Agent Name

Nitrogen tetroxide

CAS Number

10544-72-6

Formula

N2-O4

Major Category

Toxic Gases & Vapors

Synonyms

Di-nitrogen dioxide; Dinitrogen tetraoxide; Dinitrogen tetroxide; Nitrogen dioxide, di-; Nitrogen oxide (N2O4); Nitrogen tetraoxide; [ChemIDplus] UN1067

Category

Oxidizers

Description

Colorless gas; [HSDB] Red-brown liquid with a sharp unpleasant odor (kept liquid by compression); bp = 21.15 deg C; [CAMEO]

Sources/Uses

Exposure occurs where nitric acid is used, especially in acid baths for metal cleaning. Like NO2, it is also generated during welding operations. [HSDB] Used in rocket fuels; [REPROTOX]

Comments

Highly toxic; [Quick CPC] Like other nitrogen oxides, inhalation of NO4 may induce delayed pulmonary edema. Concentrations of 25-50 ppm cause irritation of the eyes and nose while 50-100 ppm can cause pulmonary edema and death. Cases of irritant-induced asthma have been reported. In animal experiments, methemoglobin level of 55% were produced in one hour after application of NO4 to the skin of rats. [HSDB] Liquid is an equal mixture of nitrogen dioxide and nitrogen tetroxide (evolves toxic vapors); A strong oxidizing agent; Reacts with water producing nitric acid and nitric oxide; [CAMEO] Classifications in the EU: Causes burns; Highly toxic by inhalation; Human exposures most commonly associated with "silo-fillers disease." Three members of Apollo/Soyuz Test Project crew were exposed to an estimated average concentration of 250 ppm in flight; Each member displayed signs and symptoms of chemical pneumonitis and increased methemoglobin levels; "Since N2O4 is in equilibrium with NO2, the toxic properties observed in clinical and toxicological cases have not distinguished between the two." [IUCLID] Causes impaired liver function tests in 30-week intermittent inhalation studies of rabbits; [RTECS] See "Nitrogen dioxide."

Exposure Assessment
TIH

Yes

Vapor Pressure

646 mm Hg

Lethal Concentration

LC50 (rat) = 105 mg/m3

Adverse Effects
Toxic Pneumonitis

Yes

Hepatotoxin

Hepatotoxin, Secondary

Methemoglobinemia

Methemoglobinemia, Secondary

Dermatotoxin

Skin Burns

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