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).
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