doi:10.3850/978-981-08-7724-8_07-04

ABSTRACT

This study is driven by the need for a fire and explosion hazard assessment of potential hydrogen releases in garage-like enclosures with the use of a ``typically'' designed pressure relief device (PRD). Computational fluid dynamics and a phenomenological model have been used to examine the dynamics of a hydrogen release in a garage. The hypothetical worst-case scenario considered involves a high mass flow rate release from a onboard hydrogen storage tank at 350 bar, through a 5.08 mm diameter orifice, representing the PRD in a small garage with a single vent equivalent in area to a typical brick. The dynamics of flammable hydrogen-air mixture formation within the enclosure, and the development of an external flammable jet are discussed. It was found that a flammable atmosphere engulfs almost 50% of the garage in less than 1s. Pressure build up due to the un-ignited release was studied and results indicate that overpressure within the enclosure has a characteristic maximum, which is essentially higher than simplified estimates of overpressure for an assumption of 100% by volume of hydrogen in the garage. For the scenario chosen, pressure at a third of this maximum level is already sufficient to destroy the garage within 3 s. The conclusion is drawn that PRDs currently available for hydrogen-powered vehicles should be re-designed if the vehicle is intended for garage parking and regulation, codes and standards should reflect this finding.

Keywords: Hydrogen safety engineering, Release, Pressure relief device, Pressure dynamics.

© 2011 CPD Unit, University of Leeds