Estimating Yields and Quantities of Mass Releases of Toxic Products from Fires

Abstract

The concentrations and doses of toxic substances received by those exposed to fire effluents determine the toxic hazards of a fire. The dose depends on the respiratory minute volumes of those exposed, the atmospheric concentrations of the toxic substances at their location, and the duration of exposure. The concentrations, in turn, depend on the dispersal of effluents from the fire, on the materials being burnt, and on the nature of the burning process. One method for assessing such hazards is to sample toxic species directly during an actual fire incident or during a full-scale reconstruction of a fire incident scenario. In most cases the critical period for fire hazards involves the first few minutes after ignition, so that opportunities for real-time sampling are limited, and full-scale reconstruction experiments can be technically challenging and extremely expensive, so are limited to a few cases. For both the acute life-threatening hazards and environmental hazards from fires, the assessment of toxic hazards therefore depends at least to some extent on fire modelling calculations involving the use of input test data on a range of parameters related to fire growth and development, combustion chemistry, and fire plume dispersal. Fire dynamics models vary from relatively simple algebraic calculations to complex computational fluid dynamics simulations. In all cases the methods involve making estimates of the changing mass burning rates and heat release rates of the fuels, the yields of a range of combustion products, and the dynamics of air entrainment and dispersal of the effluent plume. This chapter describes the basis of simple fire dynamics calculations and test methods designed to measure the yields of toxic combustion products under a range of different fire conditions as described in Chapter 2. Data are presented on toxic product yields from building fires and wildfires, and aspects of their application to full-scale fire hazard assessments in situations ranging from acute lethal scenarios to environmental contamination and health hazards.