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: 7664-41-7; Chemical Formula: NH3
OSHA's former exposure limit for ammonia was 50 ppm as an 8-hour TWA. OSHA proposed to revise this limit to 25 ppm TWA and to add a 35-ppm 15-minute STEL, based on the limits established by the ACGIH. NIOSH indicated its agreement with these proposed limits (Ex. 8-47, Table N1). However, in the final rule, the Agency has determined that it is not appropriate to establish a 25-ppm TWA limit for ammonia; the final rule does revise OSHA's exposure limit to 35 ppm as a 15-minute STEL. Ammonia is principally used as a feedstock in the manufacture of fertilizers and other chemical substances and is also used as a refrigerant.
Ammonia is a primary eye and upper respiratory tract irritant. An unpublished study conducted by the Detroit Department of Health and cited by the ACGIH (1986/Ex. 1-3, p. 27) reports that ammonia concentrations in the range of 20 to 25 ppm elicited complaints of discomfort from workers engaged in blueprinting and copying operations. In addition, a study of pigs conducted by Stombaugh et al. (1969) apeared to demonstrate that exposure to ammonia also causes systemic effects. Thus the ACGIH established both a full-shift TWA of 25 ppm to protect against chronic effects and a 35-ppm STEL to protect against ammonia's irritant effects.
OSHA also considered NIOSH's recommended 5-minute ceiling limit for ammonia of 50 ppm. When making this recommendation, NIOSH relied on several reports that ammonia concentrations as low as 50 ppm are moderately irritating (Vigliani and Zurlo 1955/Ex. 1-164; Mangold 1971; Industrial Bio-test Laboratories 1973, all as cited in NIOSH 1974a/Ex. 1-238; MacEwen, Theodore, and Vernot 1970/Ex. 1-827; Pagnotto 1973, as cited in ACGIH 1986/Ex. 1-3, p. 27). NIOSH concluded that the "irritating or annoying effects...[of exposure to ammonia are] more dependent upon concentration than length of exposure," and that "a standard expressed as a time-weighted average is inappropriate since it would permit fluctuations to concentrations considerably higher than 50 ppm" (NIOSH 1974a/Ex. 1-238, p. 69). In the proposal, OSHA preliminarily concluded that NIOSH's recommended 50-ppm ceiling limit was above the effect level reported in the Detroit Department of Health studies (1965-1970, as cited in ACGIH 1986/Ex. 1-3, p. 27) for sensory irritation.
Several rulemaking participants objected to a reduction in the current 50-ppm TWA limit (Exs. 3-375, 3-582, 3-756, 3-869, 3-888, 3-902, 3-939, 3-1012, 3-1118, 8-25, 8-29, 8-62, 8-68, 8-123, Tr. VIII 121-136). At the rulemaking hearing, Lucas Seeman, Technical Advisor for the Association of Reproduction Materials Manufacturers (ARMM), testified that there was no basis for the proposed revision since the effects associated with exposure to 50 ppm of ammonia did not, in his opinion, constitute impairment of health:
- The Detroit Health Department studies, which make reference to "worker complaints" of ammonia exposures, appear to be based on subjective reactions of workers and not any manifestation of health impairment or physical evidence of severe irritation. None of the reference data added [by the ACGIH] in 1980...made reference to any health impairment at the 25-ppm TWA or 35-ppm STEL levels of exposure. References added in 1980 did indicate that at 50 ppm workers reported no irritation, or minor to moderate irritation, and that they quickly became accustomed to the ammonia exposure up to that level (Tr. VII, pp. 222-224).
In reviewing the record evidence, OSHA finds that the 50-ppm 5-minute ceiling limit recommended by NIOSH is not sufficiently protective against ammonia's irritant effects. The evidence discussed by NIOSH (Ex. 150) and the testimony presented by Mr. Seeman (Tr. VII, pp. 222-224) show that, at levels below 50 ppm, some workers experience eye and upper respiratory tract irritation. This view is supported by Proctor, Hughes, and Fischman (Chemical Hazards of the Workplace, 2nd ed., 1988, p. 71), who report that even 5-minute exposures to 32 ppm caused nasal dryness in 10 percent of exposed volunteers, and that 5-minute exposures to 50 ppm ammonia caused nasal irritation and dryness in 20 percent of exposed volunteers. Deborah Berkowitz of the AFL-CIO testified that two companies in the meat packing industry evacuate the work place if airborne concentrations of ammonia reach 25 ppm (Tr. pp. 6-310 to 6-311).
OSHA finds that sensory irritation, such as that experienced by volunteers exposed to ammonia (Proctor, Hughes, and Fischman, 1988) constitutes material impairment of health. OSHA also finds that the fact that some workers may become acclimatized to ammonia exposures at concentrations as high as 50 ppm may account for the belief expressed by Mr. Seeman and others that 50 ppm is an acceptable exposure level. However, OSHA does not agree with this view of acclimatization because the long-term consequences of a continual assault on the sensory nerves are not known. In addition, acclimatization lessens the ability of workers to discern airborne concentrations of other hazardous materials.
The ACGIH (1986/Ex. 1-3) believes that an 8-hour TWA limit is necessary for ammonia because a study by Stombaugh, Teague, and Roller (1960/Ex. 1-29) reports that pigs exposed continuously to 103 to 145 ppm ammonia reduced their consumption of food and lost weight. The ACGIH interprets this study to mean that systemic toxicity occurs as a result of chronic exposure to ammonia. However, OSHA interprets this study differently, believing instead that it shows a secondary effect of the irritation traditionally associated with ammonia exposure. That is, in OSHA's view, these pigs stopped eating because they were experiencing too much respiratory and eye irritation to be interested in their food.
Thus, OSHA does not find it necessary in the final rule to establish an 8-hour TWA limit for ammonia to protect against chronic effects. Instead, the Agency concludes that a 15-minute STEL of 35 ppm will protect against this substance's irritant effects, which have been demonstrated to occur in workers exposed to ammonia at and below 50 ppm. OSHA concludes that the eye and upper respiratory tract irritation associated with ammonia exposure constitute material impairments of health and pose a significant risk to exposed workers.
- Page last reviewed: September 28, 2011
- Page last updated: September 28, 2011
- Content source:
- National Institute for Occupational Safety and Health Education and Information Division