Substance profile
Ethylene oxide
Ethylene oxide is a colorless gas at ordinary room temp and pressure; liquid below 12 °C with a sweet odor.
01 · Identification
What Ethylene oxide is
Ethylene oxide is a colorless gas at ordinary room temp and pressure; liquid below 12 °C with a sweet odor. Its molecular formula is C2H4O and its molecular weight is 44.05 g/mol. It boils at 10.6 °C, melts at -112 °C, is soluble in water.
Under the GHS it carries the signal word Danger. It is classed as hazardous Air Pollutants (HAPs).
02 · Identifiers
Ethylene oxide identifiers and molecular data
Ethylene oxide CAS number and EC number
Ethylene oxide molecular formula and molecular weight
Other names for Ethylene oxide
- EtO
- EO
- oxirane
- 12/88
- Alpha, Beta-Oxidoethane
- Amprolene
- Anprolene
- Anproline
- Ciba-Geigy 9138
- Dihydrooxirene
- Dimethylene Oxide
- E O
- E.O.
- Ent-26263
- 1,2-Epoxy Ethane
03 · GHS classification
Ethylene oxide hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Ethylene oxide pictograms and signal word
Ethylene oxide hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Flammable gases GHS chapter 2.2 | Category 1A | H220 | GHS02 |
| Acute toxicity - oral GHS chapter 3.1 | Category 3 | H301 | GHS06 |
| Acute toxicity - inhalation GHS chapter 3.1 | Category 3 | H331 | GHS06 |
| Skin corrosion/irritation GHS chapter 3.2 | Category 1A or 1B or 1C | H314 | GHS05 |
| Serious eye damage/eye irritation GHS chapter 3.3 | Category 1 | H318 | GHS05 |
| Germ cell mutagenicity GHS chapter 3.5 | Category 1A or 1B | H340 | GHS08 |
| Carcinogenicity GHS chapter 3.6 | Category 1A or 1B | H350 | GHS08 |
| Specific target organ toxicity - single exposure GHS chapter 3.8 | Category 3 | H335 | GHS07 |
| Specific target organ toxicity - single exposure GHS chapter 3.8 | Category 3 narcotic | H336 | GHS07 |
| Specific target organ toxicity - repeated exposure GHS chapter 3.9 | Category 1 | H372 | GHS08 |
Where two values are shown with “or”, the hazard statement is shared by more than one category or by more than one class, and the code alone does not say which. H272, for example, belongs to oxidising liquids and to oxidising solids — the physical state decides. The binding answer for a specific entry is in the CLP Annex VI table itself.
Ethylene oxide hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H220 | Extremely flammable gas. |
| H350 | May cause cancer <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>. |
| H340 | May cause genetic defects <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>. |
| H360Fd | May damage fertility. Suspected of damaging the unborn child. |
| H331 | Toxic if inhaled. |
| H301 | Toxic if swallowed. |
| H335 | May cause respiratory irritation. |
| H336 | May cause drowsiness or dizziness. |
| H372 | Causes damage to organs <or state all organs affected, if known> through prolonged or repeated exposure <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>. |
| H314 | Causes severe skin burns and eye damage. |
| H318 | Causes serious eye damage. |
This page lists only the codes assigned to Ethylene oxide. The full reference lives on the hazard statements hub, the precautionary statements hub and the GHS pictograms hub.
Safety Data Sheet
Getting an SDS for Ethylene oxide
Our own Ethylene oxide safety data sheet walks through all sixteen sections of the published data. What it is not is the document an inspector asks for: an SDS is issued for a product by its supplier, so the sheet covering the grade actually standing in your store exists only in that supplier’s version. Collecting those and keeping them current as suppliers revise them is a separate job.
04 · Precautionary statements
Ethylene oxide precautionary statements
CLP Annex VI assigns 18 precautionary statements to Ethylene oxide. They are grouped the way a label groups them: what to do before handling, what to do when something has already happened, how to store it and how to dispose of it.
Prevention
What to do before and during handling so the hazard never happens.
Response
What to do once exposure, spillage or fire has already happened.
Reading the notation. … is a blank the supplier fills in — not a truncated sentence.· [square brackets] mark a part printed only when it applies.
05 · Names in the regulation
Ethylene oxide name in 23 EU languages
CLP Annex VI Part 3 is published in every language edition of the regulation, and the identification column is written out in each of them. Nothing below is translated by us: each line is the name as that edition prints it. Under Art. 18(2) the substance name from Annex VI is a lawful product identifier, so this is the wording to put on a label going to that market — and where the cell lists several designations, any one of them qualifies.
| Language | Name in CLP Annex VI Part 3 |
|---|---|
| Bulgarian български | етиленов оксид оксиран |
| Spanish español | Óxido de etileno oxirano |
| Czech čeština | ethylenoxid oxiran |
| Danish dansk | ethylenoxid oxiran |
| German Deutsch | Ethylenoxid Oxiran |
| Estonian eesti | etüleenoksiid oksiraan |
| Greek ελληνικά | αιθυλενοξείδιο οξιράνιο |
| English English | ethylene oxide oxirane |
| French français | oxyde d’éthylène oxiranne |
| Croatian hrvatski | etilen-oksid oksiran |
| Italian italiano | ossido di etilene ossirano |
| Latvian latviešu | etilēnoksīds oksirāns |
| Lithuanian lietuvių | etileno oksidas oksiranas |
| Hungarian magyar | etilén-oxid oxirán |
| Maltese Malti | ossidu tal-etilen ossiran |
| Dutch Nederlands | ethyleenoxide oxiraan |
| Polish polski | tlenek etylenu oksiran |
| Portuguese português | óxido de etileno oxirano |
| Romanian română | oxid de etilenă oxiran |
| Slovak slovenčina | etylénoxid oxirán |
| Slovenian slovenščina | etilen oksid oksiran |
| Finnish suomi | Etyleenioksidi oksiraani |
| Swedish svenska | etylenoxid oxiran |
All 23 language editions of Annex VI carry this entry. Irish is the twenty-fourth official EU language and has no line here for a different reason: no consolidated CLP text has ever been published in Irish, so there is no Irish edition of Annex VI to quote a name from. Source: consolidated CLP, CELEX 02008R1272, language editions. © European Union, https://eur-lex.europa.eu — only the electronic Official Journal of the European Union is authentic.
06 · Label elements
Ethylene oxide GHS label elements
Everything CLP Annex VI fixes for Ethylene oxide, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Ethylene oxide
- Extremely flammable gas.
- May cause cancer <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>.
- May cause genetic defects <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>.
- May damage fertility. Suspected of damaging the unborn child.
- Toxic if inhaled.
- Toxic if swallowed.
- May cause respiratory irritation.
- May cause drowsiness or dizziness.
- Causes damage to organs <or state all organs affected, if known> through prolonged or repeated exposure <state route of exposure if it is conclusively proven that no other routes of exposure cause the hazard>.
- Causes severe skin burns and eye damage.
- Causes serious eye damage.
- Obtain special instructions before use.
- Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
- Keep container tightly closed.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Do not eat, drink or smoke when using this product.
- Use only outdoors or in a well-ventilated area.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- IF INHALED:
- IF IN EYES:
- IF exposed or concerned:
- Immediately call a POISON CENTER/doctor/…
- Get medical advice/attention.
- Get medical advice/attention if you feel unwell.
- Rinse mouth.
- Do NOT induce vomiting.
- Remove contact lenses, if present and easy to do. Continue rinsing.
- Store in a well-ventilated place.
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Ethylene oxide in the GHS label constructor →
07 · Health hazards
Ethylene oxide health hazards and exposure limits
Ethylene oxide hazard summary
Ethylene oxide is a flammable gas with a somewhat sweet odor. It dissolves easily in water. Ethylene oxide is a man-made chemical that is used primarily to make ethylene glycol (a chemical used to make antifreeze and polyester). A small amount (less than 1%) is used to control insects in some stored agricultural products and a very small amount is used in hospitals to sterilize medical equipment and supplies.
Source: Agency for Toxic Substances and Disease Registry (ATSDR)
Ethylene oxide carcinogenicity classification
Under the conditions of these 2-year inhalation studies, there was clear evidence of carcinogenic activity for B6C3F1 mice as indicated by dose-related increased incidences of benign or malignant neoplasms of the lung and benign neoplasms of the harderian gland in both male and female B6C3F1 mice following exposure to ethylene oxide vapors at 50 and 100 ppm. In female mice, ethylene oxide caused additional malignant neoplasms of the uterus, mammary gland, and hematopoietic system (lymphoma).
Source: US National Toxicology Program · TR-326: Toxicology and Carcinogenesis Studies of Ethylene Oxide (CASRN 75-21-8) in B6C3F1 Mice (Inhalation Studies) (1987 )
Ethylene Oxide: known to be a human carcinogen.
Source: Hazardous Substances Data Bank (HSDB)
An IARC group and a CLP classification answer different questions. IARC judges whether the evidence for cancer in humans is strong enough; CLP Annex VI is the legally binding EU classification. A substance can carry one and not the other.
Ethylene oxide occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 1.0 [ppm], STEL(OSHA) = 5 ppm | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| PEL | 1 ppm [0.5 ppm Action Level] | Occupational Safety and Health Administration (OSHA) |
| PEL | 5 ppm [15 minute excursion limit] | Occupational Safety and Health Administration (OSHA) |
| REL | <0.1 ppm (<0.18 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| REL | 5 ppm (9 mg/m³)[10 minutes] | Occupational Safety and Health Administration (OSHA) |
| REL | Ca TWA <0.1 ppm (0.18 mg/m3) C 5 ppm (9 mg/m3) [10-min/day] See Appendix A | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 800 ppm ; A potential occupational carcinogen. (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 800.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| IDLH | NIOSH considers ethylene oxide to be a potential occupational carcinogen. | Hazardous Substances Data Bank (HSDB) |
These are United States values. The European Union sets its own indicative and binding limits, and the figure that applies at a given workplace is the one in the local regulation — not the one shown here.
08 · Physical and chemical properties
Ethylene oxide properties
Every value is shown with the conditions it was measured under and the source it came from. Where sources disagree, all values are listed rather than one being picked — the difference is usually a different form of the substance, not an error.
Ethylene oxide boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 10.6 °C (51.1 °F) | HSDB | |
| 10.56 °C (51 °F) | NIOSH | ||
| 10.72 °C (51.3 °F) | at 760 mmHg | CAMEO |
Ethylene oxide melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -111.7 °C (-169.1 °F) | HSDB | |
| -112.78 °C (-171 °F) | NIOSH | ||
| -112.5 °C (-170.5 °F) | CAMEO |
Ethylene oxide density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 0.9 g/cm³ | ICSC | |
| 0.882 g/cm³ | at 10 °C | HSDB | |
| 0.82 g/cm³ | at 10 °C | NIOSH |
Ethylene oxide solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | Soluble in benzene, acetone, ethanol, ether | HSDB | |
| Miscible with... carbon tetrachloride. | HSDB | ||
| Miscible with water | HSDB |
Ethylene oxide vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 1110 mmHg | NIOSH | |
| 1095 mmHg | at 20 °C | CAMEO | |
| 1310 mmHg | at 25 °C | HSDB |
Ethylene oxide flash point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Flash point | -28.89 °C (-20 °F) | HSDB | |
| -18 °C (-0.4 °F) | open cup | HSDB |
Ethylene oxide autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | 428.89 °C (804 °F) | HSDB | |
| 429 °C (804.2 °F) | ICSC |
Ethylene oxide lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | 3 % by volume | HSDB |
Ethylene oxide upper explosive limit (UEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Upper explosive limit (UEL) | 100 % by volume | HSDB |
Ethylene oxide vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 1.49 (air = 1) | HSDB | |
| 1.5 (air = 1) | ICSC |
Ethylene oxide odor threshold
| Property | Value | Conditions | Source |
|---|---|---|---|
| Odor threshold | Recognition: 1.5 mg/cu m= 0.8 ppm, mean detection concn: 700 ppm; absolute perception limit: 260 ppm; 50% recognition: 500 ppm; 100% recognition: 500 ppm | HSDB | |
| Low: 520 mg/cu m; High: 1400 mg/cu m | HSDB | ||
| 300 ppm in air | HSDB |
Ethylene oxide critical temperature and pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Critical temperature and pressure | 196 °C (384.8 °F) | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Ethylene oxide fire and explosion behaviour
These are descriptions rather than measured values, so they are kept out of the table above and quoted here with the source that reported them.
Ethylene oxide fire potential
Flammable gas.
Source: Hazardous Substances Data Bank (HSDB)
10 · Handling and storage
Ethylene oxide storage and handling
Ethylene oxide reactive group
CAMEO Chemicals places Ethylene oxide in the reactive groups Epoxides, Polymerizable Compounds. Compatibility with other chemicals is worked out from the group, not from the individual substance — which is why two substances you have never seen react can still be flagged as a pair that must be separated.
A reactive group is a CAMEO Chemicals (US NOAA) grouping, not a GHS hazard class: it has no code, no category and no legal force. It is what the storage compatibility matrix on this site computes from.
Ethylene oxide safe storage
Fireproof. Cool.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Ethylene oxide storage conditions
Store EtO in tightly closed cylinders or tanks in a cool, shaded, well-ventilated, explosion-proof area.
Source: Hazardous Substances Data Bank (HSDB)
Ethylene oxide incompatible materials
Forms explosive mixture with air. Dangerously reactive; may rearrange chemically and/or polymerize violently with evolution of heat, when in contact with highly active catalytic surfaces such as anhydrous chlorides or iron, tin and aluminum, pure oxides of iron and aluminum, and alkali metal hydroxides. Even small amounts of strong acids, alkalis, oxidizers can cause a reaction. Avoid contact with copper. Protect container from physical damage, sun and heat. Attacks some plastics, rubber or coatings.
Source: Hazardous Substances Data Bank (HSDB)
Planning storage for a mix of chemicals? Check Ethylene oxide in the storage compatibility matrix →
11 · Transport
Ethylene oxide UN number and transport classification
Transport classification is a separate system from the GHS classification above. It decides how a package is marked and how a load may be carried; it does not follow from the workplace label, and the workplace label does not follow from it. The entries below are linked by CAS number, never by name.
Ethylene oxide under UN 1040 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| ETHYLENE OXIDE | 2 | 2TF | — | |
| ETHYLENE OXIDE WITH NITROGEN up to a total pressure of 1 MPa (10 bar) at 50 °C | 2 | 2TF | — | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 2 is “Gases” (ADR 2.1.1.1).
United States · 49 CFR 172.101 Hazardous Materials Table
| Proper shipping name (column 2) | Class or division | PG | Labels (column 6) |
|---|---|---|---|
| Ethylene oxide or Ethylene oxide with nitrogen up to a total pressure of 1 MPa (10 bar) at 50 degrees C | 2.3 | — | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 2.3 is “Poisonous gas” (49 CFR 173.2).
12 · Questions
Ethylene oxide — frequently asked questions
What is the CAS number of Ethylene oxide?
The CAS number of Ethylene oxide is 75-21-8. Its EC number is 200-849-9.
What is the chemical formula of Ethylene oxide?
The molecular formula of Ethylene oxide is C2H4O and its molecular weight is 44.05 g/mol.
What does a Ethylene oxide label have to show?
Under CLP Annex VI the label for Ethylene oxide carries the pictograms Flame, Corrosion, Skull and crossbones and Health hazard and the signal word is Danger.
Is Ethylene oxide flammable?
Yes. CLP Annex VI assigns Ethylene oxide H220 — extremely flammable gas. The flash point reported for it is -28.89 °C (-20 °F) (HSDB).
Is Ethylene oxide a carcinogen?
Yes. CLP Annex VI classifies Ethylene oxide as a category 1A or 1B carcinogen and assigns it H350: may cause cancer. IARC places it in Group 1: carcinogenic to humans.
What is the exposure limit for Ethylene oxide?
The US occupational exposure limit reported for Ethylene oxide is 1.0 [ppm], STEL(OSHA) = 5 ppm (Haz-Map, Information on Hazardous Chemicals and Occupational Diseases). Limits differ by country: the EU sets its own indicative and binding values, and the figure that applies at a given workplace is the one in the local regulation.
What is the boiling point of Ethylene oxide?
The boiling point reported for Ethylene oxide is 10.6 °C (51.1 °F) (HSDB).
What is the melting point of Ethylene oxide?
The melting point reported for Ethylene oxide is -111.7 °C (-169.1 °F) (HSDB).
How should Ethylene oxide be stored?
CLP Annex VI assigns Ethylene oxide the storage statement P403. Store EtO in tightly closed cylinders or tanks in a cool, shaded, well-ventilated, explosion-proof area. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Ethylene oxide
Keep going: substances starting with E, or search the whole database by name, CAS number, pictogram or signal word.
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