Fire Safety Science Digital Archive

The effect has been studied of relief vents on the maximum pressure reached in explosions in a mixture containing 3.37% pentane in air in a steel tube 6 ft. long x 6 in. diameter. Ignition was near one end of the tube and the vents could be placed at either end of the tube. The maximum pressure reached when open vents were used decreased inversely as the 0.75 to 1.5 power of the vent area. This pressure was 3 - 5 times greater when the vent was remote from the ignition source than when it was near this source. Howover with large open vents near the ignition source, vibrations with a large amplitude became established; the maximum pressure in these vibrations increased as the vent area increased. Calculations have been made of the venting requirements of the explosions on the assumption that the rate of combustion when a vent is present in the tube is the same as when no vent is present. When the vent was covered by a disc of thin material the maximum pressure reached depended on the static bursting pressure of the disc if this pressure was larger than the pressure reached with the open vent. Cross shaped cutters gave a large reduction of the maximum pressure reached with brown paper and aluminium discs but a negligible reduction with polythene discs.