Substance profile
Hydrogen Cyanide
Hydrogen Cyanide is a colorless gas or liquid with a bitter almond odor.
01 · Identification
What Hydrogen Cyanide is
Hydrogen Cyanide is a colorless gas or liquid with a bitter almond odor. Its molecular formula is CHN and its molecular weight is 27.025 g/mol. It boils at 25.6 °C, melts at -13.3 °C, is miscible with water.
Under the GHS it carries the signal word Danger. It is classed as hazardous Air Pollutants (HAPs).
02 · Identifiers
Hydrogen Cyanide identifiers and molecular data
Hydrogen Cyanide CAS number and EC number
Hydrogen Cyanide molecular formula and molecular weight
Other names for Hydrogen Cyanide
- hydrocyanic acid
03 · GHS classification
Hydrogen Cyanide hazard classification
Harmonised classification under CLP Annex VI. This is the legally binding classification in the EU; other jurisdictions may differ.
Hydrogen Cyanide pictograms and signal word
Hydrogen Cyanide hazard class and category
| Hazard class | Category | From code | Pictogram |
|---|---|---|---|
| Flammable liquids GHS chapter 2.6 | Category 1 | H224 | GHS02 |
| Acute toxicity - inhalation GHS chapter 3.1 | Category 1 or 2 | H330 | 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 |
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.
Hydrogen Cyanide hazard statements (H-codes)
| Code | Hazard statement |
|---|---|
| H224 | Extremely flammable liquid and vapour. |
| H330 | Fatal 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 Hydrogen Cyanide. 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 Hydrogen Cyanide
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 Hydrogen Cyanide 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
Hydrogen Cyanide precautionary statements
CLP Annex VI assigns 12 precautionary statements to Hydrogen Cyanide. 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
Hydrogen Cyanide 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 | водороден цианид циановодородна киселина |
| Spanish español | Cianuro de hidrógeno ácido cianhídrico |
| Czech čeština | kyanovodík kyanovodíková kyselina |
| Danish dansk | hydrogencyanid blåsyre |
| German Deutsch | Cyanwasserstoff CyanwasserstoffsäureBlausäuregas |
| Estonian eesti | vesiniktsüaniid sinihape |
| Greek ελληνικά | υδροκυάνιο υδροκυανικό oξύ |
| English English | hydrogen cyanide hydrocyanic acid |
| French français | cyanure d'hydrogène acide hydrocyanique |
| Croatian hrvatski | cijanovodik cijanovodična kiselina |
| Italian italiano | acido cianidrico cianuro di idrogeno |
| Latvian latviešu | ūdeņraža cianīds ciānūdeņražskābe |
| Lithuanian lietuvių | vandenilio cianidas ciano vandenilio rūgštis |
| Hungarian magyar | hidrogén-cianid hidrociánsav |
| Maltese Malti | ċjanur tal-idroġenu aċidu idroċjaniku |
| Dutch Nederlands | waterstofcyanide cyaanwaterstofblauwzuur |
| Polish polski | cyjanowodór kwas cyjanowodorowy |
| Portuguese português | cianeto de hidrogénio ácido cianídrico |
| Romanian română | acid cianhidric |
| Slovak slovenčina | kyanovodík kyselina kyanovodíková |
| Slovenian slovenščina | vodikov cianid cianovodikova kislina |
| Finnish suomi | syaanivety syaanivetyhappo |
| Swedish svenska | vätecyanid cyanvätesyra |
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
Hydrogen Cyanide GHS label elements
Everything CLP Annex VI fixes for Hydrogen Cyanide, laid out the way it appears on a label. The greyed lines are the parts only the supplier can fill in.
Danger
Hydrogen Cyanide
- Extremely flammable liquid and vapour.
- Fatal 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.
- Use explosion-proof [electrical/ventilating/lighting/…] equipment.
- Use only non-sparking tools.
- 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 Hydrogen Cyanide in the GHS label constructor →
07 · Health hazards
Hydrogen Cyanide health hazards and exposure limits
Hydrogen Cyanide hazard summary
Cyanide is used in a number of industries and is found at low levels in air from car exhaust. Cyanide is extremely toxic to humans. Chronic (long-term) inhalation exposure of humans to cyanide results primarily in effects on the central nervous system (CNS). Other effects in humans include cardiovascular and respiratory effects, an enlarged thyroid gland, and irritation to the eyes and skin. No data are available on the carcinogenic effects of cyanide in humans via inhalation. Animal studies have suggested that oral exposure to cassava (a cyanide-containing vegetable) may be associated with malformations in the fetus and low fetal body weights. EPA has classified cyanide as a Group D, not classifiable as to human carcinogenicity.
Source: EPA Hazardous Air Pollutants
Hydrogen Cyanide occupational exposure limits
| Limit | Value | Source |
|---|---|---|
| PEL | 10.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
| PEL | 10 ppm (11 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| PEL | TWA 10 ppm (11 mg/m3) [skin] See Appendix G | The National Institute for Occupational Safety and Health (NIOSH) |
| REL | 4.7 ppm (5 mg/m³) | Occupational Safety and Health Administration (OSHA) |
| REL | ST 4.7 ppm (5 mg/m3) [skin] | The National Institute for Occupational Safety and Health (NIOSH) |
| IDLH | 50 ppm [From NPG: Hydrogen cyanide] (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 50 ppm (NIOSH, 2024) | CAMEO Chemicals |
| IDLH | 50.0 [ppm] | Haz-Map, Information on Hazardous Chemicals and Occupational Diseases |
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
Hydrogen Cyanide 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.
Hydrogen Cyanide boiling point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Boiling point | 25.63 °C (78.1 °F) | HSDB | |
| 25.56 °C (78 °F) | NIOSH | ||
| 25.56 °C (78 °F) | at 760 mmHg | CAMEO |
Hydrogen Cyanide melting point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Melting point | -13.28 °C (8.1 °F) | HSDB | |
| -13.89 °C (7 °F) | NIOSH |
Hydrogen Cyanide density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Density | 0.69 g/cm³ | NIOSH | |
| 0.6875 g/cm³ | at 20 °C | HSDB |
Hydrogen Cyanide solubility
| Property | Value | Conditions | Source |
|---|---|---|---|
| Solubility | Miscible with water | HSDB | |
| Miscible with ethanol, ethyl ether | HSDB | ||
| Miscible with alcohol; slightly soluble in ether | HSDB |
Hydrogen Cyanide vapor pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor pressure | 630 mmHg | NIOSH | |
| 742 mmHg | at 25 °C | HSDB |
Hydrogen Cyanide flash point
| Property | Value | Conditions | Source |
|---|---|---|---|
| Flash point | -17.78 °C (0 °F) | HSDB |
Hydrogen Cyanide autoignition temperature
| Property | Value | Conditions | Source |
|---|---|---|---|
| Autoignition temperature | 537.78 °C (1000 °F) | HSDB | |
| 540 °C (1004 °F) | CAMEO | ||
| 538 °C (1000.4 °F) | ICSC |
Hydrogen Cyanide lower explosive limit (LEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Lower explosive limit (LEL) | 5.6 % by volume | HSDB |
Hydrogen Cyanide upper explosive limit (UEL)
| Property | Value | Conditions | Source |
|---|---|---|---|
| Upper explosive limit (UEL) | 40 % by volume | HSDB |
Hydrogen Cyanide vapor density
| Property | Value | Conditions | Source |
|---|---|---|---|
| Vapor density | 0.932 (air = 1) | HSDB | |
| 0.901 (air = 1) | CAMEO | ||
| 0.94 (air = 1) | ICSC |
Hydrogen Cyanide odor threshold
| Property | Value | Conditions | Source |
|---|---|---|---|
| Odor threshold | Detection in air of hydrogen cyanide of an unspecified purity or grade: 1X10-3 mg/L. | HSDB | |
| High odor threshold was 5 mg/cu m; Low odor threshold was 0.9 mg/cu m. | HSDB |
Hydrogen Cyanide critical temperature and pressure
| Property | Value | Conditions | Source |
|---|---|---|---|
| Critical temperature and pressure | 183.5 °C (362.3 °F) | HSDB |
Hydrogen Cyanide corrosivity
| Property | Value | Conditions | Source |
|---|---|---|---|
| Corrosivity | Liquid hydrogen cyanide will attack some forms of plastics, rubber, and coatings. | HSDB |
Values compiled from PubChem Laboratory Chemical Safety Summary. Temperatures converted to Fahrenheit for reference.
09 · Fire and explosion
Hydrogen Cyanide 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.
Hydrogen Cyanide fire potential
Flammable and dangerous fire hazard ... May be ignited by fires, heated materials, and sparks.
Source: Hazardous Substances Data Bank (HSDB)
Corrosivity
Although HCN is a weak acid and normally not considered corrosive, it has a corrosive effect under two special conditions: (1) water solutions of HCN cause transcrystalline stress-cracking of carbon steels under stress even at room temperature and in dilute solution; (2) water solutions of HCN containing sulfuric acid as a stabilizer severely corrode steel above 40 °C and stainless steels above 80 °C.
Source: HSDB
Odor
Approximately 60 to 70% of the population can detect the bitter almond odor of hydrogen cyanide. The odor threshold for those sensitive to the odor is estimated to be 1 to 5 ppm in the air. However, even at high toxic concentrations, up to 20% of all individuals are genetically unable to smell hydrogen cyanide.
Source: HSDB
10 · Handling and storage
Hydrogen Cyanide storage and handling
Hydrogen Cyanide safe storage
Store only if stabilized. Fireproof. Cool. Separated from food and feedstuffs and incompatible materials. See Chemical Dangers. Store in an area without drain or sewer access.
Source: ILO-WHO International Chemical Safety Cards (ICSCs)
Hydrogen Cyanide storage conditions
Keep cylinders of hydrogen cyanide (HCN) cool and away from open flames. Make certain that HCN cylinders are adequately supported and grounded during storage and emptying. Store cylinders in a vertical position. Do not drop cylinders or damage them by impact. Cylinders must be returned to the supplier within 90 days of the filling date marked on the cylinders, regardless of whether or not the contents have been used. This is due to the possibility of HCN becoming unstable over time. If there is any indication that the HCN is becoming unstable, such as a darkening of the product or an increase in cylinder pressure, contact the supplier immediately for instructions.
Source: Hazardous Substances Data Bank (HSDB)
Hydrogen Cyanide incompatible materials
Preparation of alkyliminoformate chlorides by passing hydrogen chloride rapidly into alcoholic hydrogen cyanide proceeds explosively (probably owing to a sudden exotherm), even with strong cooling.
Source: Hazardous Substances Data Bank (HSDB)
Hydrogen Cyanide reactivity
HYDROGEN CYANIDE, ANHYDROUS presents a severe explosion hazard when exposed to oxidizing agents. The vapors form explosive mixtures with air. May polymerize explosively at elevated temperature (50-60 °C) or in the presence of traces of alkali [Wohler, L. et al., Chem. Ztg., 1926, 50, p. 761, 781]. In the absence of a stabilizer (such as phosphoric acid), may undergo explosively rapid spontaneous (autocatalytic) polymerization leading to a fire. The reaction is autocatalytic because of ammonia formation. [Bond, J., Loss Prev. Bull., 1991, 101, p.3]. Dissolves in water to give weakly acidic solutions. Reacts violently with acetaldehyde. During the preparation of imidoester hydrochlorides, hydrogen chloride was rapidly passed over alcoholic hydrogen cyanide. An explosion ensued, even with cooling of the process [J. Org. Chem., 1955, 20, 1573].
Source: CAMEO Chemicals
Planning storage for a mix of chemicals? Check Hydrogen Cyanide in the storage compatibility matrix →
11 · Transport
Hydrogen Cyanide 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.
Hydrogen Cyanide under UN 1051 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| HYDROGEN CYANIDE, STABILIZED containing less than 3 % water | 6.1 | TF1 | I | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 6.1 is “Toxic substances” (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) |
|---|---|---|---|
| Hydrogen cyanide, stabilized with less than 3 percent water | 6.1 | I | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 6.1 is “Poisonous materials” (49 CFR 173.2).
Hydrogen Cyanide under UN 1613 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| HYDROCYANIC ACID, AQUEOUS SOLUTION (HYDROGEN CYANIDE, AQUEOUS SOLUTION) with not more than 20 % hydrogen cyanide | 6.1 | TF1 | I | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 6.1 is “Toxic substances” (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) |
|---|---|---|---|
| Hydrocyanic acid, aqueous solutions or Hydrogen cyanide, aqueous solutions with not more than 20 percent hydrogen cyanide | 6.1 | I | |
| Hydrocyanic acid, aqueous solutions with less than 5 percent hydrogen cyanide | 6.1 | II | |
Column (4) prefix on this entry: NA — not a UN number. NA numbers are assigned by the United States, ID numbers by ICAO.
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 6.1 is “Poisonous materials” (49 CFR 173.2).
Hydrogen Cyanide under UN 1614 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| HYDROGEN CYANIDE, STABILIZED, containing less than 3 % water and absorbed in a porous inert material | 6.1 | TF1 | I | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 6.1 is “Toxic substances” (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) |
|---|---|---|---|
| Hydrogen cyanide, stabilized, with less than 3 percent water and absorbed in a porous inert material | 6.1 | I | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 6.1 is “Poisonous materials” (49 CFR 173.2).
Hydrogen Cyanide under UN 3294 — shipping name, class and packing group
Europe · ADR 2025, Table A
| Proper shipping name (3.1.2) | Class | Classification code | PG | Labels (column 5) |
|---|---|---|---|---|
| HYDROGEN CYANIDE, SOLUTION IN ALCOHOL with not more than 45 % hydrogen cyanide | 6.1 | TF1 | I | |
Source: ADR 2025, Table A of Chapter 3.2 · ECE/TRANS/352 Vol. I (UNECE). Class 6.1 is “Toxic substances” (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) |
|---|---|---|---|
| Hydrogen cyanide, solution in alcohol with not more than 45 percent hydrogen cyanide | 6.1 | I | |
Source: 49 CFR 172.101 Hazardous Materials Table · eCFR, revision 2026-08-03. Class 6.1 is “Poisonous materials” (49 CFR 173.2).
12 · Questions
Hydrogen Cyanide — frequently asked questions
What is the CAS number of Hydrogen Cyanide?
The CAS number of Hydrogen Cyanide is 74-90-8. Its EC number is 200-821-6.
What is the chemical formula of Hydrogen Cyanide?
The molecular formula of Hydrogen Cyanide is CHN and its molecular weight is 27.025 g/mol.
What does a Hydrogen Cyanide label have to show?
Under CLP Annex VI the label for Hydrogen Cyanide carries the pictograms Flame, Skull and crossbones and Environment and the signal word is Danger.
Is Hydrogen Cyanide flammable?
Yes. CLP Annex VI assigns Hydrogen Cyanide H224 — extremely flammable liquid and vapour. The flash point reported for it is -17.78 °C (0 °F) (HSDB).
Is Hydrogen Cyanide a carcinogen?
CLP Annex VI records no harmonised carcinogenicity classification for Hydrogen Cyanide. 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 Hydrogen Cyanide?
The US occupational exposure limit reported for Hydrogen Cyanide is 10.0 [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 Hydrogen Cyanide?
The boiling point reported for Hydrogen Cyanide is 25.63 °C (78.1 °F) (HSDB).
What is the melting point of Hydrogen Cyanide?
The melting point reported for Hydrogen Cyanide is -13.28 °C (8.1 °F) (HSDB).
How should Hydrogen Cyanide be stored?
CLP Annex VI assigns Hydrogen Cyanide the storage statement P403. Keep cylinders of hydrogen cyanide (HCN) cool and away from open flames. Make certain that HCN cylinders are adequately supported and grounded during storage and emptying. Store cylinders in a vertical position. Do not drop cylinders or damage them by impact. Cylinders must be returned to the supplier within 90 days of the filling date marked on the cylinders, regardless of whether or not the contents have been used. This is due to the possibility of HCN becoming unstable over time. If there is any indication that the HCN is becoming unstable, such as a darkening of the product or an increase in cylinder pressure, contact the supplier immediately for instructions. (Hazardous Substances Data Bank (HSDB))
Nearby
Substances next to Hydrogen Cyanide
Keep going: substances starting with H, or search the whole database by name, CAS number, pictogram or signal word.