OSHA's former Z-3 table listed an 8-hour TWA exposure limit of 15 mg/m3 (total particulate) for Plaster of Paris. The ACGIH has a 10-mg/m3 TWA for Plaster of Paris, measured as total dust, and this is the limit that was proposed. The final rule retains 15 mg/m3 as the 8-hour TWA PEL for the total particulate of Plaster of Paris; the 5-mg/m3 limit for the respirable fraction is also retained. Plaster of Paris is a fine, white powder.
Where occupational exposures to Plaster of Paris have been limited, no toxic effects or organic diseases of the lungs have occurred. Exposure to excessive levels of dust in the workplace may result in reduced visibility or injury to the skin or mucous membranes from the dust itself, or in damage to the skin from the rigorous skin-cleansing procedures required to remove the dust (ACGIH 1986/Ex. 1-3). Only NIOSH commented on this substance; NIOSH stated that it had not substantively reviewed the effects of Plaster of Paris exposure (Ex. 8-47, Table N4).
OSHA is retaining both the 8-hour TWA of 15 mg/m3 (total particulate) and the 8-hour TWA PEL of 5 mg/m3 (respirable particulate) for Plaster of Paris. The Agency concludes that these limits will protect against the significant risks of skin, eye, and other forms of physical irritation.