Ignited Releases of Liquid Hydrogen

If the hydrogen economy is to progress, more hydrogen fuelling stations are required. In the short term, in the absence of a hydrogen distribution network, these fuelling stations will have to be supplied by liquid hydrogen (LH2) road tanker. Such a development will increase the number of tanker offloading operations significantly and these may need to be performed in close proximity to the general public.
Several research projects have been undertaken already at HSL with the aim of identifying and addressing hazards relating to the storage and transport of bulk LH2 that are associated with hydrogen refuelling stations located in urban environments.
The first phase of the research was to produce a position paper on the hazards of LH2 (Pritchard and Rattigan 2009). This was published as an HSE research report RR769 in 2010.  
The second phase developed an experimental and modelling strategy for issues associated with LH2 spills and was published as an internal report HSL XS/10/06. The subsequent experimental work is a direct implementation of that strategy. LH2 was first investigated experimentally (Royle and Willoughby 2012, HSL XS/11/70) as large-scale spills of LH2 at a rate of 60 litres per minute. Measurements were made on unignited releases which included the concentration of hydrogen in air, thermal gradients in the concrete substrate, liquid pool formation and temperatures within the pool. Computational modelling on the un-ignited spills was also performed (Batt and Webber 2012, HSL MSU/12/01).
The experimental work on ignited releases of LH2 detailed in this report is a direct continuation of the work performed by Royle and Willoughby.
The aim of this work was to determine the hazards and severity of a realistic ignited spill of LH2 focussing on; flammability limits of an LH2 vapour cloud, flame speeds through an LH2 vapour cloud and subsequent radiative heat and overpressures after ignition. The results of the experimentation will inform the wider hydrogen community and contribute to the development of more robust modelling tools. The results will also help to update and develop guidance for codes and standards.