BLEVE prevention using vent devices

The main features of accidents involving BLEVEs (boiling liquid expanding vapour explosions) occurring in fires are analysed. Simple mathematical models describing liquid or vapour discharge through the perforation of vessels by superheated liquids and liquid behaviour in a vessel heated by fire are formulated. These models are verified on the basis of experimental data available in the literature. An analysis of the well known accident at Alma-Ata in 1989 is presented. This accident involved the BLEVE of a railway tank engulfed by fire, with the resulting formation of a fireball. It is shown that this accident could have been prevented by means of a vent device (safety valve or breaking diaphrgm) with cross-sectional area greater than 77 cm ² and operational pressure below 1.6 MPa. The use of such vent devices could prevent the occurrence of BLEVEs when tanks containing superheated liquids or liquefied gases are subjected to thermal loading from fires.