Trains on the new Elizabeth Line have faults which could see metal boxes explode, whistleblowers claimed weeks after the London route’s grand opening.

       Up to 70 trains fitted with special devices on passenger doors could blow up from a build-up of gas that could potentially send metal flying, it has been claimed.

       Alstom, the company which built the trains, urged engineers working on the trains in depots not to go near the boxes, which contain electrical converters.

       The document, seen by the Daily Mail, said that engineers can walk past the devices while trains are switched on if no other route is available, but “make sure you are as far away from the converter as possible, do not loiter by the converter, walk as quickly past as possible, take no longer than four seconds to pass”.

       It added that staff should choose routes that avoid the boxes, which weigh about 15lbs.

       The whistleblower told the newspaper it was “odd” that the company had issued safety instructions to staff but not to customers.

       The source added that if the train passed people “and one of the doors comes off, it’s a 7kg lump of metal that could cause chaos and wipe quite a few people out”.

       It is understood a further 70 trains have the boxes, which are used by Greater Anglia on services from London to East Anglia.

       Spokesmen for both Alstom and Transport for London (TfL) insisted that the boxes did not pose a risk to passengers or anyone standing on platforms because the devices are placed below the doors, so beneath platform level.

       The Alstom spokesman said: “There is no risk to passengers using our Aventra trains, or on station platforms, from this small, potential fault affecting a train component. Detailed risk assessments support the continued operation of all potentially affected train fleets, including on the Elizabeth Line and on Greater Anglia.

       “Mitigating even the smallest risk for our depot maintenance staff is our absolute priority, which is why we have proactively introduced a temporary maintenance procedure pending the rollout of a modified component by the end of this month.”

       The Elizabeth Line, formerly known as Crossrail, opened last month and runs between Reading and Heathrow Airport to Abbey Wood, south-east London, and Shenfield, Essex.

       A TfL spokesman said: “Safety is our number one priority and we would never operate trains that are unsafe. Alstom, the manufacturer and maintainers of Elizabeth Line trains, informed us that there is a potential fault with a component on some of their trains, but assure us that it poses no risk to our customers.

       “This assessment has been supported by industry experts.”