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HCN Gas and its Sensor

Intro to Hydrogen Cyanide Gas

Hydrogen cyanide is an industrial viable chemical compound with the formula HCN and a structure of H-C=N. It's characterized as a colorless gas or liquid with an almond-like odor that irritates the eyes, and respiratory tract, and has toxic systemic effects. HCN is naturally present in many food and plants— small doses aren't a problem for people as cyanide is converted to thiocyanate and eliminated from the body.

It is manufactured from ammonia and natural gas and is used for industrial purposes as a precursor to many chemical compounds ranging from polymers to pharmaceuticals. The risk for industrial workers is explosion hazards if in the presence of heat, chemical asphyxiant in poorly ventilated areas, and unintentional generation. HCN is also found in various tobacco products and is released by the combustion of nitrogen-containing organic materials. As an indicator of it's high level of toxicity, in the past, this compound has been used as a chemical weapon agent.

Gas Characteristics

  • Colorless (or pale blue) gas or liquid
  • Strong pungent odor, bitter almond-like scent 
  • Highly toxic
  • Flammable
  • Molecular formula is HCN or CHN
  • The tautomer of HCN is HNC, hydrogen isocyanide
  • Also known as formic anammonide,  hydrogen cyanide, hydrocyanic acid, formonitrile, prussic acid, methanenitrile, cyanwasserstoff
  • CAS 74-90-8
icon ghs whmis toxic depicting dangers of sulfur dioxide released in industrial processes involving chemical hazards

Industrial HCN hazards and sources

  • Fire and Hazmat - Any substance containing carbon and nitrogen (e.g. polyurethane foams used in furniture and mattresses) can release hydrogen cyanide when burned under certain conditions. As such, it is one of the more dangerous gases first responders may be exposed to during a fire.  Please read our guide: Are there gaps in your fire and hazmat gas detection program?
  • Chemical manufacturing - creating polymers and pharmaceuticals. Large-scale applications produce potassium cyanide for mining, adiponitrile for plastics
  • Manufacturing - HCN is used in the production of paper, nylons, plastics, textiles and fumigants
  • Mining  and metals - HCN is used to produce sodium cyanide (NaCN) and potassium cyanide (KCN) which are used in electroplating of gold and silver. 
  • Byproducts - from blast furnaces, coke ovens, photo engraving, smoke from burning nitrogen-containing compounds, the exhaust of vehicles, and smoking cigarettes. 
  • Fumigants - against many insects that infest food production facilities and disinfect enclosed spaces. Workers who fumigate ships and buildings.
  • Metal extraction and refining - steel and iron workers who work in plants that harden iron and steel.
  • Agricultural workers who fumigate outdoor pests in areas like fruit orchards. HCN is found in fruit pits so chewing them can be hazardous. 
  • Petroleum production and refining
  • Factory workers that manufacture acrylic fibers, synthetic rubber, and plastics can risk exposure.
  • Photographic processing
  • Pharmaceutical industry
  • Jewelry making
  • Steel producing
  • Electroplating
  • Metallurgy

Humans retained 58% of hydrogen cyanide in the lungs after inhaling the gas through normal breathing.

U.S. Dept Health & Human Services/Agency for Toxic Substances & Disease Registry; Toxicological Profile for Cyanide p.75 (July 2006)

High Risk Scenarios

  • Explosion hazards - confined polymerization exposure to heat or flame and from the run-off of sewers all create severe explosion hazards for HCN. 
  • Chemical asphyxiant - hazardous concentrations may develop quickly in enclosed or poorly-ventilated areas.
  • Cyanide poisoning - can occur as a result of a fire when certain materials are burning. "Carbon monoxide and hydrogen cyanide are called the 'toxic twins' of smoke inhalation" (Science and Technology, 2021). These fumes are so toxic that even low quantities can be a higher risk than the fire itself. Cyanide exposure is difficult to measure and differentiate from carbon monoxide exposure and requires different treatments.
  • Cyanide exposure has become more of a problem since the 1960s and 1970s because of the increased use of synthetic materials such as the polyurethane foams used in furniture and mattresses and similar materials.
  • Hydrogen cyanide interferes with the body's use of oxygen and may cause harm to the brain, heart, blood vessels, and lungs. Individuals exposed may develop hypoxia. 
  • Two ways of unintentional hydrogen cyanide generation are the accidental mixing of acid and cyanide solutions in electroplating baths and the inadvertent pouring of cyanide waste solutions into acid waste containers with a pH below 10.5-11.
  • Industrial workers can accidentally create large quantities of HCN by mixing water-soluble cyanide salts with water, for example, having a shower in clothes contaminated with cyanides.
  • The toxicity of hydrogen cyanide is due it inhibiting metal-containing enzymes like those containing iron. HCN blocks those enzymes responsible for providing energy to cells where oxygen is used. This inhibits cell respiration so functions cease, becoming fatal. 

HCN Sensor Info

Type: Electrochemical
Range: 0-30 ppm (0.1ppm resolution)

Alarm Levels

Low Alarm: 4.7 ppm
High Alarm: 10ppm
STEL — 15 minute — Short Term Exposure Limit: 10 ppm
TWA  — 8 hour time weighted average: 4.7 ppm

Blackline devices that can detect HCN

Questions about the detection of HCN?


Special Applications and Considerations

  • Corrosion: HCN water solutions can cause transcrystalline stress-cracking of carbon steels. Also, HCN water solutions that contain sulfuric acid can severely corrode steel above 40°C and stainless steel above 80°C. Liquid hydrogen cyanide can deteriorate some plastics, rubber, and coatings.
  • Infamous use as Zyklon B (aka prussic acid) used in Nazi Germany extermination camps during WW11, a component of their Final Solution genocide program.
  • Common short-term exposure symptoms are headaches, eye irritation, fatigue, chest discomfort, palpitations, loss of appetite, and nosebleeds.
  • Electroplaters and picklers who have regular exposure to cyanide solutions may develop a cyanide rash, with itching, and macular, papular, and vesicular eruptions.
  • Acetone cyanohydrin, potassium cyanide, and sodium cyanide can release large amounts of HCN when mixed with water.
  • Cyanide is a potent oral poison producing symptoms in minutes and death in minutes to hours. One teaspoon of 29% liquid hydrogen cyanide has been fatal. (PubChem, 2022).
  • Cyanide is rapidly absorbed and distributed throughout the body following inhalation exposure.
  • Due to genetics, 20-40% of the population can't smell the bitter almond odor.
  • North America is on its way to becoming the global leader in the production and consumption of hydrogen cyanide. Increased demand for the automotive industry is a factor driving this increase. Agriculture is another growth opportunity as HCN fertilizers improve crop yields (Businesswire, 2022).
  • PPE -  wear special protective clothing, eye protection, and positive pressure self-contained breathing apparatus. A Teflon barrier is beneficial.

Health Risks and Handling of HCN

1 - 2 ppm
Irritation of the eyes and respiratory tract, discomfort, loss of appetite, nausea, dizziness, lightheadedness.
2.5 - 6 ppm
Irreversible or other serious, long-lasting adverse health effects or an impaired ability to escape. Rapid breathing, nausea, vomiting, and feeling of neck constraint.
7 - 27 ppm
Can cause life-threatening health effects or death with longer exposures. Coma, apnea, seizures, slowness of the heart rate, and pulmonary edema.
100- 200 ppm
After 10 - 60 minutes can be life-threatening or fatal.
600 - 700ppm
Inhalation for 5 minutes may be fatal.
2000 ppm +
Immediately life-threatening
  • If INHALED move the impacted person to fresh air. Administrator 100% oxygen and assist ventilation as required.
  • If breathing is difficult, offer respiratory support if available. Avoid mouth-to-mouth resuscitation.
  • If this compound has been INGESTED get medical attention right away. Administer 100% oxygen. With a physician's direction prepare a cyanide antidote kit.
  • If SKIN CONTACT is made immediately wash the skin with water. It's very important to remove contaminated clothing and seek medical attention.
  • If the EYES are contacted, immediately wash the eyes with large amounts of water for at least 15 minutes. Get medical attention immediately.
  • Amyl nitrite, sodium nitrite, and sodium thiosulfate are antidotes for cyanide toxicity. However, amyl nitrite and sodium nitrite shouldn't be administered to patients suffering from smoke inhalation.
  • First remove all ignition sources. Next ventilate area of spill or leak. Then stop the flow of gas, or remove cylinder to open air.
  • Evacuate the area immediately. Consult an expert. If permissible absorb any liquid into sand. Never wash into a sewer. Prevent gas from entering a confined space.
  • Environmental considerations - in the case of a land spill, dig a pit or lagoon to hold the contamination. Build a barrier using soil, sand bags, foamed polyurethane or foamed concrete.
  • Generators of waste (100kg/mo) or more of this contaminant. EPA hazardous waste #P063 and D003 must conform with USEPA regulations in storage, transportation, treatment, and disposal.


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