Three workers were taken to the hospital as a precaution, Phillips 66 said in a statement. They were all contract workers and their conditions weren’t known Friday.

The gas leak occurred about 5 p.m. in the refinery at 3901 Unick Road.

“Our internal response team immediately activated the emergency response plan and the leak was contained within the property,” Phillips 66 stated.

Phillips and emergency responders said the leak was contained quickly. It occurred in the alkylation unit.

“There was no threat to the public, to anybody in the area,” said Assistant Chief Larry Hoffman of Whatcom County Fire District 7, which serves the Ferndale area.

Other workers “sheltered in place as a precaution,” Phillips 66 said.

There also was a report of a precautionary evacuation. A horn was blown at 6:13 p.m., signaling the all-clear for people to resume normal work activity.

What caused the leak is under investigation. Hydrofluoric acid is used to create gasoline, and its use has created concerns.

Further details about the incident were not immediately available Friday night.

The refinery processes a variety of domestic and foreign crude oils, including Alaskan North Slope, Canadian and U.S. shale. The 850-acre facility was built in 1954.

More than 400 employees and on-site contractors work there, according to its website.