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

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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 °C was used as a no-harm criteria for assessment of thermal hazards to people and threshold 300 °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.
Original languageEnglish
Article number107771
JournalJournal of Energy Storage
Early online date24 May 2023
Publication statusPublished (in print/issue) - 15 Sept 2023

Bibliographical note

Funding Information:
Overall, thorough assessment of the hazards associated with unintended hydrogen releases from a TPRD installed on a FCEV in an underground car parking are currently missing. This study aims at fulfilling this gap by means of numerical simulations of unignited and ignited hydrogen releases in a realistic underground car park scenario. This work has been performed within the framework of FCH JU funded project HyTunnel-CS on “Pre-normative research for safety of hydrogen driven vehicles and transport through tunnels and similar confined spaces” ( https://hytunnel.net ). The ambition of HyTunnel-CS project was to underpin the allowance of hydrogen-powered vehicles to enter the underground traffic infrastructure by closing the knowledge gaps and technological bottlenecks in the provision of safety associated to the use of such vehicles in underground transportation systems. This paper demonstrates how the safety strategies developed in HyTunnel-CS project [ 12 ] can be realised for underground car parking. Firstly, the research assesses the use of validated reduced tools available in literature for free unignited and ignited hydrogen jets for an underground car park scenario, defining the range of applicability of the reduced models. The scenarios involving complex geometries and hydrogen jets impinging on the ground are found to be outside the range of reduced models applicability. Thus, these scenarios are investigated using validated computational fluid dynamics (CFD) models. A systematic approach is employed to scrutinise the effect of a TPRD diameter and direction of an unignited and ignited hydrogen releases in the context of underground parking and/or traffic systems. Focus is posed on the investigation of the hydrogen release interaction with a typical for car parking mechanical ventilation system, compliance to current RCS requirements, facilitation of passengers' evacuation and rescue operations. The final aim is to propose suitable TPRD characteristics and safety strategies for the inherently safer introduction of FCEV in an underground car park without requiring modifications to the infrastructure.

Publisher Copyright:
© 2023


  • Hydrogen safety
  • Unignited release
  • Jet fire
  • Mechanical ventilation
  • Underground parking
  • TPRD
  • CFD


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