Sulfur dioxide

(Sulfurous oxide, sulfur oxide, sulfurous anhydride)

CAS 7446-09-5





Physical Properties

Colorless gas or liquid under pressure

bp -10.0 °C, mp -75.5 °C

Soluble in water (10 g/100 mL at 20 °C)



Pungent odor detectable at 0.3 to 5 ppm

Vapor Density

2.26 (air = 1.0)


Vapor Pressure

1779 mmHg at 21 °C


Flash Point



Toxicity Data

LC50 inhal (rat)

2520 ppm (6590 mg/m3; 1 h)


LCLO inhal (human)

1000 ppm (2600 mg/m3; 10 min)



5 ppm (13 mg/m3)



2 ppm (5.2 mg/m3)



5 ppm (13 mg/m3)

Major Hazards

Intensely irritating to the skin, eyes, and respiratory tract; moderate acute toxicity.

The acute toxicity of sulfur dioxide is moderate. Inhalation of high concentrations may cause death as a result of respiratory paralysis and pulmonary edema. Exposure to 400 to 500 ppm is immediately dangerous, and 1000 ppm for 10 min is reported to have caused death in humans. Sulfur dioxide gas is a severe corrosive irritant of the eyes, mucous membranes, and skin. Its irritant properties are due to the rapidity with which it forms sulfurous acid on contact with moist membranes. When sulfur dioxide is inhaled, most of it is absorbed in the upper respiratory passages, where most of its effects then occur. Exposure to concentrations of 10 to 50 ppm for 5 to 15 min causes irritation of the eyes, nose, and throat, choking, and coughing. Some individuals are extremely sensitive to the effects of sulfur dioxide, while experienced workers may become adapted to its irritating properties. Sulfur dioxide is regarded as a substance with good warning properties except in the case of individuals with reactive respiratory tracts and asthmatics. Exposure of the eyes to liquid sulfur dioxide from pressurized containers can cause severe burns, resulting in the loss of vision. Liquid SO2 on the skin produces skin burns from the freezing effect of rapid evaporation.

Sulfur dioxide has not been shown to be carcinogenic or to have reproductive or developmental effects in humans. Chronic exposure to low levels of sulfur dioxide has been shown to exacerbate pulmonary disease.

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