Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this...

8
Part 2-Conser~ation, Management, Ethics: Werker-Materials Section B-D'eveloping Cave Management Programs Materials Considerations for Cave Installations, Jim C. Werker I What materials te safe and cost effective for long-term use in the harsh environments of caves? Characteristics of common construction materials are described in 'this chapter. Emphasis is placed on materials that are considered corrosion resistant, tough, and readily available. Other exotic materials, though their characteristics may be beneficial to the protection of underground ha~itats, tend to be expensive, less available, and sometimes require special fabrication procedures. Before planning and designing cave construction projects, evaluate the material options'and fabrication requirements. Several reference manuals are especially useful when considering options. I MachinelY"s Handbook (Industrial Press) Manual a/Steel Construction (American Institute of Steel Construc- tion. Inc.) I Electrode Pocket Guide (Airco) Ryerson Steels Stock List and Data Book and Ryerson Special Metals Data Book (Joseph T. Ryerson and Son, Inc.) Most materials rlference books are updated regularly and contain useful infonnation for any construction project. For example, Machinery 5' Handbook contains sections on types and properties of materials, welding specifications, and finishes. The strength of materials section in Machinery 50 Ha;'dbook provides simplified mathematical fonnulas to use in calculating material strengths. Stainless Steels Chromium-nickel austenitic steels are commonly known as stainless steels, Both names refer to the same family of steel materials. The corrosion resistance and totighness of stainless steels make them highly suitable for cave installations. The longevity of stainless is ten-fold that of mild steels. Even though stainless is more costly than other materials, it is increasingly used to replace wood and steel structures in caves, Stainless steel life expectancy and corrosion resistance far exceed the characteristics of most other materials. Any of the chromium-nickel austenitic steels otfer good characteristics for cave installations, however there are important fabrication requirements for these stainless steel materials. There are a number of weldable chromium-nickel austenitic steels on the market. If the project is fabricated in a controlled, clean welding shop, any of the weldable austenitic stainless steels will work wcll. Find complete listings of the characteristics of austenitic steels in Machinery:\' Handbook. For austenitic stainless steels, welding requirements call for shielded gas metal arc welding processes to minimize the potential for carbide precipita- 167 What materials are safe and cost effec- tive for long-term use in the harsh environments of caves? Character- istics of common construction materials are described in this chapter. The corrosion resistance and toughness of stain- less steels make them highly suitable for cave installations.

Transcript of Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this...

Page 1: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

Part 2-Conser~ation, Management, Ethics: Werker-Materials

Section B-D'eveloping Cave Management Programs

Materials Considerationsfor Cave Installations,Jim C. Werker

I

What materials te safe and cost effective for long-term use in the harshenvironments of caves? Characteristics of common construction materialsare described in 'this chapter. Emphasis is placed on materials that areconsidered corrosion resistant, tough, and readily available. Other exoticmaterials, though their characteristics may be beneficial to the protection ofunderground ha~itats, tend to be expensive, less available, and sometimesrequire special fabrication procedures.Before planning and designing cave construction projects, evaluate the

material options'and fabrication requirements. Several reference manualsare especially useful when considering options.

IMachinelY"s Handbook (Industrial Press)Manual a/Steel Construction (American Institute of Steel Construc-tion. Inc.) IElectrode Pocket Guide (Airco)Ryerson Steels Stock List and Data Book and Ryerson Special MetalsData Book (Joseph T. Ryerson and Son, Inc.)

Most materials rlference books are updated regularly and contain usefulinfonnation for any construction project. For example, Machinery 5'Handbook contains sections on types and properties of materials, weldingspecifications, and finishes. The strength of materials section inMachinery 50 Ha;'dbook provides simplified mathematical fonnulas to usein calculating material strengths.

Stainless Steels

Chromium-nickel austenitic steels are commonly known as stainless steels,Both names refer to the same family of steel materials. The corrosionresistance and totighness of stainless steels make them highly suitable forcave installations. The longevity of stainless is ten-fold that of mild steels.Even though stainless is more costly than other materials, it is increasinglyused to replace wood and steel structures in caves,Stainless steel life expectancy and corrosion resistance far exceed the

characteristics of most other materials. Any of the chromium-nickelaustenitic steels otfer good characteristics for cave installations, howeverthere are important fabrication requirements for these stainless steelmaterials.There are a number of weldable chromium-nickel austenitic steels on the

market. If the project is fabricated in a controlled, clean welding shop, anyof the weldable austenitic stainless steels will work wcll. Find completelistings of the characteristics of austenitic steels in Machinery:\' Handbook.For austenitic stainless steels, welding requirements call for shielded gasmetal arc welding processes to minimize the potential for carbide precipita-

167

What materials aresafe and cost effec-tive for long-termuse in the harshenvironments ofcaves? Character-istics of commonconstructionmaterials aredescribed in thischapter.

The corrosionresistance andtoughness of stain-less steels makethem highly suitablefor caveinstallations.

Page 2: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

168

Characteristics ofManganal" includehigh-strength,ductility, toughness,and substantiallongevity.

Cave Conservation and Restoration

tion; for example, tungsten inert gas (TIG), or metal inert gas (MIG)processes are often recommended.Generally, stainless cannot be properly fabricated in the field unless

special welding equipment is used to purge the welds with argon tominimize corrosion-inducing carbide precipitation. If welding must bedone at the cave site, chromium-nickel austenitic steel types 304L, 316L,or 321 are recommended. These steels are less vulnerable to the harmfulcarbide precipitation that enhances weld corrosion (rust) tendencies.For field applications, optional construction methods may apply. For

example, predrill and countersink holes in a fabrication shop, transport thepieces to the site, then use bolts to assemble the pieces. Holes for the rivet-like bolting can be drilled in the shop. If bolts are used for stainless gatedesigns, after installing stainless bolts with countersunk heads, tlatten theheads with a hammer, then grind the nuts to a cylindrical shape so they willnot accept a vandal's wrench.

Manganal@

A high-manganese. austenitic, work-hardening steel that is currently usedin some cave gates is available under the trade name Manganal. Typically,the chemical composition is manganese (12.00-14.00%) and carbon (1.00-J .25%). Manganal bars, plates, and castings are used for high-impactindustrial applications. Cost of these high-manganese materials tends to runtwo to three times that of mild steel (Stulz-Sickles Steel 2002).Manganal is used in extreme wear conditions and is hardened by impact,

hammering, and abrasion. This surface characteristic is known as workhardening. As this alloy work hardens, strength and resistance increase(Amodt and Mesch 2004). In other steels (for example, carburized orcasehardened), the depth of hardness is fixed. When Manganal is subjectedto wear, the surface toughens and the material remains ductile underneath.Characteristics include high strength, ductility, toughness, and substantial

longevity. Corrosion resistance (resistance to rust and attack by acids) isabout the same as ordinary steels. Manganal is extremely tough when workhardened and may tolerate harsh environments. Functional mine rails madefrom this material are over 100 years old (Louis Arnodt, personal commu-nication). Cave gates constructed of Manganal can deter vandals usinghacksaws. However, power tools or cutting torches can breach the closures.Manganal is used for wear resistance in jail bars, bulldozers, scrapers, stonechutes, and military equipment.Continuous high temperature can embrittle the high-manganese, austen-

itic steels. In electric arc welding processes, no local area should remain atvisible red heat for more than two or three minutes. If there is build up withmultiple layers from weld passes, the welder should either skip weld, orweld intermittently to reduce localized heat.Manganal is a good choice for field fabrication if the high cost is

justified. Preferred applications tend to be in remote sites where minimalacidic conditions exist and where vandals cannot easily use power tools.Manganal is durable and has excellent longevity characteristics.

Structural Steels

Because mild steels (structural cold-rolled steels) corrode quickly, thesematerials should be carefully evaluated before installing within caveenvironments. However, structural steels often provide cost-effectivesolutions for cave gates. When constructing cave gates, stainless steel lifeexpectancy and corrosion resistance far exceed the characteristics of othersteel materials. However, since repetitious vandalism is a key issue at some

Page 3: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

Part 2-Conservation, Management, Ethics: Werker-MaterialsI

cave sites, and ~ince replacing stainless is expensive, cost may dictate theuse of structural steel for gate construction. If the environment is too harshfor mild steels to survive, the site conditions may dictate that stainless beselected for its increased life expectancy.The most common grade of structural steel (sometimes called mild steel)

is ASTM A-36. :The high-strength structural steels ASTM A-529 and A-440have high carb6n content for strength but they are no more durable thanmild steels. Co~osion-resistant, high-strength steels have one advantageover the mild varieties in that they are more difficult to vandalize.Mild steels are easy to fabricate, readily available, and cost less than

most other options. Mild steel is available in a variety of structural shapesthat are easily welded and fabricated in the field. For gate construction atcave entrances, the life expectancy is 50 to 100 years. However, withincaves, the life e~pectancy of structural steels may be tremendously reducedby the environmental conditions, and habitat may be compromised by rapiddegradation of the material.

Aluminum

Aluminum can deteriorate rapidly and the degradation may introducetoxins into cave habitats. For example, an aluminum ladder left in a cavelocated in the arid southwestern U.S. literally deteriorated to a pile of scrapin less than 20 years (Werker 2003). Aluminum carabiners left in caves forvarying time int1ervalsrapidly show signs of pitting and corrosive deteriora-tion (Storage 1994). Aluminum will probably work for gates placed in dry,nonalkaline environments. However, aluminum is easy to vandalizebecause, generally, it is not as strong as steel.When aluminum structures are exposed to the atmosphere, a thin,

invisible oxide skin forms immediately and protects the surface fromadditional oxid~tion. This self-protecting characteristic gives aluminum itshigh resistance to corrosion unless it is exposed to some substance orcondition that destroys the oxide coating. Alkalies are among the fewsubstances that will attack the oxide skin-thus, the alkaline conditions ofmost limestone ~aveswill cause aluminum to corrode.When aluminum is placed in direct contact with other metals, the

presence of an electrolyte (moist conditions or high humidity) will causegalvanic corrosion of the aluminum at the contact points. Dissimilar metalsin direct contact with each other within a moist environment will definitelyinduce corrosion.Ifdissimilar metals are already in place, nylon or neoprene washers can

be used to separate or isolate the materials from each other and delay thecorrosion. (A moisture film may eventually form across barriers andcorrosion will continue.)Depending on the site conditions, protective coatings may increase the

life expectancy of aluminum. Chromate coating can be brushed on in thefield, but anodizing must be done at a coating lab. However, once any kindof coating is br~ached by a scratch or nick, the integrity of the surface iscompromised and the electrochemical process begins to produce pitting anddeterioration as'the metal corrodes (Spate and others 1998).Because aluminum is especially susceptible to both vandalism and

corrosion, it is usually a less desirable material for cave applications.

IConcrete

IConcrete works well in most environments. It is resistant to chemical andcorrosive attack~mdhas extremely good longevity characteristics. Stmctures

II

169

Since repetitiousvandalism is a keyissue at some cavesites, and sincereplacing stainless isexpensive, cost maydictate the use ofstructural steel forgate construction.

Aluminum candeteriorate rapidlyand the degradationmay introducetoxins into cavehabitats. Forexample, analuminum ladder leftin a cave located inthe arid south-western U.S.literally deterioratedto a pile of scrap inless than 20 years.

Page 4: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

170

Figure I. Thesealuminum carabinerswere left on a traversein Virgin Cave, NewMexico. After only sixmonths in the cave,pitting and corrosionwas abundant.Material strength wasgreatly reduced, andsome of the biller gatesno longer closed.Stainless steelcarabiners are recom-mended for long-termuse in cave environ-ments. (See page 6 ofcolor section.)

Concrete works wellin most environ-ments. It is resistantto chemical andcorrosive altack andhas extremely goodlongevitycharacteristics.

Cave Conservation and Restoration

built with 3,000 psi (20,680 kilopascal) concrete reinforced with rebar willdeter vandals and will hold up for many decades in most circumstances. Thechemical composition of concrete resembles the natural composition of somecave passages and it introduces few toxins to cave systems. Cement, which isbasically burned limestone, is also known as Portland cement. Sand, gravel,and water are added to cement products to make concrete.An Australian paper by Spate and others (1998) recommends applying a

protective membrane between natural floors, rock, or flows tone before pouringconcrete. Also, fine sand is recommended for covering microgours and sharpsurfaces and can be vacuumed away if the concrete is removed in the future.If concrete is chosen for cave projects, use high tensile strength cement

with low-content calcium hydroxide, which will last longer in most caveenvironments. The calcium hydroxide in cement products is very solubleand it will quickly dissolve and redeposit to form new "soda straws" or"flowstone" below concrete structures (Horrocks and Roth 2006, page 369in this volume). (For additional information on cement choices, sec thespeleothem repair section (page 476).

Culvert and Pipe

Culverts and pipes installed as cave access structures can be made from avariety of materials. Several material types are addressed below. Be awarethat culverts or pipes may not be the best option for protecting bat coloniesand habitats for other animals. Small diameter flyways and absence ofnatural barriers can set the stage for easy predation. Culverts and pipes canchange the natural airflow of a cave, alter air temperatures and relativehumidity, and impede or increase the presence of biota. However, wherecave entrances have been enlarged for human access, a culvert may providethe best protection.

Galvanized SteelFor decades, galvanized steel culvert has been used in roadway construc-tion where it seems to function well. However, in caves, galvanized culvertmay deteriorate rapidly. For example, a galvanized culvert installed inLechuguilla Cave in 1986 showed visible signs of degradation by 1994,and had severely deteriorated by the time it was replaced in 2000 (Werker

Page 5: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

Part2-Conserv~tion,Management, Ethics: Werker-Materials

~

!•~I

~"2004). IAs the zinc coating of galvanized steel

degrades, it maylgenerate toxins that areharmful to flora, fauna, and perhaps tospeleothems (Jameson and Alexander 1996;Spate and others 1998). Welding galva-nized material results in noxious fumes thatcan be hazardous to human health andcave-dwelling a~imals. The breakdown,outgassing, and deterioration of galvanizedsteel culvert result in byproducts that maybe especially toxic to bats and other cave-dwelling biota. I

PlasticsI

Little is known about the degradationprocesses of plastics that are used in caveenvironments. Polyvinyl chloride (PVC)used in water lines and air conduits tends tobecome brittle over time. PVC alsooutgasses potentially harmful substances.Until studies further define the longevityand degradation characteristics of PVCand various plastics placed in subterraneanenvironments, other construction materialsare preferred for (ve use.

Recycled Materials Developed for Environmental UseI

Advances in fabrication technologies have provided recycled constructionproducts that are'intended to be environmentally friendly. These materialsare generally des'igned for aboveground applications. Time will tell howwell these products endure subterranean environments. Timpanogos CavesNational Monument, Oregon Caves National Monument, and various othersites are using products made from recycled materials for in-cave installa-

171

Figure 2. In 1986,aller digging open theentrance, a galvanizedculvert with a solidsteel gate was installedin Lechuguilla Cave.Aller only a few years,it was visibly rustingand deteriorating. (Secpage 6 of color section.)

Figure 3. In 2002, therusted culvert wasreplaced. A stainlesssteel culvert with anair lock entry wasinstalled in Lech-uguilla Cave. (See page6 of color section.)

Page 6: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

172

All products willbreak down overtime, but archivalproducts areformulated to do lessharm than those onthe general market.

Cave Conservation and Restoration

tions. The durability, degradation, and outgassing characteristics of theseinnovative materials may prove to be appropriate for underground applicationsin cave environments .. (See anthropogenic chemicals, page 57.)

Archival Epoxies and Adhesives

All glues break down over time. Many epoxies and adhesives are known tobe composed of detrimental materials and display degradation characteris-tics that will destroy or harm biota.Any new product should be checked by research chemists and biologists

who understand the cave environments where use is proposed. What are thecomponents of the agent and how will the degradation and outgassingcharacteristics ofthase compounds afTect cave-dwelling biota, ecosystems,chemistry, water quality, or the minerals of a cave system? Arrange for achemist or a materials engineer to evaluate long-term degradation andpotential chemical interactions. Get the federally regulated Material SafetyData Sheets (MSDS) and understand recommended safety precautions. Wiseproduct choices for cave environments are based on thorough research.Updated information is often available on the Web. (See MSDS, page 70.)Epoxies, bonding agents, and quick glues found in neighborhood hardware

and variety stores are certainly easier to obtain than the archival-qualityadhesives, but the mass market products can introduce toxins and nasty agentsinto caves. All products will break down over time, but archival products areformulated to do less haml than those on the general market.To augment safe travel in caves, stainless steel bolts are sometimes

installed. For outdoor applications, adhesives have been used in theinstallation of climbing bolts. However, an archival-grade epoxy may bethe best choice for installing bolts in cave systems because most consumerepoxies have not been studied in underground environments.When adhesives are necessary. use archival products, museum-grade

epoxies, or pure forms of cyanoacrylate adhesives. All products willdegrade over time, but some compounds are formulated to be more archivalthan others. The following recommended adhesives, used in subterraneanapplications over the past several decades, appear to be relatively safe forlong-term use in cave environments.

Epon 828@With Versamid@ or Epi-cure@ 3234 (TETA)Epon 828 epoxy has been successful in underground environments fordecades.Epon 828 epoxy resin combined with Versamid 40 curing agent worksfor dry surfaces, even in humid cave environments.For wet applications, Versamid 28 hardener cures more efliciently.Epon 828 with Versamid 25 curing agent will bond underwater.The Epon family of archival adhesives will develop strong bonds withshear strengths up to 6,000 pounds per square inch-6,000 psi (41,370kilopascal).Curing time can take 24--72 hours and sometimes longer. Shrinkage isminimal. The bond is resistant to a broad range of chemicals.Mixing ratio is typically I: l--one part Epon to one part Versamid(50:50 mix). However, for a more rapid drying time, use just a littlemore hardener for a 40:60 mix.Epon 828 and the Versamid hardeners were lab tested for long-termunderground use at the US Department of Energy Nevada Test Site andhave proved successful in cave applications for several decades.These products are available from the Shell' Chemical Company andthrough local chemical or plastic product suppliers. However, theVersamid curing agents are increasingly difficult to locate and fabrica-

Page 7: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

Part 2-Conserva;tion, Management, Ethics: Werker-Materials

tors in the plJstics industry are recommending a replacement Shellproduct, Epi-'cure 3234, which is a highly concentrated curing agent withbonding propertiesand archival characteristics similar to Versamid.Epi-cure 3234 (TETA) is now the recommended curing agent for Epon828 and is typically mixed in a 12: I ratio, twelve parts Epon to onepart TETA. I .

HoI Sluff" Super T and Special TFast-drying cyanoacrylate adhesives are useful for repairing soda straws,helictites, thin dnlperies, and other delicate speleothems or small applica-tions in caves. Hot Stuff adhesives are industrial-strength products contain-ing a very pure form of cyanoacrylate that remains clear when it cures. Oilis not added to lengthen shelflife (as it is in many other instant glues).

Hot StuffsuJerT is often used in paleontological applications andmodel-building and works well for small repairs in caves.Hot Stuff Special T is a more viscous product, formulated to fill ingaps and is extremely useful for cave applications.In most caves, Hot Stuff cures in 30-90 seconds, but bonding can beaccelerated with NCF-Mild Accelerator. Shear strength is weakened byaccelerated curing times, but cyanoacrylate does not bond quickly inlarge quantities. One spritz from a spray pump bottle of Hot StuffNCF-Mild will cause chain reaction bonding.Hot Stuff Super T, Special T, and NCF-Mild Accelerator can bepurchased in model-building stores, quality woodworking shops,museum supply catalogs, and through a few sources on the Web.

Finishes and PaintsI

Finishes applied to the surfaces of materials are intended to enhancelongevity but may introduce contaminants to cave environments. All paintsand finishes deteriorate over time. Flaking onto the habitat floor is obvi-ously detrimental~ but there are more subtle degradation characteristics.Outgassing and:chemical deterioration of finishing products may

introduce potentially toxic materials to cave systems. Increased corrosionmay be generated:ifa paint layer is compromised-severe corrosion mayresult when an ele1ctrolyte,perhaps a simple film of moisture on a scratchedfinish, reacts with' the large metal anode area under the paint (Spate andothers 1998). Resbarch is needed to investigate the potential benefits andharms of various finishes applied to installations within caves and nearcave entrances.

Common Sense

Function and cost are important components of materials selection for caveenvironments. Characteristics of materials and finishes are vital factors inany design and phlnning process. Assessment of site environmentalconditions and evaluation oflongevity criteria are essential to projectplanning. For each material historically used in caves-stainless steels.Manganal, mild structurql steels, concrete, aluminum, galvanized steel,plastic products. epoxies, adhesives. paints. and other finishes-there arebeneficial as well as disadvantageous characteristics. Specific knowledgeabout species that use the cave. habitat requirements. chemical composi-tions within the cave, and general common sense must dictate design andmaterial selection.!

I

173

Finishes applied tothe surfaces ofmaterials areintended to enhancelongevity but mayintroduce contami-nants to caveenvironments.

Page 8: Materials Considerations for Cave Installations,€¦ · Functional mine rails made from this material are over 100 years old (Louis Arnodt, personal commu- ... invisible oxide skin

174 Cave Conservation and Restoration

The arduous tasks of investigating the multitude of material choices,evaluating their varying characteristics, analyzing the costs, considering thepotential for vandalism, and understanding the inherent longevity of thematerials may appear overwhelming. First, evaluate the site, the habitat,and the purposes for any structure or installation. Simplify the goals, statethe site objectives. and then allow common sense to dictate materialchoices and construction techniques. When planning projects to protectcaves, the priority is to be realistic about the habitat, the site requirements,and the budget. Keep it simple and remember that opting for no construc-tion is sometimes the best decision.

Cited ReferencesAireo. No date. Electrode Pocket Guide. Airco Welding Products. Union(NJ). 161 p.

Amodt LA, Mesch MR. 2004. Round har Manganal@steel "jail bar" batgate. In: Vories KC, Throgmorton D, Harrington A, editors. Proceed-ings of Bat Gate Design: A Technical Interactive Forum held in Austin,Texas, March 4-6,2002. Carbondale (IL): USDOI Office of SurfaceMining, Alton, Illinois and the Coal Research Center, Southern IllinoisUniversity at Carbondale. 434 p. Proceedings available on the internet<http://www.mcrcc.osmre.gov/bats>. Accessed 2004 March 30.

American Institute of Steel Construction, Inc. 1973. Manual o/SteelCons/ruction. 7th Edition. New York. 999 p.

Horrocks RD, Roth JE. 2006. Rcmoving artificial fill from developedcaves. In: Hildreth- Werker V, Werker JC, editors. Cave Conservationand Restoration. Huntsville (AL): National Speleological Society. p367-380. [This volume.]

Jameson RA, Alexander EC Jr. 1996. Zinc leaching from galvanizedsteel in Mystery Cave, Minnesota. In: Rea GT, editor. Proceedings ofthe 1995 National Cave Management Symposium: Spring Mill StatePark, Mitchell, Indiana, Octoher 25-28. 1995. Indianapolis (IN):Indiana Karst Conservancy. p 178-186.

Joseph T. Ryerson and Son, Inc. 1967. Ryerson Special Metals DataBook. Denver (CO). 288 p.

Joseph T. Ryerson and Son, Inc. 1987. Ryerson Steels Stock List andData Book. Denver (CO). 432 p.

Oberg E, Jones FD, Horton HL. 1985. MochinelY's Handbook. 22ndRevised Edition. RyfTei HH, Geronimo JH, editors. New York:Industrial Press, Inc. 2512 p. [Editors' note: Machinery's' Handbookhas been updated continuously since 1914. See Oberg, Jones, Horton,RyfTel, McCauley, Heald, Hussain. 2000. MachineIY:' Handbook, 26thRevised Edition. New York: Industrial Press, Inc. 2640 p.]

Spate A, Hamilton-Smith E, Little L, Holland E. 1998. Best practice andtourist cave engineering. In: Smith DW, editor. Cave and KarstManugement in Australasia XII. Carlton South, Victoria (AU):Australasian Cave and Karst Management Association. p 97-109.

Storage B. 1994. Techniques and safety: Aging carabiners. NSS News,52(9):277-279.

Stulz-Sickles Steel Company. 2002. FAQ About Munganol.<www.stulzsicklessteel.eom/faq.html>. Accessed 2004 March 30.

Werker, JC. 2004. Characteristics of materials used in cave and minegates. In: Vories KC, Throgmorton D, Harrington A, editors. 2004.Proceedings of Bat Gate Design: A Technical Interactive Forum heldin Austin, Texas, March 4-6. 2002. Carbondale (lL): USDOI Office ofSurface Mining, Alton, Illinois and the Coal Research Center, SouthernIllinois University at Carbondale. 434 p. Proceedings available on theinternet <http://www.mcrcc.osmre.gov/bats/>. Accessed 2004 March30.