Beta This is a new way of showing guidance - your feedback will help us improve it.

10 Year Review of the Health and Safety Executive's enforcement policy for the replacement of iron gas mains

Gas and Pipelines Unit,  May 2012


The Health and Safety Executive's (HSE) enforcement policy for the Iron Mains Replacement Programme (IMRP) addresses societal concern regarding the failure of iron gas mains and the consequent risk of injuries, fatalities and damage to buildings. Over the last 35 years various iron mains replacement programmes have been followed. Since 2002 the objective of the IMRP has been to remove the risk to members of the public from all iron mains within 30 metres of property over a 30-year period (the IMRP is often referred to as the '30/30' programme).

This review sets out HSE's position with respect to the first 10 years of implementation of the '30/30' programme. In December 2010 HSE and Ofgem jointly commissioned an independent report to assess the progress of the IMRP to date and evaluate potential options for the remaining 20 years of the original programme, taking into account the benefits and costs of each option. Cambridge Economic Policy Associates (CEPA), working in partnership with Advanced Engineering Solutions Ltd (AESL), were contracted to carry out this work. Their report is published on HSE's website at RR888 - HSE/Ofgem: 10 year review of the Iron Mains Replacement Programme (the CEPA/AESL report) and this also provides more detail on previous replacement programmes.

Legal Requirements

The Health and Safety at Work etc. Act 1974 (HSWA), section 3(1), requires pipeline operators to conduct their undertakings to ensure, so far as is reasonably practicable, that persons not in their employment are not exposed to risks to their health and safety.

In addition, the Pipelines Safety Regulations 1996 (PSR), regulation 13 requires the operator to ensure that a pipeline is maintained in an efficient state, in efficient working order and in good repair. This duty is absolute, with a limited defence if a breach is caused by a third party.

In November 2003 the Pipelines Safety (Amendment) Regulations 2003 came into force. This created a statutory defence under PSR regulation 13A to a breach of regulation 13 if the failed iron gas pipe was included in a decommissioning programme approved by HSE. Initially decommissioning programmes were approved for a period of twelve months although submissions for longer periods have also been approved since 2011.

The arrangements for meeting the replacement programme form part of the gas distribution network (GDN) operators' safety cases prepared under the Gas Safety (Management) Regulations 1996 (GS(M)R). The GDN operators have a duty to follow these arrangements alongside other network management responsibilities such as gas odourisation, pressure management and providing an emergency response to gas escapes.

Arrangements for Prioritising Iron Mains Decommissioning 2006 - 2013

In June 2005 Transco completed the sale of four of its original eight GDNs. Along with National Grid Gas plc (Transco's successor), Scotland Gas Networks plc, Northern Gas Networks Ltd, Wales & West Utilities Ltd, and Southern Gas Networks plc are now responsible for complying with the IMRP within their respective gas distribution networks.

Iron mains are currently prioritised for decommissioning using a model developed in consultation with HSE. The model is used to select those mains to be decommissioned each year with the aim that all 'at risk' iron pipes are decommissioned by December 2032. 'At risk' pipes are iron pipes within 30 metres of occupied buildings. The model does not predict pipe condition but instead provides a risk score for each 'at risk' pipe so that the higher risk mains can be targeted earlier. The risk score for a pipe is expressed in terms of the likely number of incidents per kilometre per year.

The policy and procedures and use of the model are described in documents which have been adopted by all the GDN operators and are referred to in their GSMR safety cases. The model has been reviewed and updated regularly by the GDN operators since 2001.

Initial estimates of the achievable risk reduction rates were based on decommissioning mains in a top-down risk ranking order. However, in 2002 an alternative approach to the selection of mains for replacement was adopted that enabled an appropriate balance to be struck between operational efficiency and risk reduction. This new approach was based on allocating network's annual decommissioning workloads in the proportions 20:70:10 whereby 20% of the annual workload is allocated to decommissioning the highest risk pipes, 70% to the medium-risk pipes and 10% to lower-risk pipes.

This approach allowed efficiency gains in the deployment of resources and reduced the potential for repeated disruption of gas supplies and traffic movements. HSE accepted this approach providing an equivalent amount of risk was removed from the network as when using the top-down approach. Given the inherent uncertainties in the risk models used to develop the projects, HSE was satisfied that the new approach was both sensible and would in reality lead to a potential shortening of the 30-year programme.

Since 2005, and against a background of decreasing risk scores, some GDN operators have adopted a 20:80 approach whereby 20% of the annual workload is allocated to decommissioning the highest risk pipes and 80% to the medium-risk pipes. This refinement was accepted by HSE on the justification that the majority of lower-risk pipes adjacent to future decommissioning projects had been removed and that the difference between medium and lower risk scoring pipes was becoming less pronounced.

During late 2010 and early 2011 CEPA and AESL, funded jointly by HSE and Ofgem, independently reviewed the current arrangements for the IMRP.  The findings are important both for how HSE approaches this work in future and also in relation to the Ofgem 2013 - 2021 Price Control Review. Although HSE has used the report to inform its 10-year review of the IMRP the CEPA/AESL report represents the views of the consultants.

The CEPA/AESL report reached a number of conclusions regarding the IMRP as well as providing options to refine it to ensure that risks from the network are better targeted and consumer value improved. These are:

Review of HSE's Enforcement Policy for the Replacement of Iron Gas Mains 2006 - 2013

The CEPA/AESL report has concluded that the IMRP has been successful in removing the highest risk iron pipes from the gas distribution network. However, costs have been high and are not justifiable on safety grounds alone. Also, having been successful in removing the iron pipes at greatest risk of failure, the remaining 'at risk' iron pipe population now has an increasingly flat risk profile. Additionally the model used to predict iron pipe incidents has over estimated the risk at larger diameters.

The following principles have directed the review of the IMRP:

In reviewing the 2006 – 2013 enforcement policy HSE has taken into account the conclusions of the CEPA/AESL report as well as the views of the GDN operators and Ofgem.  In the revised approach the emphasis of the enforcement policy will be on the management of risk, with greater account being taken of changes in how iron pipes fail as their diameter increases.  HSE has concluded that this can be best achieved through a three tiered approach to the management of risk across the 'at risk' iron mains population.

The programme will be known as the Iron Mains Risk Reduction Programme (IMRRP) to reflect the change in emphasis from wholesale decommissioning to targeted risk management.

HSE's Enforcement Policy for the Replacement of Iron Gas Mains 2013 – 2021: The Three Tier Approach

The three tiers of pipe diameter are:

At risk pipes in Tier 1

The CEPA/AESL report concluded that the 'at risk' iron pipe population at 8" diameter and below represents the most significant risk to the public. However, there is still no effective alternative to decommissioning for pipes in this diameter range. 

As in the 2006 – 2013 enforcement policy each GDN operator will set a length of Tier 1 pipes to be decommissioned over the period of their approved programmes. This should be sufficient to ensure that all Tier 1 pipes are removed by the end of 2032 or earlier. For approved programmes lasting longer than one year the GDN operators will be allowed to adopt a flexible approach to their annual delivery so long as arrangements are in place to ensure that their approved target is met. This will facilitate the delivery of large or complex decommissioning projects which require significant preparation and will also allow the GDN operators to take remedial action should their progress with decommissioning fall short in a particular year.

The approach to decommissioning Tier 1 pipes will continue to be prioritised on the basis of the risk of an incident presented by each pipe. This will be calculated using the existing risk model, although this will continue to be subject to improvements by the GDN operators. Twenty percent of the Tier 1 set length of pipes to be decommissioned will be drawn from the highest risk pipes identified by the risk model. The remaining 80% of the set of pipes to be decommissioned will be drawn from any part of the remaining Tier 1 population. This will ensure the delivery of an efficient programme and reflects the overall reduction and flattening of risk scores within the Tier 1 pipe population.

In contrast to the 2006 – 2013 enforcement policy, any pipes decommissioned on the basis of their condition, or those selected for reasons of reliability or joint leakage, may be counted towards the approved programme target.

As in the 2006 – 2013 enforcement policy, the GDN operators will be able to 'profile' their work to take account of the scaling down of workload towards the end of 2032.

At risk pipes in Tier 2

Tier 2 pipes scoring above a risk-action threshold, set by the GDN operator, will be selected to receive appropriate attention over the period of the approved PSR regulation 13A programme. Appropriate attention means that Tier 2 pipes scoring above the risk-action threshold will either be decommissioned or, where a suitable and sufficient technique exists,  assessed for continued use if found to be in good condition or remediated to allow for lifetime extension.  In addition, those Tier 2 pipes scoring above the risk-action threshold will be subject to the condition monitoring arrangements described below.

Since the onus is on the GDN operators to demonstrate that they control the risks in their network they have developed proposals to determine a risk-action threshold. These proposals have been reviewed by HSE and are considered appropriate. Each GDN operator's PSR regulation 13A programme submission will contain a detailed description of the method used to set the risk-action threshold.

No annual decommissioning length target will be set for Tier 2 pipes scoring above the risk-action threshold as part of their approved PSR regulation 13A programme. This is because the Tier 2 pipes selected by the GDN operators within their networks to receive appropriate attention may not be decommissioned if a suitable and sufficient alternative to decommissioning is applied instead. No suitable and sufficient alternatives to decommissioning have been yet proposed by the GDN operators, however, it is anticipated that Ofgem funding incentives will drive innovation in this area. With increasing innovation HSE expects that decommissioning will be supplemented by alternative risk management methods.

As part of their approved programme submissions the GDN operators will be required to provide details of their arrangements for managing the risk from those Tier 2 pipes that have migrated to above the risk-action threshold during the course of the approved programme period and cannot reasonably be subjected to appropriate attention during that same period.

Pipes in Tier 2 scoring below the risk-action threshold may still be subject to decommissioning where a cost benefit analysis agreed with Ofgem is justified. Examples of this might include the decommissioning and replacement of pipes that enable greater efficiencies in Tier 1 decommissioning projects.

At risk pipes in Tier 3

The CEPA/AESL report concluded that iron pipes of 18" diameter and above are the least likely to fail of all those within 30 metres of buildings. As such Tier 3 pipes will be subject to the condition monitoring arrangements described below. In addition, Tier 3 pipes may still be subject to decommissioning where a cost benefit analysis agreed with Ofgem is justified.

Setting the Tier 2 Risk-Action Threshold

In August 2011 the GDN operators provided HSE with four possible options for setting the Tier 2 risk-action threshold. These were:

HSE has accepted that each of these proposed options could potentially form the basis of that part of a 'suitable and sufficient' programme submitted under PSR regulation 13A.  However, all four of the proposed options will be significantly enhanced by improvements in the risk model for iron pipes above 12" in diameter. This will improve risk targeting of those pipes scoring above the 'risk-action' threshold and also assist in the business cases made by the GDN operators to address those pipes which have scored below the threshold.

Condition Monitoring

As part of their approved programmes the GDN operators should establish suitable condition monitoring regimes, for example using leakage surveys, for pipes in Tier 2 scoring above the risk-action threshold and for all pipes in Tier 3 throughout the approval period. Details of these regimes should be provided by the GDN operators as part of their approved programme submissions.

The GDN operators will continue to respond to all public reported gas escapes from all pipes as required by GS(M)R regulation 7(4), the procedures for which are detailed in their GS(M)R safety cases.

HSE expects the GDN operators to systematically analyse the outputs from these activities in order to pinpoint any pipe failure 'hotspots'. Where pipes are found not to comply with Regulation 13 of PSR the GDN operators should take suitable and sufficient action to remedy this, including decommissioning where the pipe is judged to have deteriorated beyond safe or effective repair.

In addition, HSE expects the GDN operators to take advantage of innovative techniques that may allow them to pro-actively monitor the condition of pipes in Tier 2 scoring above the risk-action threshold and pipes in Tier 3 to predict the likelihood of failure and to improve asset integrity data.

Decommissioning of Iron Mains

Any iron pipe should be decommissioned when it can no longer be effectively repaired or remediated and becomes unsafe for use. As structured above, the three-tiered approach requires that all Tier 1 pipes will be decommissioned by the end of 2032 or earlier. Pipes in Tiers 2 and 3 will be decommissioned on the basis of asset integrity assessment processes covered by supporting documentation to be provided by the GDN operators with their PSR regulation 13A programme submissions.

Within a GDN operator's approved programme there may be pipes in Tiers 2 and 3 pipes that, if subject to appropriate condition monitoring and/or remediation, will remain suitable for continued use. These pipes are included within the population of iron pipes benefiting from the statutory defence provided by PSR regulation 13A providing that the approved programme has been followed by the GDN operator.

HSE will consider an iron pipe to be decommissioned when it is no longer used to carry gas. Where a polyethylene (PE), or other pipe, has been inserted into an iron pipe, or effectively a new pipe has been constructed using a spray-lining technology that uses an existing pipe as a mould for a new pipe, the existing iron pipe will be considered to be decommissioned. Iron pipes will only be considered to be decommissioned where the internal pipe is itself capable of meeting the requirements of PSR regulation 5 without any contribution from the external iron structure.

Changes to the Iron Pipe Risk Model

The CEPA/AESL report recommended that the GDN operators adopt Gas in Buildings as the principal output of risk from their decommissioning prioritisation model. The GDN operators have begun the process of examining the feasibility of this modification to the model as well as examining other issues such as refining the model further to take account of differences between small and large diameter iron pipe failure modes, population density and other pipe materials. This work has proved difficult for the GDN operators to achieve within the timescales required to prepare their approved programme submissions for April 2013 and to comply with Ofgem's price control review (RIIO) processes. The GDN operators will continue to examine the possibility of improving the risk model and are expected to bring forward proposals in due course.

Until the risk model has been modified by the GDN operators HSE will accept use of the existing risk model to determine the prioritisation of Tier 1 pipes for decommissioning and as the basis for setting the Tier 2 risk-action threshold.

Approval of Iron Mains Risk Reduction Programmes from 1st April 2013

HSE will modify the way in which iron mains risk reduction programmes are approved in response to the three tier approach. From 1st April 2013 each PSR regulation 13A approval granted by HSE will specify only the length of Tier 1 pipes to be decommissioned and the time period over which this will be achieved. However, the GDN operators should provide additional information in their submission regarding the length of Tier 2 pipes above the risk action threshold that will receive appropriate attention over the period of the approved programme. Each GDN operator should also provide details of how pipes in Tier 2 that score above the risk action threshold and pipes in Tier 3 will be monitored.

From 1st April 2013 HSE will grant PSR regulation 13A approvals to the GDN operators for periods of up to eight years.

Review of PSR 13A

HSE will undertake a review of the Pipeline Safety Regulations 1996 Regulations 13 and 13A as they bear upon iron mains risk reduction programme and the absolute requirement to maintain network pipes. HSE anticipates that this work will inform decisions on how best to approach the management of risk from the iron mains network, what the GDN operators need to do to discharge their duties and if any changes of approach are appropriate as part of the Ofgem mid-term price review in 2017. Subject to HSE Board and Ministerial approval it is our intention that, by this time, the GDN operators will be required to maintain all of the iron pipes within their networks (along with pipes made from other materials and operated at below 7 barg) to a 'so far as is reasonably practicable' standard. It is our expectation that this standard will be met by the same arrangements that have been put in place to support the PSR regulation 13A programmes approved for 1st April 2013 onwards.