Uneven exposure of compressed natural gas (CNG) and hydrogen (H2) cylinders: Fire and extinguishment tests
Jonatan Gehandler, Anders Lönnermark
Abstract
Vehicles that are powered by gaseous fuel, e.g., compressed natural gas (CNG) or hydrogen (H 2 ), may, in the event of fire, result in a jet flame from a thermally activated pressure relief device (TPRD), or a pressure vessel explosion. There have been a few incidents for CNG vehicles where the TPRD was unsuccessful to prevent a pressure vessel explosion in the event of fire, both nationally in Sweden and internationally. If the pressure vessel explosion would occur inside an enclosure such as a road tunnel, the resulting consequences are even more problematic. In 2019 the authors investigated the fire safety of CNG cylinders exposed to localized fires. One purpose of the tests conducted in 2021 reported in this paper is to investigate whether extinguishment with water, e.g., from a tunnel deluge system, may compromise the safety of vehicle gas cylinders in the event of fire. Steel cylinders handles the situation with localizde fire and/or cooling with water well. Composite tanks can rupture if the fire exposure degrades the composite material strength, and the TPRD is not sufficiently heated to activate, e.g., if the fire is localized or if the TPRD is being cooled by water, which prevents its activation. • The article reports on 15 fire and extinguishment tests (i.e., uneven heating and cooling) of CNG and hydrogen cylinders. • The article investigates the risk of pressure vessel explosion and the characteristics of jet flames from TPRDs. • The article finds that steel cylinders are robust against fire exposure and water cooling. • The article finds that composite cylinders may leak gas through the damaged material or fail to activate the TPRD.