f Kiwa Energy Hazardous Areas Report

As part of the UK’s transition towards net zero carbon emissions by 2050, the possibility of using hydrogen to replace natural gas for heating domestic and small commercial properties is being investigated. One of the areas that needs to be considered is whether the conversion to hydrogen would bring about new issues regarding hazardous areas.
This report presents the results of a literature review which looks at the existing natural gas standards and hazardous area procedures. A comparison is then made to relevant work considering hydrogen including review of the IGEM SR/25 Hydrogen Supplement published by the HSE. Discussion and recommendations are made as to whether existing industry guidance continues to be suitable if the gas being used is hydrogen and not natural gas.
The focus of this work is on domestic and small commercial installations (e.g., single units with simple boiler and hot water installations) operating at gas pressures below 25 mbarg. It is important to note however, that most available guidance and standards are for larger commercial environments. Although these are not directly applicable to domestic installations they have been considered as a reference point, particularly for estimation of potential leak sizes.
Zoning of hazardous areas is not applicable in a domestic setting. However, separation distances between electrical and gas installations within a domestic property are advised within BS 6891. Should a property be converted to hydrogen, no changes are recommended to these distances. This is because in a low-pressure domestic situation, fires do occasionally occur with copper pipe rubbing on electric cables, but as both natural gas and hydrogen will ignite immediately the risk from the leak is essentially independent of the gas being carried. On many (probably most) occasions causing secondary fires. It is also advised that pliable meter connections should be wrapped to reduce the risk of fire from accidental electrical contact, and this will be included within PAS4441.
Any workplace (including the small commercial properties discussed within) that has a natural gasinstallation and where explosive atmospheres may occur, is required under DSEAR to classify hazardous andnon-hazardous areas within the facility. IGEM SR/25 and UP/16 are available to aid installers to complete hazardous area classification and design safe gas installations. It is recommended that UP/16 should be updated for hydrogen, and this is currently underway (April 2023).
From experimental findings at low gas pressures, it has been shown that the flammable zone for hydrogen in a vertical direction is 130% that of natural gas. However, the values proposed within the SR/25 hydrogen supplement give flammable zones that are between 200% and 350% greater at low pressure. It may be that these are driven by an assumption that general deflagration can occur at the hydrogen published lower explosive limit (LEL) of 4%. In practice, such deflagration does not occur below about 6% and does not propagate downwards until 8%. The implications of the move from wind driven ventilation (for natural gas) to buoyancy driven ventilation (for hydrogen) also needs thoroughly exploring. It could be argued (for low and medium pressure releases) that the ‘motive force’ provided by the low density of hydrogen is more reliable at clearing hydrogen concentrations than the wind-driven ventilation used for natural gas. In terms of general compliance with DSEAR, acknowledgement should be made that Hy4Heat recommends the use of hydrogen detection and AIV’s in properties with a demand in excess of 20m3/h.
This report was submitted to HSE for their assessment of the safety evidence for 100% hydrogen heating, which can be found at Hydrogen heating: HSE assessment of the safety evidence - GOV.UK.
Queries should be directed to DESNZ: https://www.gov.uk/guidance/contact-desnz.