of potentially harmful pollutants to the environment. It was also asked to consider appropriate health-based approaches for demonstrating that an incineration facility meets and maintains established levels of health protection. Issues related to communication of information on waste incineration were also within the study charge. The committee was asked to consider types of information that should be provided to government officials, industry managers, and the general public to help them in future efforts to understand and weigh the risks associated with waste incineration and its alternatives. Finally, the committee was asked to consider factors that might affect public perceptions of waste incineration.
The committee was not charged to assess risks posed by any particular waste-incineration facility or to compare the risks of incineration with risks posed by various waste-management alternatives, such as landfilling. The committee focused its attention on wastes that have reached an incineration facility—it was not asked to address the collection or storage of wastes at, or their transportation to, any incineration facility; nor was it asked to consider treatment of residual ash away from a facility.
The principal gaseous products of waste incineration, like other combustion processes, are carbon dioxide and water vapor. And, like many combustion processes, incineration also produces byproducts such as soot particles and other contaminants released in exhaust gases, and leaves a residue (bottom ash) of incombustible and partially combusted waste that must be emptied from incinerator chambers and properly disposed. The composition of the gas and ash byproducts is determined, at least in part, by the composition of the wastes fed into an incineration facility. This feedstream composition can be altered by other waste-management activities, such as reducing the amount of waste generated, reusing materials, and recycling waste materials for use as feedstocks for various manufacturing processes.
The exhaust gases from waste incineration facilities may contain many potentially harmful substances, including particulate matter; oxides of nitrogen; oxides of sulfur; carbon monoxide; dioxins and furans; metals, such as lead and mercury; acid gases; volatile chlorinated organic compounds; and polycyclic aromatic compounds. Some pollutant emissions are formed, in part, by incomplete combustion that may in turn lead to the formation of pollutants such as dioxins and furans. The formation of products of incomplete combustion is governed by the duration of the combustion process, the extent of gas mixing in the combustion chamber, and the temperature of combustion. Good combustion efficiency depends upon maintaining the appropriate temperature, residence time, and turbulence in the incineration process. Optimal conditions in a combustion chamber must be maintained so that the gases rising from the chamber mix thoroughly and continuously with injected air; maintaining the optimal tempera-