Dangers of Fire Smoke Exposure


The Fire Smoke Coalition has been spreading the word around the world about the dangers of fire smoke and the Toxic Twins™-hydrogen cyanide (HCN) and carbon monoxide (CO). It does not take a critical examination of scientific data to determine that fire smoke is a toxic soup of dangerous gases and a deadly enemy to firefighters and responders. What is still confusing for responders is how to decide which toxins must be given attention, how to identify them among the other gases and particulates in fire smoke, and at what point the air is safe to breathe without self-contained breathing apparatus (SCBA) or other respiratory protection.

Although gas detection is common in the hazardous materials response side of the fire service, the typical line firefighter is unfamiliar with gas detection, gas detection devices and manufacturers, and methods and procedures for detecting toxic gases at every fire scene. It is important to note that there is no industry standard best practice when it comes to detection and monitoring in the fire environment, specifically during overhaul.

To that end, agencies are investing in technologies for detecting toxic gases at the fire scene without a clear understanding of the mission, the limitations of the devices, or the results. That is slowly changing as a result of the rising level of awareness of the dangers of fire smoke and the need to identify the presence of toxins at fire scenes. Change is slow primarily because of the strong fire service culture that includes the use, or lack of use, of SCBA; an ingrained belief that breathing smoke is part of the job and unavoidable; and the lack of familiarity with gas detection devices among nonhazardous materials personnel in the fire service.

Up until the past few years, there have been three primary uses for detection devices for a typical fire department outside of the traditional hazmat response team:

  • rescue response including confined space,
  • building collapse and trench rescue, and
  • CO detector responses.

However, it is known that the extensive commercial and residential use of synthetic materials (plastics, nylons, and polymers such as Styrofoam™ and polyurethane foam) have a significant impact on combustion and fire behavior as well as on the smoke produced during a structure fire. Synthetic substances ignite and burn fast, causing rapidly developing fires and toxic smoke and making structural firefighting more dangerous than ever before.

Understanding the flurry of activity and education regarding fire gas toxicity and firefighter safety, the need for atmospheric monitoring on every scene adds an entirely new category for detection-outside of the hazmat response. Ideally, the ultimate goal is to create a new paradigm for the fire service: Gas detection is user-friendly for all firefighters on the scene of everyday fires.


Recently, the Coalition conducted a survey of 244 firefighters to assess the base level of knowledge regarding the use of gas detection devices at the scene of a fire. The demographics of those responding were as follows:

  • Volunteer-25 percent.
  • Combination career/volunteer-34 percent.
  • Career-40 percent.

The majority of respondents were line firefighters working in the field. When asked about standard operating procedures (SOPs) for using gas detection devices at fire scenes, 80 percent of the respondents replied they had no SOPs for detecting/monitoring HCN in the field. Forty-nine percent of the respondents had no operating procedures for detecting/monitoring CO on the fire scene, and 79 percent of the respondents had no SOPs for detecting/monitoring any toxic gas on the fire scene. The conclusion to be drawn is that an overwhelming majority of the firefighters have no guidance when it comes to detecting and monitoring for toxic gases on a fire scene.

More than 20 percent of the respondents replied that they have been treated for smoke inhalation. More interesting is the fact that 90 percent stated they have never been treated for smoke inhalation; however, they suffered headaches, nausea, and sore throats following a fire. This finding indicates a lack of understanding of the signs and symptoms of smoke inhalation, which points directly back to detection and monitoring. If firefighters do not have a reference point about the quality of air they are breathing, there is no correlation to the fact that smoke may be the culprit for feeling ill after a fire or for causing long-term health effects.

The majority of firefighters who attend the Coalition’s “Know Your Smoke: The Dangers of Fire Smoke Exposure” training program go back to their departments with new education and awareness about the need for atmospheric monitoring on every fire scene, but they don’t know where or how to begin the process of developing procedures and practices.

Think about it this way: If any one of these gases were leaking from a tank truck or a cylinder on a highway, first responders (firefighters) would establish an isolation perimeter and only personnel in chemical protective clothing would be allowed into the hot zone. Now, combine all of these dangerous gases and dump them into a high-temperature environment of the everyday house fire with firefighters running toward the situation-sometimes with and sometimes without proper protective clothing. Structural fires, vehicle fires, dumpster fires-frankly, any type of fire-will produce toxic gases. What vary from fire to fire are the types and amounts of gases. Merely heating certain items, such as plastics, can produce toxic gases. If you are a firefighter with a few years of experience, at some point you’ve probably suffered from a headache or nausea following a fire, which is indicative of exposure to one or more of the toxic gases. These exposures can add up over a firefighter’s career, creating long-term health issues and even causing death.

The post-World War II introduction of the SCBA to the fire service represented a significant step forward in the protection of firefighter lives. Improved SCBA design and increased regulatory pressure have now made the SCBA a standard firefighting tool in the United States. This tool has made it possible for firefighters to quickly get deep into smoke-filled, burning structures and to be more effective in protecting life and property.

Recent scientific examination of the fireground has revealed hazards in addition to those made obvious by simple observation. These additional hazards are associated with the content of fire smoke, where and when it is present, and how it interacts with the human body. This article addresses these issues and, where possible, makes suggestions for the amelioration of the hazards. Keep in mind that firefighters recognize and accept a substantial amount of risk when they come to the job and that it is not possible to eliminate all hazards.


The U.S. Occupational Safety and Health Administration (OSHA) terms environments that present immediate threats to life as immediately dangerous to life or health (IDLH). Any worker exposed to threatening environments is required to wear appropriate respiratory protection. Current fireground protocols generally require the use of SCBA inside an active fire (burning) structure. The interior environment of a burning structure may be monitored for one or more gases and declared a non-IDLH environment (SCBA not required) when threatening gas levels drop below recommended exposure limits, provided that air monitoring can account for all of the toxins that may be present. Further, the exterior of a burning structure is generally considered a non-IDLH environment but is not monitored.

During a recent research burn we conducted in Carmel, Indiana, a structure was burned intact with contents [as opposed to the National Fire Protection Association (NFPA) 1403, Standard on Live Fire Training Evolutions, 2012 edition, protocol]. We monitored the exterior environment for CO and HCN. Monitors were set up at 10, 20, and 30 feet on each of the four corners of the structure. During the growth phase of the fire, HCN and CO concentrations were recorded at all points in excess of IDLH levels. This suggests that monitoring should be considered outside the structure as well as inside.


Heat generated by a fire causes gases (including atmospheric air) to expand rapidly. This rapid expansion creates an area of high pressure that begins pushing smoke and combustion products out of its way. As a result, smoke and superheated gases are pushed throughout the structure. Even though ventilation of the structure provides an escape route for smoke, not all of the smoke and products of combustion will leave the structure.

An example is a recent NFPA 1403 burn conducted in Indianapolis. All NFPA 1403 requirements were followed from preparation through burning. Between burns, we monitored the inside of the structure for CO, HCN, and hydrogen sulfide (H2S). During overhaul and after the structure had been deemed safe for removal of SCBAs, we encountered a half-bath on the first floor that was essentially a gas chamber. This small, nonventilated bathroom measured 85 parts per million of HCN. Fortunately, the research team wears breathing protection at all times. Without a monitor, a nonprotected individual would have inhaled a potentially fatal dose of cyanide. This is just one example of how these potentially toxic gases can hide in a structure, even when current safety protocols say the environment is safe.

Another factor to consider about where these gases can form is temperature. As a gas is heated, it expands and becomes less dense. If its density becomes less than that of the surrounding gases, it will rise. Heat from a structural fire will not only create toxic gases but will also cause them to rise in this manner. During the growth phase of a fire, these gases rise to the structure’s ceiling, where they accumulate and begin creating high levels of gas pressure. Pressurization of the room causes smoke and gases to be pushed out of the room. More heat equals more pressure and increased velocity of gas movement, a familiar concept to firefighters. Following extinguishment, however, the whole system tries to reverse. As gases cool, they become dense and move downward in the environment. This commonly occurs during overhaul and is a potential source of toxic exposure. So, gases move around during overhaul, making continuous monitoring necessary to protect firefighters.


Toxins enter the human body by several routes including ingestion, inhalation, injection, and absorption. The total toxic load encountered by a body is the sum of all possible routes of entry. On the fireground, only inhalation and absorption through the skin are relevant.

With an exchange surface area approximately that of a tennis court and a very small diffusion distance, the lung is designed for the exchange of gases between inhaled gas and the bloodstream. Although the lung is set up this way to facilitate the exchange of oxygen and carbon dioxide as part of normal respiration, it also provides an effective pathway for toxic gases to enter the bloodstream. The two most important fireground toxic gases that use this pathway are CO and HCN. CO works as an asphyxiant by binding hemoglobin 200 times more effectively than oxygen. It eliminates the blood’s ability to deliver oxygen throughout the body. HCN is also an asphyxiant, but it attacks the cell’s ability to use oxygen and generate energy. Significant exposure to HCN generally results in penalization of respiratory muscle and asphyxiation. More importantly, both HCN and CO are produced in a structure fire. They work synergistically to hurry death by attacking respiration from two sides, oxygen delivery and oxygen use.

Skin absorption of a toxic substance is far more complicated than inhalation exposures. Many factors affect the rate or even whether or not a substance is absorbed through the skin. The skin can be pictured as a two-layer system. The outer layer, the stratum corneum or epidermis, is a thin layer of dead cells that acts as a primary barrier to absorption. Below the epidermis is a much thicker layer of living tissue that contains blood vessels, sweat glands, hair follicles, and nerves. Absorption through this system is driven by diffusion alone. When a substance is deposited on or comes in contact with skin surface, a concentration gradient is established that drives diffusion. This relationship is described as “Fick’s Law of Diffusion,” which, in essence, says that how much of the material reaches the bloodstream and contributes to a toxic load is determined by the characteristics of both the compound and the tissue. Fick’s Law indicates that the rate of diffusion is determined by several factors including the surface area for diffusion (area of skin contaminated) and the concentration of the contaminant on the skin.

In addition, the chemical characteristics of the contaminant are also important. The epidermis is a hydrophobic layer, meaning it repels water. Therefore, compounds similar to water will have a difficult time getting through. Organic compounds, like solvents, cross the epidermis more easily. Gases, like HCN and H2S, move easily across the dermis and, in appropriate concentration, can contribute substantially to a toxic load. Following the movement of a compound from the skin surface to the perfusion-rich area of the skin, the amount of blood flow through the skin is another factor that contributes to toxic load. When the skin is hot, more blood flow is routed to the skin and provides the final sink for a contaminant’s diffusion gradient. Of course, this is a common situation for the firefighter who works vigorously on the fireground.

A firefighter’s turnout gear provides substantial protection from dermal exposure during suppression operations. However, current fireground protocols that may clear the removal of SCBA could provide an exposure risk with removal of the hood and mask. In addition, contaminants that adhere to the exterior of the turnout gear can provide a source of postfire exposure if handled extensively before cleaning.

To protect yourself and your crew, atmospheric monitoring should not be a one-time exercise. To be effective, it must be continuously performed around the perimeter to protect incident command (not on air) during the initial stage of the fire and throughout the overhaul process, with the complete understanding that gases will travel throughout the fire scene. For absolute protection, wear and use SCBAs through overhaul, and keep your personal protective equipment clean; otherwise, the toxicant exposures will continue to invade your body.


1. Schnepp, R; Gagliano, M; Jose, P; Reilly, K; Ricci, F; O’Brien, D; Augustine, J; Walsh, D. 2009. “SMOKE Cyanide and carbon monoxide: The toxic twins of smoke inhalation.” Cyanide Poisoning Treatment Coalition Educational Supplement. Vol. 2. March 2009.

2. Bolstad-Johnson, DM; Burgess, JL; Storment, S; Gerkin, R; Wilson, JR. Characterization of firefighter exposures during fire overhaul. Phoenix (AZ) Fire Department.

3. Code of Federal Regulations 29 CFR 1910.156. Washington, DC: US Government Printing Office, Federal Register. (1989).

4. Sample, S. 2004. “Dermal exposure to chemicals in the workplace: just how important is skin absorption?” Occup. Environ. Med. 61:376-382.

ROB SCHNEPP is chief of special operations for the Alameda County (CA) Fire Department. He is the author of Hazardous Materials Awareness and Operations and an editorial advisory board member of Fire Engineering. He is a member of the National Fire Protection Association (NFPA) Technical Committee on Hazardous Materials Response Personnel and a task force member charged with revising NFPA 473, Standard for Competencies for EMS Personnel Responding to Hazardous Materials. He is co-author and instructor of the Special Operations Program for the National Fire Academy and an instructor for the U.S. Defense Threat Reduction Agency, providing hazmat and weapons of mass destruction training overseas. He is a founding member of the Cyanide Poisoning Treatment Coalition and a board member of the Fire Smoke Coalition.

JAMES BROWN is a consulting applied physiology research scientist and research director for the Indianapolis (IN) Fire Department. He has authored multiple reports on the physiological aspects of structural and wildland firefighting. His current research is focused on the physical stress imposed by structural firefighting.

Rob Schnepp and James Brown will present “Dangers of Fire Smoke Exposure” on Monday, April 22, 1:30 p.m.-5:30 p.m., at FDIC 2013 in Indianapolis.

More Fire Engineering Issue Articles
Fire Engineering Archives

No posts to display