Two full scale pilot fire experiments in a tunnel

Two full scale pilot experiments were carried out in a tunnel in a limestone quarry 45 m below ground. The tunnel was 140 cm long, 6 m wide and 5 m high, and had natural calcite rock surfaces which were unprotected and without reinforcements. The first experiment was designed to simulate a fire in a subway car stalled in a tunnel. The second experiment simulated the case when one car in a queue of cars in a tunnel catches fire. Forced ventilation of fresh air at the rate of 7 m3/s was used. The fire load was made of wood cribs (moisture 17 %) nailed together in a way that allowed an air space of 50 % of the total volume. Temperatures of air, rock surface of the walls and the ceiling and temperatures of the steel and concrete columns placed on the floor were recorded on several locations. Also, concentrations of O2, CO2 and CO and air flow velocities were measured close to the exit of the tunnel. Fuel burning rate was determined by measuring the mass loss of wood on a weighing platform. Smoke level and visibility were observed visually close to the exit. The original uncorrected plottings of the measured data are given in the Appendices. In the first experiment the fire load of 7600 kg was distributed over an area of 3,2 m x 48 m. After ignition at one end of the tunnel the load burned without flashover with a constant velocity of 0,7 mm/s for 21,5 hours. In the second experiment the fire load consisted of eight piles of wood cribs, 1,6 m x 1,6 m of area and 0,8 m of height each with a mass of 500 kg. The free space between piles was 1,6 m. Two adjacent piles were ignited simultaneously at one end. As they burned, a peak power of 8 MW was obtained, but the third pile was not ignited. During both experiments 10 - 20 cm thick layers of rock scaled off the walls and the ceiling in regions close to the fire. Theoretical calculations based on existing room fire codes did not reliably predict occurrence of flashover.