Skip directly to local search Skip directly to A to Z list Skip directly to navigation Skip directly to site content Skip directly to page options
CDC Home
May 1994

Documentation for Immediately Dangerous To Life or Health Concentrations (IDLHs)


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:






TimeAdjusted 0.5-hr


Derived value
RatFassett & Roudabush 1953 LC66: 3,600 -----6 hr8,280 ppm (2.3)828 ppm
RatSmyth et al. 1951 LC83: 4,000-----4 hr8,000 ppm (2.0)800 ppm
RatVernot et al. 1977 9,000-----1 hr11,250 ppm (1.25)1,125 ppm

Lethal dose data:






Adjusted LDDerived value
RatBiofax 1970oral891-----1,896 ppm190 ppm
MouseLeslie et al. 1973 oral1,500-----3,191 ppm319 ppm
RatSmyth et al. 1951 oral1,580 -----3,362 ppm386 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 Unpublished paper presented to the American Industrial Hygiene Association Conference, Los Angeles, CA.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.

Contact Us: The U.S. Government's Official Web PortalDepartment of Health and Human Services
Centers for Disease Control and Prevention   1600 Clifton Road Atlanta, GA 30329-4027, USA
800-CDC-INFO (800-232-4636) TTY: (888) 232-6348 - Contact CDC–INFO