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NETWORK / 19 / DECEMBER 2016/JANUARY 2017 is recommending a limit lower than that of 53.25MJ/m 3 to allow sufficient headroom for any variations in appliance condition. SGN describes this extension as "cautious", being within the range of WI used in countries such as Spain. Implementing it would allow more than 90% of global LNG imports to be used in the network, and save £325 million a year in nitrogen ballasting costs. SGN have now presented a range of key project conclusions (see opposite), and a series of recommendations and proposals for further works have been made which would allow the project's findings to be rolled out across Great Britain and become business as usual; one of the NIC's key objectives. Doing so will be a long and difficult process, requiring fundamental changes to the way gas is specified in the UK. But it would achieve a more secure and affordable future for GB's gas networks. Recommendations SGN has made six recommendations as part of a rollout across Great Britain: 1. The upper WI limit to be increased to 53.25MJ/m 3 2. No changes to the lower WI limit at the current time 3. The interchangeability diagram to be updated 4. Transfer GS(M)R to IGEM Standard 5. Review CO guidance message 6. Permanent GS(M)R exemptions for the SUIs The upper WI limit to be increased to 53.25MJ/m3 SGN is recommending an increase of the WI from 51.40MJ/m 3 to 53.25MJ/m 3 , leaving a safety margin of approximately 1.5 units for factors such as: • Appliance safety device performance • Ambient temperature effects • Start of exponential increase of CO around53.50MJ/m 3 for some appliances • Sub-optimal adjustment of air/gas ratio controlled fully premix boilers • Other deleterious unknowns and poor condition of appliances This upper limit is also only marginally above the current GS(M)R emergency limit of 52.85MJ/m 3 . Using Oban as a statistical example, 4% of GB appliances are at risk and 2% are immediately dangerous, but increasing the WI does not materially affect CO risk across the board. Instead appliance installation condition is the most significant contributor to risk. No changes to the lower WI limit at the current time No safety issue was found testing gases as low as 45.66MJ/m 3 WI, and more work is required in this area to investigate mal- adjustment of boilers with gas/air ratio controls. Extending the upper WI limit to SGN's proposal and retaining the 47.20MJ/ m 3 lower limit would widen the WI range beyond the 5-6MJ/m 3 safe operational range identified by the project. Movement at the top therefore leaves less scope for expansion at the bottom without potentially having to readjust boilers from their G20 factory set point. The "Oban limits" identified allow for WI headroom allocated to on-site appliance issues. Indeed notwithstanding this, many appliances (such as flued and room sealed) pose no potential for CO spillage to room. This is, however, an issue that should be considered in any unconstrained development, such as that being considered under the Real-time networks project, the follow-on from Opening up the market. This is an example of where both the appliance industry and gas supply chain must continue to closely co-operate to understand future widening of sources in terms of thermal energy and gas quality management. The need to widen the lower WI limit may become more pressing as new renewable and unconventional gas sources with lower WIs become available. The interchangeability diagram to be updated The interchangeability diagram is a visual representation of the WI, ICF and SI limits, and is a simplification of the limits introduced by the British Gas Corporation prior to 1996. It has served GB well and was fit for purpose based on the gases available and type of appliances in use at that time. Based on the project, SGN believes the GB Limit New Proposed Limit Cumulative (nominal) LNG capacity, million t/y Wobbe index, MJ/m 3 50.0 50.5 51.0 51.5 52.0 52.5 53.0 53.5 54.0 300 250 200 150 100 50 0 Cumulative LNG production capacity Daily WI ranges - June 2015 to August 2016 Wobbe Index (MJ/m 3 ) 54 53 52 51 50 49 48 47 Jun 2015 Jul 2015 Aug 2015 Sep 2015 Oct 2015 Nov 2015 Dec 2015 Jan 2016 Feb 2016 Mar 2016 Apr 2016 May 2016 Jun 2016 Jul 2016 Avonmouth LNG Zeebrugge LNG Grain LNG Montoir LNG GSMR Upper Limit Exemption Limit Existing interchangeability diagram 54 53 52 51 50 49 48 47 46 45 Wobbe Index (MJ/m 3 ) Equivalent (C 3 H 8 +N 2 ) mol% 0 10 20 30 40 50 60 1 Upper emergency limit 2 Upper limit 3 Normal limit 4 Soot limit 5 Lower normal limit 6 Lower emergency limit 1 2 3 4 5 6

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