AN explosion that occurred on a Guildford to Waterloo service after a South West Trains driver applied power, is being investigated by the Rail Accident Investigation Branch (RAIB).

There were no reported injuries, but some quite sizeable pieces of debris were deposited on platforms and in the car park.

The explosion took place last month inside an under-floor equipment case, as the eight-car class 455 train was leaving Guildford station.

RAIB revealed similar, smaller explosions had occurred on at least two previous occasions, and they had been attributed to a manufacturing defect, leading to a build-up of explosive gas within the traction equipment. Class 455 coaches are having new traction equipment fitted and the mechanism which caused the explosion is reported to have been at fault.

The RAIB has launched an investigation focussing on the management processes applied to retrofitting the traction units and management response to the previous similar incidents. They are also assessing the adequacy of any risk-control measures implemented and any other relevant factors.

The RAIB said in a statement: “We will publish our findings, including any recommendations to improve safety, at the conclusion of our investigation.”

• SWT will be replaced by First-MTR as the region’s rail operator on August 20.