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Nitric acid

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

CAS number: 7697–37–2

NIOSH REL: 2 ppm (5 mg/m3) TWA, 4 ppm (10 mg/m3) STEL

Current OSHA PEL: 2 ppm (5 mg/m3) TWA

1989 OSHA PEL: 2 ppm (5 mg/m3) TWA, 4 ppm (10 mg/m3) STEL

1993-1994 ACGIH TLV: 2 ppm (5.2 mg/m3) TWA, 4 ppm (10 mg/m3) STEL

Description of substance: Colorless, yellow, or red, fuming liquid with an acrid, suffocating odor.

LEL: . . . Noncombustible Liquid

Original (SCP) IDLH: 100 ppm

Basis for original (SCP) IDLH: The chosen IDLH is based on the statement by MCA [1961] that pulmonary edema may result from an exposure of 100 to 150 ppm for only 0.5 to 1 hour. It is not clear if MCA [1961] was referring to nitric acid specifically, or to nitrogen oxides. The chosen IDLH seems reasonable, however, because an IDLH of 100 ppm was also selected for hydrogen chloride.

Short-term exposure guidelines: None developed


Lethal concentration data:

Species Reference LC50 (ppm) LCLo (ppm) Time Adjusted 0.5-hr LC (CF) Derived value
Rat Gray et al. 1954 138 ----- 30 min 138 ppm (1.0) 14 ppm

Other animal data: Rats receiving a single exposure to 63 mg/m3 nitric acid (24 ppm) exhibited no apparent adverse effects [Diggle and Gage 1954].

Human data: A maximum allowable workplace concentration of 10 ppm has been proposed [Fairhall 1957]. It has been reported that 430 mg/kg is the lethal oral dose [Gekkan Yakuji 1980]. [Note: An oral dose of 430 mg/kg is equivalent to a worker being exposed to about 2,300 ppm for 30 minutes, assuming a breathing rate of 50 liters per minute and 100% absorption.]

Revised IDLH: 25 ppm

Basis for revised IDLH: The revised IDLH for nitric acid is 25 ppm based on acute toxicity data in humans [Gekkan 1980] and animals [Diggle and Gage 1954]. This may be a conservative value due to the lack of relevant acute inhalation toxicity data for workers.


1. Diggle WM, Gage JC [1954]. The toxicity of nitrogen pentoxide. Br J Ind Med 11:140-144.

2. Fairhall LT [1957]. Industrial toxicology. 2nd ed. Baltimore, MD: Williams & Wilkins Company, pp. 83-84.

3. Gekkan Yakuji (Phamaceuticals Monthly) [1980]; 22(4):651-656 (in Japanese).

4. Gray EL, Patton FM, Foldberg SB, Kaplan E [1954]. Toxicity of oxides of nitrogen. II. Acute inhalation toxicity of nitrogen dioxide, red fuming nitric acid, and white fuming nitric acid. AMA Arch Ind Hyg Occup Med 10:418-422.

5. MCA [1961]. Chemical safety data sheet SD-5: properties and essential information for safe handling and use of nitric acid. Washington, DC: Manufacturing Chemists Association, pp. 1-17.