P

Worker ProtectionWorker Protection

WeldingSafety

Assessing and controlling exposure to hexavalent chromiumBy Jerome E. Spear

PURSUANT TO A COURT ORDER, OSHA issued afinal rule on Feb. 28, 2006, that addresses occupa-tional exposure to hexavalent chromium [Cr(VI)].OSHA determined that the rule was necessary toreduce significant health risks due to Cr(VI) expo-sure. Certain Cr(VI) compounds have been found tocause lung cancer and nasal cancer in humans.Inhaling relatively high concentrations of Cr(VI) canalso cause a wide range of other health effects (e.g.,runny nose, sneezing, itching, nosebleeds, ulcers,holes in the nasal septum). Ingestion of very highdoses of Cr(VI) can cause kidney and liver damage,nausea, irritation of the gastrointestinal tract, stom-ach ulcers, convulsions and death. Dermal expo-sures may cause skin ulcers or allergic reactions.

Activities with the potential for Cr(VI) exposureinclude:

•production and use of chromiummetal and chromium metal alloys;

•chromium electroplating;•welding of metals containing

chromium such as stainless steel orother high chromium steels, or chromi-um coatings;

•production and use of Cr(VI)-con-taining compounds [such as Cr(VI) pig-ments, Cr(VI) catalysts and chromicacid];

•production of chromium-contain-ing pesticides;

•painting activities involving theapplication of strontium chromate coat-ings to aerospace parts;

•removal of lead chromate.According to OSHA, a total of

380,000 workers are exposed to Cr(VI).However, welders represent nearly halfof the workers covered by OSHA’sstandard. This article summarizesmajor provisions of OSHA’s Cr(VI)standards, the nature of Cr(VI) in weld-

ing fumes, common welding processes and fumegeneration rates (FGR), factors for Cr(VI) exposurefrom welding, exposure monitoring strategies andconsiderations for feasible engineering controls.

Major Provisions of OSHA’s Cr(VI) StandardsOSHA issued separate but similar standards for

general industry, construction and shipyard sectors.Major provisions are summarized in Table 1 (p. 24).

Cr(VI) in Welding FumesChromium has been used commercially in the

U.S. for more than 100 years. It occurs mainly inthree forms, described by its valence state. Metallicchromium [Cr(0)] is a steel-gray solid with a highmelting point that is used to make steel and otheralloys. Chromium metal does not occur naturallybut is produced from chrome ore.

Trivalent chromium [Cr(III)] occurs naturally inrocks, soil, plants, animals and volcanic emissions.Cr(III) is used industrially as brick lining for high-temperature industrial furnaces and to make metals,metal alloys and chemical compounds.

Cr(VI) occurs through the oxidation of chromiumcompounds with lower valence states. It is consid-ered the greatest occupational and environmentalhealth concern as it is the most toxic. Other valencestates are unstable so they are less common. Theywill most likely be quickly converted to either Cr(III)or Cr(VI) (OSHA, 2006).

Chromium metal is found in stainless steel andmany low-alloy materials, electrodes and filler mate-rials. The chromium present in electrodes, weldingwires and base materials is in the form of Cr(0).Therefore, welders do not ordinarily work withmaterials containing Cr(VI). However, the high tem-peratures created by welding oxidize chromium insteel to the hexavalent state. The majority of thechromium found in welding fume is typically in theform of Cr2O3 and complex compounds of Cr(III).Some metal oxides in hexavalent form are also in the

Jerome E. Spear, M.B.A., CSP, CIH,is president of J.E. Spear Consulting LP

in Magnolia, TX. He has 20 years’experience helping organizations

control losses and prevent injuries andillnesses. Spear holds a B.S. inIndustrial Engineering with a

specialization in Safety Engineeringfrom Texas A&M University and an

M.B.A. from Sam Houston StateUniversity. In his career, he has been

corporate industrial hygiene managerfor Chicago Bridge and Iron Co. and

technical services manager for XLSpecialty Risk Consulting. Spear

regularly helps steel fabricators andconstruction companies assess and

control welding fume and gasexposures, and also advises the Steel

Tank Institute and Steel PlateFabricators Association on regulatory

issues related to welding andhexavalent chromium.

22 PROFESSIONAL SAFETY SEPTEMBER 2010 www.asse.org

www.asse.org SEPTEMBER 2010 PROFESSIONAL SAFETY 23

requires a higher electrical current than SMAW, itproduces fewer fumes since the electrode has no flux-ing agents. However, due to the intense current lev-els, GMAW produces significant levels of ozone,nitrogen oxide and nitrogen dioxide gases.

•Flux-cored arc welding (FCAW) is commonlyused for mild steel, low-alloy steel and stainless steelwelding. This process has similarities toboth SMAW and GMAW. The consumableelectrode is continuously fed from a spooland an electric arc flows between the elec-trode and base metal. The electrode wirehas a central core containing fluxingagents and additional shielding gas maybe supplied externally. This process gener-ates a substantial amount of fumes due tothe high electrical currents and the flux-cored electrode. However, FCAW gener-ates little ozone, nitric oxide and nitrogendioxide gases.

•Gas tungsten arc welding (GTAW) is alsoknown as tungsten inert gas (TIG) weld-ing. GTAW is used on metals such as alu-minum, magnesium, mild steel, stainlesssteel, brass, silver and copper-nickelalloys. This technique uses a nonconsum-able tungsten electrode. The filler metal isfed manually and the shielding gas is sup-plied externally. High electrical currentsare used, which causes this process to pro-duce significant levels of ozone, nitricoxide and nitrogen dioxide gases. How-ever, GTAW produces very few fumes.

•Submerged arc welding (SAW) is acommon welding process used to weldthick plates of mild steel and low-alloysteels. In this process, the electric arc flowsbetween the base metal and a consumablewire electrode; however, the arc is not vis-ible since it is submerged under flux mate-rial. This flux material keeps the fumeslow since the arc is not visible. Littleozone, nitric oxide and nitrogen dioxidegases are generated. The major potentialairborne hazard with SAW is the fluoride com-pounds generated from the flux material.

Fume Generation RatesThe primary sources of information when deter-

mining the components likely to be in the fume isthe MSDS and/or the manufacturer’s technical datasheet of the consumable electrode/wire. About 90%to 95% of the fumes are generated from the fillermetal and flux coating/core of consumable elec-trodes (Lyttle, 2004).

Since the base metal weld pool is much coolerthan the electrode tip, the base metal contributesonly a minor amount of the total fumes. However,the base metal may be a significant factor of thefume exposure if the metal or surface residue con-tains a highly toxic substance (e.g., chromate-con-taining coatings, lead-based paint).

In addition to the welding process, studies have

form of CrO3. Pure CrO3 is extremely unstable; how-ever, other metal oxides, especially alkali metals,tend to stabilize Cr(VI) compounds (Fiore, 2006).

Welding fume is a complex mixture of metaloxides. Fumes from some processes may also includefluorides. The predominant metal fume generatedfrom mild, low-alloy and stainless steel welding isiron oxide. Oxides of manganese are also typicallypresent. Fumes from stainless steel and some low-alloy steel welding also typically contain chromiumand nickel. Chromium is usually not intentionallyadded to mild steels or mild steel consumables, yetdue to the use of scrap steel in the steel productionprocess, some low levels of chromium metal may bepresent. However, in most mild steel welding, theexposure limits for fume constituents other thanCr(VI) (such as manganese) will be exceeded beforethe PEL for Cr(VI) is reached (Fiore, 2006).

Common Welding Processes& Fume Generation Rates

Different welding processes have different FGR.One must have a basic understanding of theseprocesses and their relative FGR in order to assessthe risk of exposures to welding fumes and gases.Following is an overview of common weldingprocesses and their relative FGR (Spear, 2004).

•Shielded metalarc welding (SMAWor “stick welding”)is commonly usedfor mild steel, low-alloy steel and stain-less steel welding. InSMAW, the electrodeis held manually,and the electric arcflows between theelectrode and thebase metal. The elec-

trode is covered with a flux material, which providesa shielding gas for the weld to help minimize impuri-ties. The electrode is consumed in the process, andthe filler metal contributes to the weld. SMAW canproduce high levels of metal fume and fluoride expo-sure; however, SMAW is considered to have littlepotential for generating ozone, nitric oxide and nitro-gen dioxide gases.

•Gas metal arcwelding (GMAW) isalso known as metalinert gas (MIG)welding. GMAW istypically used formost types of metaland is faster thanSMAW. This processinvolves the flow ofan electric arc between the base metal and a continu-ously spool-fed solid-core consumable electrode.Shielding gas is supplied externally, and the elec-trode has no flux coating or core. Although GMAW

Photo 1: Shielded metal arcwelding, down-flat weldingposition.

Photo 2: Gas metal arc welding.

Photo 3: Flux-cored arc welding,down-flat welding position.

Photo 4: Gas tungsten arc welding.

Photo 5: Submerged arc welding.

Abstract: This articlesummarizes majorprovisions of OSHA’sCr(VI) standards, thenature of Cr(VI) inwelding fumes, com-mon welding process-es and fumegeneration rates, fac-tors for Cr(VI) expo-sure from welding,exposure monitoringstrategies and consid-erations for feasibleengineering controls.

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•Arc voltage. FGR generally increases when thearc voltage increases.

•Electrode diameter. The electrode diameter hasa modest effect on FGR because of the differences in

shown that FGR is influenced by the following fac-tors (Spear, 2004):

•Electrical current. In general, FGR is exponen-tially proportional to the current.

Table 1Table 1

Summary of Major Provisions ofOSHA’s Final Rule for Hexavalent Chromium

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Exposure FactorsWelding fume exposure tends to be highly vari-

able due to several factors that should be consideredwhen assessing potential exposures to Cr(VI). Basedon the author’s experience, the primary Cr(VI) expo-sure factors are as follows:

•Welding process.As noted, the welding processused has a significant effect on FGR.

•Chromium content and flux ingredients in theconsumable. Stainless steel and chromium alloystypically contain between 11.5% and 30% chromium,by weight. Obviously, as the chromium content inthe consumable increases, the amount of Cr(VI)emitted from the welding process will likelyincrease. Other ingredients in the electrode also mayhave some affect in stabilizing Cr(VI), resulting inhigher Cr(VI) concentrations.

•Chromate coatings on basematerial.Chromatesmay be contained in pigments in coatings and paintsto provide corrosion-resistant properties. When per-forming repair work on painted structures, be sure toanalyze bulk samples of the coating to ensure that thepaint or coating does not contain chromates.

•Welding rate. High welding rates increase thefumes generated. However, information pertainingto an individual’s welding or production rate is sel-dom accurately and consistently measured whenmonitoring exposure. Consider using an arc timer toaccurately collect and document actual weldingtime; this information may also prove useful inexplaining unusually high or low exposure monitor-ing results and/or in better categorizing similarexposure groups (SEGs).

•Relative welding position. The welding posi-tion plays a significant role in exposure primarilydue to the plume’s path of travel. Welding in adown-flat position (such as a tank bottom or wherethe workpiece is positioned below the welder’swaist) tends to present the highest potential fumeexposures. Welding in a horizontal direction (such aswhen welding the girth seam of a tank) can also cre-ate relatively high fume exposures depending on theplume’s path of travel in relation to the welder’sbreathing zone. Welding in a vertical direction (suchas a vertical seam of a tank shell) tends to have thelowest potential fume exposure since the welder’sbreathing zone is typically not in the plume’s travelpath since the plume stays close to the heat-affectedzone as it naturally rises.

•Local exhaust ventilation (LEV). It has beenshown that the use of LEV can lower fume exposure.However, the effectiveness of LEV depends on sev-eral factors, including work practices and propermaintenance of the LEV units. (The use of LEV forfume control is discussed on p. 28.)

•Welding environment (inside or enclosed space).Welding inside buildings or an enclosed space pres-ents the potential for an accumulation of fumes thatmay increase exposures to the welder as well as toother personnel inside the building or enclosed space.

•General/dilution ventilation and natural aircurrents. Although general/dilution ventilation is

voltage and current. In general, a small diameterelectrode has a higher FGR than a large diameterelectrode, all else remaining equal. However, there isusually a step up in electrical current when usinglarger diameter electrodes.

•Electrode angle. The angle of the electrode to theworkpiece has a slight (but unpredictable) effect onFGR.

•Shielding gas. In gas-shielding arc welding,the FGR tends to be greater when 100% carbon diox-ide (CO2), as compared to argon, is used as theshielding gas.

•Speed of welding.As the welding rate increases,the FGR increases.

•Steady/current pulsed current welding. Tech-nology has advanced to power sources that havepulsing capabilities. Studies have shown that using apulsing current during welding generates fewerfumes than under a steady current welding process.

In general, FCAW produces the greatest FGR (formild steel welding), followed closely by SMAW.However, when welding chromium-containing steel,Cr(VI) contained in the fumes generated fromSMAW tends to be greater than Cr(VI) generatedfrom FCAW. Alkali metals, such as sodium andpotassium, stabilize Cr(VI) and are often SMAW elec-trode coatings and also may be present in FCAW flux(Fiore, 2006), which may explain why Cr(VI) concen-trations from SMAW operations are often higherthan those from FCAW. GMAW tends to have a mod-erate relative FGR. GTAW and SAW are inherentlylow fume-generating processes.

Other ancillary processes (such as air arc gougingand plasma arc cutting) can also generate a signifi-cant amount of fumes due to the high electrical cur-rent and arc voltage associated with them. Potentialexposures to the operator and other personnel in thework area can be significant from such processes,especially in enclosed and confined spaces. Fewresearch studies are available that examine potentialCr(VI) exposure associated with air arc gouging andplasma-cutting operations.

Exposure MonitoringOSHA requires employers to determine Cr(VI)

exposures to employees. This can be achieved usinginitial and periodic exposure monitoring and/orobjective data. If objective data are used, they mustreflect workplace conditions closely resembling theprocesses, types of material, control methods, workpractices and environmental conditions.

If the scheduled monitoring option is used, mon-itoring must be performed initially and periodically.For exposures determined to be at or above OSHA’sPEL of 5 µg/m3 (8-hour TWA), monitoring must beperformed at least every 3 months. For exposuresdetermined to be at or above OSHA’s action level of2.5 µg/m3 (8-hour TWA), monitoring must be per-formed every 6 months. Additionally, exposuremonitoring must be performed whenever changesmade to work processes or materials may result innew or additional exposures to Cr(VI).

OSHArequiresemployersto determineCr(VI)exposures toemployees.This can beachievedusing initialand periodicexposuremonitoringand/orobjectivedata.

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relationship between sample location and measuredcontaminant may not be as clear as once believed. Atotal of 20 volunteers performing SMAW in a con-trolled laboratory environment were monitored.Twenty-three sample sets were collected from thebreathing zones inside the helmets and at the shoul-ders of the participants, who welded inside a 506 ft3test chamber. Little difference was found betweenfume concentrations inside the helmet and thoseoutside the helmet.

More recently, Harris, Longo, DePasquale, et al.(2005) support the findings of Liu, et al. (1995). Aspart of a larger study, Harris, et al. examined air-borne concentrations of manganese and total fumeduring SMAW inside a 2,194.5 ft3 test chamber fordifferent electrodes and different ventilation rates.The researchers concluded that in more restrictedwork environments (such as fabricating structuresthat include enclosed or restricted spaces such asships, tubs, barges, petroleum and chemical process-ing equipment, or offshore platforms), fume concen-tration distribution may be relatively uniform andwith little difference between concentrations insideand outside the helmet.

Based on the results of the cited studies, the fumeconcentrations outside the helmet have the potentialto be higher than fume concentrations inside the hel-met when welding outdoors or in other nonenclosedwork environments, whereas the difference in fumeconcentrations appears to have little difference whenwelding in more restricted environments.

Sampling VariabilityTwo types of variations should be considered

when conducting exposure monitoring: 1) variationsdue to sampling and analytical errors (SAE) and2) variations due to the workplace or environment.OSHA requires that the sampling method used be atleast ±25% accurate.

The SAE for Cr(VI) collected on PVC membranesfrom welding operations and analyzed in accordancewith a method based on OSHA ID-215 is ±12.9%,which complies with OSHA’s requirement. However,variations due to the workplace or environment areconsiderably larger than SAEs.

If objective data are used, OSHArequires that theconditions closely resemble the workplace condi-tions that the data represent. This attempts toaddress the environmental variability to somedegree. The primary strategy to control for environ-mental variation should be to define and categorizeexposure determinations by SEGs.

Consider the exposure factors discussed whendefining and categorizing SEGs. Next, use profes-sional judgment and relevant sampling data (ifavailable) to prioritize data collection needs basedon potential exposure levels.

For example, all things being equal, down-flatwelding is expected to result in higher exposuresthan vertical welding positions. Also, FCAW andSMAW operations are expected to result in higherexposures than GTAW and SAW operations.

For SEGs with minimal exposures, only a few

often used when welding indoors or inside enclosedspaces, local exhaust ventilation is preferred forfume control since it attempts to capture fumes atthe source. The effect on the plume’s travel path isunpredictable when using only general ventilation.

•Other welding (or ancillary/allied processes)performed in the area. The amount of welding orother related activities (such as air arc gougingand/or plasma cutting) may affect potential expo-sures to welding fumes and Cr(VI) inside enclosedspaces, especially if the space is poorly ventilated.

OSHA Method ID-215OSHA requires that exposure monitoring be per-

formed using a sampling method that is at least±25% accurate. OSHA specifically references expo-sure monitoring to be performed using OSHAMethod ID-215 (or equivalent). This method involvescollecting an air sample onto a 5.0 micron polyvinylchloride (PVC) membrane mounted in a 37-mm or25-mm polystyrene cassette holder. The recommend-ed flow rate is 2.0 liters per minute for 480 minutes(i.e., 960 liters). NIOSH Analytical Method 7605 iscomparable to OSHA Method ID-215.

Cr(VI) samples collected on PVC from weldingoperations do not require field stabilization as withCr(VI) samples collected from other operations (suchas chromium plating samples). However, Cr(VI)samples collected from welding operations must beanalyzed within 8 days of sampling in accordancewith OSHAID-215 to minimize the effects caused bythe interaction of Fe(II) and Cr(VI) to form Cr(III).Storage stability tests showed that these sampleswere not stable for longer periods of time. Studiesindicate that the loss exceeded 10% after 7 days.

Significant amounts of Cr(VI) are often depositedon the interior walls of sampling cassettes. Testsshowed that Cr(VI) equivalent to 0% to 123% of theamounts found on the PVC filter were present on theinterior walls of cassettes. Therefore, it is now routineanalytical procedure for the lab analyst to wipe inte-rior walls of sampling cassettes for all metal samples.

Sample Media LocationOSHA ID-215 does not address sample location

or position other than to state that the cassetteshould be in a vertical position with the inlet facingdown. The location of sample media during weldingfume sampling has been a subject of discussion forseveral years.

Goller and Paik (1985) describe the results ofsimultaneously air sampling with collection sites atfour locations: the welder’s left front shoulder, rightfront shoulder, front chest and inside the helmet. Atotal of 40 sets of four samples was collected on eachwelder at each location. The welders monitoredwere using FCAW while building railroad locomo-tives. Goller and Paik conclude that fume concentra-tions inside the helmet were 36% to 71% of thosemeasured outside the helmet, which supports theprotocol of sampling inside the helmet recommend-ed by the American Welding Society (AWS).

Liu, Wong, Quinlan, et al. (1995) showed that the

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The reduction factor for a 10-hour work shiftwould be 0.7; for a 12-hour work shift, it would be0.5. A contaminant with a TLV of 5µg/m3 would bereduced to 3.5 µg/m3 for a 10-hour work shift usingthis model and 2.5 µg/m3 for a 12-hour work shift.The reduction factor for a 7-day-per-week workschedule is calculated by the following:Reduction factor = [40/(hours worked perweek)] x [(168 - hours worked perweek)/128]

Engineering ControlsOSHA requires that exposures above PEL be

reduced using feasible engineering controls, which isconsistent with other substance-specific standardsand good industrial hygiene practice. If such controlsdo not sufficiently reduce exposures, then exposuresmust be maintained as low as feasibly achievable viaengineering controls and supplemented with respi-ratory protection. Job rotation is specifically prohibit-ed to achieve compliance. Compliance with thefeasible engineering controls provision took effectMay 31, 2010. This provision does not apply whereemployees are not exposed to Cr(VI) for 30 or moredays per 12 consecutive months.

SubstitutionEliminating or minimizing potential Cr(VI) expo-

sures by substituting materials and processes thatgenerate fewer Cr(VI) fumes should be the first con-sideration for feasible engineering controls. Followingare several options for substituting materials andprocesses to reduce potential Cr(VI) exposures.

Welding ProcessesAs noted, different welding processes have differ-

ent FGR. GTAW and SAW are inherently low in fumegeneration. GMAW also tends to be a relatively lowfume process. SMAW and FCAW operations tend toproduce the most fume.

However, not all welding processes can be usedin all situations. SAW is limited to flat and horizon-tal positions. GTAW has a very low deposition rateand is not a good choice for production welding.Conversely, FCAW has a high deposition rate, whichmakes it a popular choice for heavy productionwelding. SMAW is a popular choice for repair weld-ing due to its low cost, portability and ease of use.

Automatic & Mechanized EquipmentUse of automatic and mechanized equipment may

help reduce exposure in certain situations by furtherdistancing the operator’s breathing zone from thewelding zone. Again, however, mechanized equip-ment may not be practical in many situations due tosetup time and cost. The amount of welding and/orthe size of a tank or job, the type of weld joint andweld position are factors to consider when determin-ing the viability of this option. Also, be aware that useof mechanized equipment tends to increase the weld-ing rate and, thus, tends to increase FGR.

samples may be needed to justify and document thatexposures are below OSHA’s action level. The pri-mary focus should be on collecting sufficient data toproperly characterize those SEGs with potentiallyhigh Cr(VI) exposures.

Sampling Protocols for Extended Work ShiftsOSHA’s lead standards for construction and gen-

eral industry are the only federal OSHA standardsthat require PEL adjustments with respect to extend-ed work shifts. The PEL for Cr(VI) is based on an8-hour time-weighted average (TWA). To minimizeerrors and assumptions associated with fluctuationsin exposure, conduct representative full-shift sam-pling for air contaminants when determining compli-ance with an 8-hour TWA. OSHA’s Technical Manualdefines full-shift sampling as a minimum of the totaltime of the shift less 1 hour (e.g., 7 hours of an 8-hourwork shift or 9 hours of a 10-hour work shift).

OSHA does not include provisions for adjustingthe Cr(VI) PEL for an extended work shift; however,the agency has two approaches for evaluating com-pliance for employees who work shifts that lastmore than 8 hours:

1) Sample what is believed to be the worst con-tinuous 8-hour work period of the entire extendedwork shift.

2) Collect multiple samples over the entire workshift. Sampling is conducted so that multiple per-sonal samples are collected during the first 8-hourwork period and additional samples are collectedfor the extended work shift. The employee’s expo-sure (for OSHA compliance purposes) in thisapproach is based on the worst 8 hours of exposureduring the entire work shift.

Using this method, the worst 8 hours need not becontiguous. For example, for a 10-hour work shift,10 1-hour samples or five 2-hour samples could betaken and the eight highest 1-hour samples or thefour highest 2-hour samples could be used to calcu-late an employee’s 8-hour TWA, which would becompared to the 8-hour TWA-PEL.

Some organizations and standards suggest differ-ent protocols for addressing extended work shifts.For example, Cal/OSHA requires the 8-hour TWAbe calculated using the following formula (in accor-dance with CCR, Title 8, Section 5155):8-hour TWA = [(C1)(T1) + (C2)(T2) + … +(Cn)(Tn)]/8where T is the duration in hours of the expo-sure to a substance at the concentration C; 8 isused as the denominator regardless of the totalhours of the work shift.American Conference of Governmental Indus-

trial Hygienists (ACGIH) refers to the Brief andScala model for adjusting its threshold limit values(TLVs) for extended work shifts. This model reducesthe TLV according to a reduction factor calculated bythe following formula:Reduction factor = [8/(daily hours worked)] x

[(24 - daily hours worked)/16]

Eliminatingor minimiz-ing potentialexposures bysubstitutingmaterialsand processesthat generatefewer Cr(VI)fumes shouldbe the firstconsiderationfor feasibleengineeringcontrols.

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compositions have good weldability, strength andductility comparable to welds made with Type308L/304L filler metal. The corrosion resistance isalso comparable (Kim, Frankel & Lippold, 2006).Research is continuing to identify specific composi-tion ranges for these consumables and to commer-cialize a shielded metal arc welding electrode.However, a CR-free consumable for welding stain-less steel is not commercially available at this time.

Finally, metal concentrations and flux composi-tions of welding consumables can differ substantial-ly between manufacturers. In addition, as noted,alkali materials, such as sodium and potassium, areoften present in many flux coatings and stabilizeCr(VI) (Fiore, 2006). Therefore, the composition ofthe flux coating can be a factor in stabilizing Cr(VI)compounds. However, more field studies are need-ed in this area.

Local Exhaust VentilationLocal Exhaust Ventilation Components

A local exhaust ventilation (LEV) system consistsof five basic components. All LEV systems have atleast a fan that supplies static pressure and physical-ly moves the air, ductwork and a hood. The hood (ifpresent) comes in various configurations and direct-ly affects the capture efficiency. A major mistake byLEV users, especially those using portable LEVunits, is failing to use a hood type that minimizeshood entry losses. A system with merely a plainexhaust duct as its hood has the lowest capture effi-ciency as compared to other hood types (e.g.,flanged hoods, cone-shaped hoods).

The duct is a significant contributor to airflow lossdue to friction. Airflow loss also occurs from elbowsand bends, expansions and contractions, branchentries and transition pieces to fans or air cleaners.Calculating the amount of airflow loss of a systemcan be cumbersome and complicated. Friction loss ina duct depends on the roughness of the material,diameter, velocity pressure and duct length. The keypoint regarding ducts is to avoid long runs of ductand minimize kinks, bends and elbows.

The LEV system may or may not be equippedwith an air cleaner. Using LEV systems equippedwith an air cleaner is particularly important whenair is recirculated. This is often the case when weld-ing inside large tanks or vessels where it is not prac-tical to run several ducts to the outside or inlocations where long lengths of duct would be nec-essary and may create too much airflow loss to beeffective. Options for air cleaning devices found infume extraction systems include: 1) electrostatic pre-cipitators (ESPs); and 2) cartridge/fabric filtration.Both can capture submicron particles. ESPs are goodfor removing submicron-sized particles but theycannot handle heavy fume loadings and require fre-quent maintenance.

Depending on the filtration system, some car-tridge/fabric filters may be able to collect sub-micron particles suitable for welding fumes. It iseasier to maintain filtration systems than ESPs, but

Pulsed Power WeldingPulsed power welding is a GMAW process in

which the power is cyclically programmed to pulseso that effective, but short duration values of powercan be utilized. Small metal droplets are transferreddirectly through the arc to the workpiece. The cur-rent alternates from a low background current,which begins to melt the wire while maintaining thearc, to a high peak current during which spray trans-fer occurs. One droplet is formed during each highpeak current pulse. The average arc energy duringthis pulsed process is significantly lower during con-ventional GMAW spray transfer, thus reducing theamount of welding wire that is vaporized.

Wallace, Landon, Song, et al. (2001) showed a24% significant reduction in total weld fume person-al air sampling results for pulsed power welding ascompared to conventional GMAW welding whenwelding mild steel in production environments. Thestudy also showed that average airborne concentra-tions of metal fume constituents from conventionalGMAW were significantly higher than airborne con-centrations during pulsed GMAW. As a result, stud-ies conducted in both laboratories and productionenvironments have shown that GMAW with a puls-ing-power source produces fewer fumes thanGMAW using a steady current power source. How-ever, pulsed power welding is only a viable option-al for GMAW operations; this technology is notsuitable for flux-cored wire.

Substituting Consumable MaterialsThe amount of Cr(VI) produced is largely influ-

enced by the composition of the welding consumable,including the flux ingredients. Substituting materialsfor stainless steel or other steels with a lower chromi-um is often not a viable option. Stainless steel andother Cr-alloy steels have certain desired properties(e.g., corrosion resistance, durability, ductility) thatadequate substitutes are not available.

However, Ohio State University researchers areworking to develop a Cr-free consumable that iscompatible with welding stainless steel material,including Types 304 and 316. The consumable com-position is a nickel-copper-based system and maycontain additions of molybdenum and palladium toimprove the corrosion resistance of the deposit.

Initial testing has shown that these consumable

Photo 6: Localexhaust ventilationcapture hood. Thesehoods come in vari-ous configurations

and directly affect thecapture efficiency.

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draft ventilation system.Some systems even have acanopy hood; however, suchsystems are not an effectiveoption since the fumes willlikely pass through thewelder’s breathing zone be-fore being captured by thehood and exhausted.

Fixed systems also canhave movable extractionarms, which provide moreflexibility than backdraftwelding booths. Free-hang-ing air cleaners are found in some shops and facili-ties, but these systems are not an LEV option sincefumes are not captured at the source; therefore,fumes are likely to pass through the breathing zonebefore being captured by the air cleaner.

Advantages of fixed fume extraction systemsinclude the following:

•Airflow losses can be more easily controlled.•The system is more readily available for use

once the initial setup is complete.•The system can be designed with higher capac-

ity fan to increase airflow, if needed. Therefore,longer runs of duct (as compared to portable units)can be used.

Disadvantages of these systems include thefollowing:

•Initial setup cost is relatively high.•The object being welded may partially block the

airflow, thereby obstructing the capture efficiency.Backdraft welding booths are limited to weldingsmall parts for this reason.

•Fixed systems with flexible fume extractionarms must be properly positioned and/or adjustedbefore and during welding.

Portable Fume Extraction UnitsThe two most common types of portable units are

high-volume, low-vacuum systems and high-vacu-um, low-volume systems. High-volume, low-vacu-um systems use large diameter ducts or hoses thatprovide for larger capture distances. High-vacuum,low-volume systems tend to be more portable butthey use smaller hoses; as a consequence, the cap-ture distance is generally smaller. Also, if equippedwith a filtering system, the smaller units tend tohave lower fume loading capacities. A welder usingportable fume extractors must frequently adjust thehood placement. Also, long runs of flexible ductsmay be needed (causing more airflow loss) unlessthe unit is equipped with an air cleaner.

Advantages of portable fume extraction unitsinclude the following:

•Portable units are available in different sizes.Mobility is increased with smaller units.

•Setup cost is relatively low compared to fixedsystems.

Disadvantages of these units include the following:•The welder must adjust the hood placement

frequently.

filters must be periodically replaced and/or cleaned.Depending on the fume loading, the filters mayneed to be changed frequently to avoid excessivestatic pressure drops. In some situations, filterchanges and cleaning may need to occur daily.Regardless of the type of air cleaner utilized, poormaintenance results in poor fume collection.

Respirators and protective clothing also may beneeded when changing or cleaning filters. Be sure tocharacterize the waste to determine whether the fil-ters and particulates need to be treated as hazardouswaste. Recall also that some Cr(VI) compounds maybe converted to Cr(III), especially after several days.

Fume Control ConsiderationsSome studies have examined the effectiveness of

LEV in controlling welding fume exposures. In gen-eral, the overall conclusions are that LEV may sig-nificantly reduce fume exposure. Wallace andFischbach (2002) examined the effectiveness of twotypes of portable LEV units during SMAW inside abuilding and outside in a semi-enclosed tank at aboilermaker union training facility. The study indi-cated that LEV does not capture all the fumes and,thus, does not eliminate exposure. There are also sit-uations where LEV will not reduce exposures belowapplicable occupational exposure limits.

Key fume control characteristics and considera-tions are summarized as follows:

1) Fumes are greatly influenced by air currents.Air currents created by either natural or mechanicalventilation can affect how well the fumes are cap-tured. Using LEV outdoors (or even semi-enclosedspaces) has been shown to be less effective in cap-turing fumes due to opposing air currents.

2) Studies have shown that LEV significantlyreduces fume exposure but does not eliminate expo-sures because not all the fumes will be captured.Using LEV systems also does not guarantee thatexposures will be below applicable PELs.

3) The amount of fumes captured and the result-ing exposures depend on the configuration of theLEV unit, the capture velocity, the welder’s workpractices and maintenance of the LEV units.

4) For fume extraction systems without an aircleaner (such as a filtration system or ESP), considerwhere the fumes are being exhausted. Are fumesexhausted to a different area in the work environ-ment? Does it create a potential exposure problemfor other workers? For fixed systems with a stack,where is the stack exhaust located? Is it near any airintakes that may cause the exhausted fumes to re-enter the building or structure?

Types of Fume Extraction SystemsFume extraction systems can generally be catego-

rized as 1) fixed and flexible systems; 2) portableLEV units; and 3) fume extraction guns. The follow-ing discussion provides examples of these systems/units and their advantages and limitations.

Fixed/Flexible Fume Extraction SystemsAn example of a fixed fume extraction system is

a welding booth that contains a backdraft or down-

Photo 7: Portablefume extraction unitwith movableextraction arms.Such a system pro-vides more flexibilitythan backdraftwelding booths.

30 PROFESSIONAL SAFETY SEPTEMBER 2010 www.asse.org

the velocity necessary to overcome opposing air cur-rents to allow welding fumes to be captured. In itsIndustrial Ventilation Manual, ACGIH (1998) recom-mends that the capture velocity be between 100 to200 ft per minute (fpm) for contaminants released atlow velocity into moderately still air, such as typicalwelding operations. For welding involving toxicmetals [e.g., Cr(VI)], the capture velocity should benear the upper end of this recommended range.Generally, hoods need to be within 12 in. to maintainthis velocity. However, in many cases, the hood mayneed to be just a few inches from the welding zone.

The maximum acceptable distance to maintainthe minimum capture velocity depends on severalfactors. These include (Spear, 2007):

•Duct size. The smaller the duct or hood, the clos-er the hood needs to be to the welding arc to effec-tively capture the fumes. As a rule of thumb, capturedistance should be within 1.5 times the duct’s diam-eter. For instance, a 2-in. duct usually requires theexhaust inlet to be just within 3 in. from the weldingzone to have some effect in capturing the fumes.

•Airflow through the duct/hood. As airflow de-creases, a shorter capture distance may be needed.

•Presence and type of hood. Different hood con-figurations have different capture efficiencies.Asim-ple hood with no flange has the lowest capturingefficiency. A square hood also tends to have a lowercapture efficiency than a round hood. ACGIH (1998)publishes hood entry loss coefficients for several dif-ferent types of hoods.

•The magnitude and direction of other air cur-rents. These factors also play a role in capture dis-tance. If strong opposing currents are present, thehood must be positioned just a few inches to havesome effectiveness, if any, depending on the magni-tude of the opposing air currents. For this reason,using LEV outdoors is of limited effectiveness forcontrolling welding fumes. LEV is also not a viableoption for some activities (e.g., air arc gouging oper-ations) due to the large opposing air currents gener-ated by the process.

•Hood location in relation to the natural plumetravel. When welding a vertical seam inside a tankwith little or no opposing air current, the plume tendsto rise straight up. In this situation, the hood can bepositioned further away providing it is reasonably inline with the plume’s natural path of travel.

For flexible and portable systems, the nozzle orhood should be repositioned regularly during thecourse of welding. Adding a flange to the nozzleincreases the capture distance, which also increasesthe length of weld that can be made before the exhaustnozzle (or hood) needs to be repositioned. The follow-ing discussion provides typical airflow rates and cap-ture distances for LEV equipment (Fiore, 2006).

High-Vacuum, Low-Volume LEV Systems•For an airflow rate of 50 to 110 ft3/minute with

a duct diameter of 1.5 to 2 in., the typical capture dis-tance is 2 to 3 in. The weld length before reposition-ing the hood is 4 to 6 in. (for a plain duct inlet) and8 to 12 in. (for a flanged hood).

•The fan size is restricted due to size limitationsof the unit, therefore, limiting the airflow and maxi-mum duct length of the system.

•Air cleaners, if equipped, tend to have less fumeloading capacities (as compared to fixed units).Thus, more frequent maintenance is required.

Fume Extraction GunsOne solution to the problems associated with fre-

quently repositioning exhaust hoses is to use a fumeextraction gun (FEG).

FEGs are available in two basic designs. Oneincorporates the ventilation direction into the gundesign. Lines for the shielding gas and welding wireare encased in a large, single line leading from thegun. The other type is a conventional type in whichthe lines for the shielding gas, welding wire and airexhaust remain separate from welding gun.

Wallace, Shulman and Sheehy (2001) examinedthe effectiveness of FEGs during mild steel FCAWoperations. The study concluded that FEGs appearto help reduce exposures but do not effectively con-trol all welding fume emissions. The study furthershowed that even when using FEGs, the breathingzone airborne concentrations of welding fume andits components were still above recognized occupa-tional exposure limits.

FEG advantages include the following:•The devices allow for high welder mobility.•FEGs eliminate the need for welders to fre-

quently reposition the exhaust hood as welding pro-gresses.

Disadvantages include the following:•Use of FEGs is limited to GMAW and FCAW

processes.•The added weight of the welding gun can create

ergonomic issues, especially for those who spend aconsiderable amount of time welding.

•Welding in positions other than flat or horizon-tal positions may reduce the capture efficiency.

•FEGs do not remove residual fumes. A weldertends to move the gun away from the welding zonewhen s/he breaks the arc, which causes residualfumes to be uncaptured.

Capture VelocityCapture velocity is the key measure in evaluating

the effectiveness of an LEV system. It is defined as

Photo 8: A fumeextraction gun is onesolution to the prob-lems assocated withfrequently reposi-tioning exhaust

hoses.

www.asse.org SEPTEMBER 2010 PROFESSIONAL SAFETY 31

for using LEV when engaging in certain types ofwelding activities and/or in enclosed spaces; meas-uring capture velocities frequently; establishing amaintenance schedule for fume extraction systems(such as cleaning and/or changing the filtering sys-tem); and establishing PPE requirements to supple-ment engineering controls (when needed). Thesepolicies and procedures should be enforced as areother safety and health requirements.

General/Dilution VentilationAlthough general/dilution ventilation is often

used when welding indoors or inside enclosedspaces, LEV is preferred for fume control since itattempts to capture fumes at the source. The effecton the plume’s travel path is unpredictable whenusing only general/dilution ventilation. When usingboth general/dilution ventilation and LEV, be awareof the air currents that the general/dilution ventila-tion is creating as they may affect LEV effectiveness.

Also, note that welding outdoors does not guar-antee that welding fume and Cr(VI) exposure levelswill be below occupational exposure limits. Gen-eral/dilution ventilation and natural ventilationhave limited effectiveness if they cause the plume totravel through the welder’s breathing zone. �

ReferencesAmerican Conference of Governmental Industrial Hygien-

ists (ACGIH). (1998). Industrial ventilation: A manual of recommend-ed practice (23rd ed.). Cincinnati, OH: Author.

Fiore, S. (2006). Reducing exposure to hexavalent chromiumin welding fumes. Welding Journal, 85(8), 38-42.

Goller, J.W. & Paik, N.W. (1985). A comparison of iron oxidefume inside and outside of welding helmets. American IndustrialHygiene Association Journal, 46, 89-93.

Harris, M., Longo, W., DePasquale, C., et al. (2005). Manga-nese exposures during shielded metal arc welding (SMAW) in anenclosed space. Journal of Occupational and Environmental Hygiene,2, 375-382.

Kim, Y., Frankel, G. & Lippold, J. (2006). Development of achromium-free consumable for austenitic stainless steels: Effectsof dilution and the behavior of bead-on-plate welds. ISIJ Inter-nationa, 46, 698-704.

Liu, D., Wong, P., Quinlan, P., et al. (1995). Welding helmetairborne fume concentrations compared to personal breathingzone sampling. American Industrial Hygiene Association Journal, 56,280-283.

Lyttle, K. (2004, March/April). Optimizing consumable selec-tion increases productivity, decreases fumes. Gases & WeldingDistribution, 45-47.

OSHA. (2006). Occupational exposure to hexavalent chromi-um: Final rule. Federal Register, 71, 10100-10385.

Spear, J. (2004). Welding fume and gas exposure. Tools of theTrade, 3(4), 10-13.

Spear, J. (2007, June). Using local exhaust ventilation to con-trol welding fume exposure. Presentation at AIHA Conferenceand Exposition, Philadelphia, USA.

Wallace, M. & Fischbach, T. (2002). Effectiveness of localexhaust for reducing welding fume exposure during boiler rehabili-tation. Applied Occupational and Environmental Journal, 17, 145-151.

Wallace, M., Landon, D., Song, R., et al. (2001). A field evalu-ation of the effect of pulsed arc welding technique on reducingworker exposures. Applied Occupational and Environmental Hygiene,16, 93-97.

Wallace, M., Shulman, S. & Sheehy, J. (2001). Comparingexposure levels by type of welding operation and evaluating theeffectiveness of fume extraction guns. Applied Occupational andEnvironmental Hygiene, 16, 771-777.

•For an airflow rate of 160 ft3/minute with a ductdiameter of 3 in., the typical capture distance is 5 to6 in. The weld length before repositioning the hoodis 9 to 12 in.

High-Volume, Low-Vacuum LEV Systems•For an airflow rate of 500 to 600 ft3/minute with

a duct diameter of 4 to 6 in., the typical capture dis-tance is 6 to 9 in. The weld length before reposition-ing the hood is 12 to 18 in.

•For an airflow rate of 800 to 1,000 ft3/minutewith a duct diameter of 6 to 8 in., the typical capturedistance is 9 to 12 in. The weld length before reposi-tioning the hood is 18 to 24 in.

Note that the required capture distance typicallyranges from 2 to 12 in. depending on the type of sys-tem used. The high-volume, low-vacuum systemsgenerally allow for greater capture distances and agreater weld distance before the hood needs to berepositioned.

LEV GuidelinesThe following discussion summarizes guidelines

and considerations for using LEV for welding fumecontrol.1) Minimize airflow losses. The duct is a major

source of airflow loss due to friction. Smooth, shortducts with no bends are ideal but usually not practi-cal. So, keep duct runs as short as possible. Mostportable fume extraction units limit the extractionarm to 10 to 15 ft for this reason. Also, periodicallyinspect flexible ducts for holes as this may be anoth-er source of air loss.2) Avoid using plain ducts as capture hoods.

Exhaust inlets without a flange require about 25%more airflow.3) Perform frequent maintenance of LEV units.

For units with a filtration system, the airflow willdecrease as the filter or air cleaner becomes loaded.This static pressure drop can be significant. There-fore, filters must be changed frequently. This fre-quency depends on fume loading. On low-volume,high-vacuum units (i.e., smaller more portableunits), the filters may need to be cleaned and/orchanged daily.4) Assess/control opposing air currents. LEV

has limited effectiveness outdoors or in semi-enclosed areas because fumes are greatly affected byair currents. Opposing air currents can be assessedby simply observing how the plume behaves. If itdissipates rapidly before it reaches the hood, thismay indicate that the opposing air currents are toogreat for the LEV unit to be effective.

To minimize the effects of opposing air currents,increase the airflow of the LEV system, shield thewelding area from natural drafts or other opposingair currents, and/or if possible, locate the capturehood in the plume’s natural path of travel.5) Implement administrative procedures to

increase LEV effectiveness. Providing LEV units towelders is not enough. Some administrative controlsare needed as well. These may include establishingpolicies and procedures that outline requirements