Width effect on upward flame spread

Numerical modelling of early flame spread in warehouse fires

Previous work has demonstrated that flame height is one of the two most important parameters determining the rate of vertical flame spread on a wall. Flame spread models rely on empirical flame height correlations of the form X-f = K(Q) over dot(/n), but there have been no carefully controlled experiments designed to establish the validity of such correlations and there are no data for values of (Q) over dot(/) less than c.25 kW/m. Two new sets of data are presented here, one based on experiments with 6 mm thick PMMA slabs (heights 25-250 mm, width 50-150 mm) as the fire source, measuring (Q) over dot (/) and X-f simultaneously. This set relates to the early stages of a wall fire when (Q) over dot(/) less than 30 kW/m. The other set of data was obtained with a vertical gas-fired panel which consisted of an array of 14 independent burners arranged to allow the aspect ratio of the burning surface to be varied. The data confirm that the flame height correlates with (Q) over dot(/), but reveal (inter alia) that there are two regions, for values of (Q) over dot(/) greater than and less than c. 20 kW/m. An existing upward flame spread model was modified to allow these two correlations to be incorporated to predict the development of a small fire on a vertical surface for these two regions, which would provide more realistic modelling information.

Flame height correlation and upward flame spread modelling

Incident wall heat flux distributions have been measured for square propane burner fire sources placed against the wall. Peak heat fluxes of 40-120 kw/m2 were measured for heat release rates of 50-500 kw/m2 and burner edge lengths of 0.28-0.7 m. Peak heat fluxes were found to be a strong function of heat release rate but were insensitive to flame aspect ratio or burner size. Correlations of the data were developed to represent the measured flux distributions. These correlations are intended for use in wall flame spread modeling.

Wall Incident Heat Flux Distributions Resulting From An Adjacent Fire

Influence of sidewalls on width effects of upward flame spread

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Papers

An Upward Fire Spread And Growth Simulation