At around 10:00 a.m., a leak was detected on an underground gas service lateral at the junction between a 3-m-long section of grey cast-iron pipe (DN 80) and a steel pipe. The leak caused a gas pocket to form in a confined space. Emergency services set up a cordon and 10 occupants in the building were evacuated. Traffic was halted. The gas distribution company replaced the pipe by a steel one.

Causes

The gas distribution company last inspected the gas service lateral in April 2014 and found no particular issues. However, its inspection procedure did not require precise identification of indoor pipes made from materials other than lead. Furthermore, the pipe was registered in its CMMS as being made of steel when actually it was made of grey cast iron.

Measures taken

Following the event, the authorities asked the gas distribution company to clarify how it determines the materials of gas service laterals and especially how it searches for brittle cast iron pipes. It also inspected similar pipes throughout the city (underground indoor pipes of DN>40 put in service prior to 1971). Of the 20 or so structures identified, none were made of grey cast iron.

According to the distributor’s commitments, the following measures will be taken in the event of a similar situation and if there is uncertainty about pipe materials:

• analysis and visit of connections on low-pressure islands;
• increased monitoring of gas service laterals;
• use of appropriate safety measures in the event grey cast iron is found

In addition, the distributor must also report the aforementioned measures in its operating report to the authorities. Its procedure on maintaining manifold connections around the country is also being modified.