HYDROGEN CYANIDE

      The former OSHA limit for hydrogen cyanide was a 10-ppm 8-hour TWA, with a skin notation. The ACGIH has a 10-ppm ceiling limit, also with a skin notation. NIOSH (1976e/ Ex. 1-240) has recommended that workplace exposures to hydrogen cyanide not exceed 4.7 ppm (5 mg/m³) as a 10-minute ceiling. OSHA proposed a 10-minute ceiling of 4.7 ppm for hydrogen cyanide, and the final rule establishes this limit as a 15-minute STEL. The skin notation is retained. NIOSH (Ex. 8-47, Table N1) concurs with the selection of this PEL. Hydrogen cyanide is a colorless gas at room temperature.

       The ACGIH (1986/Ex. 1-3) has summarized the extensive body of human evidence on the adverse effects resulting from exposure to hydrogen cyanide. The Documentation notes that exposure to levels of 45 to 54 ppm hydrogen cyanide can be tolerated for one hour with no immediate or delayed effects, but that 18 to 36 ppm produces "slight" symptoms after several hours of exposure. The ACGIH also cites Grabois (1954/ Ex. 1-1150), who reported that workers in apricot kernel processing plants experienced no ill effects when exposed to hydrogen cyanide at a concentration of approximately 10 ppm.

       The NIOSH recommendation of 4.7 ppm as a 10-minute ceiling limit is based largely on an epidemiologic study by El Ghawabi et al. (1975/Ex. 1-632) that showed an increase in symptoms of headache, weakness, throat irritation, vomiting, dyspnea, lacrimation, colic, and nervousness among workers exposed to cyanide for an average of 7.5 years. The 36 male workers that were studied were employed in three electroplating factories. Breathing zone samples (15 minutes in duration) were collected and ranged from 4.2 to 12.4 ppm. Cyanide levels at two of the three plants did not exceed 9.6 ppm. El Ghawabi et al. (1975/Ex. 1-632) also reported that two workers in one plant suffered from psychotic episodes; these conditions were reported to be similar to cases that occurred during the therapeutic use of thiocyanate. Mean values of urinary thiocyanate in the 36 workers correlated well with air concentrations of cyanide (El Ghawabi, Gaafar, El-Saharti et al. 1975/Ex. 1-632).

       Symptoms resulting from chronic exposure to cyanide were also reported by Radojicic (1973, as cited in NIOSH 1976e/Ex. 1-240) among workers exposed to HCN levels between 5.4 and 12.3 ppm, and by Saia, DeRosa, and Galzigna (1970, as cited in NIOSH 1976e/Ex. 1-240). NIOSH (1976e/Ex. 1-240) interpreted the significance of these studies as follows:

Colle (1972)...advanced the belief that these symptoms of headache, dyspnea, epigastric burning, vertigo, tinnitus, nausea, vomiting, tremor, and precordial pain represent a true clinical entity and that they are sufficiently documented and characteristic of chronic cyanide exposure to be grouped into a true syndrome.... Chaumont (1960)...also stated that there is no clinical evidence to deny that cyanides can cause this type of occupational intoxication. He apparently found the debate on whether this intoxication is truly chronic or whether it involves repeated subacute symptoms to be semantic in nature and opted for the admission that chronic intoxication caused by HCN and the cyanide salts is a true occupational disease.... Thus, one might describe chronic cyanide poisoning as a slow deterioration of resistance, and, therefore, an intensified sensitivity, due to inadequate time between exposures for replacement of damaged ;tissues, enzyme systems and metabolic stores, the elimination of detoxication products, and the regeneration of homeostatic mechanisms (NIOSH 1976e/Ex. 1-240, pp. 90-91).

       OSHA received a few comments, in addition to that made by NIOSH (Ex. 8-47), on its proposal to revise the PEL for HCN to 4.7 ppm (5 mg/m³) as a short-term limit. Dr. Lawrence Hecker, representing Abbott Laboratories (Ex. 3-678), recommended that OSHA retain its former skin notation for HCN; OSHA's intention to do so was inadvertently omitted from the discussion of hydrogen cyanide in the NPRM. There is ample evidence that cyanide penetrates the skin in sufficient quantities to cause systemic effects (NIOSH 1976e/Ex. 1-240).

       Accordingly, OSHA is retaining its skin notation for HCN in the final rule. BP America (Ex. 8-57; Tr. 9-127) urged OSHA to establish the ACGIH TLV rather than the NIOSH REL for HCN, and the New Jersey Department of Health urged use of EPA's IRIS data to set a PEL for this substance (Ex. 144). In response to these commenters, OSHA notes that the ACGIH is not, in the Agency's opinion, sufficiently protective. Use of the IRIS data is discussed in Section VI.A.

       OSHA concludes that a variety of symptoms are associated with exposure to hydrogen cyanide at levels less than 10 ppm. This shows that neither the former PEL nor the ACGIH TLV is sufficiently protective. In the final rule, OSHA is therefore establishing a 4.7-ppm 15-minute STEL as the PEL. The Agency finds that the final rule's short-term limit will protect workers from the significant risk of headache, weakness, colic, and nervousness, which together constitute material impairment of health; these effects have been observed in individuals exposed at the 10-ppm level over a full working shift. OSHA concludes that this limit will substantially reduce these significant risks.