Hydrogen Cyanide (HCN) — properties & hazards overview
Boiling point
≈ 26 °C
Flash point
−18 °C
Explosive limits
LEL 5.6 % · UEL 40 %
Water solubility
Miscible (forms weak acid)
Flammability
Highly flammable
Toxicity
Extremely toxic
Chronic risk
Neurological effects
Environmental
Aquatic toxicity
| Property | Value / Note |
|---|---|
| Physical state | Colourless, volatile liquid or gas with faint bitter-almond odour (not always detectable). |
| Density (gas, 25 °C) | ≈ 0.94 kg/m³ (lighter than air) |
| Odour threshold | ≈ 1 ppm, but perception varies — odour cannot be relied upon for safety. |
| Typical sources | Metal finishing, acrylonitrile manufacture, coke ovens, nitrile cracking, and combustion of nitrogen-containing plastics. |
| Best analytical detection | Electrochemical or FTIR monitoring — both give rapid, continuous, and highly selective detection down to ppb range; ideal for leak and process safety monitoring. |
*Typical exposure limits: TLV-TWA 4.7 mg/m³ (≈ 5 ppm); IDLH = 50 ppm — verify per jurisdiction.