Hexavalent Chromium in Foundries
Understanding OSHA’s Hexavalent Chromium Standard (1910.1026) may have compliance implications for your foundry. The standard only applies to chromium with a valance of six plus [Cr (VI)]. While Cr (VI) may be present in chromate surface coatings, exposures in foundries are primarily because of the oxidation of elemental chromium to the hexavalent state when chromium is subjected to high temperatures. If the amount of chromium in the alloy is low, it is unlikely that significant amounts of Cr (VI) will be formed. OSHA states iron and steel foundries may have Cr (VI) exposures and they have cited foundries for not doing exposure assessments.
The standard does not apply if employee breathing zone exposures are less than 0.5 µg/m3 as an 8-hour time weighted average (TWA). If there is objective evidence that exposures do not exceed this trigger level, there is no requirement to do exposure assessments. The action level is 2.5 µg/m3 and the permissible exposure level (PEL) is 5 µg/m3, both as TWAs.
The amount of chromium in an alloy is important. In general, gray iron and ductile iron alloys contain low amounts of chromium, although some specialty alloys may contain higher amounts. It would be rare to find exposures exceeding the trigger level with a few exceptions noted later. On the other hand, stainless alloys and other high corrosion resistant alloys may contain much higher amounts of chromium and are more likely to create compliance obligations.
OSHA has noted the primary sources in iron and steel foundries are furnace operations, torch cutting, and gouging and welding, and data from foundries would support this. NIOSH reviewed Cr (VI) data collected from a wide variety of industries, including foundries. Melting and pouring operations with alloys containing less than 0.25% to 26% had no exposures exceeding the trigger level. The same was true in the ductile iron foundries. NIOSH classified these operations as having “minimal Cr (VI) exposures.”
A survey of Steel Founders’ Society of America members indicated that some Cr (VI) exposures for steel and stainless steel melters, crane operators and pourers exceeded the trigger level, but none were over the action level. Other non-published data from foundries showed exposures were well below the trigger level in melting, grinding and shakeout operations; the alloy’s chromium content was 15%. In one foundry where higher chromium content alloys (over 25%) were processed, exposures for melters and pourers were over the trigger level but below the action level.
Thermal processes (welding, carbon arc gouging and plasma cutting) used to remove unwanted metal or repair castings can create high Cr (VI) exposures becaues of the high temperatures of these processes. In welding processes, the consumable wire is the primary source of the fumes generated. Mild/carbon steel welding wire usage results in very little Cr (VI) formation no matter what welding process is used due to the low chromium content of the wire.
If the chromium content of the wire is 2% or greater, exposures could exceed the trigger level depending on the welding process used. TIG (GTAW) and Sub-arc welding are low fume forming processes and are unlikely to result in exposures that exceed the trigger level. Stick (SMAW), MIG (GMAW) and flux core (FCAW) welding can generate significant amounts of Cr (VI) and exposures may exceed not only the trigger level but may also exceed the action level or PEL.
Arc gouging and plasma cutting are high fume forming processes, and Cr (VI) exposures are more dependent on the alloy’s chromium content, although without adequate ventilation, exposures may exceed the trigger level even when done on low chromium content alloys. This is also the case if chromite sand burn-in must be removed using arc gouging. Exposures are highly likely to exceed the action level and PEL when higher chromium alloys are cut, even if the exposure time is short.
Maintenance on dust collection equipment is an additional source of Cr (VI) exposure when dust is disturbed. The degree of exposure will depend on the chromium content of alloys and the dustiness of the work.
If your foundry produces low chromium content alloys, it is unlikely that the Cr (VI) exposures will be over the trigger level. If you produce higher chromium content alloys, conducting Cr (VI) exposure assessments is recommended, especially for melting, pouring, welding and thermal cutting jobs.
“Criteria for a Recommended Standard: Occupational Exposure to Hexavalent Chromium” DHHS (NIOSH) Publication No. 2013–128, pp. 12-13. 2013.
“Hexavalent Chromium Exposure Testing in Steel Foundries” S. Fiore. Presented at the 2006 Steel Founders’ Society of America National Technical & Operations SFSO T&O) Conference (www.sfsa.org/news/2007/hexcr-fiore.pdf)