An explosion on an empty passenger train which showered broken glass over carriage seats was caused by a build-up of gases in an electrical equipment box, a rail safety inquiry has found.

The blast on September 26 last year is thought to have taken place shortly after the CrossCountry train left Bombardier’s Central Rivers maintenance depot at Barton-under-Needwood, Staffordshire, en route to Birmingham New Street.

A Rail Accident Investigation Branch (RAIB) report published on Thursday said the train driver was the only member of staff on board and he was unaware of the explosion in the rearmost coach until he arrived at New Street.

The report noted: “The damage sustained included buckling to the inter-vehicle doors, detached covers from the equipment case and damage to the ceiling.

“The door between the vestibule and the saloon was blown off its runners. Fragments of safety glass from the glazed area of this door were found throughout the adjacent saloon seating area.”

The explosion was caused by the failure of an electrical capacitor, the report found, which generated hydrocarbon gases which mixed with air and then ignited.

Modifications to the equipment cases have since been carried out, the RAIB said, and CrossCountry Trains have issued a national incident report to alert other users of similar equipment.