NITROGEN DIOXIDE

Nitrogen dioxide
(Nitrogen peroxide)
CAS 10102-44-0

NO₂

Yellow-brown liquid to reddish brown gas; generally a mixture of NO₂ and N₂ O₄
(at -11 °C liquid is 0.01% NO₂ , at 21 °C liquid is 0.1% NO₂ and gas is 15.9% NO₂ )
bp 21 °C, mp -11 °C
Miscible in all proportions with water reacting to form nitric and nitrous acids

Pungent, acrid odor detectable at 0.12 ppm

1.58 (air = 1.0)

720 mmHg at 20 °C

Noncombustible

LC₅₀ inhal (rat) 88 ppm (4 h)

PEL (OSHA) 5 ppm (9 mg/m³; ceiling)

TLV-TWA (ACGIH) 3 ppm (5.6 mg/m³)

STEL (ACGIH) 5 ppm (9.4 mg/m³)

Highly toxic by inhalation; high concentrations of the gas and liquid NO₂ -N₂ O₄are corrosive to the skin, eyes, and mucous membranes.

The acute toxicity of nitrogen dioxide by inhalation is high. Inhalation may cause shortness of breath and pulmonary edema progressing to respiratory illness, reduction in the blood's oxygen carrying capacity, chronic lung disorders and death; symptoms may be delayed for hours and may recur after several weeks. Toxic effects may occur after exposure to concentrations of 10 ppm for 10 min and include coughing, chest pain, frothy sputum, and difficulty in breathing. Brief exposure to 200 ppm can cause severe lung damage and delayed pulmonary edema, which may be fatal. Nitrogen dioxide at concentrations of 10 to 20 ppm is mildly irritating to the eyes; higher concentrations of the gas and liquid NO₂ -N₂ O₄are highly corrosive to the skin, eyes, and mucous membranes. Nitrogen dioxide can be detected below the permissible exposure limit by its odor and irritant effects and is regarded as a substance with adequate warning properties.

Animal testing indicates that nitrogen dioxide does not have carcinogenic or reproductive effects. It does produce genetic damage in bacterial and mammalian cell cultures; however, most studies in animals indicate that it does not produce heritable genetic damage.

Nitrogen dioxide is not combustible (NFPA rating = 0) but is a strong oxidizing agent and will support combustion. Cylinders of NO₂ gas exposed to fire or intense heat may vent rapidly or explode.

Nitrogen dioxide-nitrogen tetroxide is a powerful oxidizer and can cause many organic substances to ignite. This substance may react violently with alcohols, aldehydes, acetonitrile, DMSO, certain hydrocarbons, and chlorinated hydrocarbons. Metals react vigorously and alkali metals ignite in NO₂ .

Because of its high acute toxicity, nitrogen dioxide should be handled using the "basic prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with compounds of high toxicity (Chapter 5.D) and compressed gases (Chapter 5.H). In particular, cylinders of nitrogen dioxide should be stored and used in a continuously ventilated gas cabinet or fume hood.

If large amounts of this compound are inhaled, the person should be moved to fresh air and medical attention should be sought at once. In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. In case of eye contact, wash promptly with copious amounts of water for 15 min (lifting upper and lower lids occasionally) and obtain medical attention. If nitrogen dioxide is ingested, obtain medical attention immediately.

In the event of a release of nitrogen dioxide, use appropriate protective equipment and clothing. Positive pressure air-supplied respiratory protection may be required in cases involving a large release of nitrogen dioxide gas. If a cylinder is the source of the leak and the leak cannot be stopped, remove the leaking cylinder to a fume hood or a safe place, if possible, in the open air, and repair the leak or allow the cylinder to empty.

Excess nitrogen dioxide and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.

The information in this LCSS has been compiled by a committee of the National Research Council from literature sources and Material Safety Data Sheets and is believed to be accurate as of July 1994. This summary is intended for use by trained laboratory personnel in conjunction with the NRC report Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. This LCSS presents a concise summary of safety information that should be adequate for most laboratory uses of the title substance, but in some cases it may be advisable to consult more comprehensive references. This information should not be used as a guide to the nonlaboratory use of this chemical.

Copyright 1995 National Academy of Sciences. All rights reserved.