A study of critical conditions in mine fires

In the present analysis, time-dependent calculations are made to determine the size of a stationary source fire within a ventilated duct (or passageway) necessary to ignite a combustible duct liner (or distributed fuel elements, such as timber sets). Heat transfer to the combustible surface includes both convective and radiative components while heat is conducted into the combustible and re-radiated to the surroundings. The combustible is assumed to ignite when the net heat transfer to its surface is sufficient to raise the surface temperature to some minimum temperature, defined as the ignition temperature. A non-dimensional parameter, whicl characterizes the source-fire intensity in the presence of ventilation flow, emerges as a parameter for a criterion of the critical conditions. The results of these calculations indicate that the minimum fire size necessary for ignition increases with increasing ventilation rate and increasing duct cross-section. These results are compared with experimental data obtained from fires in a duct measuring 0.8 m×0.8 m ×11, m long and a full-scale gallery mesuring 2.4 m×2.4 m×65 m long. Agreement between the theory and the data is good.