Carbon monoxide

CAS number: 630–08–0

NIOSH REL: 35 ppm (40 mg/m³) TWA, 200 ppm (229 mg/m³) CEILING

Current OSHA PEL: 50 ppm (55 mg/m³) TWA

1989 OSHA PEL: 35 ppm (40 mg/m³) TWA, 200 ppm (229 mg/m³) CEILING

1993-1994 ACGIH TLV: 25 ppm (29 mg/m³) TWA

Description of Substance: Colorless, odorless gas.

LEL: . . 12.5% (10% LEL, 12,500 ppm)

Original (SCP) IDLH: 1,500 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by Patty [1963] that a 1-hour exposure to 1,000 to 1,200 ppm would cause unpleasant, but no dangerous symptoms [Henderson et al. 1921]. Patty [1963] also reported that 1,500 to 2,000 ppm might be a dangerous concentration for an exposure of 1 hour [Henderson et al. 1921].

Existing short-term exposure guidelines: National Research Council [NRC 1987] Emergency Exposure Guidance Levels (EEGLs):

10-minute EEGL: 1,500 ppm

30-minute EEGL: 800 ppm

60-minute EEGL: 400 ppm

24-hour EEGL: 50 ppm

ACUTE TOXICITY DATA

Lethal concentration data:

Species	Reference	LC50 (ppm)	LCLo (ppm)	Time	Adjusted 0.5-hr LC (CF)	Derived Value
Rat Rat Human Rat Mouse G. pig Human	Hartzell et al. 1985 Hartzell et al. 1985 Lefaux 1968 Rose et al. 1970 Rose et al. 1970 Rose et al. 1970 Tab Biol Per 1933	8,636 5,207 ----- 1,784 2,414 5,647 -----	----- ----- 4,000 ----- ----- ----- 5,000	15 min 30 min 30 min 4 hr 4 hr 4 hr 5 min	6,822 ppm (0.79) 5,207 ppm (1.0) 4,000 ppm (1.0) 3,568 ppm (2.0) 4,828 ppm (2.0) 11,294 ppm (2.0) 2,750 ppm (0.55)	682 ppm 521 ppm 400 ppm 357 ppm 482 ppm 1,129 ppm 275 ppm

Other animal data: The median effective concentrations to produce incapacitation (EC₅₀s) in rats have been determined to be 2,667 ppm and 1,450 ppm in 15 and 30 minutes, respectively [Hartzell et al. 1985].

Other human data: It has been stated that a 1-hour exposure to 1,000 to 1,200 ppm would cause unpleasant but no dangerous symptoms, but that 1,500 to 2,000 ppm might be a dangerous concentration after 1 hour [Henderson et al. 1921a, 1921b]. In general, a carboxyhemoglobin (COHb) level of 10-20% will only cause slight headaches [NIOSH 1972] and a COHb of 11-13% will have no effect on hand and foot reaction time, hand steadiness, or coordination [Stewart and Peterson 1970]. At a COHb of 35%, manual dexterity is impaired [Stewart 1975]. At 40% COHb, mental confusion, added to increasing incoordination, precludes driving an automobile [Stewart 1975]. A 30-minute exposure to 1,200 ppm will produce a COHb of 10-13% [NIOSH 1972].

Revised IDLH: 1,200 ppm Basis for revised IDLH: The revised IDLH for carbon monoxide is 1,200 ppm based on acute inhalation toxicity data in humans [Henderson et al. 1921a, 1921b; NIOSH 1972; Stewart and Peterson 1970].

REFERENCES:

1. Hartzell GE, Priest DN, Switzer WG [1985]. Modeling of toxicological effects of fire gases. II. Mathematical modeling of intoxication of rats by combined carbon monoxide and hydrogen cyanide. J Fire Sci 3:115-128.

2. Henderson Y, Haggard HW, Teague MC, Prince AL, Wunderlich RM [1921]. Physiological effects of automobile exhaust gas and standards of ventilation for brief exposures. J Ind Hyg III(3):79-92.

3. Henderson Y, Haggard HW, Teague MC, Prince AL, Wunderlich RM [1921]. Physiological effects of automobile exhaust gas and standards of ventilation for brief exposures. IV. Concordance of the standard here proposed with the observations of other investigators. J Ind Hyg III(4):137-146.

4. Lefaux R [1968]. Practical toxicology of plastics. Cleveland, OH: Chemical Rubber Co.

5. NIOSH [1972]. NIOSH criteria for a recommended standard: occupational exposure to carbon monoxide. Cincinnati, OH: U.S. Department of Health, Education, and Welfare, Public Health Service, Center for Disease Control, National Institute for Occupational Safety and Health, DHEW (NIOSH) Publication No. HSM 73-11000.

6. NRC [1987]. Emergency and continuous exposure guidance levels for selected airborne contaminants. Vol. 7. Ammonia, hydrogen chloride, lithium bromide, and toluene. Washington, DC: National Academy Press, Committee on Toxicology, Board on Toxicology and Environmental Health Hazards, Commission on Life Sciences, National Research Council, pp. 17-38.

7. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., p. 930.

8. Rose CS, Jones RA, Jenkins LJ Jr, Siegel J [1970]. The acute hyperbaric toxicity of carbon monoxide. Toxicol Appl Pharmacol 17:752-760.

9. Stewart RL [1975]. The effect of carbon monoxide on humans. Am Rev Pharmacol 15:409-423.

10. Stewart RL, Peterson MR [1970]. Experimental human exposure to carbon monoxide. Arch Environ Health 12:154-164.

11. Tab Biol Per [1933]; 3:231 (in German).