Experimental study on thermal exposure of pipes to steady hydrogen jet fire impingement

Jet fires resulting from the accidental release of pressurized hydrogen represent a critical issue, especially due to their potential to trigger a domino effect. The lack of studies on the characterisation of the conditions experienced by, and response of, structures and process equipment directly engulfed in a hydrogen jet fire is of concern to industry. This work presents a characterisation study of a hydrogen jet fire with respect to the conditions experienced by an engulfed object. The total heat flux, along with its radiative component, was measured for hydrogen mass flow rates ranging from 0.05 to 0.2 kg/s. Heat fluxes exceeding 700 kW/m2 were measured at a location that coincided with the point of jet impact. The maximum radiative fraction measured was 20 % at the back of the tube where the specimen could receive radiation from the majority of the flame plume. It is concluded that conditions within hydrogen jet fires are notably more severe than those in hydrocarbon jet fires (for which a heat flux of 350 kW/m2 is considered high). This suggests that PFP systems should not be automatically assumed to provide protection against hydrogen jet fires without further research or actual test evidence of performance.