Substance profile
Methanethiol
Methanethiol is a water-white liquid when below boiling point, or colorless gas with an odor of rotten cabbage.
01 · Identification
What Methanethiol is
Methanethiol is a water-white liquid when below boiling point, or colorless gas with an odor of rotten cabbage. Its molecular formula is CH4S and its molecular weight is 48.11 g/mol. It boils at 6 °C, melts at -123 °C, is soluble in water.
Under the GHS it carries the signal word Danger. It is classed as flammable agents - 4th degree.
02 · Identifiers
Methanethiol identifiers and molecular data
Methanethiol CAS number and EC number
Methanethiol molecular formula and molecular weight
Other names for Methanethiol
- methyl mercaptan
03 · GHS classification
Methanethiol hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Methanethiol pictograms and signal word
Methanethiol hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Flammable gases GHS chapter 2.2 | Category 1A | H220 | GHS02 |
| Acute toxicity - inhalation GHS chapter 3.1 | Category 3 | H331 | GHS06 |
| Hazardous to the aquatic environment - acute GHS chapter 4.1 | Category 1 | H400 | GHS09 |
| Hazardous to the aquatic environment - chronic GHS chapter 4.1 | Category 1 | H410 | GHS09 |
Methanethiol hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H220 | Extremely flammable gas. |
| H331 | Toxic if inhaled. |
| H400 | Very toxic to aquatic life. |
| H410 | Very toxic to aquatic life with long lasting effects. |
This page lists only the codes assigned to Methanethiol. 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 Methanethiol
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 Methanethiol 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
Methanethiol precautionary statements
CLP Annex VI assigns 10 precautionary statements to Methanethiol. 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
Methanethiol 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 | метантиол метилмеркаптан |
| Spanish español | Metanotiol metilmercaptano |
| Czech čeština | methanthiol methylmerkaptan |
| Danish dansk | methanthiol methylmercaptan |
| German Deutsch | Methanthiol Methylmercaptan |
| Estonian eesti | metaantiool metüülmerkaptaan |
| Greek ελληνικά | μεθανοθειόλη μεθυλομερκαπτάνη |
| English English | methanethiol methyl mercaptan |
| French français | méthanethiol méthylmercaptan |
| Croatian hrvatski | metantiol metil-merkaptan |
| Italian italiano | metantiolo metilmercaptano |
| Latvian latviešu | metāntiols metilmerkaptāns |
| Lithuanian lietuvių | metantiolis metilmerkaptanas |
| Hungarian magyar | metántiol metil-merkaptán |
| Maltese Malti | metanetjol merkaptan tal-metil |
| Dutch Nederlands | methaanthiol methylmercaptaan |
| Polish polski | metanotiol merkaptan metylowy |
| Portuguese português | metanotiol metilmercaptano |
| Romanian română | metantiol metil-mercaptan |
| Slovak slovenčina | metántiol metylsulfán |
| Slovenian slovenščina | metantiol metil merkaptan |
| Finnish suomi | metaanitioli metyylimerkaptaani |
| Swedish svenska | metantiol metylmerkaptan |
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
Methanethiol GHS label elements
Everything CLP Annex VI fixes for Methanethiol, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Methanethiol
- Extremely flammable gas.
- Toxic if inhaled.
- Very toxic to aquatic life.
- Very toxic to aquatic life with long lasting effects.
- 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.
- Use only outdoors or in a well-ventilated area.
- Avoid release to the environment.
- IF INHALED:
- Immediately call a POISON CENTER/doctor/…
- Collect spillage.
- Store in a well-ventilated place.
- Dispose of contents/container to …
Supplier name, address and telephone number· Product identifier·Nominal quantity
Need this as an actual label? Open Methanethiol in the GHS label constructor →
07 · Health hazards
Methanethiol health hazards and exposure limits
Methanethiol hazard summary
Methyl mercaptan is a colorless gas with a smell like rotten cabbage. It is a natural substance found in the blood, brain, and other tissues of people and animals. It is released from animal feces. It occurs naturally in certain foods, such as some nuts and cheese. Methyl mercaptan is released from decaying organic matter in marshes and is present in the natural gas of certain regions in the United States, in coal tar, and in some crude oils. It is manufactured for use in the plastics industry, in pesticides, and as a jet fuel additive. It is also released as a decay product of wood in pulp mills.
Source: Agency for Toxic Substances and Disease Registry (ATSDR)
Methanethiol occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 0.5 ppm (1 mg/m³) [Construction and Maritime Industries only] | Occupational Safety and Health Administration (OSHA) |
| PEL | 10 ppm (20 mg/m³) [General Industry only] | Occupational Safety and Health Administration (OSHA) |
| PEL | C 10 ppm (20 mg/m3) See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 0.5 ppm (1 mg/m³) [15 minutes] | Occupational Safety and Health Administration (OSHA) |
| REL | C 0.5 ppm (1 mg/m3) [15-minute] | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 150 ppm (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 150.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| IDLH | 150 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
Methanethiol 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.
Methanethiol boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 5.95 °C (42.7 °F) | at 760 mmHg | HSDB |
| 6.11 °C (43 °F) | NIOSH | ||
| 5.94 °C (42.7 °F) | at 760 mmHg | CAMEO |
Methanethiol melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -123 °C (-189.4 °F) | HSDB | |
| -121.11 °C (-186 °F) | NIOSH |
Methanethiol density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 0.9 g/cm³ | ICSC | |
| 0.8665 g/cm³ | at 20 °C | DOE PAC | |
| 0.96 g/cm³ | at 25 °C | HSDB |
Methanethiol solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | Soluble in alcohol and ether; slightly soluble in chloroform | HSDB | |
| Soluble in petroleum naptha | HSDB | ||
| In water, 15,400 mg/L at 25 °C | at 25 °C | HSDB |
Methanethiol vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 1292 mmHg | NIOSH | |
| 400 mmHg | CAMEO | ||
| 1510 mmHg | at 25 °C | HSDB |
Methanethiol flash point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Flash point | -17.78 °C (0 °F) | HSDB |
Methanethiol lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | 3.9 % by volume | HSDB |
Methanethiol upper explosive limit (UEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Upper explosive limit (UEL) | 21.8 % by volume | HSDB |
Methanethiol vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 1.66 (air = 1) | HSDB |
Methanethiol odor threshold
| Property | Value | Conditions | Source |
|---|---|---|---|
| Odor threshold | 0.0021 ppm (purity not specified) | HSDB | |
| High odor threshold= 0.0820 mg/m (purity not specified) | HSDB | ||
| Odor Threshold Low: 0.0000002 [ppm] | Haz-Map |
Methanethiol critical temperature and pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Critical temperature and pressure | 196.8 °C (386.2 °F) | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Methanethiol 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.
Methanethiol fire potential
Very dangerous, when exposed to heat, flame; can react vigorously with oxidizing materials.
Source: Hazardous Substances Data Bank (HSDB)
10 · Handling and storage
Methanethiol storage and handling
Methanethiol safe storage
Fireproof. Separated from strong oxidants and acids. Cool. Store in an area without drain or sewer access.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Methanethiol storage conditions
Separate from oxidizing materials. Store in a cool, dry, well-ventilated location.
Source: Hazardous Substances Data Bank (HSDB)
Methanethiol incompatible materials
Can react dangerously with strong oxidizing agents and mercury (II) oxide.
Source: Hazardous Substances Data Bank (HSDB)
Methanethiol reactivity
METHYL MERCAPTAN is a reducing agent--can react vigorously with oxidizing agents. Dangerous fire or explosion hazard when exposed to heat, flame, sparks or strong oxidizing agents (e.g., calcium hypochlorite). When heating to decomposition emits highly toxic fumes of oxides of sulfur [Lewis, 3rd ed., 1993, p. 862]. Violent reaction with mercury(II) oxide [Klason P., Ber., 1887, 20, p. 3410].
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Methanethiol in the storage compatibility matrix →
11 · Transport
Methanethiol 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.
Methanethiol under UN 1064 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| METHYL MERCAPTAN | 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) |
|---|---|---|---|
| Methyl mercaptan | 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
Methanethiol — frequently asked questions
What is the CAS number of Methanethiol?
The CAS number of Methanethiol is 74-93-1. Its EC number is 200-822-1.
What is the chemical formula of Methanethiol?
The molecular formula of Methanethiol is CH4S and its molecular weight is 48.11 g/mol.
What does a Methanethiol label have to show?
Under CLP Annex VI the label for Methanethiol carries the pictograms Flame, Gas cylinder, Skull and crossbones and Environment and the signal word is Danger.
Is Methanethiol flammable?
Yes. CLP Annex VI assigns Methanethiol H220 — extremely flammable gas. The flash point reported for it is -17.78 °C (0 °F) (HSDB).
Is Methanethiol a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Methanethiol. 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 Methanethiol?
The US occupational exposure limit reported for Methanethiol is 0.5 ppm (1 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 Methanethiol?
The boiling point reported for Methanethiol is 5.95 °C (42.7 °F), at 760 mmHg (HSDB).
What is the melting point of Methanethiol?
The melting point reported for Methanethiol is -123 °C (-189.4 °F) (HSDB).
How should Methanethiol be stored?
CLP Annex VI assigns Methanethiol the storage statement P403. Separate from oxidizing materials. Store in a cool, dry, well-ventilated location. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Methanethiol
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