Boiling Liquid Expanding Vapor Explosion — Fireball & Thermal Radiation
Height of person or equipment above grade (typically 6 ft for personnel)
Understand BLEVE mechanisms, fireball correlations, thermal radiation modeling, safe separation distances, and mitigation strategies
A BLEVE (Boiling Liquid Expanding Vapor Explosion) occurs when a vessel containing pressurized liquefied gas fails catastrophically, usually due to fire impingement weakening the vessel wall. The sudden depressurization causes the superheated liquid to flash to vapor, and if the contents are flammable, the expanding vapor cloud ignites forming a fireball. The fireball rises buoyantly and can produce intense thermal radiation at significant distances.
Fireball diameter is calculated using the CCPS correlation: D = 5.8 * M^0.333, where D is the maximum fireball diameter in meters and M is the mass of flammable material in kilograms. This correlation is based on experimental data from large-scale BLEVE tests and is widely used in consequence analysis per API 2510 and the TNO Yellow Book.
Thermal radiation injury thresholds depend on both intensity and duration. For BLEVE fireballs: 37.5 kW/m2 causes significant structural damage; 12.5 kW/m2 is the threshold for first-degree burns with brief exposure; 25 kW/m2 causes second-degree burns; and 37.5 kW/m2 causes third-degree burns. Safe separation distances are typically set at 4.7 kW/m2 (pain threshold at 60 seconds) or 1.6 kW/m2 for public exposure.