Deflagrations of Non-uniform Hydrogen/Air Clouds in a Tunnel

This paper presents work undertaken by the HSE as part of the Hytunnel-CS project, a consortium investigating safety considerations for fuel cell hydrogen (FCH) vehicles in tunnels and similar confined spaces.
Hydrogen vehicles typically have a Thermally activated Pressure Release Device (TPRD) providing protection to the on-board storage of the vehicle. Upon activation, the content of the vessel is released in a blowdown. The release of this hydrogen gas poses a significant hazard of ignition. The consequences of such an ignition could also be compounded by confinement or congestion.
HSE undertook a series of experiments investigating the consequences of these events by releasing hydrogen into a tunnel and causing ignitions. A sub-section of these tests involved steel structures providing congestion in the tunnel. The mass of hydrogen released into the tunnel prior to ignition was varied by storage pressure (up to 59 MPa), release diameter, and ignition delay. The ignition delays were set based on the expected worst-case predicted by pre-simulation models. To assess the consequences, overpressure measurements were made down the tunnel walls and, for the tests with congestion, at the face and rear of the congestion structures. The flame arrival time was also measured using exposed-tip thermocouples, resulting in an estimate for flame speed down the tunnel. The measured overpressure and flame extent results are presented and compared against overpressure levels of concern.