Workers at the QCLNG project on Curtis Island were told to stay in their rooms yesterday morning after a vapour leak was detected.
A monitor picked up the leak at 4:30am and a text message was sent to employees about the indecent advising them to stay in their crib huts.
Bechtel Gladstone general manager Kevin Berg said the cause was still being investigated.
"The vapour is from the LNG produced through the first production train and currently being stored in the LNG holding tank," Berg said.
"It is currently understood to have originated from a flanged component in one of the LNG pumps in the tank, which in turn triggered a local gas alarm alerting the plant operations staff to take appropriate action," he said.
"The pump was powered down and isolated from the system, emptied of LNG and corrective action is expected over the coming days in working with the LNG pump supplier."
Workers returned to work after lunch when it was deemed safe to do so.