Hydrogen Cyanide: The Real Killer Among Fire Gases

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Smoke that is present during a structure fire is composed of several irritating, toxic and asphyxiant chemicals, depending on the materials that are burning. These chemicals may include hydrochloric acid, ammonia, carbon dioxide, carbon monoxide, hydrogen sulfide and hydrogen cyanide. According the U.S. Fire Administration (USFA), smoke is the killer in 60% to 80% of all fire deaths. Recent research has revealed that hydrogen cyanide present in smoke generated at building fires may play a more significant role in injuries and deaths of firefighters and civilians than once thought.

Smoke generated in structural fires from products composed of carbon and nitrogen contains various concentrations of hydrogen cyanide. Commercial products made up of materials such as wool, paper, cotton, silk and plastics may produce hydrogen cyanide when they burn. Hydrogen cyanide is formed when natural fibers, such as wool and silk, and synthetic polymers, such as polyurethane and nylon, are not completely consumed during a structure fire. These materials are used in insulation, floor coverings, and other construction materials and furnishings that may be present in a building.

The USFA estimates that approximately 20,800 residential building fires occur annually involving fuels such as mattresses, pillows and bedding materials. Synthetic components of these fuels have a tendency to burn hotter and faster than conventional materials, which results in room temperatures reaching flashover sooner. Flashover promotes the degradation of synthetics resulting in the release of hydrogen cyanide and other toxic gases.

The National Institute of Standards and Technology (NIST) investigated the fire that occurred at The Station Nightclub in West Warwick, RI, in February 2003. NIST concluded that cyanide played a key role in the 100 deaths that occurred as a result of that fire. Testing of Providence firefighters also revealed positive results for exposure to cyanide. Live-fire testing using a full-scale mockup of the nightclub demonstrated that within a few seconds of ignition of the fire, concentrations of carbon monoxide and hydrogen cyanide increased dramatically while oxygen levels in the room decreased.

Studies in other countries have produced similar conclusions. The Paris Fire Brigade studied 43 fire-related deaths and discovered a direct relationship between the blood cyanide concentration and the resulting fire death. A study in Argentina following a prison fire in which 35 inmates died produced additional evidence. Carbon monoxide levels in the victims were well within the non-lethal range, but blood cyanide levels exceeded the lethal range.

According to the Cyanide Poisoning Treatment Coalition (CPTC), exposure to hydrogen cyanide in building fires is the leading cause of cyanide poisoning. The CPTC is a non-profit organization made up of individuals and groups. Members of the coalition all have direct involvement with the identification and treatment of cyanide exposure. Their mission is, "To foster a rational approach to the diagnosis and treatment of cyanide poisoning through research, advocacy and education, thereby reducing the morbidity/mortality from cyanide-related causes." At present, there are few resources available to increase awareness of the risk of exposure to cyanide. The CPTC hopes to become an important source of information concerning cyanide poisoning and an advocate towards improvement of early recognition and appropriate treatment.

Firefighters can take actions to prevent exposure to hydrogen cyanide, which may also help to reduce some of the heart attacks that are the leading cause of firefighter deaths. One target organ of hydrogen cyanide is the heart. Most firefighters in the U.S. have access to self-contained breathing apparatus (SCBA), the primary component of personal protective equipment (PPE) to keep firefighters from being exposed to hydrogen cyanide and its effects. Firefighters should wear SCBA anytime smoke is present. Hydrogen cyanide is present not only in visible smoke, but can be present during overhaul when smoke is no longer evident - and when SCBA is often removed. That's a big mistake, as toxic gases may still be present. It's time to make operational changes that require firefighters to wear SCBA whenever smoke is present and throughout the time they are inside a structure that has been on fire, unless air monitoring concludes that the air is safe to breathe.

Chemical Properties

Hydrogen cyanide (HCN), also known as hydrocyanic acid, is a colorless gas or liquid with a characteristic faint odor of bitter almonds. In addition to being an important industrial chemical, hydrogen cyanide is a chemical warfare agent. It is categorized as a blood agent because it enters the blood stream and prevents intracellular oxygen utilization, resulting in chemical asphyxiation even in the presence of adequate oxygen in the atmosphere.

The U.S. Department of Transportation (DOT) classifies hydrogen cyanide as a 6.1 poison. The National Fire Protection Association (NFPA) lists a 704 System designation for hydrogen cyanide as Health 4, Flammability 4 and Reactivity 2. Hydrogen cyanide can be absorbed into the body by inhalation, through the skin and by ingestion. The organs most susceptible to cyanide are the central nervous system (CNS) and the heart. The minimum fatal dose is approximately 50 mg for adults. Approximately 90 parts per million (ppm) is fatal in 30 minutes and 300 ppm is fatal within a few minutes.

There is little that can be done in the field to detect cyanide poisoning in victims of fires or other accidents. The diagnosis of acute cyanide toxicity is primarily a clinical one, based on rapid onset of CNS toxicity and cardiorespiratory collapse. Response personnel must therefore make certain assumptions in order to initiate life-saving treatment in a timely manner. When there are victims at the scene of a fire who were exposed to smoke, cyanide poisoning should be suspected. The presence of soot in the mouth, around the nose and altered levels of consciousness also indicate the high probability of cyanide poisoning. Signs and symptoms of cyanide poisoning can vary based on the source and route of exposure as well as the dose received. Initial signs of low-concentration exposure include rapid breathing, dizziness, weakness, nausea/vomiting, eye irritation, pink or red skin color, rapid heart rate and perspiration. Delayed signs of moderate to high concentrations include loss of consciousness, respiratory arrest, cardiac arrest, coma and seizures. Victims exposed to hydrogen cyanide require supportive care and rapid administration of specific antidotes.

Victims of smoke inhalation should be suspected to be suffering from cyanide poisoning. It is important to treat them as quickly as possible. Treatment protocols include removing the victim from further exposure, restoring or maintaining an open airway, and administering 100% oxygen via a non-rebreather mask or bag-valve mask technique. Research has shown that oxygen has some antidotal effects on cyanide poisoning victims.

If severe carbon monoxide and hydrogen cyanide poisoning is suspected, then once at the hospital hyperbaric oxygen may be administered, although there is no known success in using hyperbaric oxygen for cyanide poisoning alone. Perform aggressive advanced airway management, including early intubation if necessary. Provide cardiopulmonary support and stabilize vital signs, including the use of trauma and burn management. When clinically indicated, appropriate medical interventions, such as an antidote, should be used to control seizures, stabilize cardiovascular function and correct metabolic acidosis if known.

Protection from exposure to hydrogen cyanide and other toxic materials through the wearing of PPE and breathing apparatus is the best procedure for firefighters to follow. However, in the event that an exposure does occur, Cyanide Antidote Kits are available and effective if administered quickly following an exposure. Some paramedics may be trained and able to administer cyanide kits in the field, but most antidotes are administered at a hospital emergency room, so it is important that emergency medical personnel know which hospitals have Cyanide Antidote Kits available.

Antidote kits available for cyanide poisoning in the U.S. contain three medications that must be administered in a specific order. First, amyl nitrite is given through inhalation. If oxygen and amyl nitrate is not successful in treating the victim, then sodium nitrite is infused intravenously. This is followed by the infusion of intravenous sodium thiosulfate. Other antidotes that can be administered in the field have been used in other countries, but are not available in the U.S. These include hydroxocobalamin, a precursor of vitamin B12 that has been used safely and effectively in France under the trade name Cyanokit. Dicobalt ededate is used in the United Kingdom to treat cyanide poisoning and 4-dimethylaminophenol (DMAP) is used in Germany as an antidote for severe cyanide poisoning in patients who are in a deep coma and who have dilated non-reactive pupils and deteriorating cardiorespiratory function.

A new type of personal detection device called the Chameleon uses chemical reactive tabs in a wristband holder to determine when dangerous levels of gases are present in a given atmosphere. The interchangeable tabs undergo a color change indicating the presence of a suspected type of gas. Each wristband has the capability of detecting eight gases simultaneously. The person wearing the wristband just needs to watch for the color changes. Cyanide is one of the gases that the Chameleon can detect. This device could be helpful during overhaul when invisible toxic gases such as hydrogen cyanide may be present.

The National Association of EMS Educators (NAEMSE) provides one-day seminars titled "Cyanide Detection and Treatment." Information can be obtained at www.naemse.org.


ROBERT BURKE, a Firehouse contributing editor, is the fire marshal for the University of Maryland-Baltimore. He is a Certified Fire Protection Specialist (CFSP), Fire Inspector II, Fire Inspector III, Fire Investigator and Hazardous Materials Specialist, and has served on state and county hazardous materials response teams. Burke is an adjunct instructor at the National Fire Academy and the Community College of Baltimore, Catonsville Campus, and the author of the textbooks Hazardous Materials Chemistry for Emergency Responders and Counter-Terrorism for Emergency Responders. He can be contacted at robert.burke@att.net.

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