Highlights  Study on pressure peaking for ignited hydrogen releases in enclosures  Description and validation of CFD model for ignited pressure peaking phenomena  Focuses on a small-scale validation case and a real scale residential garage  Heat transfer, vent size and release rate impact on the pressure peak  Pressure peak for ignited release 2 orders of magnitude greater than unignited case *Highlights (for review)

Highlights Hydrogen release from onboard storage in a covered car park is numerically investigated  Release and dispersions from a range of TPRD diameters is simulated  A 0.5 mm diameter TPRD was found to be inherently safer for 700 bar storage  The angle of TPRD release was shown to have implications for passenger egress  Results support the inherently safe design of hydrogen fuel cell vehicles *Highlights (for review)

Highlights 1. Overpressure due to ignited hydrogen release in a garage examined 2. Pressure due to ignited and unignited release in enclosure compared 3. Pressure from ignited release two orders of magnitude greater than unignited 4. Phenomenon should be considered by regulators and engineers *Highlights (for review)

Hydrogen jet fires from a thermally activated pressure relief device (TPRD) on onboard storage are considered for a vehicle in a naturally ventilated covered car park. Computational Fluid Dynamics was used to predict behaviour of ignited releases from a 70 MPa tank into a naturally ventilated covered car park. Releases through TPRD diameters 3.34, 2 and 0.5 mm were studied to understand effect on hazard distances from the vehicle. A vertical release, and downward releases at 0°, 30° and 45° for TPRD diameters 2 and 0.5 mm were considered, accounting for tank blowdown. direction of a downward release was found to significantly contribute to decrease of temperature in a hot cloud under the ceiling. Whilst the ceiling is reached by a jet exceeding 300 °C for a release through a TPRD of 2 mm for inclinations of either 0°, 30° or 45°, an ignited release through a TPRD of 0.5 mm and angle of 45° did not produce a cloud with a temperature above 300 °C at the ceiling during blowdown. The research findings, specifically regarding the extent of the cloud of hot gasses, have implications for the design of mechanical ventilation systems.