HYDROGEN CYANIDE

Hydrogen cyanide
(Hydrocyanic acid; prussic acid)
CAS 74-90-8

HCN

Colorless or pale blue liquid or gas
bp 26 °C, mp -13 °C
Miscible in water in all proportions

Bitter almond odor detectable at 1 to 5 ppm; however, 20 to 60% of the population are reported to be unable to detect the odor of HCN

750 mmHg at 25 °C

-18 °C

538 °C

Approx LD oral (rat) 10 mg/kg

Approx LD skin (rabbit) ~1500 mg/kg

LC₅₀ inhal (rat) 63 ppm (40 min)

PEL (OSHA) 10 ppm (11 mg/m³)--skin

TLV-TWA (ACGIH) Ceiling 10 ppm (11 mg/m³)--skin

High acute toxicity; inhalation, ingestion, or skin contact may be rapidly fatal.

The acute toxicity of hydrogen cyanide is high, and exposure by inhalation, ingestion, or eye or skin contact can be rapidly fatal. Symptoms observed at low levels of exposure (e.g., inhalation of 18 to 36 ppm for several hours) include weakness, headache, confusion, nausea, and vomiting. Inhalation of 270 ppm can cause immediate death, and 100 to 200 ppm can be fatal in 30 to 60 min. Aqueous solutions of HCN are readily absorbed through the skin and eyes, and absorption of 50 mg can be fatal. In humans, ingestion of 50 to 100 mg of HCN can be fatal. Because there is wide variation in the ability of different individuals to detect the odor of HCN, this substance is regarded as having poor warning properties.

Effects of chronic exposure to hydrogen cyanide are nonspecific and rare.

Hydrogen cyanide is a highly flammable liquid. Liquid HCN contains a stabilizer (usually phosphoric acid), and old samples may explode if the acid stabilizer is not maintained at a sufficient concentration.

HCN can polymerize explosively if heated above 50 °C or in the presence of trace amounts of alkali.

Because of its high acute toxicity, hydrogen cyanide should be handled using the "basic prudent practices" of Chapter 5.C, supplemented by the additional precautions for work with compounds of high toxicity (Chapter 5.D) and flammability (Chapter 5.F). In particular, work with HCN should be conducted in a fume hood to prevent exposure by inhalation, and splash goggles and impermeable gloves should be worn at all times to prevent eye and skin contact. Never work alone with hydrogen cyanide. HCN should be used only in areas free of ignition sources. Containers of HCN should be protected from physical damage and stored in areas separate from ignition sources and other materials. Hydrogen cyanide should not be stored for extended periods (>90 days) unless testing confirms product quality.

In the event of skin contact, immediately wash with soap and water and remove contaminated clothing. In case of eye contact, promptly wash with copious amounts of water for 15 min (lifting upper and lower lids occasionally) and obtain medical attention. If hydrogen cyanide is ingested, obtain medical attention immediately. If HCN is inhaled, move the person to fresh air and seek medical attention at once. Specific medical procedures for treating cyanide exposure are available but usually must be administered by properly trained personnel. Consult your environmental safety office or its equivalent before beginning work with hydrogen cyanide.

In the event of a spill, remove all ignition sources. Cleanup should be conducted wearing appropriate chemical-resistant clothing and respiratory protection.

Excess hydrogen cyanide and waste material containing this substance should be placed in an appropriate container, clearly labeled, and handled according to your institution's waste disposal guidelines.

The information in this LCSS has been compiled by a committee of the National Research Council from literature sources and Material Safety Data Sheets and is believed to be accurate as of July 1994. This summary is intended for use by trained laboratory personnel in conjunction with the NRC report Prudent Practices in the Laboratory: Handling and Disposal of Chemicals. This LCSS presents a concise summary of safety information that should be adequate for most laboratory uses of the title substance, but in some cases it may be advisable to consult more comprehensive references. This information should not be used as a guide to the nonlaboratory use of this chemical.

Copyright 1995 National Academy of Sciences. All rights reserved.