METHYL ACETYLENE

OSHA comments from the January 19, 1989 Final Rule on Air Contaminants Project extracted from 54FR2332 et. seq. This rule was remanded by the U.S. Circuit Court of Appeals and the limits are not currently in force.

CAS: None; Chemical Formula: C₃H₄ isomers

OSHA formerly had a standard of 1000 ppm TWA for MAPP. The ACGIH also has an 8-hour TWA limit of 1000 ppm, with a TLV-STEL of 1250 ppm. OSHA proposed to retain the 8-hour PEL of 1000 ppm and to add a STEL of 1250 ppm, and the final rule establishes these limits, with which NIOSH (Ex. 8-47, Table N1) concurs. MAPP contains 58 percent of a mixture of propadiene (a colorless, unstable gas with a strong, unpleasant odor) and methyl acetylene (a colorless gas with a sweet odor); the balance of the mixture consists of paraffinic and olefinic C3 and C4 hydrocarbons.

Tests of rabbits, dogs, and guinea pigs exposed to an average concentration of 5000 ppm for seven hours/day, five days/week for four months resulted in no adverse health effects except decreased lung weights. No changes at all were observed in animals exposed to 1000 ppm for four months (Dow Chemical Company 1964, as cited in ACGIH 1986/Ex. 1-3, p. 368).

On the basis of these data, which show MAPP to be a chemical mixture of low toxicity in experimental animals, the Agency is retaining its 8-hour TWA PEL of 1000 ppm and adding a STEL of 1250 ppm. The Agency concludes that both of these limits are necessary to ensure that workers are protected and that good industrial hygiene practice is maintained.