Substance profile
Chlorine
Chlorine is a yellowish-green gas with a suffocating odor.
01 · Identification
What Chlorine is
Chlorine is a yellowish-green gas with a suffocating odor. It boils at -34 °C, melts at -101 °C.
Under the GHS it carries the signal word Danger. It is classed as hazardous Air Pollutants (HAPs).
02 · Identifiers
Chlorine identifiers and molecular data
Chlorine CAS number and EC number
Chlorine molecular formula and molecular weight
Other names for Chlorine
- chlorine gas
- Cl2
- Bertholite
- Chlorine Mol.
- Chlorine Molecule (Cl2)
- Diatomic Chlorine
- Dichlorine
- Molecular Chlorine
03 · GHS classification
Chlorine hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Chlorine pictograms and signal word
Chlorine 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 3 | H331 | GHS06 |
| Skin corrosion/irritation GHS chapter 3.2 | Category 2 | H315 | GHS07 |
| Serious eye damage/eye irritation GHS chapter 3.3 | Category 2A | H319 | GHS07 |
| Specific target organ toxicity - single exposure GHS chapter 3.8 | Category 3 | H335 | GHS07 |
| Hazardous to the aquatic environment - acute GHS chapter 4.1 | Category 1 | H400 | GHS09 |
Chlorine hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H270 | May cause or intensify fire; oxidiser. |
| H331 | Toxic if inhaled. |
| H335 | May cause respiratory irritation. |
| H315 | Causes skin irritation. |
| H319 | Causes serious eye irritation. |
| H400 | Very toxic to aquatic life. |
This page lists only the codes assigned to Chlorine. 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
Our own Chlorine 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
Chlorine precautionary statements
CLP Annex VI assigns 16 precautionary statements to Chlorine. 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 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 | хлор |
| Spanish español | Cloro |
| Czech čeština | chlor |
| Danish dansk | chlor |
| German Deutsch | Chlor |
| Estonian eesti | kloor |
| Greek ελληνικά | χλώριο |
| English English | chlorine |
| French français | chlore |
| Croatian hrvatski | klor |
| Italian italiano | cloro |
| Latvian latviešu | hlors |
| Lithuanian lietuvių | chloras |
| Hungarian magyar | klór |
| Maltese Malti | klorur |
| Dutch Nederlands | chloor |
| Polish polski | chlor |
| Portuguese português | cloro |
| Romanian română | clor |
| Slovak slovenčina | chlór |
| Slovenian slovenščina | klor |
| Finnish suomi | kloori |
| Swedish svenska | klor |
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 GHS label elements
Everything CLP Annex VI fixes for Chlorine, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Chlorine
- May cause or intensify fire; oxidiser.
- Toxic if inhaled.
- May cause respiratory irritation.
- Causes skin irritation.
- Causes serious eye irritation.
- Very toxic to aquatic life.
- Do not breathe dust/fume/gas/mist/vapours/spray.
- Wash … thoroughly after handling.
- 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 ON SKIN:
- IF INHALED:
- IF IN EYES:
- Immediately call a POISON CENTER/doctor/…
- Get medical advice/attention.
- If skin irritation occurs:
- If eye irritation persists:
- Remove contact lenses, if present and easy to do. Continue rinsing.
- Wash with plenty of water/…
- 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 in the GHS label constructor →
07 · Health hazards
Chlorine health hazards and exposure limits
Chlorine hazard summary
At room temperature, chlorine is a yellow-green gas that is heavier than air and has a strong irritating odor. It can be converted to a liquid under pressure or cold temperatures. Chlorine is mainly used as bleach in the manufacture of paper and cloth and to make a wide variety of products.
Source: Agency for Toxic Substances and Disease Registry (ATSDR)
Chlorine occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 1 ppm (3 mg/m³) [Construction and Maritime Industries only] | Occupational Safety and Health Administration (OSHA) |
| PEL | 1 ppm (3 mg/m³) [General Industry only] | Occupational Safety and Health Administration (OSHA) |
| PEL | C 1 ppm (3 mg/m3) See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 0.5 ppm (1.45 mg/m³) [15 minutes] | Occupational Safety and Health Administration (OSHA) |
| REL | C 0.5 ppm (1.45 mg/m3) [15-minute] | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 10 ppm (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 10.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| IDLH | 10 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 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 boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | -34.04 °C (-29.3 °F) | HSDB | |
| -33.89 °C (-29 °F) | NIOSH | ||
| -34.61 °C (-30.3 °F) | at 760 mmHg | CAMEO |
Chlorine melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -101.5 °C (-150.7 °F) | HSDB | |
| -101.11 °C (-150 °F) | NIOSH |
Chlorine density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 0.0029 g/cm³ | HSDB | |
| 1.424 g/cm³ | at 15 °C, pressurized liquid | CAMEO |
Chlorine solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | 0.7% | NIOSH | |
| In water, 6,300 mg/L at 25 °C | at 25 °C | HSDB |
Chlorine vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 5168 mmHg | NIOSH | |
| 5048 mmHg | at 20 °C | ICSC | |
| 5830 mmHg | at 25 °C | HSDB |
Chlorine autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | Not flammable (USCG, 1999) | CAMEO |
Chlorine lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | Nonflammable Gas, but a strong oxidizer. | NIOSH |
Chlorine vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 2.48 (air = 1) | HSDB | |
| 2.49 (air = 1) | CAMEO | ||
| 2.5 (air = 1) | ICSC |
Chlorine odor threshold
| Property | Value | Conditions | Source |
|---|---|---|---|
| Odor threshold | Low odor threshold= 0.0300 mg/cu m. High odor threshold= 15.0000 mg/cu m. Irritating concn= 9.00 mg/cu m. | HSDB | |
| Odor Threshold Low: 0.2 [ppm] | Haz-Map |
Chlorine critical temperature and pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Critical temperature and pressure | 144 °C (291.2 °F) | HSDB |
Chlorine corrosivity
| Property | Value | Conditions | Source |
|---|---|---|---|
| Corrosivity | Chlorine will attack some forms of plastics, rubber, and coatings | HSDB | |
| Highly corrosive to all metals in the presence of any humidity factor | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Chlorine 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.
Chlorine fire potential
Most combustibles will burn in chlorine, forming irritating and toxic gases. Cylinders may vent rapidly or explode when heated. Flame impingement upon steel chlorine container will result in iron/chlorine fire causing rupture of the container.
Source: Hazardous Substances Data Bank (HSDB)
Solubility
Solubility in water at 25 °C with formation of aqueous Cl2 (0.062 M), HOCl (0.030 M), chloride ion (0.030 M); total solubility: 0.092 M; more soluble in alkalies
Source: HSDB
Odor
Water odor threshold: 0.0020 mg/L. Air odor threshold: 0.31 ppm. Odor Safety Class: C. C= Odor safety factor from 1-26. Less than 50% of distracted persons perceive warning of threshold limit value.
Source: HSDB
10 · Handling and storage
Chlorine storage and handling
Chlorine reactive group
CAMEO Chemicals places Chlorine in the reactive groups Halogenating Agents, Oxidizing Agents, Strong. 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.
Chlorine safe storage
Fireproof if in building. Provision to contain effluent from fire extinguishing. Separated from food and feedstuffs. See Chemical Dangers. Cool. Dry. Keep in a well-ventilated room. Store in an area without drain or sewer access.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Chlorine storage conditions
Keep container tightly closed in a dry and well-ventilated place. Contents under pressure. Storage class (TRGS 510): Gases.
Source: Hazardous Substances Data Bank (HSDB)
Chlorine incompatible materials
Incompatible materials: Alcohols.
Source: Hazardous Substances Data Bank (HSDB)
Planning storage for a mix of chemicals? Check Chlorine in the storage compatibility matrix →
11 · Transport
Chlorine 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.
The same CAS number is shipped under more than one UN number. Which entry applies follows from the form and the concentration of the consignment — read the proper shipping name, not the CAS.
Chlorine under UN 1017 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| CHLORINE | 2 | 2TOC | — | |
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) |
|---|---|---|---|
| Chlorine | 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).
Chlorine under UN 3520 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| CHLORINE, ADSORBED | 2 | 9TOC | — | |
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) |
|---|---|---|---|
| Chlorine, adsorbed | 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
Chlorine — frequently asked questions
What is the CAS number of Chlorine?
The CAS number of Chlorine is 7782-50-5. Its EC number is 231-959-5.
What does a Chlorine label have to show?
Under CLP Annex VI the label for Chlorine carries the pictograms Flame over circle, Gas cylinder, Skull and crossbones and Environment and the signal word is Danger.
Is Chlorine flammable?
CLP Annex VI assigns Chlorine 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.
Is Chlorine a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Chlorine. 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?
The US occupational exposure limit reported for Chlorine is 1 ppm (3 mg/m³) [Construction and Maritime Industries only] (Occupational Safety and Health Administration (OSHA)). 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?
The boiling point reported for Chlorine is -34.04 °C (-29.3 °F) (HSDB).
What is the melting point of Chlorine?
The melting point reported for Chlorine is -101.5 °C (-150.7 °F) (HSDB).
How should Chlorine be stored?
Keep container tightly closed in a dry and well-ventilated place. Contents under pressure. Storage class (TRGS 510): Gases. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Chlorine
Keep going: substances starting with C, or search the whole database by name, CAS number, pictogram or signal word.
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