1.1 Transco operates approximately 275,000 km of gas pipelines in Great Britain and over 20 million service connections to individual properties. Of these, some 91,000 km are iron mains located within 30 metres of property and operating at pressures between 25mbar and 2 bar. These iron pipes were mostly laid during the first half of the 20th Century and their current physical condition is difficult to determine without extensive and costly investigative work.
1.2 Since 1977 Transco has managed a mains replacement programme designed to reduce the risk of fire or explosion incident arising from the failure of iron mains. Much of this replacement activity has been carried out by laying polyethylene (PE) pipelines in place of the iron mains. Transco currently considers PE to be the most suitable material for this application as it exhibits high resistance to fracture under ground loading and corrosion.
1.3 On 18th September 2001, HSE published an enforcement policy describing a programme of activity that it believed to be the most reasonable and appropriate approach to the eventual elimination of the risks arising from the failure by fracture or corrosion of ageing iron mains. It is expected that this programme will be completed within 30 years. The 30-year programme was developed by HSE in conjunction with Transco and its economic regulator, OfGEM. HSE believes the programme represents a reasonably practicable approach to the mitigation of risk. It will be subject to review at intervals no greater than five years.
1.4 The selection and scheduling of mains for replacement will be undertaken in accordance with Transco policy. The risk based models; i.e. the Mains Risk Prioritisation System (MRPS), developed following the Tripartite Review1 of Transco's Mains Replacement Methodology and used to prioritise cast iron (CI) and LP ductile iron (DI) replacement work since January 2000, will inform this policy. Traditionally mains replacement work has been prioritised based on listings of mains by score or risk value in descending order, from the top down. However, Transco are currently reviewing options that will enable improvements in the efficient planning and management of the 30 year mains replacement programme. HSE reserve the right to ensure that Transco reduces risk from the system appropriately and should be consulted regarding any significant changes to Transco policy in this area, before implementation.
1.5 The primary objectives of the HSE Monitoring and Reporting of the Transco Distribution Mains Replacement programme are to provide HSE with:
(a) Assurance that operational programme targets are being met in line with the objectives of the replacement programme; and
(b) A more strategic longer-term overview of the on-going effectiveness of the 30 year replacement programme.
1.6 The HSE has powers to enforce this programme under existing legislation, namely the Health and Safety at Work etc. Act 1974 and the Pipelines Safety Regulations 1996 (SI 1996/825). The appropriate use of enforcement powers is important; both to secure compliance with the law and to ensure those who have duties under it may be held to account for failures to safeguard health, safety and welfare. Therefore, HSE may, where appropriate, take enforcement action against Transco to ensure the objectives of the programme are met.
1.7 In order to carry out this monitoring and enforcement, the HSE will require Transco to provide them with extracts from its routine management and monitoring systems. These extracts will be considered by HSE as evidence of achievement against Transco's mains replacement programme. HSE might also choose to commission, or require Transco to commission, independent investigations or assessments of Transco's activity in order to assure itself of the validity of the information provided by Transco.
1 In 1997, the Monopolies and Mergers Commission (MMC) reported on the referral concerning the Ofgas price control review for BG plc. When giving evidence to the MMC, HSE advised that a review of BG's methodology for assessing its priorities for mains replacement had begun. The MMC recommended that HSE should consult Ofgas (now OfGEM) in this process