Fire Safety Science Digital Archive

This report discusses the mechanisms of flame spread and extinction over a thermally thick PMMA surface in a low-oxygen-concentration flow, based on experimental investigations. The temperature distribution in the condensed phase when the oxygen concentration in an air current decreases was measured in detail using holographic interferometry and thermography. The energy balance in the condensed phase was investigated based on the detailed temperature distribution, and the dominant heat transfer path in a low-oxygen-concentration flow was clarified. The net heat transfer rate in the direction normal to the surface, Qy is little changed with a decrease in oxygen concentration, while the heat transfer rate in the direction parallel to the surface, Qx decreases with oxygen concentration. The total heat transfer rate, QT also decreases, due to the decrease in QX. The radiative heat loss from unburned surface to surroundings, QR increases with decreasing oxygen concentration. The balance of heat in the unburned fuel falls drastically due to the increase in the ratio of radiative heat loss to the total heat transfer rate, QR/QT. This leads to flame extinction.