Effect of TPRD diameter and direction of release on hydrogen dispersion and jet fires in underground parking

The paper presents safety strategies to support choice of diameter and release direction for thermally activated pressure relief device (TPRD) onboard a hydrogen fuel cell electric vehicle. Analytical and numerical modelling campaigns were performed to study hazards of unignited and ignited hydrogen releases from a vehicle in a real underground parking. TPRD diameter to prevent flammable mixture formation during upward release was determined using similarity law for hydrogen concentration decay along jet centreline. Parametric CFD simulations studied effect of different TPRD diameter, release direction, vehicle distance from obstacles, ceiling height, influence of carpark ventilation on hydrogen hazards. Hazards of unignited releases were associated with the lower flammability limit of hydrogen-air clouds. For ignited releases the temperature threshold 70 degrees C was used as a no-harm criteria for assessment of thermal hazards to people and threshold 300 degrees C as a damage criteria for mechanical ventilation system following requirements of BS 7346-7-2013 standard for carpark ventilation. Recommendations on TPRD design were formulated to support safe integration of hydrogen-powered vehicles in the existing underground parking facilities and infrastructure.