Gas build-up and the frequency of explosions following releases of natural gas/hydrogen mixtures in buildings

The work described in this thesis was undertaken as part of an EC funded project called NATURALHY. The NATURALHY project is an investigation of the feasibility of using the existing natural gas infrastructure that exists throughout Europe and worldwide to transport hydrogen as a natural gas/hydrogen mixture. If hydrogen is introduced into the natural gas system then it is necessary to revaluate the risk to which the public might be subjected. The part of the problem that is addressed in this thesis concerns low and high pressure release into confined vented enclosures.

A model was developed to simulate the build-up of a low pressure released of a natural gas (methane)/air mixture within a room of domestic property. Both the variation in concentration and the volume occupied by the gas/air mixture with time was predicted. A second model was developed to simulate the build-up of a high pressure release of natural gas (methane)/air mixture within an industrial enclosure. This second model was first formulated as a three zone model which was then improved by increasing the number of zone to five. The predictions of all of these models were composed the data obtained from full-scale experiments referred by Loughborough University.

Finally, an event tree was developed which traced the sequence of events that could occur following a release of gas into a domestic property and an explosion. The event tree was used to construct a model to determine the frequency of a explosion given the number of released of gas that might occur per year. The model covers the range of typical room sizes, release sizes and ventilation rates that occur in domestic properties and the range in the levels of occupation of domestic properties. The model also allows for an explosion to be prevented through the actions of a member of the public or an engineering arriving in response to an emergency call.