Staff spotted two broken parts near Old Street Station, east London, on 8 March after a passenger train driver reported water pouring on to the train's roof.

BBC: Construction drill came from site above rail tunnel

The Barlow train shed with its single span roof, a marvellous feat of Victorian engineering, is being restored.

BBC: St Pancras - the new link to the Channel Tunnel

If something gets in the way of the door--a person's foot or a roof panel that's hanging down--the electric motor that closes the train door has to work harder and produces more current.

FORBES: Magazine Article

The danger was compounded by an overhead power cable, which broke loose and fell on the roof of the rear car, causing further arcing and a large amount of smoke inside the train.

BBC: Metro train fire