Nitric oxide

Synonyms

Amidogen, oxo-; Bioxyde d'azote [French]; INOmax; Mononitrogen monoxide; Nitric oxide; Nitrogen monoxide; Nitrogen oxide (NO); Oxyde nitrique [French]; Stickmonoxyd [German]; [ChemIDplus] UN1660

Category

Oxidizers

Description

Colorless gas. (Note: Shipped as a nonliquefied compressed gas.) [NIOSH] NO is converted to NO2 spontaneously in air. [ACGIH]

Sources/Uses

Used in the production of nitric acid; formed in high temperature combustion such as welding and detonation of explosives; it is generated in fires and in the exhaust from internal combustion engines; nitric oxide is present in the toxic gas that causes fatal "silo-fillers' disease" at concentrations reaching 140 ppm; Most exposures to NO include exposure to other nitrogen oxides as well. In oxytorch welding at about 6000 deg C, NO comprises about 95% of the nitrogen oxides. [ACGIH]

Comments

Unlike NO2, NO diffuses into the blood without injuring lung tissue. Methemoglobinemia has been reported in workers exposed to concentrations above 10 ppm. [Rom, p. 1476] Methemoglobinemia has been reported in patients who received nitrous oxide contaminated with 1.5% nitric oxide. Listed in the table "Examples of Industrial Chemicals for Which Methemoglobin Formation is NOT the Principal Cause of Toxicity"; [ACGIH] Nitric oxide can induce methemoglobinemia. NO by itself is nonirritating, but it is usually accompanied by NO2 and other irritating nitrogen oxides. Nitrogen oxides in high concentrations cause delayed pulmonary edema. [ATSDR Medical Management]

Reference Link #1

Biomedical References

Methemoglobin in blood = 1.5% of hemoglobin during or at end of shift. [ACGIH]

Insufficient data

Yes

25 ppm

25 ppm

0.5 ppm

100 ppm

Excerpts from Documentation for IDLHs

Other animal data: Guinea pigs have survived an exposure at 175 ppm for an unstated period [Bodansky 1951]. . . . Human data: It has been stated that exposures to oxides of nitrogen between 100 and 150 ppm are dangerous for exposures of 30 to 60 minutes [Sax 1975].

0.29 ppm

Odor Threshold High

0.97 ppm

LC50 (rat) = 1,068 mg/m3/4H

Explanatory Notes

Odor thresholds from HSDB;

will not burn

Yes

MetHgb is secondary toxic effect

Diseases

Occupational diseases associated with exposure to this agent:

• Pneumonitis, toxic

Processes

Industrial Processes with risk of exposure:

• Farming (Respiratory Hazards)
• Gas Welding and Cutting
• Welding

Activities

Activities with risk of exposure:

• Smoking cigarettes