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NETWORK / 20 / DECEMBER 2016/JANUARY 2017 diagram can be simplified and updated to reflect current requirements. The abscissa in the current interchangeability diagram is based on the propane and nitrogen content of the equivalent mixture. An alternative approach that has been adopted within Europe is to plot WI against RD. This offers a number of advantages such as simplification and harmonisation with Europe. The following proposals are therefore made to the interchangeability requirements of the GS(M)R: - Incomplete combustion factor is removed as a requirement The ICF parameter was introduced by Dutton, and was based on the performance of instantaneous water heaters which were commonly found in homes in the 1970s and generally generated flue gas CO/CO2 ratios that doubled when WI was increased by approximately 1.5MJ/m 3 . These appliances are now rare and today's equivalent of the central heating/hot water boiler do not show such severe sensitivity to WI. As a result Dutton's method overpredicts the ratio for today's appliances. - Sooting Index is replaced by relative density An upper limit was created based on limiting sooting associated with higher density gases and is based on visual assessment of the discolouration of ceramic radiants of gas fires commonly in use at the time. Sooting at this level is not a safety consideration and becomes a concern only when considering excessive deposition in the flues of flame-effect fires. - No change to the lower WI limit The lower WI value of 47.20MJ/m 3 was originally proposed by Dutton on the basis that heat output from instantaneous water heaters led to consumer complaints if WI falls by more than 5% of the reference gas. The low emergency limit of the GS(M) R permits WI as low as 46.50MJ/m 3 to be conveyed in order to prevent a gas supply emergency. No change is currently proposed, although there is scope for revision should it be required in the future. - No change to the hydrogen limit Prior to 1996 the British Gas Corporation used a normal limit of hydrogen content of 10% (mol/mol). The limit was proposed in anticipation of an imminent arrival of Substitute Natural Gases (SNGs) manufactured from petroleum feedstocks. In practice, SNGs have not figured in GB energy mix to date and a new limit of 0.1 mol% was set in 1996. No change in the hydrogen limit is proposed at the current time, although there is scope for revision should this be needed. Transfer GS(M)R to IGEM Standard An IGEM Gas Quality Standard working group should be established based on representation from the whole GB industry to consider evidence and determine the appropriateness of a new upper WI limit. If a change is supported this should take the form of an IGEM Standard, simplifying the process for further changes to be accommodated within the area of the industry. A structure has been agreed in principle by the industry that will oversee the transfer of schedule 3 of the GS(M)R to an industry produced standard. This will support the rollout of the Oban findings and other work in GB. Simultaneously a wider review of the GS(M)R will be undertaken to ensure much-needed changes are incorporated into the revised legislation at the same time. The IGEM standard will be regularly reviewed and amended, and provides a robust approach with the flexibility of allowing the specification to be appropriately developed. The working group should compose subject matter experts from across the gas industry and other key stakeholders. It should be an umbrella gas quality working group that initially considers the gas quality changes proposed in Oban project, and then subsequently evaluates, identifies and facilitates projects toward gas quality changes. Review CO guidance message The project has revealed that the importance of CO safety lies predominantly Modify interchangeability diagram showing position of globally available LNG 55 53 51 49 47 45 Relative density 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90 0.95 1.00 OGM final proposal Easee gas specification Worldwide LNG Roadmap for roll-out 1 2 3 4 FUTURE OF GAS Wobbe Index (MJ/m 3 )

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