HAZMAT - Meeting the ‘Toxic Twins’ CO and HCN

CarolinaFireJournal - By Todd Shoebridge
By Todd Shoebridge
01/11/2012 -

Hypoxia, asphyxia, cardiac arrest, and then death. Hopefully, I have your attention. Modern technology has changed the way we fight fires, and the ways fire burn. Due to the chemical make-up of manufactured materials, fires today burn hotter, flashovers occur more rapidly, and the smoke is much more toxic. As a result of these factors, firefighters have been dying at a greater rate than ever before from toxic chemical compounds like Carbon Monoxide (CO) and Hydrogen Cyanide (HCN).

In the mid 70s George Kimmerle listed eight major factors that can cause death in fires and to those that are involved in them.1 They are as follows:

  1. Direct consumption by the fire (flame contact)
  2. Very high temperature (thermal insult, burns)
  3. Oxygen deficiency
  4. The presence of CO



5.  The presence of other toxic gases

6.  Presence of smoke

7.  The development of fear, shock, and panic

8.  Secondary fire effects because of mechanical reasons (trauma, fractures, etc.)

This article will focus on four, five and six.

In the fall 2011 issue of Carolina Fire Rescue EMS Journal, I focused on the need for increased awareness in firefighter safety, and the way we handle day to day incidents. I also touched on the need for understanding and adopting the 16 life safety initiatives developed by “Everyone Goes Home” program (National Fallen Firefighters Foundation, Life Safety Summit 2004). Their goal was to change the way the fire service thinks, and to reduce the number of firefighter LODD’s by 50 percent within a 20 year period. In that article, I also touched on the importance of the Rules of Air Management (ROAM) in today’s fire service.

Twenty to 30 years ago the smoke that firefighters were exposed to was not the same as it is today. Wood, cellulose, cotton, silk, wool, etc. were bad, but no where near as toxic as the chemically manufactured material of today. They are often referred to as “THE BREATH FROM HELL”,2 and include chemicals compounds like;

  • Acetals — aerosol containers, combs, lighters, and pens
  • Acrylics — glues, food packages, and skylights
  • Nylons — various household containers, brushes, sewing thread, and fishing line
  • Polyesters — hair dryers, computers, and kitchen appliances
  • Polypropylene — bottles, diapers, and furniture
  • Polyurethanes — shoes, and cushions
  • Polyvinyl chlorides (PVC) — carpet, clothes, purses, records, and shower curtains
  • Thermo sets — televisions, coatings, toilets buttons, flooring, and insulation

Other chemicals included in this toxic mix are carbon monoxide, nitrogen dioxide, polynuclear aromatic hydrocarbons, formaldehyde, acid gases, phosgene, benzene, and dioxins. The smoke of today is a highly complex mixture of solids, liquids, fumes, vapors and gases that are produced when there is a thermal decomposition of materials (simply put a fire).

As firefighters, we are exposed to these toxic compounds regularly, and though treatable at the time of onset, over a period of time they can build up in our system and eventually become life threatening. As firefighters we need to be aware, that where there is smoke there is also carbon monoxide (CO) and hydrogen cyanide (HCN), but did you know that HCN is 33 percent to 35 percent more dangerous than CO. Both are colorless, CO is odorless, but HCN does have a faint smell of almonds, which you would never pick up on in a fire, and they work in different ways. CO attaches to the oxygen molecules in the body, and prevents oxygenation to your vital organs, and will, after a short period of time, suffocate you. HCN on the other hand, targets the central nervous system, cardio vascular system, thyroid, and the blood causing firefighters to become disoriented, agitated, lose focus on the task at hand, and have even gotten to the point where they have fought and run away from their rescuers until becoming physically exhausted and overcome by smoke. This is why you hear of so many firefighters who become lost and disoriented, then take off their masks once they have run out of air.

On average we are losing 100 firefighters a year. That number appears to be dropping slightly over the last several years. Not all are from asphyxiation. Cardiac related fatalities are still the number one cause of death in the fire service, with traumatic injuries number two, followed by asphyxiation. The key point, and the part that you need to remember, is that the cardiac related fatalities that we are experiencing may very well be related to CO and HCN exposures. Higher levels of CO combined with HCN will mimic the signs and symptoms of cardiac related emergencies. Acute exposure to HCN can result in symptoms including weakness, headache, confusion, vertigo, dyspnea, and occasionally nausea and vomiting. Respiratory rate and depth are usually increased at the onset, and will later become slow and gasping. Coma and convulsions occur in some cases. If the firefighter gets to the point where he or she loses color, becomes ashen, or cyanosis is present, it usually means that respirations have ceased or have been inadequate for an extended amount of time.

In the event that a larger dose of HCN has been absorbed into the body, collapse is usually instantaneous, unconsciousness, convulsions, are followed by almost immediate death. This adds substance to the stories you hear of a firefighter walking out of a burning structure, taking off his or her mask and collapsing, or working a shift, going to bed and not waking up in the morning.

Today’s firefighters, company officers, and chief officers need to change their mind-set and give up “The Old School” ways of the past, and open their minds up to the new dangers that face today’s firefighters at every fire that we go to. Standard operating guidelines (SOGs), and standard operating procedures (SOPs) need to be put in place and strictly adhered to.

Fire departments need to train their members about the hazards of these potentially deadly gases, and refresh this information with them at a minimum of once a year. In that training, explain why CO and HCN are more significant today than they were 20 or 30 years ago. Explain the chemistry of the two compounds, when in a fire they are found, and identify the chemical make-ups and materials where HCN is found.

Identify all the medical concerns of cyanide, and why firefighters cannot merely rely on their past experiences to determine whether or not an atmosphere is safe from these gases. Train your department personnel in the proper ways of monitoring for these gases. Train the members of your department on how to correctly use your monitoring equipment, what to look for, such as Lower Explosive Limits (LEL levels), Part per Million concentration levels (PPM), CO and HCN levels. Adopt NFPA 1404, Standard for Fire Service Respiratory Protection Training; 2006 ed., and use it as a guide in the training of your members. Company officers must focus on the protection and safety of their crew members. They need to ensure that anytime their crews are working in or around an IDLH (Immediate Danger to Life and Health) environment SCBA’s are utilized, and that the only time that their face pieces are removed is at a point when they are well outside the contaminated area.

This does not just pertain to structure fires, although this is the focus of this article. Vehicle fires, trash fires, and dumpster fires are included in this as well. All of the same chemically manufactured materials found in a structure fire, (PVC, plastics, synthetic leathers, aerosols etc.) can also be found in vehicles and the trash that we throw away. Why risk killing yourself over a trash filled dumpster, or a vehicle that the insurance company is going to pay for anyway?

Take the time and put on your SCBA. As firefighters, our job is just that, fighting fires, but we need to change our way of thinking and start doing it in a safer way. The fires you fight today, may not kill you today, but what about those exposures you faced 15 or 20 years ago, or better yet, what about those that you will face in the months and years to come. We have SCBA’s in our departments, on our trucks. The air in those bottles is free and readily available. Why not use them, and save a life — YOUR OWN! We want to make sure that Everyone Goes Home.


  1. Kimmerle G. Aspects and methodology for the evaluation of toxicological parameters during fire exposure. Combustion Toxicology. 1974;1:4-51.
  2. Fire, Frank L., Combustibility of Plastics, Fire Engineering Books, 1991

Todd Shoebridge is a 30-year fire service veteran and Captain/EMT with the Hickory (N.C.) Fire Department, where he has served for 20 years. He serves as North Carolina’s Lead Advocate for the “Everyone Goes Home” program; He holds certifications as a National Registry (PROBOARD) Fire Officer III, Rapid Intervention and NFA Mayday Instructor, Hazardous Materials Technician, Level II Fire Service Instructor, Basic VMR Rescue Technician, and Fire/Arson Investigator (CFI) through the NC Fire and Rescue Commission. Shoebridge has associate’s degrees in Biology and Ecology from Montreat College and is completing his Bachelor’s Degree in Fire Science at the University Maryland.
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