A fire is complex physicochemical process that generate heat, light, combustion products and volatilized/aerosolized substrate chemicals. The nature of the fire directly affects the types and distribution of products generated [14-18]. This variation can be considerable in magnitude, even when attempts are made to duplicate experimental conditions [19]. In the case of real structural fires, combustion conditions are known to vary considerably both within and between fires [17, 20]. The combustion products generated reflect: molecular structure of the material, including additives such as fire retardants; type, quantity and mixture of materials; storage, container and building construction; temperature; oxygen content; decomposition pathways; and, fire type and evolution stage.
The variety of products generated during combustion is vast and irrespective of the exact fire conditions at the time. The general groups of combustion products generated [22-25] can be described and include: carbon dioxide; particulates such as carbon; carbon monoxide; undecomposed product, or monomers; unsaturated hydrocarbons including aromatic hydrocarbons and polycyclic aromatic hydrocarbons; saturated hydrocarbons; partially oxygenated organics including organic acids, aldehydes and ketones such as acrolein; partially nitrogenated and sulphurated organic compounds like propyl nitrile; partially halogenated organics like vinyl chloride; simple inorganic molecules like nitrogen oxides, sulfur oxides and hydrogen cyanide; and volatile metal/non-metal oxides or other metal/non-metal complexes such as arsine.
Minimal specific information is available regarding the combustion products generated in typical residential fires in modern houses [26,27]. Most of the scientific research into combustion products focuses on small-scale experiments of pure fuels that cannot be directly translated to the firefighting situation [25]. Those few studies that have considered actual firefighting environments tend to incorporate a large variety of fire types (residential, other structural and vehicle), and do not differentiate among them in presentation of results. In addition, the variation in residential fires internationally (due to differences in fuel loads, furnishing types, compartment size, layout and firefighting techniques) and over time (due to advancements in fire retardants, other additives and the development of new consumer products) brings into question the relevance of many of the early studies to modern firefighting approaches in the United States.
The majority of reported studies of firefighter exposure to toxic combustion products in actual fires focused on the aggregate exposure or dose accumulated from firefighting efforts overall [28-31]. This is also true for studies of firefighter exposure in training scenarios [32-33]. Some studies have focused on either the extinguishment/knockdown phase (in which the fire is brought under control) [34-35] or the overhaul/damping down phase (in which fire suppression is complete, and firefighters are searching the structure for hidden fire) [36-37]. The variability of actual fires (fuels, location, etc.) and the fire conditions makes it difficult to draw any conclusions about the relative concentrations of combustion products in extinguishment and overhaul phases of the firefighting from any of these studies. Jankovic et al. [38] took separate measurements during the extinguishment and overhaul phases of firefighting in 22 training and actual fires, including 15 residential fires. In general, many of the same air contaminants were present during both extinguishment and overhaul, but concentrations were lower during overhaul.
The routes of entry of airborne contaminants generated in a fire into the body include inhalation, ingestion, dermal, and injection. The most significant route of entry is through inhalation [1]. The contaminants (gases and particulates) can deposit or pass into the body through the lungs causing both acute and chronic adverse health effects. Despite the importance of this entry route, its significance within the firefighting environment should be considered in the context of firefighters’ use of self-contained breathing apparatus (SCBA) and their tactical methods.
Airborne contaminants (gases and particulates) generally will not be ingested because of good hygiene practices and the use of SCBA. The importance of the skin as an entry route is less certain, although one of the earliest cancer studies was conducted by Percival Pott investigating dermal soot exposure and scrotal cancer in chimney sweeps [2]. This was published more than 200 years ago. It is well established that polycyclic aromatic hydrocarbons, aromatic hydrocarbons, and acid gases will be absorbed directly from the vapor phase and penetrate the skin. The penetration rate is dependent on many factors and the dose is also affected by the body’s ability to de-toxify and excrete the contaminant. There is increasing evidence reported highlighting the importance of the skin as an entry route in the context of firefighting. Given the extensive use of SCBA within the firefighting environment, the importance of the skin as an entry route has likely been underestimated.
REFERENCES
[1] Menzie et al. Exposure to carcinogenic PAHs in the environment. Environmental Science and Technology, 26, 1278–1284, 1992.
[2] Pott, P. Chirurgical observations relative to the cataract, the polypus of the nose, the cancer of the scrotum, the different kinds of ruptures, and the mortification of the toes and feet. [London: Hawes, Clarke, & Collins]. In NCIM (1962), National Cancer Institute Monograph 10, 7‐13, 1775.
[14] Michal J. Toxicity of pyrolysis and combustion products of poly-(vinylchloride). Fire and Materials 1, 57-62, 1976.
[15] Michal et al. Toxicity of thermal degradation products of polyethylene and polypropylene. Fire and Materials 1, 160-168, 1976.
[16] Ruokojärvi et al. Toxic chlorinated and polyaromatic hydrocarbons in simulated house fires. Chemosphere 41, 825-828, 2000.
[17] Terrill et al. Toxic gases from fires. Science, 200, 1343-1347, 1978.
[18] Wang et al. Laboratory investigation of the products of the incomplete combustion of waste plastics and techniques for their minimization. Industrial Engineering and Chemical Research 43, 2873-2886, 2004.
[19] Dills RL, Beaudreau M. (2008). Chemical composition of overhaul smoke after use of three extinguishing agents. Fire Technology, 44, 419-437, 2008.
[20] DeHaan JD. Kirk's Fire Investigation. Pearson Education, Upper Saddle River, NJ, 2002.
[22] Rutkowski, J and Levin, B. Acrylonitrile-butadiene-styrene copolymers (ABS): pyrolysis and combustion products and their toxicity - a review of the literature. Fire and Materials 10, 93, 1986.
[23] Smith-Hansen, L. Toxic hazards from pesticide warehouse fires. In: Mewis et al.(eds) Loss Prevention and Safety Promotion in the Process Industries. Vol I. Elsevier Science 265, 1995.
[24] Andersson et al. Combustion products generated by hetero-organic fuels on four different fire test scales. Fire Safety Journal, 40, 439- 465, 2003.
[25] Kirk KM. Air contaminants at residential fire investigation scenes. Thesis, Queensland University of Technology, Brisbane, 2006.
[26] Blomqvist et al. Emissions from fires part II simulated room fires. Fire Technology40, 59-73, 2004.
[27] Blomqvist P. Emissions from fires consequences for human safety and the environment. Ph.D Thesis, 2005.
[28] Gold et al. Exposure of firefighters to toxic air contaminants. American Industrial Hygiene Association Journal, 39, 534-539, 1978.
[29] Treitman et al. Air contaminants encountered by firefighters. American Industrial Hygiene Association Journal, 41, 796-802, 1980.
[30] Brandt-Rauf et al. Health hazards of fire fighters: exposure assessment. British Journal of Industrial Medicine 45, 606-612, 1988.
[31] Caux et al. Determination of firefighter exposure to polycyclic aromatic hydrocarbons and benzene during firefighting using measurement of biological indicators. Applied Occupational and Environmental Hygiene, 17, 379-386, 2002.
[32] Feunekes et al. Uptake of polycyclic aromatic hydrocarbons among trainers in a fire-fighting training facility. American Industrial Hygiene Association Journal, 58, 1, 23-28, 1997.
[33] Laitinen et al. Firefighting trainers’ exposure to carcinogenic agents in smoke diving simulators. Toxicology Letters, 192, 61-65, 2010.
[34] Lowry et al. Studies of toxic gas production during actual structural fires in the Dallas area. Journal of Forensic Sciences, 30, 59-72, 1985.
[35] Austin et al. Characterization of volatile organic compounds in smoke at municipal structural fires. Journal of Toxicology and Environmental Health, Part A, 63, 437-458, 2001.
[36] Bolstad-Johnson et al. Characterization of firefighter exposures during overhaul. American Industrial Hygiene Association Journal, 61, 636-641, 2000.
[37] Burgess et al. Adverse respiratory effects following overhaul in firefighters. Journal of Occupational and Environmental Medicine, 43, 467-473, 2001.
[38] Jankovic et al. Environmental study of firefighters. Annals of Occupational Hygiene, 35, 581-602, 1991.
There are many combustion byproducts observed in structure fires, but the major ones include carbon monoxide, nitrogen dioxide, sulfur dioxide, hydrogen cyanide, hydrogen chloride, hydrogen fluoride, hydrogen bromide, phosphoric acid, nitric acid, sulfuric acid, volatile organic compounds (VOCs), aldehydes, polycyclic aromatic hydrocarbons (PAHs), and phthalate diesters. The following tables provide a brief overview of many of these combustion byproducts. The table of combustion byproducts (below) contains the information from past research demonstrating the levels of materials of operational interest to fire suppression, overhaul, deposition on surfaces, and, in one case, deposition onto protective equipment. These materials include known and suspected carcinogens and demonstrate the need for dermal penetration information to be developed at concentrations of operational interest to firefighters. The second table focuses on the byproducts that are predominantly inhalation threats at the concentrations of operational interest. These materials are not of high interest in the proposed study as they can be managed with proper self-contained breathing apparatus usage.
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In addition to the products of combustion mentioned above, there are several emerging threats of high interest in the contamination control realm. The first, and most widely discussed, are the polyfluoroalkyl substances (PFAS). The PFAS of highest interest include perfluorooctanoic acid (PFOA), perfluorooctanesulfonic acid (PFOS), and perfluorohexanesulfonic acid (PFHxS). PFAS exposures have been studied extensively [65-67]. They are ubiquitous in the environment and routinely found in food and dust. PFAS are used due to their specific properties such as high friction resistance; resistance to heat and other chemical agents; low surface energy; as well as water, grease, oil, and dirt repellency. The most significant exposure pathway for the general population is proposed to be through sources such as food, water, and dust [67-68]. In the firefighting context, there are two additional sources for potential exposure: firefighting foam and surface treatments on textiles incorporated into turnout gear.
Due to the prevalence of PFAS-related substances being linked to aqueous film forming foam (AFFF), it is also important to understand the interactions of the foam concentrates and the operational dilutions, or finished foam (range from 1 to 6 percent) with human skin. These AFFF foam concentrates rely upon fluorinated surfactants plus foam stabilizers to produce fluid aqueous films for suppressing hydrocarbon vapors. It should be noted that all foams pose both short-term and long-term environmental risk if released due to their inherent physico-chemical properties and toxicities such as chemical oxygen demand, biochemical oxygen demand, and environmental persistence. While the fluorosurfactants used in AFFF has changed from PFAS-based to 8:2 fluorotelomer and 6:2 fluorotelomer in response to regulatory issues, concerns remain.
There is little, if any, data reported in the literature characterizing the extend of firefighter exposures and the significance of the exposure pathways in the context of PFAS and AFFF use, including whether PFAS skin absorption poses a significant risk to firefighters. Franko reported dermal penetration of PFOA occurred, but the penetration was slow (ca. 48-69% over 24 hours) and the penetration rate was dependent on its ionization state [69].
REFERENCES
[65] Fitch F. Firefighting foams in Foams: physics, chemistry and structure. Springer-Verlag London, Ed Ashley J. Wilson, 1989.
[66] Buck et al. Perfluoroalkyl and polyfluoroalkyl substances in the environment: terminology, classification, and origins, Integr Environ Assess Manag. 7:513, 2011.
[67] ATSDR. Toxicological profile for Perfluoroalkyls. 2015.
[68] Froome et al. Perfluorinated compounds- exposure assessment for the general population in Western countries. Int. J. Hyg. Environ. Health. 212: 239, 2009.
[69] Franko et al. Dermal penetration potential of perfluorooctanoic acid (PFOA) in human and mouse skin. J. Tox. Environ. Health Part A. 75: 50, 2012.
Flame retardants, especially the polybrominated diphenyl ethers (PBDEs) and phosphate ester-based, are also of high concern. PDBEs are flame-retardant chemicals; there are 209 possible substances that are referred to as congeners [70]. The three PDBEs of highest concern include pentaBDE (used in foam for cushioning in upholstery), octaBDE (used in plastics for business equipment), and octaBDE (used for electronic enclosures)] [70]. The primary route of exposure of PBDEs is via ingestion of contaminated dust as the PBDEs are physically mixed into consumer products (versus chemically bound). This is estimated to account for 80-90% of the total PBDE exposures in the general population. In the firefighting context, increased doses via dermal exposure must be assessed as Alexander and Baxter demonstrated that firefighter exposures are much higher than that of the general population mainly due to contaminated personal protective gear and direct exposures at fire scenes [71].
Abdallah et al. demonstrated the dermal absorption of eight PBDEs using EPISKIN as a surrogate for human skin [72]. They found that less brominated congeners penetrated the skin faster, but the higher PBDEs displayed greater skin absorption and therefore represent slower releases but significant systemic circulation [72]. This is an excellent first step in range finding that must be backed with human skin studies.
As environmental regulations were emplaced for the PBDE-based flame retardants, phosphate-based flame retardants (PFRs) became more popular. Unfortunately, these replacement chemicals have many of the same characteristics of the PDBEs which made them environmentally persistent. Currently, data exists to suggest that chlorinated PFRs are carcinogenic and cause severe human health effects. In addition, triphenyl phosphate (TphP), diphenylcresylphosphate (DCP), diethylphosphonic acid, tricresylphosphate (TCP), tris(chloropropyl)phosphate (TCPP), and tris(2-chloroethyl)phosphate (TCEP) are not recommended alternatives due to human health effects and environmental persistence [73]. Little is known about the dermal absorption and penetration of these materials.
REFERENCES
[70] ATSDR Toxic Substances Portal. Public Health Statement – Polybrominated Diphenyl Ethers (PBDEs). March 2017. Accessed: https://www.atsdr.cdc.gov/ToxProfiles/tp207-c1-b.pdf.
[71] Alexander, B. and Baxter, C. Flame-retardant contamination of firefighter personal protective clothing – A potential health risk to firefighters. J Occup Environ Hyg. Sep;13(9):D148-55, 2016.
[72] Abdallah BPDE paper
[73] I. van der Veen, J. de Boer. Phosphorous flame retardants: Properties, production, environmental occurrence, toxicity, and analysis, Chemosphere 88 : 1119–1153, 2012.
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