Exposure Assessment

Variable Effects of Fire on Human Health

Human diversity – physical and cultural – partially accounts for the variable health impacts of fire. Individual responses to biomass smoke are conditioned by personal biophysical histories (e.g., genotype), previous and current exposures to air emissions and water contaminants, and variable coping strategies (American Thoracic Society 2000). Some segments of the population present symptoms of smoke inhalation at dose-exposures that appear not to affect others or that have a very low impact on others (Evans and Campbell 1983; Therriault 2001). The groups who are particularly vulnerable to biomass smoke are young children, the elderly, people with pre-existing conditions, and smokers.

The effects of fire due to smoke are highly variable because of the spatially variable nature of smoke. Spatial variability in smoke results from irregularities in its dispersion from a combustion site. In addition, the components of smokeand their relative proportions vary from one fire to the next. In higher intensity fires carbon dioxide, methane, and water are the principle emissions. Harmful gases (carbon monoxide, methane, nitrogen oxides, sulfur oxides, hydrocarbons, polynuclear aromatic hydrocarbons, aldehydes, free radicals) are formed during incomplete combustion that can occur in lower intensity fires or smoldering following high intensity fires.

Seasonal weather differences may affect health outcomes in the South differently than in other regions (Schwartz 1994). In the South air quality is at its worst during the summer while in the North air pollution is worse during the winter months. Some propose that air pollution does not complicate winter-time respiratory conditions in the South to the same degree as it does in other regions (Schwartz 1994). Others argue that regional differences in temperature and humidity do not affect patterns of respiratory illnesses associated with air pollution (Dockery and Pope 1994). Despite the unique qualities of the South, research conducted in other regions is incredibly helpful in improving our understanding of the relationship between human health and forest fires in general.

It is difficult to make general assessments of the health risks from biomass smoke as a whole. Information about the relation between human health and single constituents of biomass smoke is more abundant in the scientific literature than information about the health effects of some combination of constituents. Knowledge of the combined effects (additive, potentiated, and synergistic) of the multiple constituents of biomass smoke is limited because most research to date examines the effects of single constituents. Yet, people experience biomass smoke as a complex mixture of chemical compounds rather than as isolated components. Even if scientific case studies of the relation between human health and biomass smoke from particular forest fires were plentiful, generalizations could only be made with caution since the constituents of smoke and their relative proportions vary from one fire to the next.

Exposure Among the General Public

The impacts of smoke on public health are most visible in hospital and emergency rooms. Hospital admissions and emergency room visits typically rise in communities that have been exposed to smoke, sometimes by as much as 52% in severe cases (Mott and others 1999). Patients in these communities have breathing problems, acute bronchitis, chronic obstructive pulmonary disease, asthma, and chest pain (Mott and others 1999; Schwartz and others 1993). Associations also exist between ozone increases and hospital admissions, as well as between deaths and increases in particulate matter. Biomass smoke does not always cause asthma:a study in Australia found no increase in hospital admissions for acute asthma in association with bushfires (Cooper and others 1994).

Long-term exposure to smoke may also increase risks of developing more serious chronic illnesses such as cancer (Therriault 2001), and respiratory and vascular disease (Schwela and others 1999; Tan and others 2000).

Exposure Among People Who Work On or Near Fires

Firefighters encounter unique health risks while performing their occupational duties. The experiences of fire workers differ from those of the general public. They are exposed to unusual concentrations of hazards and pollutants with atypical frequencies of exposure. Physical fitness, work practices, meteorology, and fire characteristics are some sources of variation in health outcomes among individual firefighters. Fortunately there are numerous safety programs and governmental regulations for risk management to mitigate potential harmful consequences and protect the health of firefighters.

Two occupational factors that make fire workers a unique subgroup of the populationare proximity to fire events and dose-exposures to air emissions. The general public and fire workers have similar responses to forest fires, but their dose-exposure patterns differ. Fire workers tend to be relatively physically fit. Among the general public, adverse health effects appear in briefer time periods and at lower dosages (Brauer 1999; Ostermann and Brauer 2000).Within the fire crew population, individual exposures differ according to the work practices of the particular firefighter (McMahon 1999), his/her location relative to the fire, and the amount of time he/she spends at that location. At a prescribed burn, variability in exposure to pollutants occurs within a group according to each person’s particular duties. For instance, Lighters and Sawyers have higher benzene exposures due to the use of gasoline in their drip torches and chainsaws. Fireline Holders and Attack Crew have higher carbon monoxide exposures due to their proximity to the flames and denser smoke.

The gender of fire workers influences stress experiences, with women experiencing emotional and acute physical stress more often than men. Ethnicity also influences stress with Native American firefighters experiencing less stress than Caucasian and Asian firefighters. Thereare no significant differences in coping strategies between age groups, between women and men, or between ethnic groups.

Shift duration influences health risks among firefighters. Wildland firefighters typically work shifts of8 to12 hours or more. In some situations, wildland firefighters are at or near a burn site over a period of days or weeks where, even during their off-shift time, they are exposed to biomass smoke (Materna and others 1992). In other situations, some portion of the work shift is spent in transit to and from the fire site and in other places some distance from the fire thus reducing the duration of a firefighter’s exposure to biomass smoke (Reinhardt, Ottmar, and Hanneman 2000). Firefighters may be exposed to unsafe levels of pollutants for punctuated time periods, but not continuously for an entire work shift.

Variations in meteorological patterns, including wind speed and direction, can produce variable health impacts. High wind speeds keep smoke in the breathing zone of firefighters increasing their exposure to pollutants in biomass smoke (McMahon 1999). In these cases, firefighters are more likely to exceed occupational limits for the inhalation of carbon monoxide and respirable irritants such as particulate matter, acrolein, and formaldehyde (McMahon 1999).

Fire workers are exposed to variable levels of air emissions and chemical toxins. One study revealed that firefighters working in forested areaswere exposed to toxins from herbicides that were applied to forests immediately prior to burning (Malilay 1999). Other research demonstrated that the presence of herbicides from an application preceding a forest fire were not detectable in smoke (Malilay 1999).

Gharabegian and others (1985) investigated noise exposures among several groups of fire workers including, fire line/camp crews, helipad crews, and ground crews at an airbase. 100% of helipad crew members, 100% of portable pump operators, and 30% of those hot shot crew members who used chain saws received noise doses during a 14-hour work shift that exceeded OSHA allowable limits. However, among the fire line work group as a whole, only 10% of the members received a noise dose level above 100% of the OSHA allowable limits.

Firefighter injuries and deaths may occur.

Exposure to Fire by Sensitive Sub-Groups of the Population

Children (Schwartz 1994; Ostermann and Brauer 2000), the elderly (Schwartz 1994), and people with pre-existing health problems (Mott and others 1999) appear to be particularly sensitive to smoke. Asthmatic children in Birmingham, Alabama experienced a decline in lung functioning when levels of particulate matter in the air increased (Schwartz and others 1993). Children with and without pre-existing asthma conditions experience more respiratory symptoms when particulate matter and ozone concentrations increase (Schwartz 1994). Following exposure to air pollution caused by burning wood, children aged 1-5 years old experience lung dysfunction sooner than people of other ages (Ostermann and Brauer 2000).

Hospital admissions among the elderly for pneumonia and COPD (chronic obstructive pulmonary disease) increase in association with increases in particulate matter (Schwartz 1994). A study in Birmingham, Alabama showed that hospital admissions of elderly people for pneumonia and COPD increased one day after there was a incident of high particulate matter in the air (Schwartz 1994).

Exposure to Fire and Psychosocial Wellbeing

Exposure to forest fires impacts psychosocial wellbeing (Evans and Kantrowitz 2002). Psychology is a critical mediating factor for overall wellbeing. A person’s psychological condition influences the biophysical consequences of fire (Evans and Campbell 1983). It is also the case that if a person has physical illnesses or diseases resulting from forest fires, he/she may develop psychological problems such as depression or anxiety (Evans and Campbell 1983). It is possible that ethnicity influences psychological symptoms and that minorities are more vulnerable to psychological distress. For example, one study showed that Mexican-American children (not children of any other ethnic group) developed clinical PTSD following a fire disaster (Jones and others 2002). Psychological issues are not always recognized as a problem in need of attention. Sometimes, responsibility for psychological issues is considered to be a private problem.

Psychosocial effects may vary in association with the behavior and characteristics of particular fires. Psychosocial outcomes vary according to an individual’s experiences, perceptions, interpretations, and coping mechanisms. Fires have different effects on different individuals: within a community different individuals have different responses. An individual’s personal relationships, and social contexts have a great influence on his/her attitudes and behaviors related to fires. Likewise, fires have different effects on different communities: all communities within the South will not respond to forest fires in exactly the same way.