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Calcium oxide

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

CAS number: 1305–78–8

NIOSH REL: 2 mg/m3 TWA

Current OSHA PEL: 5 mg/m3 TWA

1989 OSHA PEL: Same as current PEL

1993-1994 ACGIH TLV: 2 mg/m3 TWA

Description of Substance: White or gray, odorless lumps or granular powder.

LEL: . . Noncombustible Solid

Original (SCP) IDLH*: Unknown [*Note: “Effective” IDLH = 250 mg/m3 — see discussion below.]

Basis for original (SCP) IDLH: No data on acute inhalation toxicity are available on which to base an IDLH for calcium oxide. Because Patty [1963] reported that inhalation of the dust can cause chemical pneumonia and severe respiratory tract irritation, respirators have been selected on the basis of the assigned protection factor afforded by each device up to 50 × the OSHA PEL of 5 mg/m3 (i.e., 250 mg/m3); only the “most protective” respirators are permitted for use in concentrations exceeding 250 mg/m3. The available toxicological data indicate that severe respiratory irritation could inhibit escape.

Short-term exposure guidelines: None developed


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

Human data: Strong nasal irritation has been reported to result from exposures to about 25 mg/m3, but exposures to 9 to 10 mg/m3 resulted in no observable irritation [ACGIH 1991].



1. ACGIH [1991]. Calcium oxide. In: Documentation of the threshold limit values and biological exposure indices. 6th ed. Cincinnati, OH: American Conference of Governmental Industrial Hygienists, pp. 200-201.

2. Patty FA, ed. [1963]. Industrial hygiene and toxicology. 2nd rev. ed. Vol. II. Toxicology. New York, NY: Interscience Publishers, Inc., p. 863.