External explosions” as a result of explosion venting

A series of vented explosion tests has been carried out using a 30 m³ explosion chamber. Overpressure measurements made inside and outside the chamber and high-speed cine films of the: ombustion outside the chamber show clearly that an “external explosion” occurs when the gas displaced from the chamber is ignited by the emerging flame. The overpressure generated by the external explosion increases with the velocity of the emerging jet flame but the extent to which it influences the internal pressure also depends on the relative magnitudes of the internal and external pressures and on the size of the vent. This external explosion phenomenon should be taken into account when interpreting vented explosion data and when developing methods of predicting the pressure developed in a vented explosion.