Fully pressurized shock strut from an aircraft exploded during disassembly.
Company says affected production unit shut down, the rest of the complex continues to run safely.
Fire broke out at the Philadelphia Energy Solutions Refining Complex.
Building has been evacuated and all company staff has been accounted for.
County fire Chief said there was no immediate indication of what caused the explosion.
The suspected cause is a hydrogen cylinder.
Pipeline explosion in October means supply will be reduced by 50% to 80% during the coldest months of the year.
Construction will take a few days, no timeline on when the repair work will be completed.
At the time of the explosion last week, there were as many as 3,000 workers at the refinery in Saint John, NB.
An explosion and fire Tuesday night led to a shut down of the firm’s main natural gas pipeline through British Columbia.
The blast Tuesday shut down the Enbridge natural gas pipeline about 15 kilometres northeast of Prince George.
Explosion was sparked by a fire in a gas pipeline in a coke oven battery complex during scheduled maintenance.
Explosion sent flames and black smoke into the sky but caused only minor injuries.
Blast at the Didion Milling plant killed five workers, injured 14 others and reduced the facility to rubble.
Men were doing maintenance inside a hydrogen compressor building at the Long Lake upgrader when the explosion occurred.