In 2017 the UK Health and Safety Executive commissioned a report (MH/17/27) on the suitability of the ISO 22899-1:2007 jet fire resistance test (JFRT) as a means of demonstrating performance of Passive Fire Protection (PFP) materials or systems to a range of jet fire scenarios. The aim was to address current industry concerns regarding the suitability of the test for characterising PFP materials response in' high heat flux' scenarios. The characterisation of a jet fire in terms of a single heat flux value is found to be an inadequate means of specifying the severity of the hazard. Instead, a detailed description of the nature of the release should be provided. To this end the flame characteristics are compared that influence PFP materials response for a range of release scenarios, including gas, flashing liquids, crude-oil, gas-liquid mixes (two-phase), hydrogen, cryogenic releases and releases into confined areas. The applicability of the JFRT to the various release scenarios is assessed through comparison of the conditions within the scenarios to those within the large-scale natural gas release scenario used during validation of the JFRT. (C) 2018 Institution of Chemical Engineers. Published by Elsevier B.V. All rights reserved.