Vehicles that are powered by gaseous fuel, e.g., compressed natural gas (CNG) or hydrogen (H2), may, in the event of fire, result in a jet flame from a thermally activated Pressure Relief Device (TPRD), or a pressure vessel explosion in case the cylinder rupture before the TPRD activates. There have been a few incidents where the TPRD was unsuccessful to prevent a pressure vessel explosion in the event of fire, both nationally in Sweden and internationally. Possible reasons are damaged cylinders, that the TPRD was cooled by the rescue service or a local fire exposure far away from the TPRD. If the pressure vessel explosion would occur inside a road tunnel, the resulting consequences are even more problematic. In 2019 RISE investigated the fire safety of CNG cylinders exposed to local fires. The results from that test series raised the question about what the differences would be in the case of water application. Therefore, one purpose of the new fire test series conducted during 2021 was to investigate whether extinguishment with water may compromise the safety of vehicle gas cylinders in the event of fire. Extinguishments comprise the situation that may occur when deluge systems are activated in ro-ro cargo space or in tunnels, or in the case of manual extinguishment. In total seven fire tests were carried out. The fire tests show that the TPRD indeed can be cooled with water, e.g., from a deluge system, and thus preventing it from activation. Despite, this did not compromise safety as the water also cooled the cylinder, and the three types of cylinders that were tested were robust enough to handle the situation; either the gas slowly leaked through the fire-damaged composite material, the TPRD activated, or the cylinder maintained the gas and its strength throughout the test.