SGN Project Report - Flame Visibility Risk Assessment

This report contains information on the relative risks of natural gas and hydrogen fires, particularly regarding their visibility. The fires considered are those that could occur on the H100 Fife trial network. The H100 Fife project will connect a number of residential houses to 100% hydrogen gas supply. The project includes hydrogen production, storage and a new distribution network. From a review of large and small-scale tests and incidents, it is concluded that hydrogen flames are likely to be clearly visible for releases above 2 bar, particularly for larger release rates. At lower pressures, hydrogen flame visibility will be affected by ambient lighting, background colour and release orientation, although this is also the case for natural gas. Potential safety implications from lack of flame  visibility are that SGN workers, other utility workers, or members of the public could inadvertently come into contact with an ignited release. However, some releases would be detected through noise, thrown soil or interaction with objects. From a workshop and review of risk reduction measures and analysis of historical interference damage incidents, it is concluded that flames with the potential for reduced visibility are adequately controlled. This is due to the likelihood of such scenarios occurring being low and that the consequences of coming into contact with such a flame are unlikely to be severe. These conclusions are supported by cost-benefit analysis that shows that no additional risk mitigation measures are justified for the H100 project. It is recommended that the cost-benefit analysis is revisited before applying the approach to a network wider than the H100 project. It was observed that the addition of odorant at relevant concentrations did not have an effect on the visibility of hydrogen flames.
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