HYDROGEN SULFIDE

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: 7783-06-4; Chemical Formula: H₂S

OSHA’s former limits for hydrogen sulfide were a 20-ppm STEL (10-minute maximum duration) and a 50-ppm ceiling limit. The proposed and final rule for this substance are 10 ppm as an 8-hour TWA and 15 ppm as a STEL. These limits are consistent with those of the ACGIH. NIOSH has a REL for hydrogen sulfide of 10 ppm as a 10-minute ceiling. Hydrogen sulfide is a colorless, flammable gas with the odor of rotten eggs. It is widely used as an agricultural disinfectant, chemical intermediate, analytical reagent, and in the manufacture of heavy water in the utilities sector. However, occupational exposure to hydrogen sulfide occurs most frequently when it is encountered in natural oil or gas deposits or as a by-product in chemical reactions.

The 1986 ACGIH Documentation (Ex. 1-3, p. 318) cites several reports (Brieger 1964; Kranenburg and Kessener 1935; Masure 1950; Elkins 1950a/Ex. 1-953) of the occurrence of adverse ocular effects, including conjunctivitis, associated with exposure to 20 ppm or less of hydrogen sulfide. A study by Poda and Aiken (1966/Ex. 1-115) reports that the adoption of a voluntary limit of 10 ppm in two heavy-water plants eliminated exposure problems. An early study by Flury and Zernik (1931f, as cited in ACGIH 1986/Ex. 1-3, p. 318) reports that the conjunctivitis caused by exposure to 10 to 15 ppm of hydrogen sulfide for six hours endured for several days; however, OSHA is unaware of cases in which this substance caused irreversible eye damage. The National Institute for Occupational Safety and Health (NIOSH) relied essentially on the studies discussed above (Poda and Aiken 1966/Ex. 1-115; Flury and Zernik 1931f, as cited in ACGIH 1986/Ex. 1-3, p. 318) when recommending its limit for hydrogen sulfide of 10 ppm for 10 minutes; NIOSH (Ex. 8-47, Table N7) continues to recommend this ceiling for hydrogen sulfide (this issue is discussed further below).

OSHA received several comments related to the health effects and proposed limits for hydrogen sulfide (Exs. 3-1163, 3-216, 8-37, 8-47, 129; Tr. XI, pp. 114, 225). The Atlantic Electric Company (Ex. 3-1163) pointed out an error in the proposal, which listed the short-term exposure limit for hydrogen sulfide as 5 ppm rather than 15 ppm. The Edison Electric Institute (EEI) (Tr. XI, p. 225) explained that utility workers are exposed to hydrogen sulfide when they enter utility manholes and vaults that are located near coastal areas, where this gas seeps into underground spaces. The EEI reports that utility workers use respirators and ventilate these spaces before entering. The Montana Sulphur and Chemical Corporation (Ex. 3-216), a small-business manufacturer, handler, and shipper of hydrogen sulfide, commented that, in its opinion, “the evidence presented for significantly tightening the existing standards is not at all compelling.” According to Montana Sulphur, the studies cited by OSHA in the proposal to support the revised limits of 10 ppm (TWA) and 15 ppm (STEL) for hydrogen sulfide involved concurrent exposures “to other pollutants or stressors peculiar to the incident involved” (Ex. 3-216, p. 2). In addition, Montana Sulphur objects to OSHA’s reliance on a study by Poda and Aiken (1966/Ex. 1-115) showing that voluntary compliance with an internal standard of 10 ppm at a facility in the heavy-water industry eliminated complaints of eye irritation among hydrogen-sulfide-exposed workers at this facility (Ex. 3-216). Montana Sulphur and Chemical reports that, in its long experience of manufacturing and handling this “notoriously toxic” substance, it has never had a case of eye irritation that required medical treatment; it urges OSHA to promulgate a STEL for hydrogen sulfide in the range of 25 to 30 ppm rather than the proposed 15 ppm (Ex. 3-216).

OSHA appreciates this commenter’s thoughtful and thorough discussion of his company’s experience in dealing with hydrogen sulfide in the workplace. However, OSHA’s revised 8-hour TWA for this substance is based on the best available evidence (i.e., data on a level of occupational exposure that has been shown not to produce the health effect of concern). The eye irritation potential of hydrogen sulfide at levels below 20 ppm is widely recognized; the comment from Montana Sulphur (Ex. 3-216) acknowledges that reduction of the 8-hour TWA to 10 to 12 ppm is warranted. OSHA finds that a STEL of 15 ppm is justified by reports of eye irritation caused by short-term exposures to levels below 15 ppm (ACGIH 1986/Ex. 1-3, p. 318). OSHA is also aware that conditions in industry often involve simultaneous exposures to more than one hazardous substance and that such mixed exposures may increase the severity of the effects experienced by workers. However, the Agency must establish exposure limits based on the best available evidence for each individual substance to be regulated; it cannot attempt to set different limits for substances on the basis of the enormous number of other substances with which they could potentially be associated in actual use.

OSHA also received a comment on hydrogen sulfide from NIOSH (Ex. 8-47, Table N7). NIOSH recommends a single 10-ppm 10-minute ceiling for this substance. The United Paperworkers International Union (Ex. 8-37) also recommends adoption of the NIOSH 10-minute ceiling of 10 ppm. The Agency believes that the protection provided by NIOSH’s 10-ppm short-term limit is essentially equivalent to that provided by OSHA’s combined TWA-STEL limits, and that the combination of a 10-ppm 8-hour TWA and a 15-ppm STEL established in the final rule will provide broader protection in workplaces characterized either by short-term or by steady-state exposures.

The New Jersey Department of Health (Ex. 144) urged OSHA to base its limits for hydrogen sulfide on EPA’s IRIS data. OSHA discusses this approach and New Jersey’s comment in Section VI.A of this preamble.

OSHA concludes that the former 20-ppm (10-minute) short-term limit and 50-ppm ceiling limit did not adequately protect workers against the adverse ocular effects associated with exposure to concentrations of hydrogen sulfide below 20 ppm, as reported in several studies. OSHA finds that the eye irritation and conjunctivitis associated with such exposures represent a significant risk of material health impairment to workers, who may be forced to seek medical treatment after such exposure and who may also be unable to work during the period of recovery. OSHA has accordingly established an 8-hour TWA limit for hydrogen sulfide of 10 ppm and a short-term limit of 15 ppm. These levels have been demonstrated to be effective in preventing irritation and conjunctivitis in the workplace (Poda and Aiken 1966/ Ex. 1-115). The Agency finds that this dual limit will provide protection both in continuous steady-state exposure situations and in those characterized by sharp peaks and will do so more effectively than a single, short-term limit such as that recommended by NIOSH.