Variable Effects of Fire

Human diversity – physical and cultural – partially accounts for variable health impacts.  Individual responses to biomass smoke are conditioned by personal biophysical histories (e.g., genotype), previous and current exposures to air pollutants 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.

Meteorology also confounds relationships between biomass smoke and human health. For instance, wind patterns disperse smoke from a combustion site in irregular ways thus producing spatial variability in health impacts.  The southern United States has particular meteorological traits (e.g., temperature, humidity) and ecological characteristics that dissuade researchers from using studies conducted in other regions of the United States to design forest management plans and to assess human health impacts.  Seasonal weather differences may affect health outcomes in the South differently than in other regions (Schwartz 1994).  In all regions of the United States, respiratory problems are most common during the winter.  In the South air pollution 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 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).  This issue is one among numerous instances of the overall uncertainty in the research literature about the relationships between smoke and human health.

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.