Hydrogen Cyanide

Classification

Flammable liquid, Category 1; Acute toxicity (oral, dermal and inhalation), Category 1; Serious eye irritation, Category 2; STOT single exposure, Category 1 (central nervous system, respiratory system, heart); STOT repeated exposure, Category 1 (central nervous system); Hazardous to the aquatic environment (acute and long-term), Category 1 (per Japan's government GHS classification)

Hazard statements

• H224 Extremely flammable liquid and vapor.
• H300+H310+H330 Fatal if swallowed, in contact with skin or if inhaled.
• H319 Causes serious eye irritation.
• H370 Causes damage to organs.
• H372 Causes damage to organs through prolonged or repeated exposure.
• H410 Very toxic to aquatic life with long lasting effects.

Key precautionary statements

• P210 Keep away from heat, hot surfaces, sparks, open flames and other ignition sources. No smoking.
• P260 Do not breathe gas or vapor.
• P262 Do not get in eyes, on skin, or on clothing.
• P271 Use only outdoors or in a well-ventilated area.
• P280 Wear protective gloves, protective clothing, eye protection and face protection.
• P284 Wear respiratory protection.
• P304+P340+P310 IF INHALED: Remove person to fresh air and keep comfortable for breathing. Immediately call a POISON CENTER or doctor.
• P403+P233 Store in a well-ventilated place. Keep container tightly closed.
• P405 Store locked up.

The OSHA PEL is 10 ppm as an 8-hour TWA with a skin notation (29 CFR 1910.1000 Table Z-1). NIOSH recommends a much lower 4.7 ppm short-term limit, and ACGIH and Cal/OSHA set 4.7 ppm as a ceiling. All carry skin notations, because liquid and high vapor levels pass through the skin. The NIOSH IDLH is 50 ppm. Many people cannot smell hydrogen cyanide, so odor is no warning. State OSHA plans may set different limits.

• Appearance: Colorless or pale blue liquid that boils near room temperature, giving off a colorless gas
• Odor: Bitter almond; many people cannot smell it
• Molecular weight: 27.0
• Boiling point: 78°F (26°C)
• Freezing point: 7°F (-14°C)
• Flash point: 0°F (-18°C), Class IA flammable liquid
• Explosive limits: LEL 5.6%, UEL 40%
• Vapor pressure: 630 mmHg
• Specific gravity: 0.69 (liquid)
• Water solubility: Miscible

Inhalation

Cyanide stops cells from using oxygen. Early signs include headache, dizziness, confusion, weakness, nausea and rapid breathing. High exposure quickly leads to gasping, convulsions, loss of consciousness and death within minutes.

Skin

The liquid and high vapor levels are absorbed through the skin and can cause poisoning. Contact can irritate and burn the skin.

Eyes

Irritates and can burn the eyes, and is absorbed through them.

Ingestion

Fatal in small amounts. Get emergency medical help immediately.

Target organs

Central nervous system, cardiovascular system, thyroid, blood

Long-term effects

Repeated exposure may affect the thyroid and the nervous system. Related exposures: cyanide salts give off hydrogen cyanide when they contact acids, and fires involving nitrogen-containing plastics and other materials can release it alongside carbon monoxide.

Gloves

For the liquid, NJDOH lists nitrile and neoprene gloves (more than 8 hours breakthrough). See hand protection.

Eyes and face

Non-vented chemical goggles and a face shield, or a full-facepiece respirator.

Respiratory

NJDOH advises against cartridge or canister respirators for routine work; use a pressure-demand full-facepiece supplied-air respirator above 4.7 ppm. At or above 50 ppm, or at unknown levels, use a pressure-demand full-facepiece SCBA. See respiratory protection.

Clothing

NJDOH lists Tychem TK or equivalent (more than 8 hours breakthrough for gas and liquid). Remove contaminated clothing immediately.

Store in tightly closed containers in a cool, well-ventilated area away from heat and ignition sources. Hydrogen cyanide must contain a stabilizer, such as phosphoric acid, because unstabilized material can polymerize violently and explode, especially above 122°F (50°C) or in contact with bases.

Ground and bond containers, use non-sparking tools and explosion-proof equipment, and use continuous gas detection. Keep a cyanide emergency plan in place and make sure workers are trained in it.

Keep away from

• Strong bases, including sodium hydroxide
• Ammonia and amines
• Oxidizers, such as peroxides, nitrates and chlorine
• Strong acids
• Heat (above 122°F / 50°C)

• Evacuate and isolate the area. Stay upwind.
• Remove all ignition sources.
• Only trained responders in SCBA and gas-tight protective clothing should approach the release.
• Stop the leak if it is safe. Use water spray to dilute vapors and foam to suppress them.
• Absorb liquid with dry sand or earth and seal in containers for disposal. Keep out of sewers.
• Follow ERG Guide 117 (UN1051).

Suitable extinguishing media

• Do not put out the fire unless the leak can be stopped safely
• Dry chemical
• Carbon dioxide (CO₂)
• Alcohol-resistant foam
• Water spray to cool containers and knock down vapors

Special hazards

Extremely flammable. Vapors can travel to ignition sources and flash back. Containers may explode in fire, and heat can trigger violent polymerization. Fires produce toxic gases including nitrogen oxides. Firefighters need positive-pressure SCBA and full protective gear.

• OSHA Hazard Communication (29 CFR 1910.1200): Hazardous chemical; SDS, labels and training required.
• OSHA Air Contaminants (29 CFR 1910.1000 Table Z-1): 10 ppm (11 mg/m³) TWA, skin.
• OSHA Process Safety Management (29 CFR 1910.119 Appendix A): Hydrogen cyanide, anhydrous, threshold quantity 1,000 lb.
• CERCLA (40 CFR 302.4): Hazardous substance, reportable quantity 10 lb (RCRA waste P063).
• EPCRA Section 302 (40 CFR 355 Appendix A): Extremely hazardous substance (listed as hydrocyanic acid), threshold planning quantity 100 lb, reportable quantity 10 lb.
• Clean Air Act 112(r) (40 CFR 68.130): Hydrocyanic acid, threshold quantity 2,500 lb. Covered as a hazardous air pollutant under the cyanide compounds category.
• DOT (49 CFR 172.101): UN1051, Hydrogen cyanide, stabilized with less than 3 percent water, Division 6.1 with subsidiary Class 3 label; Poison Inhalation Hazard, Zone A.

• NIOSH Pocket Guide: Hydrogen cyanide
• OSHA Occupational Chemical Database: Hydrogen cyanide
• NITE (Japan) GHS classification: Hydrogen cyanide
• NJ Department of Health Hazardous Substance Fact Sheet: Hydrogen Cyanide
• CAMEO Chemicals: UN1051 (DOT and ERG data)
• 40 CFR 302.4, CERCLA hazardous substances
• EPA: Initial list of hazardous air pollutants