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  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  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
ACUTE TOXICITY DATA:
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 . The toxicity of nitrogen pentoxide. Br J Ind Med 11:140-144.
2. Fairhall LT . Industrial toxicology. 2nd ed. Baltimore, MD: Williams & Wilkins Company, pp. 83-84.
3. Gekkan Yakuji (Phamaceuticals Monthly) ; 22(4):651-656 (in Japanese).
4. Gray EL, Patton FM, Foldberg SB, Kaplan E . 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 . 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.