Investigators say the man surrendered after a three-hour standoff Tuesday night at the Halliburton building in Clairmont, north of Grande Prairie.
Two employees had locked themselves in a room in the building and hid inside with the lights off.
They had no contact with the gunman and it appears he didn't know they were there.
Police say another employee approached a police roadblock during the standoff and told officers he knew the suspect and had him on a cellphone.
Officers were then able to negotiate with the man.
He turned himself in and officers seized a handgun and assault-style rife.
Police say gunfire damaged some of the facility, including windows and a water line.
"Fortunately, no Halliburton employees, police or other members of the public were injured in the incident and no shots were fired by the RCMP," Insp. Gibson Glavin said.
He said officers are looking at the man's employment history with the company.
"Clearly, that's probably an element of motive behind what happened," Glavin said. "We'll need to get to the bottom of that."
The 58-year-old man from Grande Prairie was to appear in court Wednesday.
His name has not yet been released.
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