Ethylene Oxide

Classification

Flammable gas, Category 1; Gas under pressure (liquefied gas); Acute toxicity (inhalation), Category 3; Skin irritation, Category 2; Eye irritation, Category 2A; Germ cell mutagenicity, Category 1B; Carcinogenicity, Category 1B; STOT single exposure, Category 3 (respiratory irritation). Japan's government classification also lists Reproductive toxicity, Category 1B, and nervous system effects from single and repeated exposure.

Hazard statements

• H220 Extremely flammable gas.
• H280 Contains gas under pressure; may explode if heated.
• H315 Causes skin irritation.
• H319 Causes serious eye irritation.
• H331 Toxic if inhaled.
• H335 May cause respiratory irritation.
• H340 May cause genetic defects.
• H350 May cause cancer.
• H360 May damage fertility or the unborn child (in some classifications).

Key precautionary statements

• P201 Obtain special instructions before use.
• P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
• P260 Do not breathe gas.
• P271 Use only outdoors or in a well-ventilated area.
• P280 Wear protective gloves, protective clothing, eye protection and face protection.
• P308+P313 IF exposed or concerned: Get medical advice/attention.
• P377 Leaking gas fire: Do not extinguish, unless leak can be stopped safely.
• P403 Store in a well-ventilated place.
• P405 Store locked up.

Ethylene oxide has its own OSHA standard, 29 CFR 1910.1047, rather than a Table Z-1 limit. The PEL is 1 ppm as an 8-hour TWA, with a 5 ppm excursion limit averaged over 15 minutes. The 0.5 ppm action level triggers duties such as periodic air monitoring and medical surveillance. NIOSH treats it as a potential occupational carcinogen and recommends less than 0.1 ppm TWA with a 5 ppm ceiling for no more than 10 minutes a day. The ACGIH TLV is 1 ppm TWA, and Cal/OSHA sets 1 ppm TWA and 5 ppm STEL. The NIOSH IDLH is 800 ppm. State OSHA plans may set different limits.

• Appearance: Colorless gas, shipped as a liquefied compressed gas (liquid below 51°F)
• Odor: Sweet, ether-like
• Molecular weight: 44.1
• Boiling point: 51°F (11°C)
• Freezing point: -171°F (-113°C)
• Flash point: -20°F (-29°C) as a liquid
• Autoignition temperature: 804°F (429°C)
• Explosive limits: LEL 3.0%, UEL 100%
• Vapor pressure: 1.46 atm
• Relative gas density: 1.49 (heavier than air)
• Water solubility: Miscible

Inhalation

Irritates the eyes, nose and throat. Causes headache, nausea, vomiting, drowsiness, weakness and poor coordination. High levels cause difficult breathing and fluid in the lungs (pulmonary edema).

Skin

Irritates the skin. The liquid or concentrated vapor causes burns and blisters, and the evaporating liquid can cause frostbite. Contaminated clothing, gloves and shoes trap ethylene oxide against the skin.

Eyes

Irritates the eyes; liquid or high vapor levels can burn them.

Ingestion

Not a likely route for the gas. The liquid is toxic if swallowed.

Target organs

Eyes, skin, respiratory system, liver, central nervous system, blood, kidneys, reproductive system

Long-term effects

Ethylene oxide is a known human carcinogen (IARC Group 1, NTP known), linked mainly to cancers of the blood and lymphatic system and to breast cancer. It damages genetic material, may harm fertility and the developing fetus, and long-term exposure can damage the nerves.

Gloves

NJDOH lists butyl and Silver Shield/4H gloves but notes breakthrough under 1 hour, so change gloves often. See hand protection.

Eyes and face

Chemical splash goggles and a face shield where liquid could splash.

Respiratory

Rely on enclosed sterilizers, aeration and local exhaust ventilation first. Up to 5 ppm, NIOSH lists full-facepiece gas masks with canisters for ethylene oxide, SCBA or supplied-air respirators. Above that, or at unknown levels, use a pressure-demand full-facepiece SCBA. See respiratory protection.

Clothing

NJDOH lists Tychem BR, TK and Responder and Trellchem HPS and VPS (more than 8 hours breakthrough). Use flash protection where levels may reach 10% of the LEL.

Store cylinders and drums upright and secured in a cool, well-ventilated area away from sunlight, heat and ignition sources. Use explosion-proof equipment, ground and bond containers, and use non-sparking tools. Avoid fittings that contain copper, silver or mercury.

Set up regulated areas where exposure may exceed the PEL, use continuous gas detection near sterilizers, aerators and storage, and give workers the training required by 29 CFR 1910.1047.

Keep away from

• Strong acids such as hydrochloric, sulfuric and nitric acid (violent polymerization)
• Strong bases such as sodium and potassium hydroxide
• Metal chlorides and metal oxides
• Oxidizers and air in closed systems
• Ammonia, amines, alcohols and mercaptans

• Evacuate and isolate the area. Stay upwind and out of low areas.
• Remove all ignition sources.
• Only trained responders in SCBA and protective clothing should approach the release.
• Stop the leak if it is safe. If a cylinder cannot be stopped, move it outdoors and turn it so the leak is at the top.
• Absorb liquid with vermiculite, dry sand or earth in closed containers. Keep out of sewers and confined spaces.
• Follow ERG Guide 119P.

Suitable extinguishing media

• Do not put out a leaking gas fire unless the leak can be stopped safely
• Dry chemical
• Carbon dioxide (CO₂)
• Alcohol-resistant foam
• Water spray to cool containers; large amounts of water dilute ethylene oxide and reduce its flammability

Special hazards

Extremely flammable across a very wide range (3–100%), so it can burn even without air. Vapor is heavier than air and can flash back from a distant ignition source. Heat or contamination can trigger violent polymerization, and containers may explode. Firefighters should wear SCBA and full protective gear.

• OSHA Ethylene Oxide Standard (29 CFR 1910.1047): 1 ppm TWA PEL, 5 ppm 15-minute excursion limit, 0.5 ppm action level; exposure monitoring, regulated areas, medical surveillance and training required.
• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical and carcinogen; SDS, labels and training required.
• OSHA Process Safety Management (29 CFR 1910.119 Appendix A): Threshold quantity 5,000 lb.
• CERCLA (40 CFR 302.4): Hazardous substance, reportable quantity 10 lb (RCRA waste U115).
• EPCRA Section 302 (40 CFR 355 Appendix A): Extremely hazardous substance, threshold planning quantity 1,000 lb, reportable quantity 10 lb.
• Clean Air Act 112(r) (40 CFR 68.130): Threshold quantity 10,000 lb. Also a listed hazardous air pollutant.
• EPA sterilizer air rule: EPA tightened its emission standards for commercial sterilizers in 2024 and in March 2026 proposed to rescind or revise them. Check EPA for the current status before relying on either version.
• DOT (49 CFR 172.101): UN1040, Ethylene oxide, Division 2.3 with subsidiary 2.1; Poison Inhalation Hazard, Zone D.

• NIOSH Pocket Guide: Ethylene oxide
• OSHA Occupational Chemical Database: Ethylene oxide
• NITE (Japan) GHS classification: Ethylene oxide
• NJ Department of Health Hazardous Substance Fact Sheet: Ethylene Oxide
• CAMEO Chemicals: UN1040 (DOT and ERG data)
• AIHA: EPA proposes to rescind or revise ethylene oxide sterilizer rules (March 2026)
• 40 CFR 355 Appendix A, EPCRA extremely hazardous substances