Abstract The adequate fire protection of liquefied petroleum gas (LPG) storage vessels to guard against their catastrophic failure is recognised to be of key importance. One means of achieving this is by directed water deluge that, in the UK for LPG vessels of 50 tonnes or larger, should be a fixed system on the vessel. The deluge rate currently recommended for such systems is designed to provide adequate protection against hydrocarbon pool fires. However, it is now recognised that the incident scenario most likely to threaten the integrity of such vessels is impingement by a hydrocarbon jet fire. HSE therefore decided to sponsor studies of the effectiveness of directed water systems in protecting against jet fires. This paper reviews current directed water deluge system designs and describes the work carried out by the Health and Safety Laboratory (HSL) to assess the effectiveness of the minimum deluge rate, currently recommended for the protection of LPG storage vessels against pool fires, in protecting against flashing liquid propane jet fires. Results show that a directed water deluge system designed to provide protection against a pool fire (using the recommended minimum rate of 9.8 dm 3 m −2 min −1) provides inadequate protection against jet fires.