Fire Safety Science Digital Archive

In this paper the effect of environmental variables on piloted ignition of wood is investigated both experimentally and theoretically. The environmental variables considered are the moisture content of the solid, wind speed and its oxygen concentration and external radiation. Simultaneous measurements of weight loss rate, ignition time, sample surface temperature, oxygen depletion and production of CO,, CO, total hydrocarbons, and water vapor were made. As expected, the presence of moisture delays the decomposition process and dilutes the decomposition products. The surface temperature and the evolved mass flux at ignition increased with increase in moisture content, decrease in oxygen concentration and increase in air velocity. A11 the ignition data are correlated according to an equation derived for surface temperature with convective and radiative heat losses. This equation reveals how the moisture content, air velocity, oxygen concentration and external radiation affect the ignition delay time. It also enables the determination of the critical incident heat flux below which piloted ignition does not occur.