Electrostatic Ignition (Summary of experiment series E4.3 results)

Work package four of the PRESLHY project focuses on ignition phenomena. This report
summarises the experimental series E4.3, which focuses on the propensity for an electrostatic
charge capable of igniting a hydrogen cloud to be generated during a release, or accidental spill
scenario. Seven experiments measuring the electric field of a multiphase hydrogen jet were
conducted at the HSE Science and Research Centre. Current measurements on an electrically
isolated section of steel pipework were also taken during a total of 30 large scale releases.
The results from the plume measurements indicate that the multiphase hydrogen jet itself does
not create a significant charge, but certain interactions with the air can cause intermittent spikes
in field strength. In particular, air in the pipework being ejected and solidified air forming
around the release point, breaking off and flowing downstream appear to be the cause of the
electrical fields measured in these experiments. This effect could be larger with different initial
conditions either at the nozzle or in the tanker.
The wall current measurements were more consistent, as the ability for LH 2 to induce a current
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on a section of electrically insulated pipework was clearly demonstrated. This charge is a
complicated function of the phase of LH 2 in the pipework, the turbulence of the flow, and the
resistance to ground of the section of the pipework. Frost formation on the outside of the
pipework dynamically changed the resistance to ground throughout each trial, making
interrogation of the results difficult.
The experiments show that electrostatic charges do pose a credible hazard when considering
LH 2 facilities. The charging, however, does not form inside the hydrogen, but on the
substances or objects that the hydrogen interacts with. For a fixed facility, maintaining
continuity to earth, paying attention to objects in the potential path of a release, would limit the
likelihood of electrostatic charging and therefore limit the hazard.