Although long considered to be less toxic than firefighting suppression activities, overhaul and fire investigation activities do potentially represent both acute and chronic toxic atmospheric events. Carbon Monoxide (CO) and Hydrogen Cyanide (HCN) detectors, although appropriate for detection of CO and HCN, respectively, are not reliable indicators of total toxicity in the post-fire environment. New multisensory “orthogonal” technologies such as the Environics’ ChemPro100i provide the opportunity: (a) to detect a much more representative array of the toxic gases and vapors present in the overhaul environment; and (b) to alert operators that there is a toxic indication that requires them to “mask up” or exit that environment.
What Is Overhaul? Overhaul is the stage of firefighting in which fire suppression is complete, firefighters are searching for and extinguishing possible sources of re-ignition, and fire investigators may begin their search for the source of the fire. It is during this stage of firefighting, where there is no fire and little or no smoke in the environment, that a firefighter is likely to remove his/her Self-Contained Breathing Apparatus (SCBA) and work “barefaced.” Because SCBAs can be heavy and bulky, it is common practice with many firefighters not to wear SCBAs during overhaul.
Overhaul Poses a Real Toxicity Threat Building materials, furnishings, paints, plastics, and the electronics found in today’s buildings all have the potential to burn and decompose into acutely acting and chronically acting toxic gases and vapors. A number of studies have demonstrated that these toxic gases and vapors are present not only during suppression activities but also during the overhaul and investigation stages of an incident. This means that many potentially toxic and carcinogenic gases and vapors may be present during the overhaul process – including but not necessarily limited to: Carbon Monoxide (CO), Hydrogen Cyanide (HCN), oxides of Nitrogen (NO and NO2), Sulfur Dioxide (SO2), Polycyclic Aromatic Hydrocarbons (PAHs), Aldehydes (Formaldehyde, for example), acids (like HCl), aromatics (like benzene), and even Phosgene (created from the thermal decomposition of refrigerants). Some of these chemicals have acceptable warning properties, but many do not.
Chronic Carcinogens Are Potentially Not Measured Acutely toxic compounds produce effects immediately or soon after the exposure. CO and HCN represent two common acutely acting toxins found during overhaul operations. However, chronic toxins can accumulate over time, and symptoms may not present themselves for years after exposure. Bladder cancer in firefighters has often been suspected as resulting from chronic, long-term exposure to a variety of not fullyentified and/or quantified agents in the firefighting environment.
The conclusion of ATF Health Hazard Evaluation Report 96-0171 (by Gregory Kinnes and Gregg Hine – see reference 1 below) demonstrates the potential for toxic atmospheres to be present during overhaul and fire investigations: “Although the environmental sampling conducted during this investigation indicated that most contaminant concentrations did not exceed the relevant evaluation criteria, it still indicated that the potential for exposure exists. In addition, the sampling indicated that the potential for exposure to carcinogens existed to some extent.”
CO and HCN Do Not Work as “Canaries” CO and HCN sensors have been described as “overhaul” sensors to provide firefighters with some sense of security that they are unmasking in a “clean” atmosphere. However, in “Characterization of Firefighter Exposures during Fire Overhaul” (Bolstad-Johnson et al; see reference 2), the authors found that “CO concentrations did not predict concentrations of other products of combustion.”
That study was published in 2000 – before the wide acceptance of HCN monitors for overhaul work – but nonetheless does provide an additional clue that HCN, like CO, does not predict concentrations of other products of combustion. In addition to CO detectors, HCN detectors were used in the Bolstad-Johnson study – which points out that “Only four samples (out of 26 fires sampled) resulted in concentrations above the LOD (Limit Of Detection). None of these four samples had concentrations of HCN above 10 mg; hence, the concentrations could not be quantified, but were all well below 1 mg/m3.”
For reference purposes, the OSHA PEL (TWA) for HCN is 11mg/m3 (or 10 ppm), so the HCN levels monitored were well below potentially toxic levels. This is not to say, though, that CO and HCN may not be present during overhaul activities in significant and perhaps even toxic concentrations. Both CO and HCN have acute toxic effects. But the CO and HCN concentrations do not correlate with total toxicity of either acute or chronically toxic compounds. Put another way, CO and HCN sensors are not appropriate “canaries” for judging total toxicity (acute and chronic) in an overhaul environment.
Cost of Ownership for CO and HCN The electrochemical (EC) sensors used in CO and HCN detectors have a finite life and require periodic calibration. CO sensors last about two years, and HCN sensors last only about one year. Calibration gas for CO sensors is stable and inexpensive – but calibration gas for HCN sensors is expensive and short-lived. Using the cost structure from a popular name-brand company, the cost per year of owning a CO sensor is about $160/year; that estimate factors in the costs of sensor replacement and calibration gas. For an HCN sensor, the comparable cost is $675/year. The on-going yearly cost, therefore, of using a CO and HCN detector for overhaul detection would be about $805/year.
An “Orthogonal” Solution In gas detection the word “orthogonal” has come to be used to characterize detectors that use multiple non-redundant sensors to solve a detection problem. The Environics ChemPro100i is just such an orthogonal detector. While at its heart there is an aspirated Ion Mobility Spectroscopy (IMS) sensor, it uses this sensor with additional sensors and “fuzzy logic” to ify chemicals. The ChemPro100i has the ability to demonstrate warning for more threatening chemicals in the overhaul environment than any handheld detection technology.
Although the ChemPro100i has a substantially higher purchase cost, it does not have the calibration and sensor replacement costs that EC sensors bring with them. With the Guaranteed Cost of Ownership (GCO) program that comes with the ChemPro100i, maintenance costs are completely covered for the first five years of ownership (Ref: Environics SN-001 for more on the ChemPro100i GCO program). In the absence of wearing an SCBA, the ChemPro100i represents a more systematic approach to monitoring the overhaul process for toxic gases and vapors. If a toxic gas or vapor is present it directs the operator to “mask up.”
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References for additional information: 1. Gregory Kinnes, Gregg Hine, “Health Hazard Evaluation Report 96-0171 Bureau of Alcohol, Tobacco, and Firearms,” 11/1997
2. Dawn M. Bolstad-Johnson, Jefferey L. Burgess, Clifton D. Crutchfield, Steve Storment, Richard Gerkin, Jeffrey R. Wilson, “Characterization of Firefighter Exposures During Fire Overhaul,” AIHA Journal 9-10/2000, pp. 636-641
Other helpful references are: Michael Donahue, “Occupational Safety and Health Programs for Fire Investigators,” Fire Engineering, 2/2001;
F.D.J.R. Feunekes, F.J. Jongeneelen, H. v.d. Laan, F.H.G Schoonhof, “Uptake of Polycyclic Aromatic Hydrocarbons Amount Trainers in a Fire-Fighting Training Facility,” AIHA Journal, 1/1997 pp. 23-27;
John R. Hall, “Whatever Happened to Combustion Toxicity?” NFPA Journal, 11-12/1996, pp. 90-101; and
Dennis L. Rogers, “Characterization of Fire Investigator’s Exposure During Fire Scene Examination,” DuPage County Arson Task Force, DuPage County, IL, March 18, 2005.
____________________________ Christopher Wrenn is the Sr. Director of Sales and Marketing for Environics USA, a provider of sophisticated gas & vapor detection solutions for the military, 1st responder and safety markets. Previously Mr. Wrenn was a key member of the RAE Systems team. Chris has been a featured speaker at more than 20 international conferences and has written numerous articles, papers and book chapters on gas detection in HazMat and industrial safety applications.