Gas supply emergencies - consumer self isolation and restoration (SI&R) of gas supply
Revised gas industry arrangements allow the Gas Distribution Network operators (GDNs) to instruct domestic consumers to self-isolate and then restore their mains gas supply following a major supply emergency during winter conditions. HSE and the gas industry have worked together to ensure regulatory and public safety requirements have been met.
In the event of a widespread or large scale gas supply emergency it may be necessary to isolate many thousands of domestic consumers from their gas supply. At the end of the emergency those same supplies will need to be restored. The gas network cannot simply be switched back on since the order in which premises are restored must be coordinated to ensure that pressure in the network is maintained.
An industry exercise in 2010 modelled such an emergency. At this time the GDNs isolated and re-established supply, and relit appliances using their own staff or other suitably qualified gas engineers. Re-establishing supply includes the purging air from the system, which would otherwise lead to incomplete combustion when gas appliances are relit. This part of the process is known as 'purge and relight'.
The exercise highlighted that isolating and then restoring gas supplies for so many domestic consumers is a complex process that could take weeks or months to achieve. In winter, this might have led to many deaths from hypothermia.
Summary of risks under previous arrangements
Under the GDNs' previous arrangements the limited number of engineers available might have led to long delays in isolating and restoring gas supply following a major gas supply emergency. These delays carried the following risks, particularly during very cold weather:
- vulnerable consumers could die from hypothermia through lack of heating
- overloading and subsequent failure of the electricity grid as people deprived of gas sought to use electricity to provide heating
- members of the public could become increasingly frustrated with delays in reinstatement and attempt uncoordinated attempts at reinstatement on an individual basis or through the use of unqualified persons without the necessary competence to carry out the work
However, the previous arrangements reflected the need to control the risk of fire and explosion that could result from a failure to properly isolate a gas supply or inadequately purge pipework and ventilate a property. There was no mechanism to make a balanced judgement between the risks to personal safety and the risks associated with a prolonged gas supply emergency. In such circumstances, and in the absence of the GDNs being able to provide an adequate demonstration for justifying the use of SI&R, the GDNs could not operate outside of their Gas Safety (Management) Regulations (GSMR) safety cases and instigate it. Following discussions with HSE, the GDNs undertook work to establish such a mechanism.
Research and development of processes
The GDNs commissioned a risk assessment from GL Noble Denton to provide guidance on when it might be appropriate to use consumer self isolation and restoration. Importantly, this work drew on a number a previous British Gas/Advantica reports regarding risks from gas escapes from domestic appliances. This work provided a balanced assessment of risk to the public from self isolation and restoration and the prevailing weather conditions.
Building on this work, HSE required the GDNs to demonstrate that the information and direction provided to consumers to enable public SI&R is both effective and reliable.
After the GDNs had developed detailed procedures to implement SI&R, HSE evaluated these to ensure satisfactory demonstrations of safety were made. HSE also engaged the Health and Safety Laboratory (HSL) to provide expert review on key aspects of this work, as described in the following reports:
HSE then conducted a review of GDNs' corporate governance to ensure that SI&R is not deployed under the following circumstances:
- during an otherwise manageable gas supply emergency and;
- outside of cold weather conditions
and unless strict corporate governance process are in place to ensure that the new arrangements complement existing ones rather than replace them.
The outputs of the HSL reviews together with HSE's examination of the GDN's corporate governance arrangements assisted HSE in agreeing the revisions the GDNs had made to their processes and procedures.
Revised industry processes for domestic consumer SI&R
The revised GDN processes for the possible use of SI&R were implemented in Autumn 2013 and now underpin the GDNs' GSMR safety cases. The GDNs can now initiate SI&R in cold weather conditions, subject to corporate approval, where a significant imbalance is found between the wider societal risks and the risks to personal safety from individuals undertaking their own supply restoration.
Key features of the revised arrangements covering SI&R
When the GDNs would consider using SI&R
The GDNs will only apply the new processes in the event of a gas supply emergency affecting tens of thousands of consumers during a period of cold weather where there is a risk of hypothermia affecting vulnerable consumers. The GDNs cannot apply SI&R to small-scale supply emergencies or those occurring outside of winter. Other emergency arrangements are unaffected.
Authorisation of use of SI&R
The decision to implement the processes can only be taken at Board level by the relevant GDN. No reference to HSE or Ministers is now necessary prior to instigation of the arrangements.
Information for domestic gas consumers
The GDNs will supply a range of information to consumers at the onset of the emergency via the internet, television, radio, press, letter-based instructions and telephone help-lines. SI&R will be carried out area by area and gas engineers will be available to help consumers having difficulty with the processes.
When a member of the public has isolated their supply, they will display a card in their window. If cards are not visible, engineers will visit properties to ensure supplies have been isolated safely. The card system adds a precaution to the previous isolation arrangements, so reducing the likelihood of undetected leaks from consumer's appliances whilst the network is out of commission
Protecting the vulnerable
The GDNs already have access to registers of people likely to need particular assistance (eg elderly and/or disabled) to restore their supply. These people will be contacted separately.
Exclusions from SI&R
Due to additional risks, high rise flats are excluded from the new SI&R arrangements and are dealt with separately by the GDNs.