Ethylene oxide

(1,2 Epoxyethane; oxacyclopropane; dimethylene oxide)

CAS 75-21-8





Physical Properties

Colorless liquid or gas

bp 10.7 °C, mp -111.3 °C

Miscible with water



Sweet odor detectable at 257 to 690 ppm (mean = 420 ppm)


Vapor Density

1.5 at bp (air = 1.0)


Vapor Pressure

1095 mmHg at 20 °C


Flash Point

-20 °C


Autoignition Temperature

429 °C


Toxicity Data

LD50 oral (rat)

72 mg/kg


LC50 inhal (rat)

800 ppm (1600 mg/m3)



1 ppm (2 mg/m3)



1 ppm (2 mg/m3)

Major Hazards

OSHA "select carcinogen"; highly flammable; severe irritant.


Ethylene oxide is a severe irritant to the eyes, skin, and respiratory tract and exhibits moderate acute toxicity by all routes of exposure. Symptoms of overexposure by inhalation may be delayed and can include nausea, vomiting, headache, drowsiness, and difficulty breathing. Ethylene oxide can cause serious burns to the skin, which may only appear after a delay of 1 to 5 hours. This substance may also be absorbed through the skin to cause the systemic effects listed above. Eye contact can result in severe burns. Ethylene oxide is not considered to have adequate warning properties.

Ethylene oxide is listed by IARC in Group 2A ("probable human carcinogen") and is classified as a "select carcinogen" under the criteria of the OSHA Laboratory Standard. There is some evidence from animal studies that ethylene oxide may be a developmental and reproductive toxin in both males and females. Exposure to this substance may lead to sensitization.

Flammability and Explosibility

Ethylene oxide is an extremely flammable substance (NFPA rating = 4). Ethylene oxide vapor may be ignited by hot surfaces such as hot plates and static electricity discharges, and since the vapor is heavier than air, it may travel a considerable distance to an

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