Fire Safety Science Digital Archive

Large-scale fire tests have been carried out with Heavy Goods Vehicle (HGV) cargos in the Runehamar tunnel in Norway. During two of the fire tests, large pulsations of the gas flow inside the tunnel occurred. These pulsations were registered only when the measured heat release rates (HRR) were higher than 125 MW - 135 MW. Two different periods of the pulsations were registered, short periods of about 4 s and longer periods of approximately 18 s. In the article, the pulsations are presented and some plausible explanations are given, using an acoustic approach. There are several factors that can affect the pulsations, e.g., the size of the experimental set-up, the size of the fire, the thermal expansion at the site of the fire, the slope of the tunnel, the wind outside the tunnel, etc., but the calculations show that the oscillation periods are properties of the system, and can be what is referred to as thermoacoustic instabilities.