Pipelines and gas supply industry: Case study of a major accident hazard pipeline near-miss incident in Great Britain

Why is it important to know about major accident hazard pipelines?

Damage to underground services is highly dangerous, costs money and can substantially delay work. When the underground service is a major accident hazard pipeline (MAH pipeline or MAHP), such as a high-pressure gas or petrochemical pipeline, then the result of any damage can be devastating.

What happens when a MAHP is damaged?

In 2004 at Ghislenghien, Belgium, a high pressure gas MAHP was damaged during the construction of a factory car park. The damage went unnoticed for 14 days until the pipeline ruptured and caused a huge explosion. Twenty five people were killed, and 150 people were seriously injured.

MAHP near-miss incident in Great Britain

In 2007 an incident occurred in Great Britain, with similar causes to the Belgian disaster. There could have been serious consequences when high pressure natural gas MAHPs were uncovered during construction of an office car park.

The project originally involved the construction of an office building under a design and build contract. Towards the end of the project the Client for the work decided that they required extra car parking space and this would be built over the MAHPs. The design and build contractors did not undertake this further work and left the site.

The Pipeline Operator had previously met with the design and build contractors and informed them of the risks of working nearby MAHPs. The Pipeline Operator also met with the Client and explained that the design and construction methods had to be agreed before work could begin on the car park extension. The Client was also told that trial holes were needed to accurately locate the pipelines and that the Pipeline Operator needed to be on site to supervise this and mark out the pipeline routes.

The Client had no experience of managing construction risks near to MAHPs and did not understand how dangerous the pipelines could be if damaged. The Client only vaguely understood their health and safety responsibilities and communication with designers, contractors and the Pipeline Operator was poor. The Client did not recognise that the car park extension was a separate Construction, Design and Management (CDM) project and so did not notify HSE.

Increasing pressure to let the office building led the Client's Chairman to hire groundwork contractors to start work on the car park extension. No one employed by the Client understood the risks well enough to challenge this decision. The Client did not inform the Pipeline Operator when the work was due to start. The Pipeline Operator did not know that the Client had employed new contractors who had not been briefed by them on the risks from the MAHPs.

The groundwork contractors had no prior experience of working near MAHPs and were not informed of the risks from the pipelines by the Client.

The groundwork contractors did not obtain underground services plans from any utility companies before starting work. They carried out the site clearance and then started digging the trial holes without authorisation or supervision from the pipeline Operator. As the groundwork contractors did not understand the risks from the MAHPs they pulled up the pipeline marker posts before reducing ground levels across the site with a mechanical excavator. The cathodic protection cables laid above the pipelines were also pulled up.

Work was stopped immediately when an inspector from the pipeline Operator visiting an adjacent site saw the unauthorised construction work. This may well have stopped the near-miss from becoming a major incident with widespread damage and loss of life.

Costs incurred by the Client included an increase in insurance premiums, lengthy delays to the construction work, and replacing the pipeline marker posts and cathodic protection. HSE also subjected them to a detailed investigation. If the construction work had caused an explosion and injury or death the Client and groundwork contractor would have been put out of business by the costs and both would have been investigated for breaches of Health and Safety legislation and Manslaughter.

Key lessons for Clients, Designers and Contractors

  • Always obtain up-to-date pipeline plans before starting work on a new site. Do not rely on old plans, second-hand or black and white photocopies.
  • Contact the pipeline Operator at the earliest opportunity to ensure that the design, method statements and construction equipment to be used on the project are safe and fit for purpose. This should be at least 7 days before start of work.
  • For more complex work, or work close to MAHPs, appoint an underground services coordinator to manage the risks on site from all buried services. Effective supervision and monitoring of the construction phase is critical for avoiding pipeline damage.
  • Confirm the location of pipelines with on-site surveys and by digging trial holes. With MAHPs the pipeline Operator needs to be on site at this stage too. Do not assume that just because you have not found the pipeline it is safe to continue with the work and do not assume pipelines always travel in straight lines.
  • Make sure that the risks from damaging the pipelines on the site are understood by all of the contractors working on the site. The more sub-contractors that are involved the more important this becomes. The pipeline Operator will be happy to give on-site briefings where MAHPs are involved.

Case study: full report

The Health and Safety Executive's (HSE's) Gas and Pipeline Unit commissioned researchers at the Health and Safety Laboratory (HSL) to highlight the underlying issues and factors that contributed to this third party MAHP infringement.  You can view the full report to find out more detail about this incident.

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Updated 2021-02-24