Todd Dunning
Todd DunningMAUnited States
Optical Materials for Laser Systems
Published
Dec 24, 2025

Hydrogen Cyanide (HCN)

Chemical Properties

Chemical Identity

CAS Number
74-90-8
Formula
HCN
Molecular Weight
27.03 g/mol

Exposure Limits Comparison

OSHA PEL
10 ppm

Health Effects

Cellular Asphyxiation
Yes
Rapid Unconsciousness
Yes
Respiratory Failure
Yes
Fatal At High Dose
Yes

Hydrogen Cyanide (HCN) safety information

Comprehensive safety and handling requirements

Detection Monitoring
Sensor Types
  • Electrochemical
  • Semiconductor
  • Photoionization detector (PID)
  • Infrared
Detection Range0-30 ppm typical (must detect sub-ppm levels)
Alarm Setpoints
Low4.7 ppm (NIOSH ceiling)
High10 ppm (OSHA ceiling)
Evacuate50 ppm (NIOSH IDLH) - IMMEDIATELY LIFE-THREATENING
Colorimetric Tubes
  • Dräger CH29901
  • Gastec 12L/12
  • Kitagawa 710
Analytical Methods
MethodTechniqueDetection Limit
NIOSH 6010Spectrophotometry (colorimetric)0.2 ppb
OSHA PV2074Ion chromatography0.03 ppm
Odor ThresholdUNRELIABLE - 20-40% of population cannot smell HCN (genetic). Odor threshold (0.58-5 ppm) overlaps toxic range. NEVER rely on odor - MANDATORY continuous monitoring with alarms.
Environmental Impact
Aquatic ToxicityExtremely toxic to aquatic life. LC50 (fish, 96h): 0.05-0.3 mg/L. Toxic at parts-per-billion levels.
BiodegradabilityReadily biodegradable by specialized bacteria. Oxidizes to carbon dioxide and ammonia. Half-life in water: hours to days.
BioaccumulationDoes not bioaccumulate. Log Kow: 0.66. Rapidly metabolized or volatilizes.
Soil MobilityHigh mobility in soil. Volatilizes rapidly. Does not adsorb to soil.
Atmospheric FateRapidly oxidizes via hydroxyl radicals. Atmospheric half-life: 1-3 years. Photolyzes in sunlight.
Ozone Depletionfalse
Reportable Releases
Water10 lbs (4.54 kg) to navigable waters - IMMEDIATELY reportable
Air10 lbs/day (CERCLA RQ) - ANY release must be reported immediately due to extreme toxicity
Ppe Requirements
RespiratoryMANDATORY: Full-face pressure-demand SCBA or positive-pressure supplied-air respirator with escape SCBA. No air-purifying respirators approved - extremely toxic.
Eye ProtectionChemical safety goggles and full face shield. Liquid contact causes severe burns.
Skin ProtectionButyl rubber gloves (>0.5mm), nitrile gloves, fully-encapsulating chemical protective suit. HCN absorbs rapidly through skin.
Reactivity
StabilityUNSTABLE. Polymerizes violently when contaminated with water, bases, or ammonia. Must be stabilized with acid.
PolymerizationMay polymerize explosively if not stabilized. Polymerization exothermic - can rupture containers and cause explosions.
Incompatible Materials
  • Water (polymerization)
  • Strong bases (sodium hydroxide)
  • Acids (releases HCN gas)
  • Oxidizers
  • Ammonia
  • Amines
  • Sulfur
  • Acetaldehyde
  • Halogens
Hazardous Decomposition
  • Nitrogen oxides (NOx)
  • Hydrogen cyanide gas
  • Carbon monoxide
  • Ammonia
Conditions To Avoid
  • Heat
  • Moisture/water
  • Alkaline conditions
  • Light
  • Flames
  • Sparks
  • Oxidizers
  • Contamination of any kind
Reactivity HazardEXTREMELY REACTIVE. Violent polymerization with alkaline materials. Reacts with oxidizers causing fire and explosion. Attacks some metals (copper, zinc) forming explosive metal cyanides.
Regulatory Classification
Un NumberUN1051 (anhydrous, stabilized), UN1613 (solution)
Dot Hazard Class6.1 (Toxic), 3 (Flammable liquid)
Dot LabelPoison, Flammable Liquid
Nfpa Codes
Health4
Flammability4
Reactivity2
Epa Hazard Categories
  • Acute toxicity (fatal if inhaled/swallowed/skin contact)
  • Flammability
  • Skin corrosion
  • Serious eye damage
Sara Title Iiitrue
Cercla Rq10 pounds (4.54 kg)
Rcra CodeP063
Storage Requirements
Temperature RangeStore below 25°C (77°F), ideally <15°C. Avoid heating above boiling point.
VentilationOutdoor storage strongly preferred. If indoors: continuous mechanical ventilation with emergency backup, HCN gas detection with evacuation alarms
Incompatibilities
  • Acids
  • Strong bases
  • Oxidizers
  • Water (polymerization catalyst)
  • Ammonia
  • Sulfur
  • Halogens
  • Amines
Container MaterialStainless steel or glass with PTFE-lined caps. Stabilized with acid (H3PO4 or H2SO4) to prevent polymerization. Never use copper, copper alloys, or iron containers.
SegregationIsolated storage area, separate from all other chemicals. Secure area with restricted access. Post "POISON GAS - AUTHORIZED PERSONNEL ONLY" signs.
Quantity LimitsMinimize quantities stored. Per OSHA, treat as extremely hazardous. Many facilities limit to <5 gallons on-site.
Special RequirementsCRITICAL: Store with stabilizer (acid). Check stabilizer level regularly. Refrigerated storage recommended. Gas detection system MANDATORY. Emergency shower/eyewash within 10 seconds travel. Cyanide antidote kits at storage location. Written emergency procedures posted.

Produced From Contaminants

Z-Beam Logo
Z-Beam Logo
Z-Beam Logo

Produced From Materials

Ceramic Matrix Composites CMCs
Epoxy Resin Composites
Metal Matrix Composites MMCs
Phenolic Resin Composites
Polyester Resin Composites
Urethane Composites

Exposure Limits

Regulatory exposure thresholds and safe concentration levels

Osha Pel Ppm
10
Osha Pel Mg M3
11
Niosh Rel Mg M3
5
Acgih Tlv Mg M3
4.7
Workplace Exposure
Osha Pel
twa_8hr: null
stel_15min: null
ceiling: 10 ppm (11 mg/m³) - Skin notation
Niosh Rel
twa_8hr: null
stel_15min: 4.7 ppm (5 mg/m³) - 10 min ceiling
ceiling: null
idlh: 50 ppm
Acgih Tlv
twa_8hr: null
stel_15min: null
ceiling: 4.7 ppm - Skin notation
Biological Exposure Indices
0: [object Object]
1: [object Object]

Physical Properties

Physical characteristics and state information

Boiling Point
25.6°C (78°F)
Melting Point
-13.3°C (8°F)
Vapor Pressure
620 mmHg @ 20°C
Vapor Density
0.94 (Air=1)
Specific Gravity
0.687 @ 20°C (liquid)
Flash Point
-17.8°C (0°F) closed cup
Autoignition Temp
538°C (1000°F)
Explosive Limits
LEL: 5.6%, UEL: 40%
Appearance
Colorless or pale blue liquid, colorless gas
Odor
Faint bitter almond odor; WARNING: 20-40% of population cannot detect odor (genetic variation)

Reactivity

Chemical reactivity and compatibility with other substances

Stability
UNSTABLE. Polymerizes violently when contaminated with water, bases, or ammonia. Must be stabilized with acid.
Polymerization
May polymerize explosively if not stabilized. Polymerization exothermic - can rupture containers and cause explosions.
Incompatible Materials
  • Water (polymerization)
  • Strong bases (sodium hydroxide)
  • Acids (releases HCN gas)
  • Oxidizers
  • Ammonia
  • Amines
  • Sulfur
  • Acetaldehyde
  • Halogens
Hazardous Decomposition
  • Nitrogen oxides (NOx)
  • Hydrogen cyanide gas
  • Carbon monoxide
  • Ammonia
Conditions To Avoid
  • Heat
  • Moisture/water
  • Alkaline conditions
  • Light
  • Flames
  • Sparks
  • Oxidizers
  • Contamination of any kind
Reactivity Hazard
EXTREMELY REACTIVE. Violent polymerization with alkaline materials. Reacts with oxidizers causing fire and explosion. Attacks some metals (copper, zinc) forming explosive metal cyanides.

Synonyms & Identifiers

Alternative names and chemical identifiers (CAS numbers)

Synonyms
  • Hydrocyanic acid
  • Prussic acid
  • Formonitrile
  • Methanenitrile
  • Carbon hydride nitride
  • HCN
Common Trade Names
  • Zyklon
  • Cyclone B (historical)
Other Identifiers
Rtecs Number
MW6825000
Ec Number
200-821-6
Pubchem Cid
768