Substance profile
Chlorine Dioxide
Chlorine Dioxide is a yellowish-brown gas with an unpleasant odor similar to chlorine and nitric acid.
01 · Identification
What Chlorine Dioxide is
Chlorine Dioxide is a yellowish-brown gas with an unpleasant odor similar to chlorine and nitric acid. Its molecular formula is ClO2 and its molecular weight is 67.45 g/mol. It boils at 11 °C, melts at -59 °C.
Under the GHS it carries the signal word Danger. It is classed as flammable agents - 4th degree.
02 · Identifiers
Chlorine Dioxide identifiers and molecular data
Chlorine Dioxide CAS number and EC number
Chlorine Dioxide molecular formula and molecular weight
03 · GHS classification
Chlorine Dioxide hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Chlorine Dioxide pictograms and signal word
Chlorine Dioxide hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Oxidising gases GHS chapter 2.4 | Category 1 | H270 | GHS03 |
| Acute toxicity - inhalation GHS chapter 3.1 | Category 1 or 2 | H330 | GHS06 |
| Skin corrosion/irritation GHS chapter 3.2 | Category 1A or 1B or 1C | H314 | GHS05 |
| Hazardous to the aquatic environment - acute GHS chapter 4.1 | Category 1 | H400 | GHS09 |
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.
Chlorine Dioxide hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H270 | May cause or intensify fire; oxidiser. |
| H330 | Fatal if inhaled. |
| H314 | Causes severe skin burns and eye damage. |
| H400 | Very toxic to aquatic life. |
This page lists only the codes assigned to Chlorine Dioxide. 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 Chlorine Dioxide
A Safety Data Sheet is written for a product, not for a substance: the supplier of the grade you actually buy issues it, so two suppliers of Chlorine Dioxide issue two different sheets. That is why there is no single authoritative SDS for a substance to download — what there is, is the job of collecting the sheets for the products you hold and keeping them current as suppliers revise them.
04 · Precautionary statements
Chlorine Dioxide precautionary statements
CLP Annex VI assigns 10 precautionary statements to Chlorine Dioxide. 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.
Disposal
What has to happen to the contents and the empty container.
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
Chlorine Dioxide 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 | хлорен диоксид |
| Spanish español | Dióxido de cloro |
| Czech čeština | oxid chloričitý |
| Danish dansk | chlordioxid |
| German Deutsch | Chlordioxid |
| Estonian eesti | kloordioksiid |
| Greek ελληνικά | διοξείδιο του χλωρίου |
| English English | chlorine dioxide |
| French français | dioxyde de chlore |
| Croatian hrvatski | klorov dioksid |
| Italian italiano | This edition prints another entry’s name here. The Italian edition prints the name of the preceding entry (017-023-00-7) here. The EC and CAS numbers in the same row, 233-162-8 and 10049-04-4, are chlorine dioxide and are correct. Regulation (EU) 2018/669, OJ L 115, 4.5.2018, p. 87 tricoloruri di [fosfinilidinetris(ossi)]tris[3-amminopropil-2-idrossi- N , N -dimetil- N -alchil C 6-18 ] |
| Latvian latviešu | hlora dioksīds |
| Lithuanian lietuvių | chloro dioksidas |
| Hungarian magyar | klór-dioxid |
| Maltese Malti | diossidu tal-kloru |
| Dutch Nederlands | chloordioxide |
| Polish polski | ditlenek chloru |
| Portuguese português | dióxido de cloro |
| Romanian română | dioxid de clor |
| Slovak slovenčina | oxid chloričitý |
| Slovenian slovenščina | klorov dioksid |
| Finnish suomi | klooridioksidi |
| Swedish svenska | klordioxid |
One or more lines above are flagged. In those language editions the Regulation as published in the Official Journal prints something that the rest of the same row contradicts — a name belonging to a different entry, or the qualifier of a paired entry. Each flag cites the amending act and the Official Journal page, so the wording can be checked at source. The lines are reproduced as printed, because Art. 18(2) points at Annex VI and not at our reading of it; the note beside each one says what the row’s own EC and CAS numbers identify.
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
Chlorine Dioxide GHS label elements
Everything CLP Annex VI fixes for Chlorine Dioxide, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Chlorine Dioxide
- May cause or intensify fire; oxidiser.
- Fatal if inhaled.
- Causes severe skin burns and eye damage.
- Very toxic to aquatic life.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Use only outdoors or in a well-ventilated area.
- Avoid release to the environment.
- Wear protective gloves/protective clothing/eye protection/face protection/hearing protection/…
- IF SWALLOWED:
- IF INHALED:
- Immediately call a POISON CENTER/doctor/…
- Do NOT induce vomiting.
- Collect spillage.
- Dispose of contents/container to …
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Chlorine Dioxide in the GHS label constructor →
07 · Health hazards
Chlorine Dioxide health hazards and exposure limits
Chlorine Dioxide hazard summary
Chlorine dioxide is a yellow to reddish-yellow manufactured gas. It does not occur naturally in the environment. When added to water, chlorine dioxide forms chlorite ion, which is also a very reactive chemical. Chlorine dioxide is used as a bleaching agent at paper manufacturing plants, and in public water treatment facilities to make water safe to drink. In 2001, chlorine dioxide and chlorite were used to decontaminate a number of public buildings following the release of anthrax spores in the United States.
Source: Agency for Toxic Substances and Disease Registry (ATSDR)
Chlorine Dioxide carcinogenicity classification
CLASSIFICATION: D; not classifiable as to human carcinogenicity. BASIS FOR CLASSIFICATION: No satisfactory human or animal studies assessing the chronic carcinogenic potential of chlorine dioxide have been located. HUMAN CARCINOGENICITY DATA: None. ANIMAL CARCINOGENICITY DATA: None.
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.
Chlorine Dioxide occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 0.1 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| PEL | 0.1 ppm (0.3 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| PEL | TWA 0.1 ppm (0.3 mg/m3) See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 0.1 ppm (0.3 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| REL | 0.3 ppm (0.9 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| REL | TWA 0.1 ppm (0.3 mg/m3) ST 0.3 ppm (0.9 mg/m3) | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 5 ppm (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 5.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| IDLH | 5 ppm | 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
Chlorine Dioxide 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.
Chlorine Dioxide boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 11 °C (51.8 °F) | HSDB | |
| 11.11 °C (52 °F) | NIOSH | ||
| 11.11 °C (52 °F) | at 760 mmHg | CAMEO |
Chlorine Dioxide melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -59 °C (-74.2 °F) | HSDB | |
| -58.89 °C (-74 °F) | NIOSH |
Chlorine Dioxide density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 1.77 g/cm³ | HSDB | |
| 3.09 g/cm³ | at 11 °C | DOE PAC | |
| 1.642 g/cm³ | at 0 °C, liq | HSDB |
Chlorine Dioxide solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | 2000 cc (gas) in 100 cc cold water | HSDB | |
| In water, 1.823X10-2 at 298.15 K | HSDB | ||
| Soluble in water | HSDB |
Chlorine Dioxide vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 757.562 mmHg | at 20 °C | HSDB |
| 760 mmHg | above this value | NIOSH |
Chlorine Dioxide flash point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Flash point | NA (Gas) ? (Liquid) | NIOSH |
Chlorine Dioxide vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 2.3 (air = 1) | HSDB | |
| 2.33 (air = 1) | CAMEO |
Chlorine Dioxide odor threshold
| Property | Value | Conditions | Source |
|---|---|---|---|
| Odor threshold | Odor Threshold Low: 0.1 [ppm] | Haz-Map | |
| Odor Threshold High: 15.0 [ppm] | Haz-Map | ||
| [ACGIH] Odor threshold from NJ "Hazardous Substance Fact Sheet" | Haz-Map |
Chlorine Dioxide critical temperature and pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Critical temperature and pressure | Critical temperature: 465K; critical pressure: 8621.6 kPa | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Chlorine Dioxide 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.
Fire and explosion
/Chlorine dioxide/ is explosive above 45 °C even in absence of light, and subject to long induction periods due to formation of intermediate dichlorine trioxide.
Source: HSDB
With over 10% chlorine dioxide in air at pressures from 0.1 to 1.0 atmosphere, chlorine dioxide is violently explosive. Explosion may be initiated by almost any form of energy such as sunlight, heat, or sparks.
Source: HSDB
A powerful explosive sensitive to spark, impact, sunlight, or heating rapidly to 100 °C. ... Concentrations of greater than 10% in air are explosive. Explodes on mixing with carbon monoxide, hydrocarbons (e.g., butadiene, ethane, ethylene, methane, propane), fluoramines (e.g. difluoramine, trifluoramine). Mixtures with hydrogen explode with sparking or contact with platinum. Explodes on contact with mercury, potassium hydroxide, phosphorous pentachloride + chlorine. Ignites or explodes on contact with non-metals (e.g., phosphorous, sulfur, sugar).
Source: HSDB
10 · Handling and storage
Chlorine Dioxide storage and handling
Chlorine Dioxide safe storage
Fireproof if in building. Separated from combustible substances and reducing agents. Cool. Keep in the dark. Ventilation along the floor.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Chlorine Dioxide storage conditions
Store separately from all other flammable materials. Prior to working with chlorine dioxide you should be trained on its proper handling and storage. This chemical is a powerful oxidizer, and is shock-, light- and heat sensitive. It is violently explosive in air at concentrations over 10%. Keep frozen when not in use. Store in tightly closed containers in a cool, dark, well-ventilated area at temperatures well below 130 °C. Gas explosions may occur above 130 °C. Use only nonsparking tools and equipment, especially when opening and closing containers of this chemical. Sources of ignition, such as smoking and open flames, are prohibited where this chemical is used, handled, or stored in a manner that could create a potential fire or explosion hazard. Use explosion-proof electrical equipment and fittings in storage area.
Source: Hazardous Substances Data Bank (HSDB)
Chlorine Dioxide incompatible materials
Explodes on mixing with carbon monoxide, hydrocarbons (e.g., butadiene, ethane, ethylene, methane, propane), fluoramines (e.g. difluoramine, trifluoramine). Mixtures with hydrogen explode with sparking or contact with platinum. Explodes on contact with mercury, potassium hydroxide, phosphorous pentachloride + chlorine. Ignites or explodes on contact with non-metals (e.g., phosphorous, sulfur, sugar). Reacts violently with /fluorine/, NHF2. Reacts with water or steam to produce toxic and corrosive fumes of /hydrochloric acid/.
Source: Hazardous Substances Data Bank (HSDB)
Planning storage for a mix of chemicals? Check Chlorine Dioxide in the storage compatibility matrix →
11 · Questions
Chlorine Dioxide — frequently asked questions
What is the CAS number of Chlorine Dioxide?
The CAS number of Chlorine Dioxide is 10049-04-4. Its EC number is 233-162-8.
What is the chemical formula of Chlorine Dioxide?
The molecular formula of Chlorine Dioxide is ClO2 and its molecular weight is 67.45 g/mol.
What does a Chlorine Dioxide label have to show?
Under CLP Annex VI the label for Chlorine Dioxide carries the pictograms Gas cylinder, Flame over circle, Skull and crossbones, Corrosion and Environment and the signal word is Danger.
Is Chlorine Dioxide flammable?
CLP Annex VI assigns Chlorine Dioxide no flammability hazard class. That is not a statement that it cannot burn: the harmonised list only records the hazards that were assessed for it. The flash point reported for it is NA (Gas) ? (Liquid) (NIOSH).
Is Chlorine Dioxide a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Chlorine Dioxide. Annex VI is a list of agreed classifications, not a list of substances found safe, so this is an absence of a classification rather than a clean bill of health.
What is the exposure limit for Chlorine Dioxide?
The US occupational exposure limit reported for Chlorine Dioxide is 0.1 [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 Chlorine Dioxide?
The boiling point reported for Chlorine Dioxide is 11 °C (51.8 °F) (HSDB).
What is the melting point of Chlorine Dioxide?
The melting point reported for Chlorine Dioxide is -59 °C (-74.2 °F) (HSDB).
How should Chlorine Dioxide be stored?
Store separately from all other flammable materials. Prior to working with chlorine dioxide you should be trained on its proper handling and storage. This chemical is a powerful oxidizer, and is shock-, light- and heat sensitive. It is violently explosive in air at concentrations over 10%. Keep frozen when not in use. Store in tightly closed containers in a cool, dark, well-ventilated area at temperatures well below 130 °C. Gas explosions may occur above 130 °C. Use only nonsparking tools and equipment, especially when opening and closing containers of this chemical. Sources of ignition, such as smoking and open flames, are prohibited where this chemical is used, handled, or stored in a manner that could create a potential fire or explosion hazard. Use explosion-proof electrical equipment and fittings in storage area. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Chlorine Dioxide
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