Fire Safety Science Digital Archive

Following an earlier report which dealt with measurements of the rate of smoke spread and the depth of the smoke layer in experimental fires in a disused railway tunnel representing a pedestrian mall, data are now given for the temperature and opacity of the smoke layer. The fall of temperature of the smoke layer as it passed along the tunnel could be accounted for entirely by convection and radiation transfer to the walls and floor of the tunnel so that there seems to have been little mixing of the layer with the cold air underneath, a factor which could also lead to a fall in temperature along the tunnel. One smoke test was made outside the tunnel under a canopy. This emphasised the dependence of smoke spread on the wind conditions and showed that smoke logging to a low level could occur even when the smoke was not completely confined. Values can be derived for the optical density of the smoke produced by burning a given weight of kerosine in a given volume, enabling an estimate of the visibility to be derived in other comparable situations where the burning rate and mixing conditions are known. The values obtained exhibit substantial variation so that the precision of an estimate of visibility is low, though sufficient for the present purpose. Such variation has a bearing on the problem of relating the behaviour of materials in a smoke test to some assumed real fire situation, a problem which itself falls outside the scope of this report.