In previous studies, the significance of synergistic action brought about by animal exposures to combinations of elements found within the combustion products in a mass fire environment was identified. An experimental program was undertaken to further define the life hazard in a mass fire environment resulting from exposures to these combustion products. Studies included exposures to combinations including the variables of carbon monoxide, temperature, oxygen, carbon dioxide, sulfur dioxide, nitrigen dioxide, hydrogen cyanide, the presence of smoke (particulate matter), and all of the trace constituents to be found. The data from these tests and the results of the histopathological studies were reviewed in an effort to define the significance of human explosure to combustion products as found within the mass fire environment.