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May 1994
Immediately Dangerous to Life or Health Concentrations (IDLH)

CAS number: 110–86–1

NIOSH REL: 5 ppm (15 mg/m3) TWA

Current OSHA PEL: 5 ppm (15 mg/m3) TWA

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 5 ppm (16 mg/m3) TWA

Description of substance: Colorless to yellow liquid with a nauseating, fish-like odor.

LEL: . 1.8% (10% LEL, 1,800 ppm)

Original (SCP) IDLH: 3,600 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by Patty [1963] that 2 of 3 rats died following a 6-hour exposure to 3,600 ppm [Fassett and Roudabush 1953].

Short-term exposure guidelines: None developed


Lethal concentration data:

Species Reference LC50




Time Adjusted 0.5-hr


Derived value
Rat Fassett & Roudabush 1953 LC66: 3,600 ----- 6 hr 8,280 ppm (2.3) 828 ppm
Rat Smyth et al. 1951 LC83: 4,000 ----- 4 hr 8,000 ppm (2.0) 800 ppm
Rat Vernot et al. 1977 9,000 ----- 1 hr 11,250 ppm (1.25) 1,125 ppm

Lethal dose data:

Species Reference Route LD50




Adjusted LD Derived value
Rat Biofax 1970 oral 891 ----- 1,896 ppm 190 ppm
Mouse Leslie et al. 1973 oral 1,500 ----- 3,191 ppm 319 ppm
Rat Smyth et al. 1951 oral 1,580 ----- 3,362 ppm 386 ppm

Human data: Nausea, headache, insomnia, nervousness, and low back or abdominal discomfort with urinary frequency have occurred in individuals exposed to concentrations averaging 125 ppm for 4 hours/day for 1 to 2 weeks [Patty 1963]. Chronic poisoning with mild symptoms of central nervous system injury occurred in workers at a plant where pyridine vapor concentrations ranged from 6 to 12 ppm [Tessinger 1948].

Revised IDLH: 1,000 ppm

Basis for revised IDLH: The revised IDLH for pyridine is 1,000 ppm based on acute inhalation toxicity data in animals [Vernot et al. 1977].


1. Biofax [1970]. Data sheet 14. Northbrook, IL: Biofax Industrial Bio-Test Laboratories, Inc.

2. Fassett DW, Roudabush RL [1953]. Toxicity of pyridine derivatives with relationship to chemical structure. Unpublished paper presented to the American Industrial Hygiene Association Conference, Los Angeles, CA.

3. Leslie GB, Hanahoe THP, Ireson JD, Sturman G [1973]. Some pharmacological properties of pyridine. Pharmacol Res Commun 5(4):341-365.

4. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., pp. 2190, 2727-2731.

5. Smyth HF Jr, Carpenter CP, Weil CS [1951]. Range-finding toxicity data: list IV. AMA Arch Ind Hyg Occup Med 4:119-122.

6. Teisinger J [1948]. Mild chronic intoxication with pyridine. Czech Med J 39(1947); abstracted in J Ind Hyg Toxicol 30:58. [From ACGIH [1991]. Pyridine. In: Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 1328-1330.]

7. Vernot EH, MacEwen JD, Haun CC, Kinkead ER [1977]. Acute toxicity and skin corrosion data for some organic and inor ganic compounds and aqueous solutions. Toxicol Appl Pharmacol 42(2):417-423.