Predicting toxic gas concentrations resulting from enclosure fires using the local equivalence ratio concept linked to fire field models

Wang, Zhaozhi (2007) Predicting toxic gas concentrations resulting from enclosure fires using the local equivalence ratio concept linked to fire field models. PhD thesis, University of Greenwich.

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Abstract

The central idea behind the newly developed toxicity model is the use of the Local Equivalence Ratio (LER). The species yields as functions of the Global Equivalence Ratio (GER) and temperature are input parameters of this model. Correlations for most building materials are available from small-scale fire experiments. Similar approaches to this method are also developed using the CO/CO2 and H2/H2O mole ratios. The LER methodology is further refined by an approach which divides the computational domain for the calculation of toxic gases into two parts, a control region in which the toxic gases are dependent on the LER and temperature, and a transport region in which the toxic gas concentrations are dependent on the mixing of hot gases with fresh air.

The toxicity model is then extended to two-fuel cases. In the two-fuel model, the LER is a function of the two mixture fractions, which are used to represent the mixture of the two different fuels, oxygen and combustion products. This model is useful in simulating residential fires, in which wood lining of sidewalls or ceilings is the second fuel.

Finally, the transportation of HCI within fire compartments is considered. A mathematical model is developed to simulate the exchange of HCI between gas boundary and wall surfaces and the reaction of HCI with walls.

All the toxicity models developed in this study can be integrated into the practical volumetric heat source approach and the Eddy Break-up (EBU) combustion model typically used in practical engineering analysis.

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