Senior fire officers are facing possible disciplinary action after allegedly putting a civilian's life at risk.
After a gas leak, at the Allied Bakeries plant, Leyton, an "on-site specialist" was given protective equipment and asked to shut off the electricity supply to a number of acetylene gas cylinders.
Although the building he was sent into was not on fire at the time, the decision was blasted by the Fire Brigades Union (FBU).
Julian Butler, general manager at the Leyton plant, said: "We had an incident with some oxy-acetylene cylinders and we evacuated the site as a matter of caution.
"A pipe from the cylinders had ruptured and there was a flame from that pipe but it was dealt with quickly."
The cylinders had been leaking gas into "an area containing a number of potential ignition sources" creating an explosion risk, according to the London Fire Brigade.
A spokesman for the FBU said: "This is an extremely dangerous practice and could have led to a member of the public losing his life."
But London Fire Commissioner Ron Dobson maintained the decision was taken only after firefighters could not shut off the electricity supply themselves.
He said: "This incident[...]placed the surrounding community at considerable risk from an explosion.
"It was necessary to shut down the electricity supply to the machinery in the building as soon as possible, but an attempt made by firefighters on the scene, under the guidance of an on-site specialist, was unsuccessful.
"Due to the complexity of the controls involved, a decision was made to issue the on-site specialist with protective equipment."
He also stated that the man was accompanied by firefighters and that his actions resulted in "bringing the incident to a safe conclusion".
"It is unfortunate that the Fire Brigades Union has chosen to sensationalise this aspect of the incident," he added.
"It would not be a normal approach for personnel other than firefighters to assist in this way, but with the risk to the community that was present and with the appropriate control measures in place, the decision was considered to be proportionate."
The incident, which took place in February this year, is now under investigation.
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