Delhi Metro Rail Corporation (DMRC) managing director Mangu Singh approved the orders of suspension based on an inquiry done by a team of three Executive Director-rank officials, DMRC chief spokesperson Anuj Dayal said.
The four officials include one deputy general manager who was the depot in charge, one assistant manager, a junior engineer and an assistant section engineer, Dayal said.
"The incident report of the inquiry revealed that this incident was solely attributable to human failure as proper procedures were not followed," Dayal said.
The brake of the train, which will run on the Botanical Garden-Kalkaji Mandir section to be launched on December 25 by the prime minister, was not functional when it was being taken for washing, the DMRC said.
It was because, as per DMRC's laid down norms, when a train enters a workshop (depot), the brakes of the train are decommissioned so that the train and its systems including the brakes can be freely checked.
"As a result, as soon as the operator brought the train at the ramp, it started rolling back, got derailed and hit the wall," Dayal said.
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He also stressed that the train, which can be enabled to run unattended or 'driverless', was not actually without a driver when the incident happened as a person was very much on board.
Trains on the new 12.38-km-long section, part of metro's upcoming Magenta Line, will initially operate with a driver with a high level of automation including platform screen doors, he said.