PAC Database - Detailed Chemical Data

Chemical Identity
Chemical CAS# UN# Health Code Numbers
Carbon dioxide 124-38-9 1013
Formula Synonyms
Co2 Carbon, dioxide
Physical Properties
Mol Wt State MP (°C) BP (°C) VP (Hg) VP (°C) SG LEL (ppm)
44.01 G -26.366 -78.464 750 78.6 0.72
PAC Values
PAC Values (Original Units: mg/m3)
54000 72000 90000
Converted PAC Values (ppm)
30000 40000 50000
Technical Basis
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.
NIOSH, 1989. Note, from the site: “This rule was reprimanded by the U.S. Circuit Court of Appeals”. As such, is provided to demonstrates interagency agreement on the published STEL values. Retrieved from
EPA summary of acute health effects:
USDA summary of acute health effects:
Permentier K, Vercammen S, Soetaert S, Schellemans C. Carbon dioxide poisoning: a literature review of an often forgotten cause of intoxication in the emergency department. Int J Emerg Med. 2017 Dec;10(1):14. doi: 10.1186/s12245-017-0142-y. Epub 2017 Apr 4. PMID: 28378268; PMCID: PMC5380556.
Hypercapnia can result in lethargy, disorientation, dizziness, vomiting. Rawat D, Modi P, Sharma S. Hypercapnea. [Updated 2023 Jul 24]. In: StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing; 2023 Jan-. Available from:
National Institute for Occupational Safety and Health (NIOSH). (1994). Documentation for Immediately Dangerous to Life or Health Concentrations (IDLH): Carbon dioxide. Retrieved from:
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