The blaze burned for several hours into the evening as firefighters used foam to douse it.
"They're making sure there are no flareups," Police Lt. Douglas Moore told Daily Voice just after 6:30 p.m.
UPDATE: PSE&G Must Wait To Find Cause Of Explosion, Fire
The vegetable oil-based substance that burned didn't contain any toxic chemicals and there was no public health risk, he said.
A firefighter sustained an ankle injury when a hose snapped from a hydrant and hit him, Moore said. No other injuries were reported.
Residents said they heard an explosion at the Hopper Avenue switching station around 10:40 a.m. A PSE&G spokeswoman blamed an equipment failure.
The fire was contained inside the perimeter, although rising columns of thick, black smoke could be seen for miles.
PSE&G de-energized the station and foam was being used to put down the blaze, Moore told Daily Voice.
NJ Transit temporarily suspended rail service between Ridgewood and Allendale and provided buses.
Power was temporarily knocked out to 2,000 or so customers in several towns besides Waldwick, including Hillsdale, River Vale, Westwood and Woodcliff Lake.
"Waldwick Day" was postponed until next Sunday.
Several area fire departments and EMS units also responded.
Responding or requested were Allendale, Franklin Lakes, Garfield, Ho-Ho-Kus FAST, Midland Park, Ramsey, Wyckoff, along with the Bergen County Office of Emergency Management and Hazardous Materials Unit.
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