Phosphoric acid

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

CAS number: 7664–38–2

NIOSH REL: 1 mg/m3 TWA, 3 mg/m3 STEL

Current OSHA PEL: 1 mg/m3 TWA

1989 OSHA PEL: 1 mg/m3 TWA, 3 mg/m3 STEL

1993-1994 ACGIH TLV: 1 mg/m3 TWA, 3 mg/m3 STEL

Description of substance: Thick, colorless, odorless, crystalline solid.

LEL :. . Noncombustible Solid

Original (SCP) IDLH*: 10,000 mg/m3 [*Note: “Effective” IDLH = 2,000 mg/m3 — see discussion below.]

Basis for original (SCP) IDLH: According to MCA [1958], phosphoric acid does not cause any systemic effect, and the chance of pulmonary edema from mist or spray inhalation is very remote. The rat oral LD50 of 1,530 mg/kg [Biofax 1970] cited by NIOSH provides a calculated IDLH of about 10,000 mg/m3. However, for this draft technical standard, respirators have been selected on the basis of the assigned protection factor afforded by each device up to 2,000 ´ the OSHA PEL (i.e., 2,000 mg/m3); only the “most protective” respirators are permitted for use in concentrations exceeding 2,000 mg/m3.

Short-term exposure guidelines: None developed


Lethal dose data:

Species Reference Route LD50




Adjusted LD Derived value
Rat Biofax 1970 oral 1,530 ----- 10,710 mg/m3 1,071 mg/m3

Human data: It has been stated that phosphoric acid does not cause any systemic effect and that the chance of pulmonary edema from mist or spray inhalation is very remote [MCA 1958].

Revised IDLH: 1,000 mg/m3

Basis for revised IDLH: The revised IDLH for phosphoric acid is 1,000 mg/m3 based on acute oral toxicity data in animals [Biofax 1970]. This may be a conservative value due to the lack of relevant acute toxicity data for workers.


1. Biofax [1970]. Data sheet 19-4/70. Northbrook, IL: Biofax Industrial Bio-Test Laboratories, Inc.

2. MCA [1958]. Chemical safety data sheet SD-70: properties and essential information for safe handling and use of phosphoric acid. Washington, DC: Manufacturing Chemists Association, pp. 1-13.

3. NIOSH [1976]. TB63000. Phosphoric acid. 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. 879.

Page last reviewed: December 4, 2014