Pollution
Humain
Environnement
Economique

Pipeline characteristics:

  • 24”
  • Pressure: 45 bar
  • Year put in service: 1958
  • Burial depth: 1 m
  • Thickness: 9 mm
  • Protected by concrete slabs

During drainage work being done by a specialist company, a trencher damaged a high-pressure gas transmission pipeline located in a field, resulting in a loss of pressure that was registered in the control room of the company operating the pipeline. The blast of gas created a 3-m-wide by 5-m-long crater. The trencher’s emergency stop was engaged (immobilising it but not cutting off its engine). The four people working on the trencher, and the two people working on an excavator located 150 m away, evacuated the area and then alerted the company. Although there were concrete slabs, the trencher’s vibratory plough pierced the pipeline’s side, opening a gash more than 10 cm in diameter. In doing so, the vibratory plough became stuck in the gash, partially sealing the leak.

Management of the leak

The pipeline’s emergency plan was implemented. Emergency services set up a 400 m cordon. Three other gas transmission pipelines were located in the immediate area. The nearby road was closed to traffic. The operator isolated (automatic isolation valves) then purged the damaged section. The trencher’s engine was turned off after the pipeline was completely decompressed.

Consequences

More than 200,000 m³ of natural gas leaked out. The distribution networks were not affected by the event.

Analysis of the causes of the damage

The work permit and notice of intent to commence work had been filed at the same time. A meeting had been held at the jobsite more than three weeks before the start of work. A representative of the contractor was present at this meeting, but they lacked a clear understanding of the jobsite. Miscommunication during this meeting is likely what caused the accident.

After visiting the site, the inspection authorities for classified facilities noted the need to conduct an analysis of:

  • The procedure implemented by the pipeline’s owner, which does not provide any layouts to the project manager (as per the work permit) or the contractor (as required during the site meeting held for marking and staking operations, which are the responsibility of the network operator in the case of safety sensitive networks).
  • Maintaining marking and staking in the absence of layouts, pictures, etc. ;
  • The notion of a ‘work area.’ Rather than being performed in the whole area of the work permit, the marking and staking has been carried out in an area on which the contractor and the pipeline’s owner both agreed during a meeting at the jobsite. However, this agreement was verbal only and had not been recorded in the marking/staking report.