Model scale tunnel fire tests with point extraction ventilation

Experimental results are presented from a series of tests in a model scale tunnel (1 : 23). This study focuses on single and two-point extraction ventilation systems to complement a previous study with the same apparatus using longitudinal ventilation only. The point extraction ventilation system in this test series was operated under different fire loads and flow conditions of either forced longitudinal ventilation or natural ventilation. Wood crib piles were used to simulate the fire source, which was designed to correspond to a 'heavy goods vehicle' fire load at full scale. The parameters varied were the number of wood cribs, the longitudinal ventilation velocity, and the arrangement of the extraction vent openings and their exhaust capacity. Measurement data were obtained for maximum heat release rates, fire growth rates, maximum excess temperatures beneath the ceiling, and heat fluxes. Fire spread between wood cribs with a separation distance corresponding to 15 m at full scale was also investigated. These data are reproduced well by empirical correlations that were established as part of the study. It is concluded that fire and smoke flows upstream and downstream of the fire source can be fully controlled if the ventilation velocities upstream and downstream are above about 2.9 and 3.8 m/s, respectively, at full scale for a single-point extraction ventilation system and greater than about 2.9 m/s on both sides at full scale for a two-point system.