Pressure Peaking Phenomena for Unignited Liquid Hydrogen Releases: Experiments and Analysis

Liquid hydrogen (LH₂) has been identified as a carbon-free fuel in the transition to Net Zero. The transport sector has a particular interest in LH₂ due to its increased density (71 kg/m³ at –253°C, 0.1 MPa) compared to pressurised gaseous hydrogen (24 kg/m³ at 20°C, 35 MPa). The Health and Safety Executive’s (HSE) Science Division has been researching and assessing LH₂ transport hazards for over a decade with supporting UK Safe Net Zero as one of the organisation’s key objectives.

Pressure peaking is a phenomenon unique to lighter-than-air gases, where an overpressure develops due to a release of unignited gas, which can be high enough to cause damage to structures. This work investigates the extent to which pressure peaking can occur in the event of significant unignited LH₂ releases inside a ventilated enclosure. The experiments presented are intended to be representative of a full-bore LH₂ hose failure inside a transfer connection space.

LH₂ releases of 180 g/s into a 1 m³ enclosure with a vent area varying from 0.0416 to 0.0104 m² were studied. It was found that pressure peaking can occur, with a maximum peak overpressure of 3.5 kPa observed for the smallest vent area. Compared to a modelled gaseous release of the same mass flow rate, the peak overpressure of the LH₂ experiment is significantly lower.