Air Monitoring at Structure Fires


Hydrogen cyanide (HCN) is an extremely dangerous and common by-product of combustion found in smoke, and it is quickly receiving recognition for its dangerous presence. HCN has long been known to be present in smoke. However, understanding the synergistic effects of HCN and carbon monoxide (CO) is somewhat new. With the assistance of the Cyanide Poisoning Treatment Coalition (CPTC), members of the Columbia (SC) Fire Department (CFD) have been making an effort to change the way they handle fires and to educate the fire service on these dangerous gases.

In October 2007, the CFD tested a single-gas meter from a local vendor. This test was designed to look at a replacement of a single-gas CO meter for the current aging inventory. The meter that was received was a Rae Systems ToxiRae® II with HCN sensor. The vendor asked that the CFD review the body of the unit and its basic operation with the intention of swapping it out for a CO meter once it became available. This was an unplanned event that made for a positive change in the way the CFD would operate at fire scenes.

Because HCN characteristics were not completely unfamiliar to Haz-Mat 1 (HM-1) personnel, the chief of training asked that they be researched. There was a significant difference in the amount of HCN information found on the Internet when compared to that of CO. Although the presence of HCN in smoke was nothing new, it was unclear exactly how dangerous it truly was. The CFD was sporadically using CO meters during overhaul for well over a decade, and we were fairly familiar with the characteristics associated with CO exposure. With only a few articles and documented incidents readily available concerning HCN, we began to look into how the CFD could learn more about this unfamiliar and dangerous by-product of combustion. 


After learning about HCN and the risks associated with exposure, we quickly decided that the CFD needed awareness training for HCN exposure. Two key documents were found to get started: Report of the Investigation Committee into the Cyanide Poisonings of Providence Firefighters, a 2006 report on the cyanide exposure of Providence, Rhode Island, firefighters, and “SMOKE perceptions, myths, and misunderstandings,” a CPTC-sponsored educational supplement.

After learning what little could be found on the subject, we compiled and presented a concise document to the CFD command staff based on the findings of the two documents. The document not only explained the problem but also presented an inexpensive solution. The first section explained the health effects and likelihood of HCN exposure. The key points include the following:

  • The immediately dangerous to life and health (IDLH) quantity for CO is 1,200 parts per million (ppm), while the IDLH of HCN is 50 ppm—24 times that of CO.
  • Low CO levels present a false sense of security as to the presence of HCN.
  • HCN has a short half-life, making it difficult to fully determine the level of exposure.
  • HCN symptoms in lower level exposures are similar to heat-related illness and CO poisoning.
  • HCN symptoms in severe or acute cases mirror those of a heart attack.
  • Many health care facilities are not capable of testing or treating HCN poisoning.
  • Suppression personnel are not properly trained on how to identify the symptoms of HCN.
  • Statistical data are not available to help educate and protect firefighting personnel.

The second section was a list of short- and long-term goals the CFD needed to achieve. Because limited evidence or support was available as to exactly when and how much HCN was present at fires, accurate data would be necessary to get the command staff’s support. With one meter already in use, we contacted two additional vendors and asked if the CFD could demo a meter from different manufacturers. Industrial Scientific’s GasBadge® Pro and MSA’s Altair® Pro were quickly obtained. In addition to collecting data, the time period would be used to field test the meter that would eventually be purchased.


HCN is 24 times more dangerous than CO. The National Institute for Occupational Safety and Health (NIOSH) recommended exposure limit (REL) for HCN is 4.7 ppm. This is considerably lower than the REL for CO, which is 35 ppm, but it is still important. If exposed to levels exceeding 270 ppm, death can occur in as little as six to eight minutes, or in 30 minutes at 135 ppm, according to the Occupational Safety and Health Administration (OSHA). An acute exposure to cyanide can result in symptoms such as weakness, headache, confusion, fatigue, anxiety, dyspnea, and occasional nausea and vomiting. Respiratory rate and depth usually increase on first exposure and will slow at later stages to become gasping.


With the plan developed, information was presented to HM-1 personnel. If accurate metering was to be involved, HM-1 personnel would also have to be involved. It was crucial that a consistent message be delivered to all shifts. A basic form was created to collect the data at fires, which was then transferred to a master spreadsheet. This data collection took place over a nine-month period and resulted in 36 recordable incidents. There were many other incidents for which the atmosphere could have been metered, but HM-1 was either late arriving or incomplete data were recorded.

We quickly learned after the first few fires that it was not a matter of when or where but of how much HCN could be found at a fire. There were few incidents where no HCN was detected. In May 2008, the chief of operations issued a memo to the CFD explaining the metering that HM-1 personnel were conducting at fires; this document helped win the support of some of the more apprehensive officers. The memo explained that personnel would continue to monitor for CO at structure fires before removing self-contained breathing apparatus (SCBA) until meters with HCN sensors could be purchased. By the end of the nine-month data-collection period, enough information was collected to show the need for a stronger SCBA policy and more air monitoring at structure fires.

To assist with the fight, the CFD piloted the To Hell and Back IV video on cyanide poisoning for the CPTC. The film was presented to the department, thus allowing an additional point of view on the subject from someone outside the CFD. This film later debuted at FDIC 2009 and has since gone on to educate firefighters across the country. During this same training session, HM-1 personnel explained how the CFD needed to handle future calls.


It was difficult to determine a pattern based on the data collected. There were small fires, such as a pot on the stove that generated light smoke that contained high HCN levels, and there were room-and-content fires that should have produced higher HCN levels based on the amount of smoke, but these registered only in the single digits. It was difficult to explain, but it made the personnel look at what was heated or burned. It is impossible to predict the composition of the smoke and its harmful contaminants based on its color and characteristics. Merely heating a pot handle during a common “pot on the stove” call produces deadly levels of HCN and CO.

HM-1 responded throughout the entire city and county to collect data. Once on scene, HM-1 personnel worked in pairs to effectively meter the structure, strategically moving through it and comparing and documenting the readings from the three meters to check for consistency. Readings would be taken at similar locations inside the structures such as at the front door, the fire room, and the room farthest from the fire. Personnel even monitored the atmosphere outside the structure where crews were staging and at the pump panel and command post. Metering would take place at various times for comparison purposes such as immediately following the knockdown of the fire and during and following ventilation.

A recent kitchen fire in a garden apartment showed the CFD the importance of metering the atmosphere (photo 1). The fire was called in at 1749 hours and was knocked down quickly after causing damage to the end unit (Bravo side) of a two-story, 12-unit building. Approximately one hour and 25 minutes after the fire was under control, crews were asked to check on the units farthest away (Delta side) from the fire to ensure it was safe for occupants to enter the structure. The ladder company that entered those units reported a light haze of trapped smoke in the units and that a quick ventilation was needed.

(1) Apartment units pictured in the foreground posted high-level readings yet were farthest from the fire and had only moderate smoke trapped. (Photo by author.)

HM-1 personnel entered the structure and found an alarming reading of 79 ppm of HCN and 49 ppm of CO. These numbers were nothing new because we had been metering for a few months up to this point. However, the amount of elapsed time with such elevated numbers was new. We had not really seen anything of that magnitude so long after the fire was under control.


In October 2008, the command staff was presented with a list of recommendations based on the information learned during the nine-month data collection period. The numbers astonished the command staff, who quickly agreed on the need for increased protection for personnel. By the end of 2008, the purchase of 10 Toxi Rae II® single-gas meters and the writing of a standard operating guideline (SOG) for atmospheric monitoring at structure fires were both approved.

By spring 2009, the meters were placed in service on four rescue trucks, four hazmat support engines, and HM-1, and one was given to the chief of training. Metering is now taking place at every fire, from a pot on the stove to two-alarm multifamily dwelling fires. The SOG covers issues such as when to monitor, who is responsible for monitoring, when to calibrate, what to do if someone is expected of having HCN exposure, and how to provide care.


Since there is so much more to learn about HCN, the CFD is continuing to look for new ways to protect firefighters. The first and easiest way is to ensure SCBA are being worn properly and at every fire. CFD chief officers are enforcing our SOG by ensuring air monitoring is taking place prior to SCBA removal. SCBA use on all calls involving smoke is being monitored; firefighter self-rescue and air management training are being taught departmentwide. The CFD is also teaming up with the University of South Carolina—School of Public Health to look for other concerns and ways HCN can affect firefighters. Ideas for grant funding are being explored to conduct further atmospheric monitoring and firefighter exposure testing.

The path CFD took was a learning experience and resulted in great changes, and the overall reception by personnel is positive. These continuing changes came about from a progressive movement to better the department, not as a result of a negative incident or mandate. Because of this and the persistent training and education, the firefighters are better protected.

JASON M. KRUSEN is a 14-year fire service veteran and a captain with Haz-Mat 1 in the Columbia (SC) Fire Department. He is on the board of directors for the Cyanide Poisoning Treatment Coalition. He is a planning manager for the State Urban Search and Rescue Team, SC-TF1, and the Midlands Region IMT and a logistics manager for the Type II Collapse Search & Rescue Regional Response. He is also the project manager and instructor for E-Med Training Services, LLC. Krusen has an associate degree in fire service administration.

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