Agent Name

Nitrogen dioxide

CAS Number




Major Category

Toxic Gases & Vapors


Dinitrogen tetroxide; Dinitrogen tetroxide, liquefied; Nitrogen dioxide, liquefied; Nitrogen oxide; Nitrogen peroxide; Nitrogen peroxide, liquefied; Nitrogen tetroxide; Peroxyde d'azote; [CHEMINFO] UN1067




Yellowish-brown liquid or reddish-brown gas (above 70 degrees F) with a pungent, acrid odor; Note: In solid form (below 15 degrees F) it is found structurally as N2O4; [NIOSH]


Generated from high temperature combustion; a common indoor air pollutant (gas ranges, kerosene heaters and improperly vented gas space heaters); occupational exposures have occurred after oxyacetylene welding, after underground blasting in mining operations, and after entering freshly filled farm silos. Other activities associated with increased NO2 levels include: glassblowing; operating motor vehicles indoors (including ice skating rink resurfacing machines); manufacture of nitric acid, oxidized cellulose compounds, lacquers and dyes, rocket propellants, and fertilizers; brazing; metal cleaning; rayon and food bleaching; fire fighting. [Rom, p. 1467]


Silo-filler's disease is an acute condition caused by NO2. [Sullivan, p. 818] This often fatal disease occurs when farmers enter a silo 1 to 10 days after fresh silage has been stored. Like phosgene and ozone, it is less soluble that other irritant inhalants and more likely to cause severe pulmonary edema without the signs of severe upper respiratory injury. (See Comments for phosgene.) [LaDou, p. 563] NO2 poisoning may also cause methemoglobinemia. [Ford, p. 685] Blasting and diesel powered machines generate NO2 at levels of 0.02-0.8 ppm during tunnel construction. " . . . Cumulative exposure to nitrogen dioxide showed the strongest association with a decrease in FEV1 in both non-smokers, and ever smokers." Two studies of miners exposed to nitrogen dioxide at 0.02-0.1 ppm found no effect on lung function. [Reference #2] Heavier than air--accumulates in enclosed spaces; TLV Basis = lower respiratory tract irritant; [ACGIH] Nitrogen dioxide is fibrogenic to the lungs in the context of an acute inhalation exposure complicated by bronchiolitis obliterans.

Reference Link

ATSDR Medical Management - Nitrogen oxides

Exposure Assessment
Skin Designation (ACGIH)

Insufficient data




0.2 ppm


Ceiling(OSHA) = 5 ppm


0.5 ppm


13 ppm

Excerpts from Documentation for IDLHs

It has been reported that 10 to 20 ppm has been mildly irritating [Patty 1963]. Exposure to 150 ppm or more (no time period given) has been reported to cause death from pulmonary edema [NRC 1979]. It has been predicted that 50% lethality would occur following exposure to 174 ppm for 1 hour [Book 1982].

Vapor Pressure

720 mm Hg

Odor Threshold Low

0.05 ppm

Odor Threshold High

0.14 ppm

Lethal Concentration

LC50 (rat) = 88 ppm/4H

Explanatory Notes

Odor threshold from AIHA (odor character = "bleach");

Reference Link

Cumulative exposure to dust and gases as determinants of lung function decline in tunnel construction workers.

Adverse Effects
Chronic Bronchitis


Toxic Pneumonitis





Methemoglobinemia, Secondary

ACGIH Carcinogen

Not Classifiable

Links to Other NLM Databases
Health Studies

Human Health Effects from Hazardous Substances Data Bank:

Toxicity Information


Chemical Information

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Biomedical References

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Related Information in HazMap

Occupational diseases associated with exposure to this agent:


Industrial Processes with risk of exposure:


Activities with risk of exposure: