Health Effects of Smoke

National Review of Health Effects

In 1996, the Environmental Protection Agency (EPA) conducted an extensive review of the science relating human health effects to particulate matter (PM), the principal pollutant of concern from fires (EPA 1996). The review found that (1) epidemiological studies suggest a variety of health effects at concentrations found in several U.S. cities and (2) ambient particles of greatest concern to health were those smaller than 10 micrometers in diameter. Results of efforts to trace the physiological and pathological responses of the body to PM are unclear, and demonstration of possible mechanisms linking ambient PM to mortality and morbidity are derived from hypotheses in animal and human studies. It is known, however, that PM produces physiological and pathological effects by a variety of mechanisms, including:

• Increased airflow obstruction by PM-induced narrowing of airways.
• Impaired clearance of lung pathways caused by hypersecretion of mucus caused by PM exposure.
• Lung responses to PM exposure including hypoxia, broncho-constriction, apnea, impaired diffusion and production of inflammatory mediators.
• Changes in the epithelial lining of the alveolar capillary membrane that increase the diffusion distances across the respiratory membrane, thereby reducing the effectiveness of blood gas exchange.
• Inflammatory responses that cause increased susceptibility to asthma, chronic obstructive pulmonary disease (COPD) and infections.

Recent information also suggests that several sub-groups within the population are more sensitive to PM than others. Children are more likely to have decreased pulmonary function, while increased mortality has been reported in the elderly and in individuals with cardiopulmonary disease. Asthmatics are especially susceptible to PM exposure. In addition, coarse (2.5 to 10µm) particles from road dust or windblown soil were found to have less toxicity than fine particles (less than 2.5µm) that include acid aerosols, diesel emissions, smoke from fires, and potentially carcinogenic PAH compounds.

Occupational Exposure to Wildland Fire Smoke

Wildland firefighters and fire managers have long been aware that smoke exposure occurs during their work (Reinhardt and Ottmar 1997; Sharkey 1997). Although the long-term health effects from occupational smoke exposure remain unknown, the evidence to date suggests that brief, intense smoke exposures can easily exceed short-term exposure limits in peak exposure situations such as direct attack and holding firelines downwind of an active wildfire or prescribed burn. Shift-average exposure only occasionally exceeds recommended instantaneous exposure limits set by the American Conference of Governmental Industrial Hygienists (ACGIH), and rarely do they exceed Occupational Safety and Health Administration (OSHA) time weighted average (TWA) limits (Reinhardt and Ottmar 2000; Reinhardt and others 2000). Overexposure increases to 10 percent of the time if the exposure limits are adjusted for unique aspects of the fire management workplace; these aspects include hard breathing, extended hours, and high elevations, all factors which intensify the effects of many of the health hazards of smoke (Betchley and others 1995; Materna and others 1992; Reinhardt and Ottmar 2000; Reinhardt and others 2000). It could be argued that few firefighters spend a working lifetime in the fire profession, and thus they should be exempt from occupational standards that are set to protect workers over their careers. But this argument is irrelevant for irritants and fast-acting health effects such as eye and respiratory irritation, headache, nausea, and angina. An exposure standard specifically for wildland firefighters and appropriate respiratory protection may need to be developed (Reinhardt and Ottmar 2000).

In spite of the studies that have been done, major data gaps remain:

• In the area of health hazards, not enough evidence is available to defend the commonly cited "inert" classification of total and respirable particulate in dust and smoke; there is little knowledge of the occurrence of crystal- line silica in dust at fires; and there is incomplete characterization of aldehydes and other respiratory irritants present in smoke (Reinhardt and Ottmar 1997, 2000).
• The differences in smoke exposure between large and small wildland fires have not been characterized in spite of the fact that one or two crews extinguish the vast majority of wildfires (Reinhardt and Ottmar 2000).
• The long-term health experience of wildland firefighters is unknown, although anecdotal reports and the biological plausibility of cumulative health effects indicate a potentially greater incidence of disease and death than in the general population of workers (Booze and Reinhardt, in press; Sharkey 1997).

Although data gaps remain, enough information has been gathered to chart a course to alleviate many of the overexposures. Respiratory protection is available for irritants such as aldehydes and particulate matter but not for carbon monoxide. Respirators can be heavy, hot, and impede the speed of work, but some new models are light, simple and could be worn only when needed (Beason and others 1996; Rothwell and Sharkey 1995). The entire costly process of medical evaluations, fitness testing, maintenance, and training must be employed if respirators are to be used. But there are immediate benefits to reducing respiratory irritant exposure. Small electrochemical dosimeters can pro- vide instant warnings about carbon monoxide levels in a smoky situation, and fire crew members equipped with respirators and carbon monoxide monitors have all the protection necessary to stay and accomplish objectives safely and withdraw when the carbon monoxide levels become the limiting factors (Reinhardt and others 1999). In the future, a respirator for use during wildland fires may be developed that offers warning and protection against carbon monoxide as well. Although some work has been done in this area, we need more significant development. Smoke exposure is a hazard only a small portion of the time and is manageable because the situation where it occurs can be predicted. A long-term program to manage smoke exposure at wildland fires could include (1) hazard awareness training, (2) implementation of practices to reduce smoke exposure such as rotating crews and providing clean air sites, (3) routine carbon monoxide monitoring with electronic dosimeters, (4) improved recordkeeping on accident reports to include separation of smoke related illness among fireline workers and fire camp personnel, and (5) improved nutritional and health habits. Fire management practices such as crew rotation, awareness training, and carbon monoxide monitoring can mitigate the hazard and allow firefighters to focus on the job of fire management, lessening the distraction, discomfort, and health impacts of smoke exposure (Reinhardt and Ottmar 2000).

Research Issues

A number of wildland fire health effect research issues flow from the EPA staff report (Clean Air Scientific Advisory Committee 1995) and occupational health exposure studies.

Research into the health effects of particulate matter is largely based on epidemiological studies conducted over long periods in urban centers with high hospital admittance or large air quality databases, or both. Consequently, inadequate information is available that relates short-term, acute smoke exposure (such as would be experienced by a visitor to a National Park or to a community near a wildfire) to human health effects. As a result, little or no specific guidance is available to wildland fire managers, air quality regulators, or public health officials who need to responsibly judge the public health risks of exposure to extremely high smoke concentrations. This gap in knowledge was clearly evident during the 1988 Yellowstone fires and later wildfire events when quick decisions had to be made on how best to protect public health in communities near major wildfires (WESTAR 1995). The best available guidelines are those published by EPA (1999) for assessing the risk to health from air pollution (table 8-1). These guidelines may or may not reflect the specific hazards of pollutants from fires, which will have a different chemical composition.

The long-term health effects of smoke exposure to wildland firefighters are unknown in spite of anecdotal evidence that indicates the possibility of a greater incidence of cardiopulmonary disease and death than in the general population. Although carbon monoxide monitoring and respiratory protection can mitigate the hazard, personal protection equipment is still needed that allows firefighters to work effectively without discomfort or distraction (Reinhardt 2000).