The previous OSHA standard for hydrogen fluoride was 3 ppm as an 8-hour TWA. OSHA proposed supplementing its 3-ppm TWA with a 15-minute STEL of 6 ppm. These limits are established in the final rule and are the same as those recommended by NIOSH (1976f, as cited in ACGIH 1986/Ex. 1-3, p. 315). In its posthearing comments, NIOSH (Ex. 150, Comments on Hydrogen Fluoride) concurred with OSHA's proposed limits for hydrogen fluoride. The ACGIH (1986/Ex. 1-3) recommends a 3 ppm TLV-ceiling for hydrogen fluoride. Hydrogen fluoride is a fuming, colorless liquid; at temperatures above 19 deg. C (66 deg. F), it becomes a colorless gas.
Guinea pigs and rabbits survived 40-ppm hydrogen fluoride concentrations for 41 hours, but exposure to 300 ppm for two hours or more was fatal (Machle, Thamann, Kitzmiller, and Cholak 1934/Ex. 1-519). Animals exposed to 3 ppm hydrogen fluoride for 30 days showed no adverse effects (Ronzani 1909, as cited in ACGIH 1986/Ex. 1-3, p. 315). Stokinger (1949a, as cited in ACGIH 1986/Ex. 1-3, p. 315) reported that animals repeatedly exposed to 7 ppm on a daily basis exhibited mild respiratory tract irritation. One study by Largent (1961/Ex. 1-1158) demonstrated kidney, liver, and lung damage in laboratory animals repeatedly exposed to 17 ppm hydrogen fluoride. At 8.6 ppm, the pathologic changes seen in exposed animals were minor, except for lung damage in one dog (Largent 1961/Ex. 1-1158).
In studies with humans, Largent (1960/Ex. 1-516; 1961/Ex. 1-1158) reported that volunteers exposed repeatedly to concentrations of hydrogen fluoride as high as 4.7 ppm for six hours/day for 10 to 50 days experienced irritation and burning of the eyes and nose, in addition to reddening of the skin, at concentrations above 3 ppm. Industrial experience has shown that direct contact of the skin with hydrogen fluoride results in severe burns that may have a delayed onset but later develop into ulcers that eventually scar (Stokinger 1981b/Ex. 1-1127). A report by Eagers (1969, as cited in Stokinger 1981b, above) described several industrial accidents in which workers died in a matter of hours after accidental splashing from ruptured containers of hydrogen fluoride (the cause of death was respiratory failure and cardiac arrest). Kleinfeld (1965/Ex. 1-514) reported a fatal case of hydrogen fluoride poisoning that caused death from pulmonary edema.
NIOSH (1976f, as cited in ACGIH 1986/Ex. 1-3, p. 315), in its criteria document, cites numerous studies that consistently show that long-term occupational exposures to hydrogen fluoride lead to fluorosis in workers. The NIOSH limit is based in part on a study by Derryberry, Bartholomew, and Fleming (1963/Ex. 1-506) showing that the threshold limit for minimal increases in bone density caused by fluoride (fluorosis) is below 4.3 ppm of hydrogen fluoride. The limits proposed by OSHA are the current NIOSH-recommended limits for this substance, and NIOSH's concurrence statement was the only comment received in the record.
Because of hydrogen fluoride's potential to cause respiratory irritation, OSHA finds that a STEL is necessary to reduce the risk associated with elevated, short-term exposures, which would be permitted under the 3 ppm TWA limit alone. The Agency has determined that the irritation caused by exposure to hydrogen fluoride constitutes a material impairment of health. Therefore, OSHA is revising the limits for hydrogen fluoride to 3 ppm as an 8-hour TWA and 6 ppm as a 15-minute STEL; these limits are established in the final rule.