Chapter 27 describes the history and development of techniques for measuring heat release rate (HRR). This chapter outlines features and details of today’s preferred instrument for measuring bench-scale HRR—the cone calorimeter. Other cone calorimeter measuring functions are

The Cone Calorimeter

Width effect on upward flame spread

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

Experimental measurements of upward flame spread on a vertical wall with external radiation

Influence of sidewalls on width effects of upward flame spread

A series of upward flame spread tests on different wood products was carried out on 2.4 m and 7.2 m high wall assemblies. The ignition source was a 1.2 m wide and 0.1 m deep propane diffusion burner applied usually at a rate of 100 kW. The measurements included gas and surface temperatures, heat fluxes to the specimen, rate of heat release, etc. After an initial growing fire, a period of decay was observed until the lower parts of the wall started to burn through. If the rear side of the board was insulated, a second phase of increased flame spread was observed, whereas in the case of a conducting substrate the intensity of the fire remained low. A thermal flame spread model was successfully applied to simulate the rate of heat release as a function of time.

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Kokkala

Papers

Upward Flame Spread On Wooden Surface Products: Experiments And Numerical Modelling