Self-extinction of methanol fire in tunnel with different configuration of blocks

摘要

Preventing the fresh air from reaching the fire seat by sealing the portals or placing obstructions is a promising approach to put out a fire in long tunnels. A series of fire tests using methanol fuel with nominal heat release rates of 5.6 kW and 11.2 kW were carried out in a 1/20 reduced-scale model tunnel with the sizes of 20.8 m long, 0.45 m wide and 0.23 m high to explore the impact of blockage in tunnel on the effectiveness of fire-fighting. Blocks of two configurations were considered, i.e., one is down-standing blocks and the other is upward blocks. The blockage ratio was fixed at 65% and two blocks were symmetrically positioned at varying distances. With down-standing blocks at 8 m, 6 m and 4 m, the self-extinction times reduces by approximately 11%, 34% and 47% respectively for a 5.6 kW fire and by 20%, 30% and 42% respectively for an 11.2 kW fire. The shorter the distance of the blocks to the fire seat, the quicker the time to self-extinct. The reduction in self-extinction time with blocks at 10 m is insignificant. A similar result was obtained for upward blocks at varying distances. Comparably, the down-standing block makes the fires extinct more quickly than its counterpart. The presence of blocks significantly promotes the mixing of smoke layer and accelerates the descent rate of smoke layer, which results in highly vitiated supplying air approaching fire seat thus a reduction in the time to self-extinct.