Fire spread and flame length in large-scale tunnel fires

An analysis of fire spread during four large-scale fire tests that were performed in the Runehamar tunnel in Norway is presented. The fire loads consisted of mock-ups simulating a Heavy Goods Vehicle (HGV) trailer. The fire spread downstream of the HGV trailer mock-ups was studied, both to large targets with the same type of commodities as used in the trailer mock-up for each tests, and to small pieces of wood and plastic poles placed at different distances from the fire. The purpose was to determine a critical distance for fire spread between HGV trailers for different heat release rate histories. The time to ignition of a second object and fire spreading distances were estimated from post-visual observations and temperature measurements. Correlations for flame length were developed from the experimental results. Since the average temperature of the cross-section often is used to estimate fire spread, results from a model for the average temperature were compared with the measured temperatures.