OSHA's former limit for carbon dioxide was 5000 ppm as an 8-hour TWA. The ACGIH has a 5000-ppm TLV-TWA with a 30,000-ppm TLV-STEL, and these were the limits proposed. NIOSH has a TWA REL of 10,000 ppm with a 10-minute 30,000-ppm ceiling limit; however, NIOSH (Ex. 8-47, Table N1) concurred that the proposed limits were appropriate. After carefully reviewing the record evidence submitted in response to OSHA's proposal for carbon dioxide, the Agency has determined that exposure limits of 10,000 ppm (8-hour TWA) and 30,000 ppm (15-minute STEL) are appropriate. Carbon dioxide is a colorless, odorless, noncombustible gas.
Both the ACGIH (1986/Ex. 1-3) and NIOSH (1976a, as cited in ACGIH 1986/Ex. 1-3, p. 102) cite studies indicating that continuous exposure to between 1.5 and 3 percent carbon dioxide (15,000 to 30,000 ppm) results in few, if any, adverse effects. However, electrolyte imbalances and other metabolic changes have been associated with prolonged exposures to 10,000 to 20,000 ppm CO(2) (Schulte 1964/Ex. 1-366; Gray 1950, as cited in ACGIH 1986/Ex. 1-3, p. 102). Increases in the rate of respiration have been observed among resting subjects exposed to 39,500 ppm for periods shorter than a day and among exercising subjects exposed to airborne concentrations below 30,000 for the same period (Sinclair et al. 1969, as cited in ACGIH 1986/Ex. 1-3, p. 102).
OSHA received comments on carbon dioxide from the American Iron and Steel Institute (AISI) (Ex. 1-1123; Tr. p. 11-24) and the Corn Refiners Association (Ex. 177), among others; both organizations listed CO(2) as a substance affecting their respective industries but did not provide further information. OSHA also received comments from the Beer Institute (Exs. 49 and 142; Tr. 8/9/88, p. 9-26) and from the Anheuser-Busch Company (Ex. 199).
The Beer Institute (Exs. 49 and 142; Tr. 8/9/88, p. 9-26) and the Brewing Industry Safety Advisory Committee submitted comments to OSHA on carbon dioxide. This industry's position is that there is no health risk to employees exposed to CO(2), even at levels between 15,000 and 20,000 ppm for an 8-hour period (Ex. 49, p. 2). In support of this position, the Beer Institute testified that the 8-hour TWA limit of 5000 ppm is "unnecessarily low and restrictive" (Ex. 49; Tr. 8/9/88, p. 9-27). The Institute also submitted a study by Riley and Bromberger-Barnea (1979/Ex. 49B) on the CO(2) exposure of brewery workers. This study monitored the full-shift exposures of these workers to CO(2) and determined that they average 1.08 percent CO(2)(10,800 ppm).
The Beer Institute testified that the beer industry "is unique relative to carbon dioxide exposure and control....no other industry faces the same engineering difficulties for controlling ambient carbon dioxide as the brewing industry" (Tr. 8/9/88, p. 9-26). These commenters identified two situations where exposure to CO(2) might be a problem for cellar workers (Tr. 8/9/88, p. 9-27). The first situation occurs when excessive CO(2) builds up in the large fermentation tanks used in the beer-making process and blows an escape valve, and the second exposure situation arises when workers must enter the fermentation tanks to flush out the sludge remaining after the tank has been drained. OSHA finds that these situations involve either upset conditions (safety valve blowout) or maintenance (tank cleaning); both of these operations are considered nonroutine, and respiratory protection may be used to protect employees when these situations arise. OSHA's analysis of the technological feasibility of achieving the final rule's limits in facilities in the beer industry is presented in Section VII of this preamble.
In response to these commenters, OSHA notes that the limit to which these industry spokesmen are objecting is the CO(2) limit that has been in force since the Agency was founded in 1971. Neither the Beer Institute nor the Brewing Industry Safety Advisory Committee objects to the only change OSHA proposed in this rulemaking (i.e., the addition of a 30,000-ppm STEL for CO 2). According to Gary Nateman, Vice President of the Beer Institute (Tr. 8/9/88, p. 9-30):
It is appropriate in our view for OSHA to adopt the 3-percent [30,000-ppm] short-term exposure limit for carbon dioxide. There is a scientific basis for this limit and in terms of real health benefit, this is the most meaningful approach (Tr. 8/9/88, p. 9-31).
The basis for the beer industry's objection to the retention of OSHA's 5000-ppm limit is that NIOSH recommended a higher 8-hour TWA limit of 10,000 ppm in its 1976 criteria document for carbon dioxide (NIOSH 1976a, as cited in ACGIH 1986/Ex. 1-3, p. 102).
After reviewing this evidence, OSHA is persuaded that a 10,000-ppm 8-hour TWA limit, combined with a 30,000-ppm STEL, will protect employees from the adverse effects associated with excessive exposures to CO(2). OSHA bases this conclusion on the fact that, while the evidence has not shown that prolonged exposures to 10,000 ppm are harmful, acute exposures to CO(2) concentrations in excess of 30,000 ppm have been demonstrated to cause changes in respiration rates in humans.
In the final rule, OSHA is establishing a 10,000-ppm PEL as an 8-hour TWA and a 30,000-ppm STEL to protect employees from experiencing the metabolic and respiratory changes, which constitute material health impairments, that are associated with elevated short-term CO(2) exposures. The Agency concludes that adding this limit will substantially reduce the risk associated with the high short-term exposures to CO(2) that are possible in the absence of a STEL. The former 8-hour TWA of 5000 ppm is retained.