CYCLOHEXANONE

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: 108-94-1; Chemical Formula: C₆H₁₀O

OSHA’s former limit for cyclohexanone was 50 ppm as an 8-hour TWA. The Agency proposed to reduce this limit to 25 ppm and to add a skin notation for this substance. NIOSH (Ex. 8-47, Table N1) concurred with this proposed limit. The final rule establishes an 8-hour TWA PEL of 25 ppm and includes a skin notation. Both the ACGIH and NIOSH recommend a time-weighted average for cyclohexanone of 25 ppm, and the ACGIH also recommends a skin notation. Cyclohexanone is a white to pale yellow, oily liquid with an odor similar to that of acetone and peppermint.

Cyclohexanone has been studied in several experimental animal species. A concentration of 2000 ppm inhaled for four hours was lethal to one of six rats; at 4000 ppm, all of the exposed animals died. In rabbits, the dermal LD(50) was 1000 mg/kg (Smyth, Carpenter, Weil et al. 1969/Ex. 1-442). Rabbits showed marked irritation and some corneal injury when undiluted cyclohexanone was instilled in the eye (Carpenter and Smyth 1946/Ex. 1-859). Guinea pigs exposed to 4000 ppm for six hours showed narcotic symptoms, lacrimation, salivation, depression of body temperature and heart rate, and corneal opacity (Specht, Miller, Valaer, and Sayers 1940/Ex. 1-1179). Rabbits exhibited degenerative changes of the liver and kidneys after 50 daily six-hour inhalation exposures to 190 ppm (Treon, Crutchfield, and Kitzmiller 1943b/Ex. 1-394). Exposures to 309 ppm cyclohexanone on the same regimen caused conjunctival congestion, while exposures to 3000 ppm were lethal to some of the exposed animals (Treon, Crutchfield, and Kitzmiller 1943b/Ex. 1-394).

In humans, Nelson and co-workers (1943/Ex. 1-66) reported that irritation caused by exposure to cyclohexanone was intolerable at 50 ppm; however, 25 ppm was not objectionable to most subjects in three- to five-minute exposures (Nelson, Enge, Ross et al. 1943/Ex. 1-66).

OSHA is adding a skin notation for cyclohexanone based on this substance’s ability to cause systemic toxicity through dermal absorption. L.H. Hecker, Director of Corporate Industrial Hygiene and Toxicology at Abbott Laboratories, comment that, in his opinion, there was no evidence for cyclohexanone’s dermal toxicity, and thus that no skin notation was necessary (Ex. 3-678). However, OSHA has determined, based on a review of the evidence for this substance, that cyclohexanone has a dermal LD(50) of 1000 mg/kg in rabbits ( Dangerous Properties of Industrial Materials, 7th ed., p. 997, Sax and Lewis 1989). The Agency believes it appropriate to establish a skin notation for substances posing a percutaneous hazard, which OSHA is defining as any substance having a dermal LD(50) in rabbits of 1000 mg/kg or less. Accordingly, the Agency is including a skin notation for cyclohexanone in the final rule (see Section VI.C.18 for a full discussion of the Agency’s policy on skin notations).

In the final rule, OSHA is establishing an 8-hour TWA for cyclohexanone of 25 ppm, with a skin notation. The Agency has determined that these limits will protect workers from the significant risks of liver and kidney damage, skin and respiratory-tract irritation, and percutaneous absorption associated with exposure to this substance. OSHA finds that skin and respiratory-tract irritation and liver and kidney damage all constitute material health impairments.