A review of available sources identified the following exposure limits: TWA (PEL, REL, TLV), STEL (PEL, REL, TLV), and IDLH (1990 and 1994). Additionally, Section 3.5.3 (Simple Asphyxiants) was reviewed, but determined to be inapplicable because: 1) the definition of simple asphyxiants as” noble gases as well as nitrogen and hydrogen”, and 2) the documented acute toxic effects of carbon dioxide, beyond asphyxiation. Data sources were selected according to the hierarchy listed in Table 3.1.
The 1990 IDLH was selected as the TEEL-3; this is both the more preferred IDLH (Section 3.2) and a value consistent with reported effects of confusion and dizziness (ESHG, 2020). Additionally, a recent medical survey of carbon dioxide intoxication, at concentrations >5% (>50,000 ppm) is reported to cause physiological effects that would impair escape (hypercapnia). As listed in the EPA summary of acute toxic health effects (Appendix B, Table B-2), a physiological tolerance for carbon dioxide is 3% for 20 minutes, supporting the use of the TLV-STEL (15-minutes) as the TEEL-1. Additionally, the reported STEL were determined to be an appropriate value between ACGIH, NIOSH, and OSHA (NIOSH, 1989).
Current research was unable to identify a TEEL-2 basis. This is consistent with Rev. 29A, where a median value between the TEEL-1 and TEEL-3 values was selected as the final TEEL-2, with:
TEEL-2 = (TEEL-1 + TEEL-3)/2 = (30000 ppm + 50000 ppm)/2 = 40000 ppm
After consideration, this review recommends the same approach as Rev. 29A. This requires revision and affirmation of a deviation from the TEEL methodology, as was previously documented and approved.
• TEEL-1 = TLV-STEL (15-min, 30000 ppm)
• TEEL-2 = 40000 ppm (see Deviation Memo)
• TEEL-3 = 50000 ppm (IDLH, 1990)
This review generated TEEL values consistent with those in Rev. 29A.