DivingManual and by DSAT (Ex. 4A) as acondition of the permanent variancewill protect Dixie’s recreational divinginstructors and diving guides at least aswell as recreational diving instructorswho use compressed air supplied toopen-circuit SCUBAs under no-decompression diving limits specifiedin paragraph (a)(2)(i) of 29 CFR1910.401.

(c) The statement in this section that‘‘[e]mployees who use high-oxygenbreathing-gas mixtures will be able tomake more or longer repetitive-training[or] excursion dives than they wouldusing compressed-air open-circuitSCUBA’’ (62 FR 58995, third column)received one comment. This commenter(Ex. 2–109) disagreed with thisstatement, claiming that nitroxbreathing-gas mixtures may not reducesusceptibility to DCS and that ‘‘[w]eknow of no studies or evidence to show

that diving to limits on the nitrox tableswhile breathing nitrox produces a lowerincidence of DCS than diving to limitson air tables while breathing air.’’

We agree that the mathematicalprobability of DCS is similar for divesthat result in equivalent levels ofnitrogen saturation (e.g., dives made toa specific depth using air, and longer-duration dives made to the same depthusing nitrox breathing-gas mixtures).Accordingly, for dives made usingnitrox breathing-gas mixtures, the risk ofDCS is lower only when these dives areat the same depths and for the samedurations as the air dives. Note,however, that Condition J of theproposed variance limits the risk of DCSby requiring that divers remain withinthe no-decompression limits of NOAA’sdecompression tables, or other tables orformulas that Dixie demonstrates areequally effective in preventing DCS.

(d) We stated in the ‘‘Background’’section of the proposed variance that‘‘[a]s a result [of using nitrox breathing-gas mixtures], the mathematicalprobability of developingdecompression sickness (DCS) isreduced compared to divers who usecompressed air under the same divingconditions (i.e., depth, bottom time, anddescent and ascent rates)’’ (62 FR 58997,first column). This statement elicitedtwo comments. The first commenter (Ex.2–98) stated that high-O2 nitroxbreathing-gas mixtures will result in areduced risk of DCS when used at thesame depths and for the same durationsas air, but only if the divers use thedepth and duration limits specified forair decompression and do not extendthe duration of the dive. The reductionin risk occurs because the nitrogenpartial pressure in the nitrox breathing-gas mixture is less than the partialpressure of nitrogen in air at thespecified depth. The second commenter(Ex. 2–109) asserted that Dixie haseconomic incentives to extend theduration of dives.

We believe these commenters arecorrect that extending the duration ofdives using high-O2 nitrox breathing-gasmixtures would increase the risk ofDCS. However, we conclude that the



resulting risk would be comparable tousing the equivalent partial pressure ofnitrogen in air for that extended period.The basis for this conclusion is theequivalent-air-depth (EAD) formulapublished by NOAA, which is thenation’s lead Federal agency fordeveloping mixed-gas decompressionschedules used in scientific andtechnical diving operations. Accordingto NOAA, EAD ‘‘is the depth at whichair will have the same nitrogen partialpressure as the [oxygen-]enriched mixhas at the depth of the dive’’ (1991NOAA Diving Manual, page 15–7).NOAA applies its EAD formula indetermining what equivalent airdecompression limits to use with nitroxbreathing-gas mixtures, and assumesthat equivalent nitrogen partialpressures and dive durations will resultin similar DCS risk. However, to provideDixie’s divers with an added margin ofsafety against DCS, the permanentvariance requires that the partialpressure of nitrogen in the high-O2

nitrox breathing-gas mixture used for aspecific dive duration must neverexceed the no-decompression limits forthe equivalent partial pressure ofnitrogen in air for that same durationpublished in the 1991 NOAA DivingManual.

Part 2. Comments to proposed section II(Proposed Alternative).

(a) Conditions A.1 and A.2 of theproposal, which specified requirementsfor CO2 scrubbers, CO2 sensors,moisture traps, moisture sensors, andover-pressure valves, received a numberof comments. Several commenters (Exs.2–98, 2–99, 2–105, and 2–117) pointedout a typographical error in the statedCO2 level in Condition A.1. The correctlevel is 0.01 ATA, not 0.1 ATA, and wehave corrected it in the permanentvariance.

Condition A.1 in the proposedvariance (Condition (4) in thepermanent variance) stated thatrebreathers must use commercially-available, pre-packed, disposablescrubber cartridges or an equallyeffective alternative. Three commenters(Exs. 2–101, 2–105, and 2–114) tookexception to the requirement that CO2

scrubbers must use sorbent cartridgesthat are commercially available, pre-packed, and disposable. Theycontended that such cartridges are notavailable for some rebreathers and,when available, are expensive. Theyalso argued that rebreathermanufacturers do not require pre-packed, disposable cartridges becausemany divers manually fill and packmost rebreather canisters. Onecommenter (Ex. 2–105) stated that ‘‘no

scientific evidence [shows that] adisposable[,] pre-packaged canisterwould perform safer or with greaterefficiency than one packed by the user.’’Another commenter (Ex. 2–117),however, stated that ‘‘[u]se [ofdisposable scrubber cartridges] inrebreathers reduces return to servicetime and reduces human error duringservicing,’’ and that [severalmanufacturers] have canisters thatsimplify replacement of sorbentmaterial, while [at least onemanufacturer] uses a disposablecartridge.’’

In reply to these commenters, we notethat Condition A.1 in the proposedvariance allowed Dixie to use analternative to pre-packed CO2-sorbentmaterials, including manually-filledcartridges; Condition (4)(b) in thepermanent variance will also permit thisalternative, if it is acceptable to therebreather manufacturer. However,Dixie bears the burden of demonstratingto us that its manually-filled cartridgesare at least as effective as pre-packedsorbent materials in removing CO2 fromthe breathing loop; Dixie likely wouldget this information from the rebreathermanufacturer.

Proposed Condition A.2 required theuse of CO2 sensors. One commenter (Ex.2–25) endorsed this proposedrequirement for closed-circuitrebreathers, but claimed these sensorswere unnecessary for semi-closed-circuit rebreathers because theserebreathers ‘‘are regularly venting gasfrom the system which is replaced withhigh oxygen content gas * * * toprevent the buildup of carbon dioxide.’’We believe that CO2 sensors arenecessary for semi-closed-circuitrebreathers because divers can‘‘overbreathe’’ these rebreathers.Overbreathing occurs when the diver’sbreathing rate is faster than the rate atwhich fresh breathing gas enters theinhalation bag; consequently,overbreathing causes the diver torebreathe exhaled gas containingelevated levels of CO2. The informationin Ex. 5 (pages P–19 through P–22)supports this conclusion. Therefore,CO2 sensors enable divers to detectincreased CO2 before it reacheshazardous levels.

The commenter in Ex. 2–98 endorsedthe use of CO2 sensors, but claimed thatthis technology is ‘‘currentlyunavailable even in the current U.S.Navy rebreathers.’’ Two othercommenters (Exs. 2–105 and 2–114) alsoasserted that continuously-functioningCO2 sensors are not availablecommercially. However, anothercommenter (Ex. 2–117) contradictedthese assertions; this commenter stated

that CO2 sensors are available in severalrebreathers.

Four commenters (Exs. 2–99, 2–106,2–113, and 2–114) claimed that few, ifany, rebreathers on the market metproposed Conditions A.1 and A.2. Oneof these commenters (Ex. 2–106) stated,‘‘[M]any of the specifications forrebreathers represent the manufacturer-specific features of an intended unit thatwas never brought forward as aproduction model. We also manufacturediving rebreathers and protest anyregulation that would arbitrarily biascompliance to one model.’’ Four othercommenters contended that theproposed variance favors or enhancesthe competitive position of one or morerebreather manufacturers (Exs. 2–99, 2–101, 2–105, and 2–114); no commenter,however, indicated whichmanufacturer(s) would benefit. Onecommenter (Ex. 2–114) stated that‘‘[implementing the proposed variance]would put every dive store andinstructor who teaches rebreather divingin the U.S. out of business,’’ andclaimed that ‘‘this [proposed] variancewould in essence be a restraint oftrade.’’

The information provided in Ex. 2–117 demonstrates that the requiredcomponents are commercially availableand used in several existing rebreathers.Other evidence in the record (Ex. 5,page 6–4) also shows that effective CO2

sensors are commercially available forclosed-circuit rebreathers. We find thateach proposed condition is necessaryfor diver safety, and that Dixie caneither purchase rebreathers, or retrofitits existing rebreathers, to meet theseconditions. In addition, we observe thatno commenter found that any requiredcomponent was unsafe.

While the proposed variance did notrequire any CO2 alarms, the commenterin Ex. 2–98 recommended that CO2

sensors activate two alarms: The firstalarm when the inhaled CO2 partialpressure is at 0.005 ATA (3.8 mmHg), towarn divers that they are approachingthe upper CO2 limit; and the secondalarm when inhaled CO2 reaches thepartial pressure limit of 0.01 ATA (7.6mmHg), to alert the diver to terminatethe dive immediately. We agree withmuch of this comment, but we believethat once the alarm is activated at a CO2

partial pressure of 0.005 ATA, it mustcontinue to provide a visual or auditorywarning to the diver to take correctiveaction or terminate the dive beforereaching the maximum CO2 limit of 0.01ATA. The use of an activation level issimilar to the action-level requirementfound in many of OSHA’s standards fortoxic substances. Therefore, thepermanent variance requires Dixie to



integrate the CO2 sensors with an alarm(either visual or auditory) that operatescontinuously at and above a CO2 partialpressure of 0.005 ATA.

The proposed variance did not specifycalibration requirements for CO2

sensors. Nevertheless, the commenter inEx. 2–98 stated that any CO2 sensoradopted for use in rebreathers must be‘‘tested both in the laboratory and inmanned diving trials,’’ and that the‘‘[d]ata from these trials must support[the] accuracy, reliability andruggedness’’ of CO2 sensors. While thiscommenter did not specify a protocol orcriteria for testing these factors, weagree that, at a minimum, Dixie mustdetermine the accuracy of CO2 sensorsbefore its divers use them. Such adetermination is necessary to enableDixie to eliminate sensors that areunreliable or that cannot function underrugged diving conditions. Therefore, indeveloping provisions for calibratingand maintaining the accuracy of CO2

sensors (see Condition (9) in thepermanent variance), we have adoptedthe requirements that Dixie specified forO2 sensors in Condition A.4 of thevariance application, with one majorrevision: Instead of using an accuracy of1 percent (1%) by volume, Condition(9)(c) of the permanent variance requiresthat CO2 sensors be accurate ‘‘to within10 percent (10%) of a CO2 concentrationof 0.005 ATA or less,’’ based on thecomments in Ex. 2–98. Using a test orstandard gas containing a CO2

concentration of 0.005 ATA or less willensure that the sensors can accuratelydetect CO2 levels that can be harmful toDixie’s divers. Additionally, in view ofthe harmful effects that can result fromhigh levels of CO2, we consider amaximum error rate of no more than 10percent (10%) of a CO2 partial pressureof 0.005 ATA to be within acceptablelimits.

The commenter in Ex. 2–98 alsoargued that, as an alternative to CO2

sensors, ‘‘the breathing apparatusmanufacturer [must] produce data frommanned trials that substantiate [the]operational CO2 canister-duration limitsover the entire depth, watertemperature, and exercise range forwhich the breathing apparatus isdesigned. Furthermore, themanufacturer must clearly state whatthese limits are.’’ While the proposedvariance did not mention such analternative, we agree with the generalapproach recommended by thiscommenter. However, we believe thatvalid and reliable data for determiningCO2-sorbent replacement schedules canbe obtained from carefully controlledand executed testing protocols that usebreathing machines instead of divers to

evaluate the canisters. Therefore,Condition (10)(a)(i) of the permanentvariance permits Dixie to use a schedulefor replacing the CO2-sorbent material incanisters if the rebreather manufacturerdeveloped the replacement scheduleusing the canister-testing protocolspecified in Appendix A of this notice.We adapted this protocol from thecanister-testing parameters andprocedure provided by the U.S. NavyExperimental Diving Unit (NEDU) (Ex.14); NEDU is the lead federal agency fortesting CO2-sorbent replacementschedules, and the diving industryrecognizes the NEDU canister-testingprotocol as the industry standard.Additionally, the employer can use aCO2-sorbent replacement scheduledeveloped by a rebreather manufactureronly if the manufacturer analyzed theprotocol results using the statisticalprocedures specified by NEDU (Ex. 14and 15).

The canister-testing protocoldeveloped by NEDU addresses the threefactors recommended by the commenterin Ex. 2–98: Depth, exercise level(ventilation rate), and watertemperature. Depth is the maximumdepth at which a diver would use theCO2-sorbent material, which for thepermanent variance is 130 fsw. Weselected three combinations ofventilation rates and CO2-injection ratesfrom the NEDU protocol to simulatethree diverse levels of exercise (light,moderate, and heavy). The four watertemperatures used in the NEDU protocolare 40, 50, 70, and 90 degrees F (4.4,10.0, 21.1, and 32.2 degrees C,respectively); these temperaturesrepresent the wide range of watertemperatures that Dixie’s recreationaldiving instructors are likely toencounter. We revised the NEDUprotocol slightly by: Limiting themaximum depth to 130 fsw; requiringan O2 fraction of 0.28 in a nitroxbreathing gas (this fraction being themaximum O2 concentration permitted atthis depth by the permanent variance);providing tolerance limits for watertemperatures; and defining canisterduration as the time taken to reach0.005 ATA of CO2 (the CO2 levelspecified in the permanent variance atwhich divers are to eliminate excessiveCO2 in the breathing gas or terminatethe dive). In addition, our protocol usesonly mandatory language, and expresslyprohibits the use of replacementschedules based on extrapolation of theprotocol results. OSHA prohibitsextrapolation of the protocol resultsbecause the statistical-analysisprocedures developed by NEDU (Ex. 15)do not provide a method for estimating

the duration of CO2-sorbent materialsbeyond the results obtained during thecanister-testing trials. OSHA believesthis approach significantly improves thevalidity and reliability of thereplacement schedules derived fromthese results. After thoroughlyreviewing the NEDU canister-testingprotocol and adapting it the conditionsof the permanent variance, we believethat CO2-sorbent replacement schedulesbased on the requirements of AppendixA of the permanent variance will enableDixie to replace CO2-sorbent materialsin a timely manner, thereby ensuringthe health and safety of its divers.

While we are confident that CO2-sorbent replacement schedulesdeveloped according to Condition (10)of the permanent variance will protectdivers under ordinary divingconditions, we believe that theseschedules do not address a conditionthat can seriously compromise canistereffectiveness: Moisture in the canister,which usually results from canisterflooding. Based on our review of therecord, we find that moisture traps andmoisture sensors can effectively controlthis condition. In this regard, proposedCondition A.2 required the use ofmoisture traps and moisture sensors.Several commenters (Exs. 2–101, 2–105,and 2–117) claimed that existingrebreathers already use moisture traps.The commenter in Ex. 2–101 stated,without explanation, that ‘‘making thema requirement would be restrictive.’’This commenter also asserted thatmoisture sensors are unnecessarybecause CO2 sensors perform the samefunction. (The commenter did notspecify the term ‘‘function,’’ but weassume that it refers to the capability toindicate canister flooding.) A secondcommenter (Ex. 2–105) noted thatmoisture sensors would be an importantsafety feature, but asserted that theywere not available commercially.However, another commenter (Ex. 2–117) claimed that moisture sensors areavailable from several companies. Onecommenter (Ex. 2–105) noted thatexcessive moisture can impair electricalsystems in rebreathers, and asked us tospecify where to place the moisturesensors to prevent these problems.

Moisture traps are necessary to keepwater out of the canisters because waterleakage into canisters can substantiallyreduce the CO2-absorbing properties ofthe sorbent material. Moisture sensors,in turn, detect excessive water orflooding inside the canister that cancompromise the CO2-sorbent material.Moisture sensors, therefore, warn thediver of hazardous water leakage intothe canister. The commenters in Exs. 2–101, 2–105, and 2–117 noted that



5 In addition, a CO2 sensor alerts the diver toincreased CO2 levels in the inhaled breathing gasthat may result from other conditions, includingdepleted sorbent material (saturated with CO2) andchanneling or overbreathing (exhaled air bypassingthe sorbent material).

6 The rapid onset of symptoms resulting from O2

toxicity provides a major rationale for requiringredundant O2 sensors.

moisture traps are availablecommercially and that existingrebreathers routinely use them. Theinformation in Ex. 2–117 also indicatesthat moisture sensors are commerciallyavailable. While we believe thatrebreather manufacturers should placemoisture sensors on the inhalation sideof the breathing loop, we leave thedesign and location of moisture sensorsand moisture traps to their technicalexpertise. Dixie must ensure that itsdivers use these components consistentwith the rebreather manufacturer’sinstructions, and that the moisturesensors alert the diver of moisture in thebreathing loop in sufficient time toterminate the dive and return safely tothe surface. We have incorporated theseconditions into the permanent variance.

In the proposed variance, ConditionA.2 specified that rebreathers containover-pressure valves. Regarding over-pressure valves, one commenter (Ex. 2–101) asked us to define the term ‘‘over-pressure valve,’’ while two commenters(Exs. 2–105 and 2–117) asserted thatexisting rebreathers already have over-pressure valves. One of thesecommenters (Ex. 2–105) noted that over-pressure valves are ‘‘importantprotection to reduce the risk of [AGE]and associated pressure[-]inducedinjuries and [rebreather] damage.’’

An over-pressure valve is a valve onthe counterlung that releases breathinggas from the counterlung when thepressure reaches a set level; we haveincorporated this meaning into thepermanent variance. Rebreathersroutinely are designed with over-pressure valves. These valves perform acritical safety function by helping toregulate breathing-gas volume andpressure.

Condition A.2 of the proposedvariance also specified that Dixie useredundant (i.e., at least two) CO2 sensorsand redundant moisture sensors; it alsorequired that these sensors functioncontinuously. One commenter (Ex. 2–101) agreed with the proposedrequirement for a continuously-functioning CO2 sensor, but did notbelieve that additional CO2 sensors werenecessary. This commenter noted thatboth CO2 and moisture sensors will alertthe diver whenever the breathing loop,most likely the CO2-sorbent material, isno longer capable of removing exhaledCO2. We agree with this commenter thatCO2 and moisture sensors serve muchthe same purpose—to inform the diverof conditions (for example, reducedefficiency of the CO2-sorbent material)that may cause CO2 to accumulate in thebreathing loop. By measuring theamount of CO2 in the inhaled breathinggas (after the gas passes through the

sorbent material in the canister toremove CO2) CO2 sensors can detect anelevated CO2 level that may indicatedepletion of the CO2-sorbent materialbecause of canister flooding. Anelevated CO2 level, in turn, warns thediver to take corrective action, includingterminating the dive.5 As notedpreviously, moisture sensors detectexcessive water or flooding inside thecanister that can reduce the sorbentmaterial’s capacity to remove CO2 fromthe inhaled breathing gas. Theindependent functions performed bythese sensors (i.e., a CO2 sensormeasures CO2 in the breathing gas,while a moisture sensor detectsexcessive moisture in the canister)indicates that a malfunction in onesensor is unlikely to result in amalfunction in the other sensor.

Several other conditions make sensorredundancy unnecessary. First, thesymptoms of excessive CO2 do notdevelop as rapidly as the symptoms ofO2 toxicity; 6 consequently, a properlytrained and experienced diver will beable to recognize a number of effectsassociated with excessive CO2 and takeappropriate action, includingterminating the dive. These effectsinclude: Reduced buoyancy (from theincreased weight caused by canisterflooding); shortness of breath (from CO2

displacing O2 in the diver’s lungs); anincrease in breathing resistance duringinhalation (caused by difficulty movingthe breathing gas through wet CO2-sorbent material); and a large number ofbubbles vented through the rebreather’sexhaust valve (venting related to theincreased exhaust pressure caused byexhaling against wet CO2-sorbentmaterial). Secondly, the permanentvariance (Conditions (7) and (8))requires that both the moisture sensorand CO2 sensor function continuously,ensuring early detection of a CO2-relatedproblem by the diver. Lastly, Condition(30) of the permanent variance requiresthat the divers use an open-circuitemergency-egress system (a ‘‘bail-out’’system); this system will provide thedivers with the capability to shift to aknown, safe, and immediately-availablebreathing gas, and to terminate the divesafely whenever a CO2-related problemoccurs.

Based on this record, we find that:Carbon-dioxide sensors and moisture

sensors provide independent means ofdetecting a CO2-related problem;symptoms related to excessive levels ofCO2 develop more slowly than thesymptoms of excessive O2; a properlytrained and experienced diver willrecognize the effects of excessive CO2 insufficient time to take correct action; therequirement that CO2 sensors andmoisture sensors be continuouslyfunctioning assures real-time detectionof CO2-related problems; and therequired bail-out system provides thediver with a safe means to terminate adive following detection of a CO2-related problem. This recorddemonstrates that the proposedrequirements for redundant CO2 sensorsand redundant moisture sensors areunnecessary; we believe that the onlybasis for requiring redundant sensors isif the rebreather manufacturer includesthem in the equipment design orspecifications. Therefore, we haverevised the conditions accordingly inthe permanent variance.

(b) Proposed Condition A.3, whichrequired the use of flexible breathingbags (also known as ‘‘counterlungs’’)with rebreathers, elicited the followingcomment (Ex. 2–105):

Not all rebreathers use breathing bags.However, they all employ some type ofcounter lung providing a compliant volume.Certain types of rebreathers utilize a largediaphragm or bellows assembly. There wouldbe no purpose in mandating a particularcounterlung configuration. The onlyregulation that could be mandated might bea minimum volumetric displacement.

We consider breathing bags to be atype of counterlung. Even though theproposed variance used the terms‘‘breathing bags’’ and ‘‘counterlungs’’interchangeably, we agree with thecommenter that the permanent varianceshould not specify a particularcounterlung configuration. We haverevised the condition accordingly in thepermanent variance. In addition, whilewe agree with the need to specify aminimum volumetric displacement, webelieve that the rebreather manufacturershould determine this value. In thisregard, Dixie must ensure that its diversuse the counterlung according to therebreather manufacturer’s instructions,and the counterlung must displaceenough volume to sustain the diver’srespiration rate during any divingcondition. We have incorporated theseconditions into the permanent variance.

(c) Proposed Condition A.4 addressed‘‘bail-out systems,’’ which aresupplemental breathing-gas systemsused by divers for emergency ascent tothe surface if the SCUBA malfunctions.The proposed condition specified thatbail-out systems must integrate the



second stage of the SCUBA regulatorwith either a separate supply ofemergency breathing gas or, for semi-closed-circuit and closed-circuitrebreathers, a diluent supply ofemergency breathing gas. Twocommenters (Exs. 2–100 and 2–105)responded to the proposed condition.The first commenter (Ex. 2–100)recommended that the system contain atleast 35 cubic feet of emergencybreathing gas. This volume was basedon maximum consumption rates relatedto a number of variables, includingwater temperature, diver’s thermalprotection, speed of current, lungvolume, and psychological stress. Thesecond commenter (Ex. 2–105) statedthat ‘‘[a] bail-out system is a necessityfor all rebreather use.’’

We agree that the bail-out systemmust enable the diver to terminate thedive safely under ‘‘worst-case’’conditions. We believe, however, thatthe rebreather manufacturer is in thebest position to determine what capacityof breathing gas is needed for safeoperation of the bail-out system. In thisregard, Dixie must ensure that its diversuse the bail-out system according to therebreather manufacturer’s instructions.Dixie must also ensure that the bail-outsystem supplies sufficient emergencybreathing gas to enable a diver toterminate the dive and return safely tothe surface; the rebreather manufacturercan make this determination after Dixieprovides the critical diving parameters(e.g., depth of dive and breathing rate).We have revised this conditionaccordingly in the permanent variance.

(d) Proposed Condition A.5 specifiedrequirements for information modules,which provide divers with informationabout the dive, including gas pressures,dive times, and descent and ascentrates. One commenter (Ex. 2–114) statedthat the information module is a divecomputer, that no rebreathers areavailable commercially that integratedive computers with breathing systems,and that no dive computer ‘‘includesdisplays that directly warn of rebreathersolenoid failure and excessive descentrates.’’ In response, although we believethat it would be advantageous if divecomputers included such informationand warning displays, neither theproposed nor the permanent variancerequire it. The permanent variancerequires Dixie to equip its divers withsensor and display systems that provideinformation on time, depth, ascent, anddescent to divers who use closed-circuitrebreathers, and time, ascent, anddescent information to divers who usesemi-closed-circuit rebreathers. Bothtypes of rebreathers must also havealarms or visual displays that warn the

diver about excessive ascent anddescent rates, as well as depth levelsthat are shallower than the ceiling-stopdepth. The permanent variance does notrequire that a dive computer providethis capability.

(e) Proposed Condition B requiredthat closed-circuit rebreathers must usethe following sensors: (1) Sensors thatmeasure supply pressures for O2 anddiluent gas; (2) depth sensors; (3)continuously-functioning andredundant temperature-compensated O2

sensors; and (4) continuously-functioning gas-loop and ambient water-temperature sensors. One commenter(Ex. 2–114) asserted that no existingrebreathers have continuously-functioning sensors for assessing gas-loop and ambient water temperatures. Asecond commenter (Ex. 2–117)contradicted this assertion, claimingthat ‘‘transducers and thermocouplesare readily available from numerouscompanies’’ for sensing pressure, depth,and ambient water temperature.

We believe that temperature sensorsare necessary for diver safety. Water-temperature sensors alert divers to thepossibility of hypothermia. In addition,gas-loop temperature sensors and water-temperature sensors allow divers toestimate the duration of their CO2-sorbent material. Efficiency of the CO2-sorbent material deteriorates withdecreasing temperatures (1991 NOAADiving Manual, page 16–9). Thus, ifdivers are able to estimate the durationof their CO2-sorbent material, they canjudge how long they can dive even iftheir CO2 sensors malfunction. Even ifno existing rebreather incorporatestemperature sensors as stated by thecommenter in Ex. 2–114, Dixie’sproposal to use such sensors willprovide its divers with additionalprotection from temperature-relateddiving hazards; therefore, we haveincluded this condition in thepermanent variance.

(f) For open-circuit SCUBA, proposedCondition C specified that theconcentration of O2 must not exceed 40percent (40%) of the breathing gas byvolume, or, for any SCUBA, an O2

partial pressure of 1.40 ATA. Threecommenters (Exs. 2–104, 2–106, and 2–113) recommended that we increase thepartial pressure of O2 in the breathing-gas mixture from 1.4 to 1.6 ATA; thesecommenters asserted that recreationaldivers use the 1.6 ATA level regularlyand safely, and that this use conformsto prevailing rebreather practices.

In reply to these commenters, webelieve that the research data cited inthe proposed variance support ourconclusion that a maximum O2 level of1.40 ATA prevents O2 toxicity. The

commenters provided no data or studiesto support a maximum O2 exposure of1.6 ATA, nor could we find any relevantdata or study to support thisrecommendation for SCUBA diving.Evidence in the record (see Exs. 4, 4A,5 (pages 3–5 through 3–15, P–15, and P–37 through P–43), and 7) alsodemonstrates that breathing 1.6 ATA ofO2 for extended periods increases therisk of O2 toxicity compared tobreathing 1.4 ATA of O2. The increasedrisk of O2 toxicity means that littletolerance exists for errors in O2 controland delivery equipment (e.g., O2

sensors, solenoids) and in calculating O2

exposures.One commenter (Ex. 2–106) noted

that we should consider both partialpressure and the duration of a divewhen determining O2 exposure limits.Another commenter (Ex. 2–109)maintained that when they use high-oxygen breathing-gas mixtures, Dixie’srecreational diving instructors anddiving guides can dive for longerperiods than when they use air as thebreathing gas. Long dive durationsextend a diver’s exposure to elevatedlevels of oxygen, thereby increasing thediver’s risk of developing O2 toxicity, aswell as DCS. Regarding the firstcomment (Ex. 2–106), we note that theO2 exposure limits specified in theproposed variance address bothduration and level of O2 exposure.Similarly, in response to the secondcommenter (Ex. 2–109) we believe thatConditions C and E in the proposedvariance address the concern about O2

toxicity expressed in Ex. 2–109; theseproposed conditions cited researchstudies attesting to the safety ofbreathing O2 at a partial pressure of 1.40ATA.

(g) Condition D in the proposallimited the diving depth to ‘‘no deeperthan 130 fsw, or to a maximum oxygenpartial pressure delivered to the diver of1.40 ATA, whichever is mostrestrictive.’’ The proposed conditionelicited two comments. The firstcommenter (Ex. 2–99) stated that theAssociation of Diving Contractors, atrade association for the commercial-diving industry, requires decompressionchambers at the dive site for divesdeeper than 80 fsw or for dives outsidethe no-decompression limits because‘‘there is still a possibility of a rapidascent to the surface and hence, a [riskof AGE] brought on by eliminated oraccelerated decompression [during] theascent.’’ The second commenter (Ex. 2–113) considered a maximum divingdepth of 160 or 170 fsw to be safe.

The proposal reduced the risk of DCSresulting from ‘‘eliminated oraccelerated decompression’’ to minimal



levels by requiring Dixie to ensure thatits divers use nationally-recognized no-decompression diving limits. Theproposal lowered the risk of AGE byincluding a number of procedural andequipment requirements (e.g., specifiedO2 levels in the breathing-gas mixtureand installation of O2 and CO2 sensors)that would minimize the need to makerapid (emergency) ascents to the surfaceduring a dive; such ascents can causeAGE by overpressurizing the lungs. Webelieve that these proposedrequirements would protect recreationaldiving instructors from the risksassociated with DCS and AGE as wellas, or better than, the provisions of 29CFR 1910.401(a)(2)(i) (the exemption inOSHA’s CDO Standard for recreationaldiving instructors who use open-circuit,air-supplied SCUBA).

We are not extending the depth limitto 160 or 170 fsw because we believethat doing so would place the diver atincreased risk of nitrogen narcosis (aswell as DCS). This increased risk wouldoccur because the partial pressure ofnitrogen in the breathing gas would behigher at 160–170 fsw than at 130 fsw.Previous research (Exs. 8, 9, and 10)demonstrates that hyperbaric air hassignificant narcotic effects even at 100fsw or about 4.00 ATA (which isequivalent to a nitrogen partial pressureof 3.16 ATA). Using 28 percent (28%)O2 at 130 fsw (equivalent to about 1.40ATA O2), the partial pressure ofnitrogen would be 3.56 ATA, which isonly slightly above the narcoticthreshold specified by the previousresearch.

(h) Proposed Condition E establishedO2-exposure limits for the breathing-gasmixtures, requiring that divers ‘‘notexceed the 24-hour single-exposure timelimits specified by the 1991 NOAADiving Manual or other oxygen-exposure limits, such as the DivingScience and Technology (DSAT)Oxygen Exposure Table, that provide alevel of oxygen-toxicity protection atleast equivalent to the level ofprotection afforded by the 1991 NOAADiving Manual.’’ The proposedcondition received two comments. Onecommenter (Ex. 2–98) agreed with usingthe NOAA O2-exposure limits and amaximum O2 partial pressure of 1.4ATA, stating that these limits ‘‘shouldnot make the probability of oxygentoxicity * * * significantly differentthan when breathing air.’’ At O2 partialpressures above 1.3 ATA, thiscommenter recommended using theexposure durations specified in Table15–1 of NOAA’s 1991 Diving Manual.According to this commenter, using theNOAA table ‘‘would make theprobability of CNS O2 toxicity

[extremely low].’’ The secondcommenter (Ex. 2–100) asserted that acommercial subsidiary of theProfessional Association of DivingInstructors developed the DSAT O2-exposure limits. The commentercontended that this subsidiary is not arecognized research authority and is‘‘motivated by profit and not necessarilythe public benefit.’’ According to thiscommenter:

NOAA is a highly regarded and recognizedsource of diving research and operationalprotocol. If oxygen exposure limits are not toexceed the 24-hour single exposure timelimits specified in the 1991 NOAA DivingManual[,] then citing additional sources ofoxygen exposure limits[] that[,] by default,can only be the same or more conservative,is unnecessary and likely confusing.

The comments in Ex. 2–98 supportthe maximum O2-exposure limit of 1.40ATA specified in proposed Condition E.We agree with the commenter that CNStoxicity is the principal basis forspecifying O2 exposure limits;accordingly, we discussed the need toprevent O2-induced CNS toxicity indetail in the proposed variance (62 FR58999–59000).

Regarding the comments in Ex. 2–100,we find that the O2-toxicity protectionafforded to divers by the DSAT tablesunder the diving conditions specified inthe variance application is at leastequivalent to the level of safety that theyget from the O2-exposure limitsspecified in the 1991 NOAA DivingManual. The rationale provided in theproposed variance, as well as additionalevidence submitted to the record (Exs.4 and 7), support this conclusion.

We have deleted the proposed generallanguage that would have allowed Dixieto use non-NOAA O2-exposure limits(other than DSAT’s) when these limits‘‘provide a level of oxygen-toxicityprotection at least equivalent to thelevel of protection afforded by the 1991NOAA Diving Manual.’’ We believe thisprovision would introduce unnecessaryuncertainty into the permanent variancewhen two adequate sources of O2 limitsare already available for Dixie’s use.Accordingly, we have revised thisprovision so that only the O2-exposurelimits identified in the proposal areacceptable for the permanent variance;these limits are from the 1991 NOAADiving Manual, and the Enriched AirOperations and Resources Guidepublished in 1995 by the ProfessionalAssociation of Diving Instructors(commonly referred to as the ‘‘1995DSAT Oxygen Exposure Table’’). Ifother O2-exposure limits becomeavailable in the future, Dixie mayrequest us to amend the permanent

variance if it provides evidence thatdemonstrates their safety.

(i) Proposed Condition F, whichrequired that ‘‘[n]itrogen shall be theonly inert gas used to obtain thebreathing-gas mixture,’’ elicited twocomments. One commenter (Ex. 2–103)asserted that recreational divinginstructors and diving guides ‘‘use gasblends to increase safety,’’ implying thatwe should allow divers to useadditional inert gases in the breathing-gas mixture. The second commenter (Ex.2–113) also noted that tri-mix breathinggases (usually consisting of O2, N2, andHe) have been used safely by manydivers.

Dixie proposed to use nitrogen as theonly inert gas in the breathing-gasmixture under the specified conditionsencountered by its divers (i.e., no-decompression dives to depths that donot exceed 130 fsw). We need notconsider the use of other inert gases aspart of Dixie’s permanent variancebecause Dixie did not seek our approvalfor the use of these gases. In any case,we believe that other inert gases (e.g.,helium) have limited, if any, applicationunder the conditions of this variance.

(j) Proposed Conditions G, H, and Ispecified, respectively, the requirementsfor: Mixing and analyzing nitroxbreathing-gas mixtures; compressorsused to produce the nitrox breathing-gasmixtures; and SCUBAs exposed to high-pressure (pressures exceeding 300 psi)nitrox breathing-gas mixtures. Theseproposed conditions received fourcomments. The first commenter (Ex. 2–99) contended that the proposal did notprovide specifications for O2-cleansystems and measurement accuracy, anddid not require the delivery of pre-mixed breathing gas ‘‘from a reliableand competent source with highstandards of documented quality controlin place.’’

The second commenter (Ex. 2–105)asked: What is the basis for the O2-cleaning and O2-service requirementsand the 300 psi limit; at what minimumO2 level would these requirementsapply; and how does OSHA define ‘‘O2

compatible.’’ The commenter agreedwith the use of oil-free compressors formixing nitrox breathing-gas mixtures.The commenter noted, however, thatemployees who use these compressorsneed proper training and that ‘‘[s]pecialconsideration must be given * * * tomaterial use, material compatibility,system design, cleaning[,] andmaintenance.’’ The commenterdescribed several hazards associatedwith mixing nitrox breathing gases,including: Partial-pressure blending intocylinders not prepared properly for O2

service; inducing O2-enriched breathing-



gas mixtures into the intake ofcompressors not designed for thispurpose; and contamination of mixtureswith hydrocarbons or oil. Thecommenter also recommended that wepermit the use of O2 analyzers thatinvolve processes or mechanisms otherthan fuel-cells (e.g., gaschromatography, thermal conductivity),stating that such analyzers are accurateand ‘‘have been in use worldwide formany years.’’

A third commenter (Ex. 2–116) madea number of recommendations toimprove the safety of mixing nitroxbreathing gases, including: Prohibit theuse of oil-lubricated air compressors formixing nitrox breathing gasescontaining 22–40 percent (22–40%) O2;require compressor and filter-systemmanufacturers to certify that theirequipment is safe for the gases used inthe breathing mixtures; require filter-system manufacturers to certify that theequipment used to clean air (for mixingwith pure O2) produces O2-compatiblebreathing gases (i.e., breathing gaseswith low hydrocarbon levels); andrequire Dixie to monitor hydrocarboncontamination continuously. Thecommenter also submitted suggestedrevisions to the proposed text based onthese recommendations.

In reply to the commenters whorequested information on whichstandards we would use to ensureaccurate mixing and decontamination(especially hydrocarbon removal) ofnitrox breathing gases, we note thatDixie must comply with 29 CFR1910.101 (Compressed Gases (GeneralRequirements)) and 29 CFR 1910.169(Air Receivers), and applicableprovisions of 29 CFR 1910.134(Respiratory Protection). We agree withthe comment in Ex. 2–105 that Dixiemust use only properly trainedpersonnel to mix breathing gases, andwe have revised the permanent varianceaccordingly.

To reduce the risk of O2 explosions,proposed Condition I required thatSCUBA using high-O2 breathing-gasmixtures or pure O2 at pressuresexceeding 300 psi be designed for O2

service. We derived the 300 psi limit byinterpolating between the pressure limit(125 psi) for pure O2 and the pressurelimit (500 psi) for compressed airspecified in paragraph (i)(3) of 29 CFR1910.430. We note, however, that§ 1910.430(i)(1) requires that equipmentusing O2 mixtures exceeding 40 percent(40%) O2 by volume be designed for O2

service; this requirement is based on theserious explosion risk associated withthese O2 mixtures. Therefore, to reducethe risk of an O2 explosion, we haverevised the permanent variance to

require that SCUBA using breathing-gasmixtures that exceed 40 percent (40%)O2 by volume at pressures over 125 psibe designed for O2 service.

The proposed variance explained thatan O2 analyzer that uses a fuel-cellprocess would be acceptable. However,O2 analyzers based on other processesare also acceptable if they meet therequirements specified in Conditions 22and 24(a) of the permanent variance.

We agree with the commenter in Ex.2–116 that Dixie must only usecompressors and filters thatmanufacturers have certified willproduce O2-compatible breathing-gasmixtures and will withstand thepressures involved. We believe theserequirements substantially reduce therisk of O2-related explosions that canoccur while mixing nitrox breathinggases under high pressure. Accordingly,we have incorporated theserequirements into the permanentvariance. Consistent with existingrequirements in our CDO Standard, thepermanent variance also requires an O2-service rating for compressors used formixing high-pressure O2 whenever O2

fractions could exceed 40 percent (40%)by volume, as specified in paragraphs(i)(1) and (i)(2) of 29 CFR 1910.430.

A fourth commenter (Ex. 2–117)stated that O2 analyzers, oil-lesscompressors, and filter-membranesystems are available commercially, andidentified several companies thatmanufacture this equipment. Thesecomments demonstrate that Dixie canreadily meet the requirements in thepermanent variance to use O2 analyzers,oil-less compressors, and filter-membrane systems when mixing nitroxbreathing gases for rebreathers.

(k) Proposed Condition J, whichidentified the no-decompression limitsthat Dixie must use, elicited threecomments. One commenter (Ex. 2–98)asserted that using high-O2 breathing-gas mixtures and diving in accordancewith the no-decompression limits for airdiving specified in the 1991 NOAADiving Manual would reduce the risk ofdeveloping DCS. This commenter alsorecommended comparing other,‘‘equivalent,’’ no-decompression limitsto the NOAA limits using a method that‘‘give[s] acceptable prediction of DCSprobability when applied to data bases* * * where the dive profile isaccurately known and the outcome(DCS or no DCS) is known.’’ Thecommenter added that ‘‘the employermust show through adequate recordsthat the DCS incidence using these otherprocedures [is] acceptably low,’’ andasserted that ‘‘an ongoing evaluation ofsafety through record keeping isessential.’’

Another commenter (Ex. 2–109) statedthat the ‘‘DSAT [no-decompression air]tables, [which] are based on a shortertissue half-time, predict more rapid out-gassing and therefore allow much longerrepetitive dives than the Navy [no-decompression air] tables wouldfollowing similar bottom times andsurface intervals.’’ This commenterconcluded, however, that the DSAT andU.S. Navy no-decompression limitsprovide similar levels of diverprotection.

The third commenter (Ex. 2–99) notedthat the proposal did not consider‘‘omitted decompression’’ that mayoccur while instructing and supervisingnovice divers. This commenter assertedthat novice divers are ‘‘prone to panicand thus more susceptible to anoccurrence that [may require] * * * adecompression chamber on site.’’

Based on these comments, weconclude that the permanent varianceneeds to contain specificrecommendations for no-decompressionlimits. Therefore, we have decided toremove the provision for ‘‘equivalent’’no-decompression limits from thepermanent variance. In doing so, wehave carefully reviewed the findingsand recommendations of Dr. R. W.Hamilton et al. in Ex. 4A (‘‘DSATRecreational Dive Planner: Developmentand Validation of No-StopDecompression Procedures forRecreational Diving’’ or ‘‘the Planner’’).Based on evidence cited in the Planner,we find that the scientific communityaccepts the DSAT no-decompressiontables; in addition, the program ofextensive laboratory and field testingdescribed in the Planner hasdemonstrated that the DSAT no-decompression tables are reliable andvalid. Accordingly, the permanentvariance allows Dixie to use the DSATno-decompression tables and the no-decompression limits in the 1991NOAA Diving Manual. Should other no-decompression limits become availablein the future, Dixie may request us toamend the permanent variance. Theapplication would need to demonstratethat the alternative no-decompressionlimits are at least as protective as thelimits specified in the permanentvariance.

In an earlier response to thecommenter in Ex. 2–109 in paragraph(d) of Part 1, we stated that NOAA’sEAD formula can accurately estimatethe DCS risk associated with nitroxbreathing-gas mixtures based onequivalent nitrogen partial pressuresand dive durations used in air diving. Inaddition, we disagree with thiscommenter’s recommendation to adoptthe U.S. Navy’s no-decompression

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limits. If we were to adopt these limits,we would unnecessarily restrict a majorapplication of rebreathers (i.e., to usehigh levels of O2 in the breathing-gasmixture to extend the diving duration ata specific depth beyond the durationlimit specified for air).

As previously noted, the commenterin Ex. 2–99 expressed concern aboutdiving-related incidents among novicedivers, and implied that recreationaldiving instructors could be placed atrisk of DCS or AGE under theseconditions. We find that the risk of DCSis negligible under these conditionsbecause the recreational divinginstructors and novice divers will beusing the NOAA or DSAT no-decompression tables and, therefore,will have no need to decompress. If anovice diver panics and makes a rapidascent to the surface, the recreationaldiving instructor has been trained andhas the necessary experience to followthe novice diver to the surface in anorderly fashion, thereby avoiding AGE.

(l) Proposed Condition K.3, whichspecified the entries that divers mustmake in the diving log, received onlyone comment (Ex. 2–109). Thiscommenter asked who would make theentries, stating that ‘‘frequently, otherthan the paying passengers * * * thereis only the boat captain and theinstructor [or] guide.’’ Dixie Diversconsists of several small commercialdiving businesses that may havedifficulty finding an employee to makeentries in the diving log. After wepublished the proposed variance, Dixieasked us to revise the proposedcondition to permit non-employees tomake entries in the log. In addition,Dixie asked for a similar revision toproposed Condition L, which requiredthe employer to verify the availability oftreatment resources for medicalemergencies, and to enter theverification in the diving log.Recognizing that any properly-qualifiedindividual can make such entries, wehave revised these provisions to permitDixie to use non-employees to performthese tasks, but only after verifying theirqualifications to do so. As the employer,Dixie will be responsible for assuringthat the entries are made, regardless ofwho makes them.

(m) Proposed Condition L requiredthat Dixie confirm, on a daily basisbefore commencing diving operations,the availability of resources to treat adiving-related medical emergency,including ‘‘transportation * * * capableof delivering [an injured diver] to thedecompression chamber within twohours of the injury.’’ A commenter (Ex.2–109) asked, ‘‘Does this imply that ifthey are told a chamber is down or the

Coast Guard can’t confirm readiness,that they’ll cancel the diving for thatday?’’ This commenter cautioned that‘‘if an accident happens after asignificant amount of time has passedsince the call, [a decompressionchamber] may not be available at thattime [because it’s in use or undergoingmaintenance].’’ Based on thesecomments, we have clarified therequirement in the permanent varianceby specifying that Dixie must confirmthat the required treatment resources are‘‘available during each day’s divingoperations.’’

This commenter (Ex. 2–109) alsoargued that a decompression chambershould be within one hour from the divesite, instead of two hours, because of the‘‘relatively short distance off-shore thatmost Florida diving is done,’’ and any‘‘[t]ime delay in getting an injured diverto a chamber can severely lessen thechances of full recovery from DCS.’’ Inreviewing this recommendation, weasked the Divers Alert Network (DAN)for assistance. DAN is the nation’sleading private-sector organizationproviding DCS treatmentrecommendations to recreational diversand diving guides.

With DAN’s assistance, we identified13 locations in Florida where suitabledecompression chambers (6.0 ATApressure capability, dual-lock,multiplace) are available to the publicfor treating diving-related medicalemergencies. These chambers are inPensacola, Panama City, Tallahassee,Gainesville, Jacksonville, Inverness,Orlando, Tampa, Fort Myers, Miami,Tavernier, Marathon, and Key West.These 13 decompression-facility sitesare within two hours transit time of anydiving location in Florida, including off-shore, state-controlled waters. Thistransit time assumes the use of surfacevehicle transportation traveling at themaximum legal speed limit, andincludes 30 minutes to make land whendiving off-shore. In response to thecommenter’s statement that increases intreatment delay will ‘‘severely lessenthe chances of full recovery from DCS,’’we sought evidence with respect to one-hour or two-hour treatment delays fromDr. Edward D. Thalmann (Ex. 12). Dr.Thalmann is a world-renowned expertin treating diving-related medicalemergencies among recreational divers;he is also the author of a number ofscientific publications that address thecauses and treatment of diving-relatedmedical emergencies, especially DCS.

In his reply (Ex. 13), Dr. Thalmanncompared the risk of AGE and DCSamong recreational divers who breatheair as opposed to nitrox. He thenestimated the maximum delay in

decompression treatment that would notworsen the treatment outcome. Dr.Thalmann noted that AGE is the mostlife-threatening diving-related medicalemergency that can occur and that, totreat the most serious cases, adecompression chamber should beavailable at the dive site. He recognizedthat this recommendation went farbeyond our existing requirements forsome types of recreational diving (e.g.,recreational diving instruction coveredby paragraph (a)(2)(i) of 29 CFR1910.401). In this regard, Dr. Thalmannstated that AGE ‘‘is a rare occurrenceand can be avoided with proper trainingand experience.’’ Dr. Thalmannconcluded that AGE ‘‘is essentiallyindependent of the time at depth’’ andthat ‘‘there is no evidence * * * [to]suggest that the occurrence and outcomeof [AGE] would be any differentbreathing a [n]itrox mixture [other] thanair.’’

Regarding DCS, Dr. Thalmannasserted that research data show that theEAD approach (see the discussion aboveunder paragraph (d) of Part 1) is validfor computing no-decompression limitsfor O2 partial pressures as high as 1.5ATA. Based on this research and hisfield experience, Dr. Thalmann statedthat DCS associated with breathing anitrox gas mixture ‘‘should not besubstantially different in incidence andseverity compared to diving on air[,]provided the [n]itrox no-decompressiontimes are computed from accepted airno-decompression limits using the[NOAA’s] EAD [formula].’’ Dr.Thalmann concluded that, within theseconstraints, ‘‘there is no rationale forhaving different requirements forrecompression chamber availability forair and [n]itrox no-decompressiondiving.’’

In addressing treatment delay, Dr.Thalmann reviewed available researchstudies, as well as data from DAN.According to Dr. Thalmann, the DANdata ‘‘apply to recreational diving onlywhere the vast majority of diving iswithin no-decompression limits.’’ Theresults show that, for both pain-onlyDCS and DCS with severe neurologicalsymptoms, a treatment delay of fourhours can occur without diminishingtreatment success (i.e., complete reliefof symptoms). In conclusion, Dr.Thalmann stated, ‘‘There is nosignificant body of evidence to suggestthat, so long as one is diving withinaccepted no-decompression limitsbreathing air or [n]itrox, having accessto a recompression facility within 4hours is inadequate.’’

Dr. Thalmann’s reply demonstratesseveral points: (1) The risk of AGE andDCS while breathing air or a nitrox gas



mixture should not differ when the diveconforms to accepted no-decompressionlimits computed using the EADapproach; (2) maintaining adecompression chamber at the dive siteto treat AGE is unnecessary andimpractical because AGE is a rareoccurrence that proper training anddiving experience can prevent; and (3)as much as a four-hour delay in treatingDCS does not diminish treatmentoutcomes. Based on this evidence, aswell as a complete review of the existingrecord, we have decided to keep theprovision permitting a two-hourtimeframe for treating DCS, as proposedby Dixie.

As part of his reply, Dr. Thalmannalso recommended that we revise thephrase ‘‘within two hours of the injury’’in proposed Condition L.1 to read ‘‘[2]hours after it is recognized thatsymptoms of [a decompression incident]are present.’’ We acknowledge that theproposed language was unclear, but wealso believe that the recommendedwording may be confusing as well.Therefore, we have adopted newlanguage in the permanent variance thatexpresses the requirement in terms ofthe maximum delay permitted intransporting the injured diver to asuitable decompression chamber; therevised language reads, ‘‘* * * withintwo (2) hours travel time from the divesite.’’

(n) Proposed Condition N specifiedthat Dixie was responsible for initialtreatment of diving-related medicalemergencies, and that it had to ensurethat ‘‘two personnel, one of whom shallbe a diver employed by [Dixie] and bothof whom are qualified in first-aid andthe administration of treatment oxygen’’were available at the dive site for thispurpose. Two commenters responded tothis provision. The first commenter (Ex.2–100) stated that the provision appearsto be ‘‘an attempt by Dixie Divers * * *to use the process to gain an unfairadvantage in the recreational divingmarket by requiring all divingoperations to contract with a ‘diveremployed by the applicant.’ ’’ Thesecond commenter (Ex. 2–109) assertedthat this requirement would be difficultto satisfy because the ‘‘typical crew ona Florida boat is [a] captain andinstructor.’’ Dixie, as a small businesswith few employees, supported thesecond commenter’s assertion, andrequested that it be permitted to usequalified non-employees to meet thisrequirement.

In reply to these comments, we notethat Dixie and all other employersengaged in commercial divingoperations must already provide, asappropriate, on-site support personnel

to perform a variety of tasks (see, e.g.,the requirements in paragraph (c) of 29CFR 1910.410 and paragraph (c)(2) of 29CFR 1910.426). These personnel canalso perform duties as specified inproposed Condition N. We recognize,however, that the main purpose of thisprovision is to ensure that properly-qualified personnel are available,regardless of their employment status.Therefore, we have revised thisprovision to permit Dixie to use non-employees for first-aid and O2

treatment. However, Dixie may do soonly if it verifies their qualifications toperform these tasks before it starts theday’s diving operations.

(o) Proposed Condition O specifiedthe training requirements for Dixie’srecreational diving instructors anddiving guides, including therequirement that an industry-recognizedtraining agency certify that the diversare capable of using the divingequipment and breathing-gas mixturesneeded for their recreational divingoperations. The National Association ofUnderwater Instructors (NAUI) (Ex. 2–100) noted its affiliates offer ‘‘a fullrange of training programs from SkinDiver through Instructor CourseDirector, including certification inoxygen enriched air, semi-closed circuitand closed circuit rebreather diver.’’Nonetheless, NAUI found the proposedcondition ambiguous because it ‘‘doesnot provide a definition of the divingindustry or outline any process orcriteria to evaluate and recognize atraining agency that would establish thelegitimacy of its training.’’

We agree with NAUI’s comment thatthis provision in the proposed variancewas confusing. Additionally, we believethat an employer is in the best positionto determine if the training that itsdivers obtain is adequate to performtheir jobs safely and effectively.Therefore, we have revised the proposedprovision and have made the trainingrequirement in the permanent varianceperformance-based; that is, Dixie mustensure that its employees receivetraining that enables them to performsafely and effectively while using open-circuit SCUBAs or rebreathers suppliedwith nitrox breathing-gas mixtures.However, we specified several criticaltasks that the recreational divinginstructors and diving guides employedby Dixie must be trained to performsafely and effectively, including:Recognizing the effects associated withbreathing excessive CO2 and O2; takingappropriate action after detecting theeffects of breathing excessive CO2 andO2; and properly evaluating, operating,and maintaining their open-circuitSCUBAs and rebreathers. We addressed

the importance of recognizing andresponding properly to the effects ofexcessive CO2 and O2 in our earlierdiscussions of Conditions A.2 and E ofthe proposed variance. Based on ourreview of Ex. 5 (especially pages 11–1through 11–15), we believe that diversmust also know how to evaluate,operate, and maintain their rebreathersunder the diving conditions that theyencounter as recreational divinginstructors and diving guides. We havespecified these revisions in Condition38 of the permanent variance.

Part 3. Comments to Proposed SectionIII (Rationale for the ProposedAlternative)

(a) In discussing Conditions A and Bin the proposed variance, we noted thatthe existing exemption for recreationaldiving instructors in paragraph (a)(2)(i)of 29 CFR 1910.401 in our CDOStandard does not refer to rebreathers.We explained that ‘‘such equipment wasnot available or in common use byrecreational diving instructors whenOSHA’s [CDO] Standard waspromulgated in 1977’’ (62 FR 58999,first column). A commenter (Ex. 2–109)noted that this statement gave the falseimpression that rebreather equipment‘‘is readily used by the recreationaldiving community.’’ Regarding theexperience of the recreational divingcommunity with rebreathers, thiscommenter asserted that ‘‘while theargument can be made that [rebreathershave] been used safely within thescientific and commercial divingindustries, it can also be argued thatthose divers are more highly trained andthe operations more closely monitoredthan is the norm in the recreationaldiving industry.’’

Our discussion of the rationale forConditions A and B as proposed notedthat ‘‘data related to the reliability andsafety of [rebreather equipment] aredifficult to obtain because its use byrecreational divers is still uncommon’’;however, we now believe that data areavailable showing that recreationaldiving instructors and diving guides canuse rebreathers safely and reliably. Werevised our opinion after reviewing Ex.5 (especially pages 2–2, 7–1, and 7–2),which shows that various militaryorganizations have a 50-year history ofusing rebreathers safely, scientific andtechnical divers have been doing so forover 20 years, and, currently,recreational diving instructors anddiving students safely performrebreather diving. We believe, therefore,that we have sufficient knowledge aboutrebreather technology and divingprocedures to determine that theconditions specified in the permanent



variance will protect Dixie’s recreationaldiving instructors and diving guides atleast as well as having an on-sitedecompression chamber.

(b) The rationale for proposedConditions C through E justified the useof DSAT’s Oxygen Exposure Table (62FR 58999, second and third columns).This rationale elicited one comment (Ex.2–109). This commenter stated thatspecifying time limits in the DSATOxygen Exposure Table in terms of totaldive time ‘‘is * * * a very commonindustry practice and not some greatconcession on Dixie’s part, as thewording of the sentence would perhapslead you to believe.’’ In this case, weagree that the use of a common industrypractice will enable Dixie to complywith the permanent variance withoutadditional effort, while providingadequate diver protection.

(c) Proposed Condition K provided arationale for using dive-decompressioncomputers, noting that no-decompression limits for repetitivedives can involve ‘‘tedious and time-consuming calculations * * * made byhand.’’ It concluded that dive-decompression computers would ‘‘assistdivers in decreasing their exposure toexcessive ascent rates, oxygen toxicity,and DCS that could result from errors incalculating repetitive no-decompressiondiving schedules manually.’’ (62 FR59000, third column.) The singlecommenter (Ex. 2–109) on this pointclaimed that manual calculations ‘‘[canbe] taught in the first or second lectureof most entry-level [SCUBA] classes’’and performed in a couple of minutes.This commenter also asserted thatmanual calculations may provide anadditional margin of safety from DCSbecause they typically determinedecompression using the deepest depthattained during a dive. By contrast,dive-decompression computers mayreduce decompression (and thereforeincrease the risk of DCS) by ‘‘measur[ingthe] exact depth every few seconds andrecalculat[ing decompression] based onactual depth.’’

In reply, we note that Condition K asproposed allowed Dixie the flexibility touse either manual calculations or dive-decompression computers.Nevertheless, manual calculation issubject to human error, and computeruse can reduce such error. Thepermanent variance will reduceproblems associated with using dive-decompression computers to avoiddecompression by restricting the no-decompression limits to the most recentdecompression tables and formulaspublished by NOAA and DSAT.

(d) The rationale for proposedConditions O and P addressed the

requirements for diver certification,noting that ‘‘Condition O providesgeneral uniformity to the diverqualification and training process, aswell as quality control over thecertifying agencies.’’ (62 FR 59001, thirdcolumn.) A commenter (Ex. 2–109)stated that the certification requirementimposed no burden on Dixie because itwas consistent with existing industrypractice; in addition, the requirementwas unlikely to bring uniformity todiver qualifications because ‘‘differentdive stores, certifying under the samenational standards, can still turn outdivers [and] instructors of varyingproficiency levels.’’ In reply, we notethat we do expect these requirements tomake training programs more uniform(than is presently the case) in the waythat they train recreational divinginstructors and diving guides, and thisuniformity should substantially reducemuch of the variability in diverproficiency.

Part 4. Comments to Proposed SectionVI (Issues)

In the proposal, we invited the publicto submit information and specificcomments and rationale on nine otherissues. Only one commenter (Ex. 2–109)did so. This commenter addressed thefirst issue, which requested commentersto differentiate the underwater tasks andtypes of diving performed byrecreational diving instructors anddiving guides, and to relate thesedifferences to the probability ofexperiencing diving-related medicalproblems. The commenter stated that,during training dives, recreationaldiving instructors ‘‘will probably domultiple ascents * * * but may beexposed to less time in the water thana dive guide since students generally areexcited and [consume more air] thanexperienced divers.’’ The commenterstated that, during the ascent-trainingphase, recreational diving instructorsmust ‘‘make multiple, generally rapid,ascents with each of the students,increasing the chances of a DCS hit.’’The commenter added that recreationaldiving instructors are ‘‘at a slightlygreater risk [than diving guides] of AGEfrom the ascents and perhaps a slightlyelevated chance of DCS due to rapidascents,’’ although ‘‘[t]he likelihood ofthe instructor getting DCS or AGE * * *is probably extremely small.’’

Regarding diving guides, thecommenter asserted that it escortsexperienced divers who, typically, areless excitable than novice divers; basedon this assumption, the commenterasserted that experienced divers wouldconsume breathing gases at slower ratesthan novice divers. The commenter

concluded that slow rates of gasconsumption would extend divedurations which, combined with thedeeper dives made by diving guidescompared to recreational divinginstructors, would increase the divingguides’ risk of DCS. In response to thiscommenter, we refer to our earlierdiscussion of this issue in Part I. In thisdiscussion, we agreed that ‘‘using high-O2 nitrox breathing-gas mixtures wouldincrease the risk of DCS,’’ but concludedthat ‘‘the resulting risk would becomparable to using the equivalentpartial pressure of nitrogen in air forthat extended period.’’

Part 5. General Comments to theProposed Variance

One commenter (Ex. 2–105) indicatedthat a number of topics neededclarification or were ‘‘so controversial orcomprehensive in nature that this levelof detail in a policy document may notbe appropriate.’’ These areas are:Validating dive-decompressioncomputers, including the programmablesafety factors used in these computers;updating decompression data;identifying programmable gas-percentage options; using failure modeand effects analysis of criticalcomponents and assemblies to developconsensus regarding the general safetyand accuracy of dive-decompressioncomputers; determining the relevanceof, and necessity for, monitoringenvironmental temperatures and thebreathing-loop gases in closed-circuitrebreathers; and recognizing standardsdeveloped by the equipmentmanufacturers. The commenter statedthat ‘‘[t]o expand on just a few of [theseareas] would make this document much[too long].’’ Nevertheless, thecommenter asserted, withoutexplanation, that ‘‘from a standpoint oftechnical diving facts [the proposedvariance] is grossly inaccurate and inmany cases written with twisted facts,’’and that the ‘‘[proposed] variance aswritten has the potential to exposeemployees (i.e.[,] dive shop technicians,instructors) to dangerous situations.’’

In large part, these areas of concernaddress the safety and standardizationof dive-decompression computers.Under the permanent variance, use ofdive-decompression computers isoptional; however, if Dixie uses thesecomputers, it must also provide itsdivers with specific decompressioninformation. Regardless of computer useor availability, Dixie must have hard-copy decompression tables at the divesite. Thus, the permanent variancespecifies the conditions that Dixie mustmeet to ensure that its employees’diving activities conform to accepted



no-decompression practices, whether ornot Dixie uses dive-decompressioncomputers.

Another commenter (Ex. 2–109) statedthat ‘‘[t]o retailers * * * nitrox ismarketed as a new profit center. In anindustry with flat growth over the pastfew years, and where profit margins aresmall to begin with, nitrox * * * can besold to the diving consumer as a ‘safer’alternative to air, thus generating moreprofits * * * through the sale of classesand equipment specific to nitrox.’’Regarding diving safety, this commenterasserted that the high level of divingskills acquired by commercial diversmade them safer than recreationaldiving instructors and diving guides,and referred to statistics from the DiversAlert Network (DAN) to support thisassertion:[T]he statistics [for 1996] show that 0.2% ofthe reported accidents involved commercialdivers, but 17.1% of the accidents involvedInstructors or Divemasters (dive guides). Thelatter are the same two categories * * * whomake up Dixie Diver’s employees who wouldbe exempt under the variance. In 1995, thenumbers were 0.5% for commercial diversversus 15.9% for instructors[-] divemasters.In 1994, the numbers were 0.0% forcommercial divers and 21.5% forinstructors[-]divemasters.

The statistics cited by this commenterdo not address the principal conditionsspecified in the permanent variance(i.e., recreational diving instructors anddiving guides who make no-decompression dives using nitroxbreathing-gas mixtures). In a recenteditorial in Alert Diver (Ex. 16, page 2),DAN’s director (Dr. Peter B. Bennett)addressed the safety of nitrox divesmade by recreational divers (whichincludes sports divers, as well asrecreational diving instructors anddiving guides). Dr. Bennett stated that‘‘[b]etween 1990 and 1993 DANcollected data on 21 cases of mixed-gasdiving injuries. In 1994 there were 10,and in 1996, 16 injuries occurred. The1996 data [are] based on 23 nitrox ormixed-gas injuries requiringrecompression treatment. * * * TheInternational Association of Nitrox andTechnical Divers * * * certified 17,780U.S. nitrox divers from 1985 to 1996.’’Based on this information, an average ofless than 0.001 per cent of recreationaldivers who use nitrox breathing-gasmixtures are injured each year.Additionally, both Dr. Bennett (Ex. 16,pages 2 and 6) and other DANrepresentatives (Ex. 4A, page 60) admitthat valid comparisons cannot be madebetween different categories of diversbecause adequate baseline data (e.g., thenumber and types of dives made by alldivers in a category) are not available.

In conclusion, we believe that theprotections afforded by the conditionsspecified in the permanent variance willreduce the prevalence of diving-relatedinjuries among Dixie’s recreationaldiving instructors (who also havesubstantial experience in using nitroxbreathing-gas mixtures) below thealready low injury rates cited in Dr.Bennett’s editorial.

Part 6. Our Revisions to the ProposedVariance

(a) When divers use rebreathers,proposed Condition A.4 provided for asupplemental supply of breathable gasduring emergency egress (referred to asthe ‘‘bail-out system’’); this supplywould consist of a diluent breathing gasconnected to the second stage of theregulator. We have added a phrase tothe permanent variance to addressalternative means of emergency egresswhen open-circuit SCUBA provides thenitrox breathing-gas mixture. It allowsDixie to use the reserve breathing-gassupplies specified in paragraph (c)(4) of29 CFR 1910.424 for this purpose. Thisalternative, specified in Condition(30)(b)(i) in the permanent variance, isan existing requirement for open-circuitSCUBA.

When the bail-out system consists ofa separate supply of emergencybreathing gas, Condition A.1 of theproposed variance permitted Dixie touse air as the emergency breathing gas.The permanent variance retains thisprovision.

(b) Conditions A.5.a and A.5.b in theproposed variance specified the use ofan information module that providestime, depth, ascent, and descent data todivers who use closed-circuitrebreathers, and time, ascent, anddescent information to divers who usesemi-closed-circuit rebreathers.Proposed Condition A.5.c required bothtypes of rebreathers to have alarms orvisual displays that warn the diverabout excessive ascent and descentrates, as well as depth levels that areshallower than the ceiling-stop depth.While Dixie’s recreational divinginstructors and diving guides could usedive-decompression computers for thispurpose, we believe that suchcomputers are unnecessary because thedivers will be diving within no-decompression limits, and the technicalcapability of dive-decompressioncomputers exceeds the requirements ofno-decompression dives. Aninformation module that provides thedivers with the specified diveinformation will permit them to remainwithin no-decompression limits and todescend and ascend the water column atthe rates specified by the diving tables.

We believe, therefore, that theinformation module will ensure thatDixie’s divers remain as safe as theywould if they used dive-decompressioncomputers.

(c) Proposed Condition A.5.c alsorequires that, for both semi-closed-circuit and closed-circuit rebreathers,the information module must warn thediver of low battery voltage. As noted inEx. 5 (page P–59), a partial or totalelectronic failure interferes with sensorand control systems and may haveserious safety consequences for thediver. We believe that the diver’s safetydepends on properly-operatingelectrical power supplies and electricaland electronic circuits. Accordingly, wehave revised the proposal by requiringthat Dixie perform the followingprocedure: ‘‘Before each day’s divingoperations, and more often whennecessary, * * * ensure that theelectrical power supplies and electricaland electronic circuits in eachrebreather are operating as required bythe rebreather manufacturer’sinstructions.’’ Condition (12) of thepermanent variance contains thisrevision.

(d) Proposed Conditions B.1 and G.1.caddressed O2 sensor and controlrequirements for closed-circuitrebreathers. Conditions (13) through(17) in the permanent varianceconsolidate these requirements in asingle location.

(e) For closed-circuit rebreathers,proposed Condition G.1.c specifies theuse of O2 sensors to assess the O2

fraction in the breathing loop, whileproposed Condition G.1.d requires Dixieto determine (i.e., calibrate) sensoraccuracy according to the rebreathermanufacturer’s instructions. As noted inthe proposal, maintaining accurate O2

partial pressures in the breathing loop iscritical to diver health and safety. Toassure safe operation of O2 sensors, webelieve that the permanent variancemust specify the frequency for assessingthe accuracy of O2 sensors. Such anapproach is consistent with therebreather community’s use of regulardiving-equipment assessments (see Ex.5,pages 4–1 through 4–13, and 14–2).Condition (15) of the permanentvariance, therefore, requires that‘‘[b]efore each day’s diving operations,and more often when necessary, [Dixie]must calibrate O2 sensors as required bythe sensor manufacturer’sinstructions[.]’’ Removing inaccurate O2

sensors from service and replacing themwith correctly-calibrated sensors is alogical and expected consequence of thecalibration process; we are specifyingthis requirement in Conditions (15)(d)and (15)(e) of the permanent variance.



(f) Proposed Condition G.1.c acceptedO2 sensors only if they wereelectromechanical. Evidence in therecord (Ex. 5, page 5–11) indicates thatO2-sensor technology is undergoingcontinued development and refinement.We believe, therefore, that specifying‘‘electromechanical’’ O2 sensors is toolimiting, and we have revised thisprovision to specify that Dixie must useO2 sensors approved by the rebreathermanufacturer (see Condition (14)(b) inthe permanent variance).

(g) Condition G.1.d in the proposedvariance required Dixie to maintain theaccuracy of the equipment used toanalyze O2 in the breathing-gas mixture‘‘in accordance with the manufacturer’sinstructions.’’ We intended thisrequirement to apply to the analyticequipment used both to calibrate O2

sensors and to determine the O2 fractionin nitrox breathing-gas mixtures. Toclarify this intention, we have includedthe requirement separately inConditions (15)(b) and (22)(b) in thepermanent variance.

(h) We have clarified the provision inproposed Condition G.2.a thataddressed the analysis of O2 in nitroxbreathing-gas mixtures obtained fromcommercial suppliers. This revisionrequires Dixie to ensure that thesupplier of the mixture analyzes the O2

fraction in the mixture in the chargedtank after disconnecting the tank fromthe charging apparatus. Thisclarification prevents the supplier fromusing the O2 sensor on the chargingapparatus for this purpose, a procedurethat could result in an incorrectdetermination. The revised provision isin Condition (23)(b) of the permanentvariance.

(i) Proposed Conditions K.3 and K.4required that Dixie maintain a divinglog and decompression tables at the divesite. The diving log documents thecritical dive parameters. Divers who donot use dive-decompression computersmust use the decompression tables; thetables also serve as a back-up resourceto divers with dive-decompressioncomputers. We have revised theproposed conditions to ensure thatDixie maintains a diving log anddecompression tables at the dive sitesfor all diving operations covered by thepermanent variance, whether or not itsdivers use a dive-decompressioncomputer. The revised provision alsoclarifies that the decompression tablesmust be hard copies and conform to theno-decompression limits specified inCondition (28) of the permanentvariance. Condition (37) of thepermanent variance contains the revisedrequirements.

(j) Regarding the term ‘‘portableoxygen,’’ proposed Condition Mspecified that ‘‘the oxygen shall beavailable for administration to the diverduring the entire period the diver isbeing transported to a decompressionchamber.’’ The O2 supplied for thispurpose must be pure O2, and theinjured diver must receive the O2

continuously from the time Dixiedetects the diving-related medicalemergency until the diver beginstreatment in a decompression chamber.We have revised the proposal to clarifythese requirements. Therefore,Condition (33) in the permanentvariance requires Dixie to ensure thatthe portable O2 equipment suppliespure O2 to the injured diver’stransparent mask, and that sufficient O2

is available to treat injured divers untilthey reach a decompression chamber.

(k) In the proposed variance, oneprovision (Condition G.1.d) requiredDixie to maintain the accuracy of theequipment used to analyze the O2

fraction of the breathing gas ‘‘inaccordance with the manufacturer’sinstructions.’’ To clarify whichmanufacturer is being addressed in thisprovision, we revised the relevantconditions of the permanent variance(Conditions (15)(b) and (22)(b)) to referspecifically to the manufacturer of theO2 analyzer (who seems to us to be inthe best position to specify how its O2

analyzer should be calibrated). We havemade similar revisions to otherprovisions of the permanent variance,including Condition (9) (which specifiescalibration requirements for CO2

sensors) and to Condition (15) (whichspecifies the calibration requirement forO2 sensors).

The permanent variance contains ageneral requirement (Condition (3)) touse rebreathers according to themanufacturer’s instructions. We repeatthis requirement in several otherimportant conditions of the permanentvariance. We have added this provisionbecause SCUBA manufacturers selectand develop the characteristics andparameters of SCUBA equipment,design and integrate the equipmentaccordingly, procure or manufacture theequipment components, and thenassemble and test the final products.There is a wide range of SCUBA designsand capabilities, and there are nouniform standards for the design,function, and use of SCUBA. Webelieve, therefore, that the SCUBAmanufacturer is in the best position tospecify the components, configuration,and operation of its product. Inaddition, the rebreather conference heldrecently in Redondo Beach, California,recommended that ‘‘[m]anufacturers

must provide written procedures, preand post dive checklists, and a schedulefor required maintenance.’’ The SCUBAmanufacturers who attended theconference endorsed thisrecommendation (see Ex. 5, page 14–2).

V. DecisionDixie Divers, Inc. seeks a permanent

variance from the decompression-chamber requirements of paragraphs(b)(2) and (c)(3)(iii) of 29 CFR 1910.423and paragraph (b)(1) of 29 CFR1910.426. These provisions require anemployer to have a decompressionchamber available and ready for use atthe dive site to treat two diving-relatedmedical emergencies that employeesmay experience—decompressionsickness (DCS) and arterial-gasembolism (AGE). Divers may developDCS after decompressing inadequatelyduring dives in which they breathe amixed gas (e.g., nitrox). AGE resultsfrom overpressurizing the lungs, usuallyduring a rapid ascent to the surface;overpressurization causes the air sacs inthe lungs to rupture and dispersebubbles into the pulmonary veins.

These decompression-chamberprovisions require employers to ensurethat: Employees remain awake and inthe vicinity of a decompression chamberfor at least one hour after the divewhenever they make no-decompressiondives, dive to depths deeper than 100feet of sea water, or use a mixed-gasbreathing mixture (paragraph (b)(2) of29 CFR 1910.423); and a decompressionchamber is located within five minutesfrom the dive site and is ready for use(paragraph (c)(3)(iii) of 29 CFR 1910.423and paragraph (b)(1) of 29 CFR1910.426).

In its variance application, Dixiestated that nitrox breathing-gas mixturesreduce the occurrence and severity ofDCS, while the equipment andprocedural safeguards specified in thevariance application lower the risk ofAGE. (See section II, ‘‘Application for aPermanent Variance,’’ of this notice fora thorough review of Dixie’s varianceapplication.) Dixie asserted that the riskof DCS and AGE for divers who use theSCUBA equipment and divingprocedures proposed in the varianceapplication would be equal to, or lessthan, that experienced by diversexempted from our CDO Standard. Thisexemption, specified in paragraph(a)(2)(i) of 29 CFR 1910.401, applies torecreational diving instructors who usecompressed air supplied to open-circuitSCUBAs under no-decompressiondiving limits. Dixie concluded,therefore, that we should not require itto maintain a decompression chamber atthe dive site if it complies with the



conditions proposed in the varianceapplication.

After reviewing the varianceapplication, comments made to therecord about the application, and othertechnical and scientific informationsubmitted to the record, we have revisedthe proposed variance to require Dixieto use specific procedures andequipment safeguards for its diverswhen they engage in recreational divinginstruction and perform services asdiving guides. Therefore, under § 6(d) ofthe OSH Act, and based on the recorddiscussed above, we find that whenDixie complies with the conditions ofthe following order, its divers will beexposed to working conditions that areat least as safe and healthful as theywould be if Dixie complied withparagraphs (b)(2) and (c)(3)(iii) of 29CFR 1910.423 and paragraph (b)(1) of 29CFR 1910.426.

VI. OrderWe issue this order authorizing Dixie

Divers, Inc. to comply with thefollowing conditions instead ofcomplying with paragraphs (b)(2) and(c)(3)(iii) of 29 CFR 1910.423 andparagraph (b)(1) of 29 CFR 1910.426:

Application of the Permanent Variance(1) This permanent variance applies

only to the recreational divinginstructors and diving guides (‘‘divers’’)employed by Dixie Divers, Inc.(designated as ‘‘you’’ or ‘‘your’’) whenyour:

(a) Recreational diving instructorstrain diving students in the use ofrecreational diving procedures and thesafe operation of diving equipment,including open-circuit, semi-closed-circuit, or closed-circuit self-containedunderwater breathing apparatus(SCUBA) during these training dives;

(b) Diving guides lead small groups oftrained sports divers who use open-circuit, semi-closed-circuit, or closed-circuit SCUBAs to local undersea divinglocations for recreational purposes; and

(c) Divers use a nitrox breathing-gasmixture consisting of a high percentageof oxygen (O2) (i.e., over 22 percent(22%) by volume) mixed with nitrogenand supplied by an open-circuit, semi-closed-circuit, or closed-circuit SCUBA.

(2) This permanent variance does notapply when your divers engage indiving activities other than recreationaldiving instruction or diving guideduties.

Equipment Requirements forRebreathers

(3) You must ensure that your diversuse rebreathers (i.e., semi-closed-circuitand closed-circuit SCUBAs) in

accordance with the rebreathermanufacturer’s instructions.

(4) Regarding CO2-sorbent materials incanisters:

(a) You must ensure that eachrebreather uses a manufactured (i.e.,commercially pre-packed), disposablescrubber cartridge containing a CO2-sorbent material that:

(i) Is approved by the rebreathermanufacturer;

(ii) Removes CO2 from your divers’exhaled gas; and

(iii) Maintains the CO2 level in thebreathable gas (i.e., the gas that yourdivers are inhaling directly from theregulator) below a partial pressure of0.01 atmospheres absolute (ATA); or

(b) You may use an alternativescrubber method if:

(i) The rebreather manufacturerpermits such use;

(ii) You use the alternative methodaccording to the rebreathermanufacturer’s instructions; and

(iii) You demonstrate that thealternative method meets therequirements specified above inCondition (4)(a) of this order.

(5) You must ensure that eachrebreather has a counterlung thatsupplies a volume of breathing gas toyour divers that is sufficient to sustaintheir respiration rate and contains anover-pressure valve.

(6) You must ensure that eachrebreather uses a moisture trap in thebreathing loop, and that the moisturetrap and its location in the breathingloop are approved by the rebreathermanufacturer.

(7) You must ensure that eachrebreather has a continuously-functioning moisture sensor thatconnects to a visual (e.g., digital,graphic, or analog) or auditory (e.g.,voice, pure tone) alarm that warns yourdivers of moisture in the breathing loopin sufficient time to terminate the diveand return safely to the surface.

(8) You must ensure that eachrebreather contains a continuously-functioning CO2 sensor in the breathingloop, and that the CO2 sensor and itslocation in the breathing loop areapproved by the rebreathermanufacturer. You must also integratethe CO2 sensor used in a rebreather withan alarm that:

(a) Operates in a visual (e.g., digital,graphic, or analog) or auditory (e.g.,voice, pure tone) mode;

(b) Is readily detectable by your diversunder the diving conditions in whichthey operate; and

(c) Remains continuously activatedwhen the inhaled CO2 level reaches andexceeds 0.005 ATA.

(9) Before each day’s divingoperations, and more often when

necessary, you must calibrate the CO2

sensor according to the sensormanufacturer’s instructions. In doing so,you must:

(a) Ensure that the equipment andprocedures used to perform thiscalibration are accurate to within 10percent (10%) of a CO2 concentration of0.005 ATA or less;

(b) Maintain this accuracy as requiredby the sensor manufacturer’sinstructions;

(c) Ensure that the calibration of theCO2 sensor demonstrates an accuracy towithin 10 percent (10%) of a CO2

concentration of 0.005 ATA or less;(d) Replace the CO2 sensor when it

fails to meet the accuracy requirementsspecified above in Condition (9)(c) ofthis order; and

(e) Ensure that the replacement CO2

sensor meets the accuracy requirementsspecified above in Condition (9)(c) ofthis order before you place a rebreatherin operation.

(10) As an alternative to using acontinuously-functioning CO2 sensor,you may use schedules for replacingCO2-sorbent material provided by therebreather manufacturer. You may usethese CO2-sorbent replacementschedules only if:

(a) The rebreather manufacturer has:(i) Developed the replacement

schedules according to the canister-testing protocol provided below inAppendix A of this order;

(ii) Analyzed the canister-testingresults using the statistical proceduresdescribed in U.S. Navy ExperimentalDiving Unit Report 2–99 (see section VII(‘‘References’’) below); and

(iii) Specified the replacementschedule in terms of the lowerprediction line (or limit) of the 95%prediction interval. In this regard, therebreather manufacturer may derivereplacement schedules by interpolatingamong, but not by extrapolating beyond,the depth, water temperatures, andexercise levels used during canistertesting; and

(b) You replace the CO2-sorbentmaterial in the canister as required byCondition (4) of this order.

(11) You must ensure that eachrebreather has an information modulethat provides:

(a) Visual (e.g., digital, graphic, oranalog) or auditory (e.g., voice, puretone) displays that will effectively warnyour divers of solenoid failure (whenthe rebreather uses solenoids) and otherelectrical weaknesses or failures (e.g.,low battery voltage);

(b) For semi-closed circuitrebreathers, visual displays for thepartial pressure of CO2, or deviations



above and below a preset CO2 partialpressure of 0.005 ATA; and

(c) For closed-circuit rebreathers:(i) Visual displays for the partial

pressures of O2 and CO2, or deviationsabove and below a preset CO2 partialpressure of 0.005 ATA and a preset O2

partial pressure of 1.40 ATA; and(ii) A visual display for the gas

temperature in the breathing loop.(12) Before each day’s diving

operations, and more often whennecessary, you must ensure that theelectrical power supplies and electricaland electronic circuits in eachrebreather are operating as required bythe rebreather manufacturer’sinstructions.

Special Requirements for Closed-Circuit Rebreathers

(13) You must ensure that closed-circuit rebreathers use supply-pressuresensors for the O2 and diluent (i.e., airor nitrogen) gases and continuously-functioning sensors for detectingtemperature in the inhalation side of thegas-loop and the ambient water.

(14) You must ensure that:(a) At least two O2 sensors are located

in the inhalation side of the breathingloop;

(b) The O2 sensors are continuously-functioning, temperature-compensated,and approved by the rebreathermanufacturer.

(15) Before each day’s divingoperations, and more often whennecessary, you must calibrate O2 sensorsas required by the sensor manufacturer’sinstructions. In doing so, you must:

(a) Ensure that the equipment andprocedures used to perform thecalibration are accurate to within 1percent (1%) of the O2 fraction byvolume;

(b) Maintain this accuracy as requiredby the manufacturer of the calibrationequipment;

(c) Ensure that the sensors areaccurate to within 1 percent (1%) of theO2 fraction by volume;

(d) Replace O2 sensors when they failto meet the accuracy requirementsspecified above in Condition (15)(c) ofthis order; and

(e) Ensure that the replacement CO2

sensors meet the accuracy requirementsspecified above in Condition (15)(c) ofthis order before you place a rebreatherin operation.

(16) You must ensure that closed-circuit rebreathers have:

(a) A gas-controller package withelectrically-operated solenoid O2-supplyvalves;

(b) A pressure-activated regulatorwith a second-stage diluent-gas additionvalve;

(c) A manually-operated gas-supplybypass valve to add O2 or diluent gas tothe breathing loop; and

(d) Separate O2 and diluent-gascylinders to supply the breathing-gasmixture.

O2 Concentration in the Breathing Gas

(17) You must ensure that the fractionof O2 in the nitrox breathing-gasmixture:

(a) Is greater than the fraction of O2 incompressed air (i.e., exceeds 22 percent(22%) O2 by volume);

(b) For open-circuit SCUBA, neverexceeds a maximum fraction ofbreathable O2 of 40 percent (40%) byvolume or a maximum O2 partialpressure of 1.40 ATA, whicheverexposes your divers to less O2; and

(c) For rebreathers, never exceeds amaximum O2 partial pressure of 1.40ATA.

Depth and O2 Partial Pressure Limits

(18) Regardless of the divingequipment your divers use, you mustensure that they dive no deeper than130 feet of sea water (fsw) or to amaximum O2 partial pressure of 1.40ATA, whichever exposes them to lessO2.

(19) Regarding O2 exposure, you must:(a) Ensure that the exposure of your

divers to partial pressures of O2 between0.60 and 1.40 ATA does not exceed the24-hour single-exposure time limitsspecified either by the 1991 NationalOceanic and AtmosphericAdministration Diving Manual (the‘‘1991 NOAA Diving Manual’’) or by thereport entitled Enriched Air Operationsand Resources Guide, published in 1995by the Professional Association ofDiving Instructors (known commonly asthe ‘‘1995 DSAT Oxygen ExposureTable’’) (see section VII (‘‘References’’)below); and

(b) Determine your diver’s O2-exposure duration using the diver’smaximum O2 exposure (partial pressureof O2) during the dive and the total divetime (i.e., from the time the diver leavesthe surface until the diver returns to thesurface).

Mixing and Analyzing the BreathingGas

(20) You must ensure that onlyproperly trained personnel mix nitroxbreathing gases, and that nitrogen is theonly inert gas used in the breathing-gasmixture.

(21) When mixing nitrox breathinggases, you must mix the appropriatebreathing gas before you deliver themixture to the breathing-gas cylinders,using the continuous-flow or partial-pressure mixing techniques specified in

the 1991 NOAA Diving Manual, orusing a filter-membrane system.

(22) Before the start of each day’sdiving operations, you must determinethe O2 fraction of the breathing-gasmixture using an O2 analyzer. In doingso, you must:

(a) Ensure that the O2 analyzer isaccurate to within 1 percent (1%) of theO2 fraction by volume; and

(b) Maintain this accuracy as requiredby the manufacturer of the analyzer.

(23) When the breathing gas is acommercially-supplied nitrox breathing-gas mixture, you must ensure that thesupplier:

(a) Determines the O2 fraction in thebreathing-gas mixture using an analyticmethod that is accurate to within 1percent (1%) of the O2 fraction byvolume;

(b) Makes this determination whenthe mixture is in the charged tank andafter disconnecting the charged tankfrom the charging apparatus;

(c) Documents the O2 fraction in themixture; and

(d) Provides you with a writtencertification of the O2 analysis.

(24) For commercially-supplied nitroxbreathing-gas mixtures, you must ensurethat the O2 is Grade A (also known as‘‘aviator’s oxygen’’) or Grade B (referredto as ‘‘industrial-medical oxygen’’), andmeets the specifications, including thepurity requirements, found in the 1991NOAA Diving Manual. In doing so, youmust:

(a) Ensure that the analytic methodused to make this determination isaccurate to within 1 percent (1%) of theO2 fraction by volume; and

(b) Obtain a written certificate to thiseffect from the supplier.

(25) Before producing nitroxbreathing-gas mixtures using acompressor in which the gas pressure inany system component exceeds 125pounds per square inch (psi), you must:

(a) Have the compressor manufacturercertify in writing that the compressor issuitable for mixing high-pressure airwith the highest O2 fraction used in thenitrox breathing-gas mixture;

(b) Ensure that the compressor is oil-less or oil-free and rated for O2 serviceunless you comply with therequirements of Condition (26) of thisorder; and

(c) Ensure that the compressor meetsthe requirements specified inparagraphs (i)(1) and (i)(2) of 29 CFR1910.430 whenever the highest O2

fraction used in the mixing processexceeds 40 percent (40%).

(26) Before producing nitroxbreathing-gas mixtures using an oil-lubricated compressor to mix high-pressure air with O2, regardless of the



gas pressure in any system componentyou must:

(a) Have the compressor manufacturercertify in writing that the compressor issuitable for mixing the high-pressure airwith the highest O2 fraction used in thenitrox breathing-gas mixture;

(b) Filter the high-pressure air toproduce O2-compatible air;

(c) Have the filter-systemmanufacturer certify in writing that thefilter system used for this purpose issuitable for producing O2-compatibleair;

(d) Continuously monitor the airdownstream from the filter forhydrocarbon contamination; and

(e) Use only uncontaminated air (i.e.,air containing no hydrocarbonparticulates) for the nitrox breathing-gasmixture.

(27) You must ensure that divingequipment using nitrox breathing-gasmixtures or pure O2 under high pressure(i.e., exceeding 125 psi) conforms to theO2-service requirements specified inparagraphs (i)(1) and (i)(2) of 29 CFR1910.430.

Use No-Decompression Limits

(28) For diving conducted while usingnitrox breathing-gas mixtures, you mustensure that each of your divers remainswithin the no-decompression limitsspecified for single and repetitive airdiving and published in the 1991 NOAADiving Manual or the report entitledDevelopment and Validation of No-StopDecompression Procedures forRecreational Diving: The DSATRecreational Dive Planner, published in1994 by Hamilton Research Ltd. (knowncommonly as the ‘‘1994 DSAT No-Decompression Tables’’) (see section VII(‘‘References’’) below).

(29) You may permit your divers touse a dive-decompression computerdesigned to regulate decompression ifthe dive-decompression computer usesthe no-decompression limits specifiedabove in Condition (28) of this orderand provides output that reliablyrepresents those limits.

Emergency Egress

(30) Regardless of the divingequipment your divers use (i.e., open-circuit SCUBA or rebreathers), you mustensure that the diving equipmentconsists of:

(a) An open-circuit emergency-egresssystem (a ‘‘bail-out’’ system) in which:

(i) The second stage of the regulatorconnects to a separate supply ofemergency breathing gas; and

(ii) The emergency breathing gasconsists of air or the same nitroxbreathing-gas mixture used during thedive; or

(b) One of the following alternativebail-out systems:

(i) For open-circuit SCUBAs, theemergency-egress systems specified inparagraph (c)(4) of 29 CFR 1910.424; or

(ii) For semi-closed-circuit andclosed-circuit rebreathers, a systemconfigured so that the second stage ofthe regulator connects to a diluentsupply of emergency breathing gas.

(31) You must ensure that the bail-outsystem performs reliably and providessufficient emergency breathing gas toenable your diver to terminate the diveand return safely to the surface.

Diving-Related Medical Emergencies(32) Before each day’s diving

operations, you must ensure that:(a) A hospital, qualified health-care

professionals, and the nearest CoastGuard Coordination Center (or anequivalent rescue service operated by astate, county, or municipal agency) areavailable for diving-related medicalemergencies;

(b) These treatment resources areavailable when you notify them of thediving-related medical emergency;

(c) A list of telephone or call numbersfor these health-care professionals andfacilities is readily available at the divesite; and

(d) Transportation to a suitabledecompression chamber is readilyavailable when no decompressionchamber is at the dive site, and that thistransportation can deliver your injureddiver to the decompression chamberwithin two (2) hours travel time fromthe dive site.

(33) You must ensure that portable O2

equipment is available at the dive siteto treat your injured divers. In doing so,you must ensure that:

(a) This equipment delivers pure O2 toa transparent mask that covers theinjured diver’s nose and mouth; and

(b) Sufficient O2 is available foradministration to the injured diver fromthe time you recognize the symptoms ofa diving-related medical emergencyuntil the injured diver reaches adecompression chamber for treatment.

(34) Before each day’s divingoperations, you must:

(a) Ensure that at least twoindividuals, either employees or non-employees, qualified in first-aid andadministering O2 treatment are availableat the dive site to treat diving-relatedmedical emergencies; and

(b) Verify their qualifications for thistask.

Diving Logs and Decompression Tables(35) You must maintain a diving log

at the dive site and ensure that:(a) Before starting each day’s diving

operations, the individual who verifies

the availability of the treatmentresources required above underCondition (32) of this order makes asigned entry to this effect in the divinglog; and

(b) The diving log contains thefollowing information for each dive:

(i) The time when the diver left thesurface, left the bottom, and returned tothe surface;

(ii) The maximum depth of the dive;and

(iii) If a diver uses a dive-decompression computer, the name ofthe manufacturer and the model andserial numbers.

(36) Before starting each day’s divingoperations, you must:

(a) Designate an employee or a non-employee to make the entries in thediving log; and

(b) Verify that the designeeunderstands the:

(i) Diving and medical terminologyrequired to make proper entries; and

(ii) Procedures for making entries inthe diving log.

(37) You must ensure that a hard-copyof the decompression tables used for thedives (as specified above in Condition(28) of this order) is readily available atthe dive site, whether or not your diversuse dive-decompression computers.

Diver Training

(38) You must ensure that your diversreceive training that enables them toperform their work safely andeffectively while using open-circuitSCUBAs or rebreathers supplied withnitrox breathing-gas mixtures.Accordingly, your divers must be able toperform critical tasks safely andeffectively, including, but not limited to:

(a) Recognizing the effects ofbreathing excessive CO2 and O2;

(b) Taking appropriate action afterdetecting the effects of breathingexcessive CO2 and O2; and

(c) Properly evaluating, operating, andmaintaining their diving equipmentunder the diving conditions theyencounter.

The Order: Notification and Duration

(39) You must notify the diversaffected by this order using the samemeans that you used to inform them ofthe variance application.

(40) This order remains effective untilmodified or revoked under section 6(d)of the Occupational Safety and HealthAct of 1970.

Appendix A (Mandatory).—TestingProtocol for Determining the CO2 Limitsof Rebreather Canisters

If the employer replaces CO2-sorbentmaterial using a schedule provided by



the rebreather manufacturer (hereafter,manufacturer), then the employer mustensure that the manufacturer developedthe schedule according to the protocolspecified below in this appendix. Theemployer must also: Use only the CO2-sorbent material specified by themanufacturer (and that is consistentwith the requirements of Condition10(b)(ii) of this order); ensure that themanufacturer analyzes the canister-duration results using the statisticalanalysis specified in U.S. NavyExperimental Diving Unit (NEDU)Report 2–99 (see Section VII(‘‘References’’) of the permanentvariance); and ensure that themanufacturer specifies the replacementschedule in terms of the lowerprediction line (or limit) of the 95%prediction interval.

1. The manufacturer must use thefollowing procedures to ensure that the

CO2-sorbent material meets thespecifications of the material’smanufacturer: NATO CO2 absorbent-activity test; RoTap shaker and nestedsieves to determine granule-sizedistribution; NEDU-derived Schlegeltest to assess friability; and NEDU’sMeshFit software to evaluate mesh sizeconformance to specifications.

These procedures involve a quality-control assessment of the CO2-sorbentmaterial. Canister durations are suspectif these procedures indicate that theCO2-sorbent material used in canistertesting either exceeds or falls below thespecifications provided by the material’smanufacturer. Therefore, for thepurposes of this canister-testingprotocol, rebreather manufacturers mustuse only CO2-sorbent materials thatmeet the specifications provided by thematerial’s manufacturer.

2. While operating the rebreather at amaximum depth of 130 feet of sea water

(fsw), the manufacturer must use abreathing machine to continuouslyventilate the rebreather with breathinggas that is at 100% humidity andwarmed to a temperature of 98.6 degreesF (37 degrees C) in the heating-humidification chamber. The breathinggas must be a nitrox mixture, with theoxygen (O2) fraction maintained at 0.28(equivalent to 1.4 ATA of O2 at 130 fsw,the maximum O2 concentrationpermitted at this depth by thepermanent variance); the manufacturermust measure the O2 concentration ofthe inhalation breathing gas delivered tothe mouthpiece.

3. The manufacturer must testcanisters using the following threeventilation rates (with requiredbreathing-machine tidal volumes andfrequencies, and CO2-injection rates,provided for each ventilation rate):

Ventilationrates (liters/

min., ATPS 1)

Breathing-machine tidal

volumes(liters)

Breathingmachine

frequencies(breaths per

min.)

CO2–injectionrates (liters/

min., STPD 2)

22.5 l.5 15 0.9040.0 2.0 20 1.3562.5 2.5 25 2.25

1 ATPS means ambient temperature and pressure, saturatedwith water.

2 STPD means standard temperature and pressure, dry; thestandard temperature is 0 degrees C.

The manufacturer must perform the CO2

injection at a constant (steady) andcontinuous rate during each testing trial.An employer cannot use a rebreather ata work rate higher than the work ratessimulated in this testing protocol unlessthe manufacturer adds the appropriatecombinations of ventilation-CO2-injection rates to the protocol.

4. The manufacturer must determinecanister duration using a minimum offour (4) water temperatures, including40, 50, 70, and 90 degrees F (4.4, 10.0,21.1, and 32.2 degrees C, respectively).An employer cannot use a rebreather ata water temperature that is lower thanthe minimum, or higher than themaximum, water temperature used inthis testing protocol unless themanufacturer adds a lower or highertemperature to the protocol.

5. The manufacturer must monitor thebreathing-gas temperature at therebreather mouthpiece (at the ‘‘chromeT’’ connector) and ensure that thistemperature conforms to thetemperature of a diver’s exhaled breathat the water temperature and ventilationrate used during the testing trial. (NEDUcan provide the manufacturer with

information on the temperature of adiver’s exhaled breath at various watertemperatures and ventilation rates, aswell as techniques and procedures usedto maintain these temperatures duringthe testing trials.)

6. Testing must consist of at leasteight (8) testing trials for eachcombination of temperature andventilation-CO2-injection rates. (Forexample, eight testing trials at 40degrees F using a ventilation rate of 22.5lpm at a CO2-injection rate of 0.90 liters/min.) While water temperature may varyslightly (± 2.0 degrees F or 1.0 degree C)between each of the eight testing trials,the manufacturer must maintain strictcontrol of water temperature (± 1.0degree F or 0.5 degree C) within eachtesting trial. The rebreathermanufacturer must use the averagetemperature for each set of eight testingtrials in the statistical analysis of theresulting data.

7. The testing-trial result is the timetaken for the inhaled breathing gas toreach 0.005 ATA of CO2. Using thecanister-duration results from thesetesting trials, the rebreathermanufacturer must: Analyze the

canister-duration results using therepeated-measures statistics describedin NEDU Report 2–99 (see Section VII(‘‘References’’) of the permanentvariance); and specify the replacementschedule for CO2-sorbent materials interms of the lower prediction line (orlimit) of the 95% confidence interval.

VII. References

This order cites the followingreferences:

(1) National Oceanic and AtmosphericAdministration (1991). NOAA DivingManual: Diving for Science and Technology.U.S. Government Printing Office,Washington, D.C.

(2) Diving Science and Technology (1995).Analysis of Proposed Oxygen ExposureLimits for DSAT Oxygen Exposure TableAgainst Existing Database of Manned OxygenTest Dives. Enriched Air Operations andResource Guide. International PADI, Inc.,Rancho Santa Margarita, California.

(3) R. W. Hamilton, R. E. Rogers, M. R.Powell, and R. D. Vann (1994). Developmentand Validation of No-Stop DecompressionProcedures for Recreational Diving: TheDSAT Recreational Dive Planner. HamiltonResearch, Ltd., Tarrytown, New York.

(4) J. R. Clarke. ‘‘Statistically Based CO2

Canister Duration Limits for Closed-Circuit



Underwater Breathing Apparatus.’’ U.S. NavyExperimental Diving Unit, Report 2–99, 1999.

Copies of these references are availablefrom the Docket Office, Room N–2625,Occupational Safety and HealthAdministration, U.S. Department of Labor,200 Constitution Avenue, NW, Washington,DC 20210; telephone (202) 693–2350 or fax(202) 693–1648.

VIII. Authority and Signature

The authority for this order is section6(d) of the Occupational Safety andHealth Act of 1970 (29 USC 655),Secretary of Labor’s Order No. 6–96 (62FR 111), and 29 CFR part 1905.

Signed at Washington, DC, this 9th day ofDecember 1999.Charles N. Jeffress,Assistant Secretary of Labor.[FR Doc. 99–32824 Filed 12–17–99; 8:45 am]BILLING CODE 4510–26–P


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