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

CAS number: 100–63–0

NIOSH REL: 0.14 ppm (0.6 mg/m3) 2-hr CEILING [skin]; NIOSH considers phenylhydrazine to be a potential occupational carcinogen as defined by the OSHA carcinogen policy [29 CFR 1990].

Current OSHA PEL: 5 ppm (22 mg/m3) TWA [skin]

1989 OSHA PEL: 5 ppm (20 mg/m3) TWA, 10 ppm (45 mg/m3) STEL [skin]

1993-1994 ACGIH TLV: 0.1 ppm (0.44 mg/m3) TWA [skin], A2

Description of substance: Colorless to pale-yellow liquid or solid (below 67°F) with a faint, aromatic odor.

LEL:. . Unknown

Original (SCP) IDLH*: 295 ppm [*Note: “Effective” IDLH = 250 ppm — see discussion below.]

Basis for original (SCP) IDLH: No data on acute or chronic inhalation toxicity are available on which to base the IDLH. Systemic effects described by Patty [1963] were caused by chronic exposures from oral dosing. NIOSH [1976] cited a rat oral LD50 of 188 mg/kg [Ekshtat 1965] which provides a calculated estimate of 1,300 mg/m3 (295 ppm) for the IDLH. Because of the assigned protection factor afforded by each device, however, 50 ´ the OSHA PEL of 5 ppm (i.e., 250 ppm) is the concentration above which only the “most protective” respirators are permitted.

Short-term exposure guidelines: None developed


Lethal dose data:

Species Reference Route LD50 (mg/kg) LDLo (mg/kg) Adjusted LD Derived value
Rat Ekshtat 1965 oral 188 —– 293 ppm 29 ppm
Mouse Ekshtat 1965 oral 175 —– 273 ppm 27 ppm
Rabbit Ekshtat 1965 oral 80 —– 125 ppm 13 ppm
G. pig Ekshtat 1965 oral 80 —– 125 ppm 13 ppm
Dog Ekshtat 1965 oral 200-250 —– 312-390 ppm 31-39 ppm


Human data: None relevant for use in determining the revised IDLH.


1. Ekshtat BY [1965]. Maximum permissible concentrations of hydrazine hydrate and phenylhydrazine in water bodies. Gig Sanit 30(8):191-197 (translated).

2. NIOSH [1976]. MV89250. Hydrazine, phenyl-. In: Registry of toxic effects of chemical substances, 1976 ed. 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. 76-191, p. 598.

3. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., pp. 2227-2228.