Upward flame spread along flammable hollow cylindrical structure

Abstract

Hollow structure combustible, e.g. vertical drainpipe, is common in buildings, and can produce chimney effect once on fire. However, investigation on flame spread over the hollow structure solids has not been addressed yet. In this study, the hollow corrugated paper tube was chosen as the sample to experimentally study the flame spread characteristics under single-sided restriction. Here, 48 experiments were carried out by varying eight kinds of thicknesses (denoted by δ, 1–8 mm) and six kinds of inner diameters (d, 30–80 mm). The experimental results show that with the increasing inner diameter, the burning inside the sample changes from non-flame (regime I) to jet flame regimes (regime II). The effect of sample thickness on mass loss rate is less evident than that of sample inner diameter. Based on the laminar boundary layer theory and chimney effect, a calculation model of the mass loss rate inside the sample is proposed. Moreover, a minimum mass fraction of pyrolysis gas to produce regime II is obtained. In regime II, a dimensionless relationship between the jet flame height and the heat release rate is proposed. In addition, for flame spread over the outer surface of sample, dimensionless average flame spread rate has an exponential dependency on the dimensionless diameter. The results of this study can provide an important reference for fire prevention and fire protection design of high-rise buildings.