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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


G. pig


Ekshtat 1965Ekshtat 1965

Ekshtat 1965

Ekshtat 1965

Ekshtat 1965













293 ppm273 ppm

125 ppm

125 ppm

312-390 ppm

29 ppm27 ppm

13 ppm

13 ppm

31-39 ppm

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

Revised IDLH: 15 ppmBasis for revised IDLH: No inhalation toxicity data are available on which to base an IDLH for phenylhydrazine. Therefore, the revised IDLH for phenylhydrazine is 15 ppm based on acute oral toxicity data in animals [Ekshtat 1965]. [Note: NIOSH recommends as part of its carcinogen policy that the “most protective” respirators be worn for phenyl hydrazine at concentrations above 0.14 ppm.]


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.