Fire impingement on vessels containing pressure liquefied gases can result in catastrophic failure of the vessel leading to a Boiling liquid Expanding Vapour Explosion (BLEVE). If the gas is flammable, this can result in the formation of very large fireballs. In safety assessments where catastrophic vessel failure is identified as a real possibility, the risk of death from a fireball tends to be higher than that from missiles or blast. Since many of the physical processes which take place in a BLEVE are scale dependent, a series of tests were undertaken at a large scale where 2 tonne propane vessels were taken to failure in a jet fire and the vessel response, mode of failure and consequences of failure characterized. The measurements taken by the Health and Safety Laboratory and BG Technology relating to fireball formation are described.