What the Hex is with Chromium

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Published on January 18, 2008

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What the Hex is with Chromium?:  What the Hex is with Chromium? OSHA’s Hexavalent Chromium Standard Summary of Hazards Initial Exposure Determinations in Stainless Steel Making, Carbon Steel Making and Stainless Steel Fabricating Industries –Welding/Torch Cutting B. Quinn, CIH 1/23/07 Welder using Plasma Cutter OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard General Industry - 1910.1026 Shipyards - 1915.1026 Construction - 1926.1126 Most requirements are generally the same for all industries Exceptions to the New Standard:  Exceptions to the New Standard Does not impact application of some pesticides (EPA regulated) Does not impact exposures to Portland cement Does not impact situations in which the employer has objective data demonstrating that a material containing chromium or specific operation or activity cannot release Cr (VI) in concentrations at or above 0.5 µg/m3 as an 8 hour TWA Partial Exemption – if exposure is less than 30 days of the year What is Hexavalent Chromium?:  What is Hexavalent Chromium? Hex Chrome means chromium with a valence of positive six, in any form or chemical compound in which it occurs. This term includes Cr+6 in all states of matter, in any solution or other mixture, even if it is encapsulated by another substance. Stainless steel does not contain hexavalent chromium. Zero state with Cr III on surface However, chrome is a raw material used in many of the specialty metals What is Hexavalent Chromium?:  What is Hexavalent Chromium? Hex chrome can be generated during certain “hot” work processes. In these instances, the chrome in the metal changes valance upon heating. The primary route of entry for hexavalent chromium (Cr+6) compounds into the body when in a fume state would be inhalation. Why Is Hex Chrome A Concern?:  Why Is Hex Chrome A Concern? POTENTIAL HEALTH EFFECTS Lung cancer Nasal septum ulcerations and perforations Asthma Skin ulcers Allergic and irritant contact dermatitis Health Concerns:  Health Concerns Permanent perforation of the nasal septum from continuous exposure performing chrome plating of small appliance parts “Chrome hole” on finger. Can also occur on hands or forearms, and on bottom surfaces of feet from chrome salts permeating through boots or shoes. Chromates have Varying Solubilities:  Chromates have Varying Solubilities Highly soluble in water: Sodium dichromate Chromic acid Slightly soluble in water: Calcium chromate Strontium chromate Zinc chromate Insoluble in water: Lead chromate Barium chromate Carcinogenic Effects: Lung Cancer:  Carcinogenic Effects: Lung Cancer Cells uptake Cr(VI) Faster for soluble forms of Cr(VI) Insoluble chromates concentrate Particles < 10 µm contact target cells Cells react with Cr(VI) to form Cr(III) and toxic byproducts, Reactive Oxygen Species DNA is damaged Cell replication disturbed Sources of Occupational Exposure:  Sources of Occupational Exposure Major operations/job tasks resulting in potential Cr(VI) exposure: :  Major operations/job tasks resulting in potential Cr(VI) exposure: Chrome plating/Electroplating Welding on stainless steel or Cr(VI) painted surfaces Painting Aerospace Auto body repair Chromate pigment and chemical production Chrome Plating Bath Major operations/job tasks resulting in potential Cr(VI) exposure: :  Major operations/job tasks resulting in potential Cr(VI) exposure: Chromium dye and catalyst production Glass manufacturing Plastic colorant production Construction Traffic painting Refractory brick restoration Paint removal from bridges Bridgework Stainless and Carbon Steel operations/job tasks with potential Cr(VI) exposure: :  Stainless and Carbon Steel operations/job tasks with potential Cr(VI) exposure: Melting Casting – Continuous & Teeming Baghouse Torch Cutting/Oxygen Lancing Grinding Hot Rolling Welding/Plasma Torch Cutting Steel Process Flow:  Steel Process Flow Steel Process Flow:  Steel Process Flow OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard In 2006, OSHA passed a new regulation pertaining to Hexavalent Chromium. General Industry Standard 1910.1026 There are 13 major provisions to the Standard The following is a summary of these provisions OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard Provision # 1 -- Scope: Who is Covered by the Standard? All occupational exposures to Cr+6 compounds except: Where employers have objective data demonstrating that a material containing chromium or a process involving chromium cannot release Cr+6 in concentrations at or above 0.5 µg/m3 as an 8-hour time-weighted average (TWA) under any condition of use. Provision # 2 – Permissible Exposure Limits PEL: 5 µg/m3 – TWA AL: 2.5 µg/m3 – TWA (50% of the PEL) OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard Provision # 3 – Exposure Determination Each employer who has a workplace or work operation covered by this Standard shall determine the 8-hour TWA exposure for each employee exposed to Hexavalent Chromium (Cr+6). Two options for determining employee exposures: Scheduled monitoring method Performance-oriented monitoring method If initial monitoring indicates exposures above the PEL or Action Level, future periodic monitoring is required: Above the AL – Monitor every 6 months Above the PEL – Monitor every 3 months OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard Provision # 4 – Regulated Areas Areas where exposures exceed or can be reasonably expected to exceed the PEL Must be demarcated from other areas Must limit access to employees who have a need to be there Performance wording of warning signs Provision # 5 – Methods of Compliance Engineering and work practice controls are the primary means of achieving exposures below the PEL. Use of respirators may be used to achieve the PEL during: Periods necessary to install or implement feasible engineering and work practice controls Maintenance or repair operations where engineering and work practice controls are not feasible Operations where all feasible controls have been used and exposures are still above the PEL Operations where exposures do not exceed the PEL for 30 or more days per year Emergencies OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard Provision # 6 – Respiratory Protection Shall be used in situations as described above and must comply with the requirements set forth 29 CFR 1910.134. We will review these requirements in a later slide. Provision # 7 – Protective Work Clothing & Equipment Must use where a hazard is present or is likely to be present from skin or eye contact with Cr+6 Must be provided and paid for by the employer Remove Cr+6 contaminated clothing and equipment when work shift or task is completed Clean, store and label Cr+6 contaminated clothing and equipment OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard Provision # 8 – Hygiene Areas and Practices Where protective clothing is required, must provide change rooms and washing facilities Employees must wash their hands and face at the end of a work shift and prior to eating, drinking, smoking Employer-provided eating areas must be kept as free as practicable of Cr+6 No eating, drinking, smoking etc. in regulated areas Provision # 9 – Housekeeping All surfaces must be kept as free as practicable of accumulations of Cr+6 Use HEPA vacuums or other methods that minimize exposure to Cr+6 Use of compressed air prohibited unless:Used in conjunction with a ventilation system to capture the dust cloud created by the compressed air, or No alternative method is feasible Dispose of Cr+6 contaminated waste in labeled, impermeable bags/containers OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard Provision # 10 – Communication of Hazards Training must be provided on the contents of the Cr+6 standard and the purpose and description of the medical surveillance program required by the standard Training must be conducted to inform employees of the protective measures being instituted to control exposures and means used to communicate potential exposure areas. Provision # 11 – Medical Surveillance Which employees must be provided Medical Surveillance? Exposed at or above the Action Level (2.5 µg/m3) for 30 or more days per year. Experiencing signs or symptoms of Cr +6 exposure Exposed in an emergency What is Medical Surveillance? Provisions for conducting baseline and periodic health assessments of exposed employees Provided by or under the supervision of a physician or other licensed health care professional (PLHCP) Provided at no cost to employee and at a reasonable place and time OSHA Hexavalent Chromium Standard:  OSHA Hexavalent Chromium Standard Provision # 12 – Recordkeeping Must maintain records of: Air monitoring data,Historical monitoring data,Objective data,Medical surveillance information, including:Health Care Professional’s written opinions,Information provided to the Health Care Professional Provision # 13 – Effective Dates New OSHA Standard Effective Date: May 30, 2006 Key Compliance Dates: All provisions except engineering controls For employers with 20 or more employees: Nov. 27, 2006 Engineering Controls For all employers: May 31, 2010 Sampling & Analytical – OSHA ID-215 Method:  Sampling & Analytical – OSHA ID-215 Method 37 mm NaOH pre-treated quartz fiber filter – preferred for chrome plating operations 37 mm PVC filter (5.0 micron pore size, can use 0.8 u as well) – can use PVC at chrome plating but must be post/prep’ed by lab. These must be analyzed within 6 days or prepared upon receipt at lab PVC filters used for welding must be analyzed within 8 days – Iron II interference Submit to AIHA accredited lab – 24 Hr Summary Exposure Determinations:  Summary Exposure Determinations Stainless Steelmaking – 6 Melt shops, 4 Casters, 2 Teeming, 5 Hot Rolling Mills, 8 A&P Lines, 7 Slitters and Related Torch Cutting/Welding Operations and baghouses Approximately, 1000+ data points – personals and areas along with settled dust and surface wipes. Exposures generally under AL sometimes a few exceeded AL, restricted to “older” Melt shops, elevated areas Charging Cranes above PELs (2 to 15 ug/m3), hand torch cutting and welding at AL or PEL. Summary Exposure Determinations:  Summary Exposure Determinations Carbon Steelmaking – HSLA, Galvanizing Lines and Tin (Chrome) Lines – 8 Melt shops, 10 Galvanizing Lines, 1-Tin Line, and associated welding/torch cutting stainless and baghouses Approximately, 500+ data points, personals and area samples Exposures have been below AL. Several area samples near spray application areas at galvanize lines have exceeded AL or PEL Hex Cr Sources – Steel Industry:  Hex Cr Sources – Steel Industry Summary Exposure Determinations:  Summary Exposure Determinations Welding and/or Plasma Torch Cutting – Stainless and Carbon Steelmaking locations-maintenance and process lines, fabrication/weld shops on stainless steel. Approximately, 100+ data points, personals and area samples. Exposures vary widely (less than AL to 5X PEL, dependent on many variables) Welding Operations:  Welding Operations Most welding operations join metals by heating the base and/or filler metal to temperatures at or above the melting point and vaporization temperature of the weld joint material. Stainless steels or other chromium-containing alloys represent the source of hexavalent chromium in welding operations. Welding Operations:  Welding Operations Except for resistance and laser welding, a weld pool of liquid metal is formed at the welding arc. A portion of the metal vapor, including chromium vapor originating from the base metal, consumable electrode, surface coating, or surface contaminants instantaneously reacts with atmospheric oxygen and condenses into solid particles (known as fume) to form metal oxides, such as iron oxide, and chromium oxides. Metallic chromium when vaporized, may react with oxygen to form both trivalent chromium (Cr2O3)and hexavalent chromium (CrO3) oxide-containing fume. Welding Operations:  Welding Operations Two General Types of Welding- Manual or Automatic Manual - welding gun and electrode holder are hand held during manual welding operations, the welder’s breathing zone is within an arm’s length of the arc . Welding Operations:  Welding Operations Common types -Manual Welding -Presented in decreasing order of relative welding fume generation rate. Flux Core Arc Welding (FCAW) consists of a wire electrode with arc shielding provided by flux contained within the electrode. One FCAW process variation uses an inert gas fed through the welding gun to provide additional shielding of the arc. Shielded Metal Arc Welding (SMAW), most common type. A short electrode with a coating. Gas Metal Arc Welding (GMAW) also known as MIG, second most common type. A wire electrode with an inert gas (e.g. argon) which is fed through the welding gun to provide a shield against oxidation. Tungsten Inert Gas Welding (TIG) uses a non-melting tungsten electrode and in some cases a metal filler that the welder introduces into the arc. An externally-supplied inert gas (e.g. helium, argon) is fed through the welding gun to shield the arc. Welding Operations:  Welding Operations Automatic welding processes - typically performed with the welding machine operator positioned at a greater distance from the welding arc. In addition, automatic welding processes can be partially enclosed or isolated from personnel in the welding area. Examples of automatic welding processes are: Submerged arc welding (SAW) uses a blanket of granular flux that is fed into the weld zone ahead of the electrode, and a shielding gas is not required. Plasma welding is performed by a plasma welding torch with a non-melting electrode located within a copper nozzle that has a small opening at the tip. The plasma is actually a gas that is heated to an extremely high temperature. The plasma gases are normally argon, and the torch also uses a secondary gas to shield the molten weld puddle. Laser welding uses a high energy beam process and the energy density of the laser is achieved by concentration of light waves. The focal spot (thousands of an inch in diameter) is targeted on the weld joint surface. Welding Operations:  Welding Operations Submerged Arc Welding Plasma Welding Laser Welding Welding Processes and Fume Generation Rates (g/min):  Welding Processes and Fume Generation Rates (g/min) FCAW-CO2 >1 FCAW-Ar/CO2 0.6 GMAW-Steady 0.5 SMAW 0.4 GMAW-Pulsed 0.2 GTAW <0.1 SAW <0.1 Welder Exposures (μg/m3):  Welder Exposures (μg/m3) SMAW 0.1 - 150 FCAW 0.1 - 38 GMAW 0.1 - 13 GTAW LDL- 5 SAW LDL - 0.7 Plasma cutting 0.1- 20 Metal cleaning (Grinding) 0.1 - 610 Controlling Welding Hex Cr Exposures:  Controlling Welding Hex Cr Exposures The Hierarchy of Controls - Hexavalent Cr 1 - Engineering 2 - Administrative 3 - Personal Protective Equipment Controlling Welding Hex Cr Exposures:  Controlling Welding Hex Cr Exposures Flexible exhaust duct positioned near the welding arc. Controlling Welding Hex Cr Exposures:  Controlling Welding Hex Cr Exposures Down-draft Welding Tables with Filtration: Another method of extracting fumes at the source is right at the table. Advantages: Ventilation requires no operator adjustment, and fume extraction occurs at any point on the table. Limitations: Less effective on large parts and part configurations that may interfere with exhaust air flow. Controlling Welding Hex Cr Exposures:  Controlling Welding Hex Cr Exposures Side-draft hoods and booths: Provides directional exhaust ventilation to draw welding fumes away from the welder. Also available with production aids such as a turntable that allows rotation of larger parts to position the welder away from welding fume. Advantages: Provides local exhaust ventilation over a relative large work area. Can accommodate larger size parts. Limitations: Less effective when welding parts with configurations that impede air flow. For some welds, part configuration may require the welder to be positioned between the source of welding fume and hood exhaust. Controlling Welding Hex Cr Exposures:  Controlling Welding Hex Cr Exposures Fume Extractor guns: Capture welding fumes at the source through a ventilation intake nozzle located immediately adjacent to, or integrated around the welding gun shielding gas/welding wire nozzle. Used on GMAW and FCAW applications. Advantages: Requires no operator positioning of the exhaust system. The fume extractor gun can provide exhaust ventilation in restricted areas not accessible by other exhaust ventilation systems. Limitations: Fume extractor guns are typically heavier, have a larger grip circumference, and the gun nozzles are larger diameter than comparable GMAW and FCAW welding guns not equipped with fume extraction. Less effective fume collection during welding on angle and corner section than when welding on flat surfaces. Welding Studies Summary (FEG):  Welding Studies Summary (FEG) A welding shop study where grade 321 stainless steel was GMAW welded, use of FEGs achieved a hexavalent chromium reduction ranging from 26 – 79% (20.2 µg/m3 reduced to 15 – 4.2 µg/m3). Source: Kura, 1998. Controlling Welding Hex Cr Exposures:  Controlling Welding Hex Cr Exposures Additional Engineering Controls – Process Modification Modify the composition of shielding gas Replace SMAW with GMAW Reduce Sodium and Potassium Content in SMAW Welding Electrodes (Rods) Replace Typical GMAW Welding Systems With Pulse-Arc GMAW Welding Studies Summary:  Welding Studies Summary Hexavalent chromium in SMAW fume ranged between 47 to 62 percent of the total chromium in the fume measured Hexavalent chromium in GMAW fume from stainless steel is approximately 4 percent of the total chromium in the fume measured. The large amount of hexavalent chromium found in most fumes created by SMAW welding of stainless steel has been shown to be associated with the sodium and potassium compounds in SMAW welding fluxes. It is almost certain that the hexavalent chromium is present in such fumes as chromates of these metals, Na2CrO4 and K2CrO4. It is possible that the stability of these compounds compared to most other metal chromates prevents or minimizes the processes leading to reduction of hexavalent chromium in GMAW fume. Sodium and potassium chromates are also stable at higher temperatures than most other chromates and this could explain the much faster formation of hexavalent chromium in SMAW fume than in GMAW fume. Welding Studies Summary (Replace SMAW with GMAW):  Welding Studies Summary (Replace SMAW with GMAW) Welding research suggests that chromium-containing fume created by GMAW welding on stainless steel can continue to evolve chemically for several minutes. In some cases, the hexavalent chromium content in the fume appears to rise to a maximum approximately 20 seconds after formation of the fume and then partly decays to trivalent chromium again. Unlike GMAW fume, no changes in hexavalent chromium concentrations were found in SMAW welding fume, suggesting that not all welding fume is subject to aging. Limitations: GMAW welding equipment is not as readily transported or moved as SMAW equipment. Unlike SMAW, GMAW equipment includes: 1- a wire feeder unit, 2- a supply of inert shielding gas – typically from a compressed gas cylinder – and 3- a welding gun supply hose/cable that carries electric power, electrode wire, and inert shielding gas to the welding gun. Sources: Gray, et. al., 1983; Karlsen, et al., 1992; Zatka, 1985 Welding Studies Summary (Modify the composition of shielding gas) :  Welding Studies Summary (Modify the composition of shielding gas) Shielding gases with high oxygen potentials, such as CO2, produce more fume than argon-based shielding gases. Although use of 100 percent carbon dioxide as a shielding gas for FCAW results in higher fume generation, it is still the most commonly used gas for FCAW welding, used in slightly more than 50 percent of FCAW applications, due to low cost and easy availability. The second most popular shielding gas for FCAW consists of 75% argon and 25% carbon dioxide. Reducing the CO2 content of shielding gas used for FCAW can reduce the fume generation rate and potentially the exposure of workers. Welding Studies Summary (Modify the composition of shielding gas) :  Welding Studies Summary (Modify the composition of shielding gas) Reductions in fume generation rates can be achieved with FCAW with stainless steel electrodes. The fume generation rate (FGR) for an E309LT electrode using 100 percent CO2 shielding gas was measured to be approximately 0.6 grams/minute (g/min). The same electrode welded using [75%] argon-25% CO2 shielding gas resulted in a reduction of FGR to as low as 0.3 g/min. Additional FGR measurements for E309LT and E316T electrodes using [95%] argon-5% CO2 shielding gas show that FGR could be as low as 0.1 g/min. Limitations: Present commercial FCAW electrodes for stainless steels are not formulated for [95%] argon-5% CO2 shielding gas. Formulation changes would be required to take advantage of the reduced FGR. Source: Edison Welding Institute, 2003 Welding Studies Summary (Reduce Sodium and Potassium Content in SMAW Welding Electrodes (Rods)):  Welding Studies Summary (Reduce Sodium and Potassium Content in SMAW Welding Electrodes (Rods)) The presence of sodium and potassium in the flux or coating of SMAW stainless steel welding rods and FCAW welding wire results in the production of fume containing higher concentrations of hexavalent chromium. Hexavalent chromium is produced when welding flux components combine with atmospheric oxygen to form Na2CrO4 and K2CrO4. When the sodium and potassium content of the coating of E-308 welding rod was lowered from the range of 2 to 5 percent - typically found in SMAW welding electrodes - to less than 1 percent, the emission rate for total chromium was reduced by 30 percent and for hexavalent chromium by 94 percent. Reducing the amount of these elements in electrodes and fluxes will reduce the production of hexavalent chromium in the welding fume by reducing the ratio of hexavalent chromium to trivalent chromium. Welding Studies Summary (Reduce Sodium and Potassium Content in SMAW Welding Electrodes (Rods)):  Welding Studies Summary (Reduce Sodium and Potassium Content in SMAW Welding Electrodes (Rods)) Welding equipment manufacturers presently offer welding rods that contain lower sodium and potassium. Limitations: Low sodium and potassium welding electrodes are not commercially popular because they reportedly produce slag that is more difficult to remove and the arc characteristics create a weld bead with a ropy or wavy appearance – compared to SMAW welding electrodes that contain typical amounts of sodium and potassium. Despite these cosmetic issues, there are no reported weld quality or performance problems associated with the low sodium or potassium welding rods on the market. Sources: Hewitt and Hirst, 1993; Kimura et. al., 1979; R.K. Tandon, et al., 1986; and Palmer, 1987 Welding Studies Summary (Replace Typical GMAW Welding Systems With Pulse-Arc GMAW) :  Welding Studies Summary (Replace Typical GMAW Welding Systems With Pulse-Arc GMAW) Advances in welding power source technology involving the use of pulsed welding current can reduce fume generation of GMAW compared to conventional procedures. For example, a significant reduction of welding fume emission, by up to 80 percent, is attainable using the pulsed arc process as compared to the short arc process. With the pulsed arc, the weld bead is transferred without short-circuiting, in much the same way as the spray arc. The pulsed arc welding process avoids increased fume emission due to explosive bead detachment as a short circuit occurs. The reduction in welding fume that can be achieved by using pulsed welding current is demonstrated by shipyard tests. Operator exposure to hexavalent chromium was measured for pulsed gas metal arc welding (GMAW-P) of HY80 and HY100 steels (which contain 0.5-1.5% chromium), stainless steel (CRES), and nickel alloys. These tests show the value of pulsed GMAW welding in reducing hexavalent chromium exposures. The overall average hexavalent chromium exposure was 0.23 µg/m3 – with a median of 0.15 µg/m3 for 8 measurements when welding several base metals with nickel alloy 625 and 276 alloy electrodes. This represents a 75% reduction compared to the GMAW baseline value. Sources: Stern, February 1985; and Edison Welding Institute, 2003. Respiratory Protection – OSHA 1910.134-APFs:  Respiratory Protection – OSHA 1910.134-APFs   Respiratory Protection – OSHA 1910.134-APFs:  Respiratory Protection – OSHA 1910.134-APFs Notes: 1Employers may select respirators assigned for use in higher workplace concentrations of a hazardous substance for use at lower concentrations of that substance, or when required respirator use is independent of concentration. 2The assigned protection factors in Table 1 are only effective when the employer implements a continuing, effective respirator program as required by this section (29 CFR 1910.134), including training, fit testing, maintenance, and use requirements. 3This APF category includes filtering facepieces, and half masks with elastomeric facepieces. 4The employer must have evidence provided by the respirator manufacturer that testing of these respirators demonstrates performance at a level of protection of 1,000 or greater to receive an APF of 1,000. This level of performance can best be demonstrated by performing a WPF or SWPF study or equivalent testing. Absent such testing, all other PAPRs and SARs with helmets/hoods are to be treated as loose-fitting facepiece respirators, and receive an APF of 25. 5These APFs do not apply to respirators used solely for escape. For escape respirators used in association with specific substances covered by 29 CFR 1910 subpart Z, employers must refer to the appropriate substance-specific standards in that subpart. Escape respirators for other IDLH atmospheres are specified by 29 CFR 1910.134 (d)(2)(ii). Respiratory Protection:  Respiratory Protection Any NIOSH approved filter P-100 (as shown) is best Can use up to 10X the PEL (50 ug/m3) Respiratory Protection:  Respiratory Protection Full-Face Respirator Any NIOSH approved filter Can use up to 50X the PEL (250 ug/m3-for hex chromium) Respiratory Protection:  Respiratory Protection Powered Respirator (PAPR) Used with full-face respirator High Efficiency (N,R or P-95) or HEPA (N,R or P-100) filter; preferably P-100 Can use up to 50X the PEL (unless mfr can attest to 1000x) Respiratory Protection:  Respiratory Protection Welder’s Hood/PAPR Combination 25x PEL or 1000x PEL with written testament of Mfr. (125 ug/m3 or 5,000 ug/m3 for hexavalent chromium) Respiratory Protection:  Respiratory Protection Air Line Respirators – Supplied Air Constant- Flow Positive Pressure No filter required Can be used up to 25X or 1000X the PEL with Mfr. Written testament Summary:  Summary New Hexavalent Chromium Std. Affects several industries – chromates-Painting, electroplating, welding stainless Stainless steel mfr. Limited exposure sources – “older” melt shop-elevated areas Chromic acid areas and operations – Carbon Steel Welding – many variables – time,type,controls, filler rods Local exhaust ventilation References:  References www.nsrp.org: Navy and National Shipbuilding Research Program 1998 published report www.ewi.org/njc: the Edison Welding Institute report contracted by NSRP and published in 2003 www.osha.gov/SLTC/hexavalent chromium/index.html - hex chrome compliance assistance www.lni.wa.gov/safety – training kit- ppt. Hex Cr

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