Altogether, OSHA has established about 500 PELs (permissible exposure limits) that regulate the exposure of workers to hazardous air contaminants, including elements, compounds (especially organic) and mineral dusts. In the plating and metal finishing industry, the most significant PELs are those for Cr6+, Cr3+ and cadmium.
US OSHA PELs
Cr2+ 500 µg m-3 (as Cr, 8-hour TWA)
Cr3+ 500 µg m-3 (as Cr, 8-hour TWA)
Cr6+ 5 µg m-3 (as Cr, 8-hour TWA)
Trivalent chromium (Cr3+) is widely considered to be much less toxic than Cr6+ and, in the US, is regarded as no more toxic than metallic chrome. In the US, the OSHA PEL for both Cr2+ and Cr3+ is currently 500 µg m-3 (as Cr, 8-hour time-weighted average) – considerably higher than the new value for hexavalent chromium. However, Denmark already classifies Cr3+ as a restricted substance, a designation that means its use is allowed but alternatives are preferred. It is not clear where regulations will go in the long term, but we would not be at all surprised to see Cr3+ ultimately becoming as regulated as Cr6+.
OSHA PEL 5 µg m-3 (8-hour TWA)
Cadmium is a very toxic heavy metal that is on the EPA’s Toxic 17 list. Because it is hazardous to both workers and consumers as well as the environment, the use of cadmium has been regulated in the US and elsewhere for many years. Cadmium electroplating, once used extensively on consumer products and automotive fasteners, is now largely restricted to aerospace applications, and even in this area several cleaner alternatives have been developed. Besides plating, industrial processes that involve cadmium include some types of welding, nickel-cadmium battery manufacturing and dry color formulation.
The 8-hour time-weighted average PEL for cadmium and its compounds, including dust and fumes, is 5 µg m-3. For a small number of industries, OSHA has also established SECALs (separate engineering control air limits) for cadmium of either 15 µg m-3 or 50 µg m-3 as the lowest feasible levels above the PEL that can be achieved by engineering and work practice controls. Among the requirements of the cadmium rule are that employees should be prohibited from eating and drinking in regulated areas.
OSHA has recently been enforcing regulations on industrial housekeeping to limit worker exposure to Cd dust.