WEST GARDINER – An East Winthrop man was killed in an explosion Wednesday afternoon at the metal recycling company where he worked, authorities said.

Tim Arnold, 34, was killed in the blast that happened at 2:15 p.m. as metal materials were being melted down outside New England Metal, said Stephen McCausland, spokesman for the Maine Department of Public Safety.

Shawn Bunker, the business owner, was taken by helicopter to Maine Medical Center, where he was treated for shrapnel wounds and second- and third-degree burns, McCausland said.

Bunker, who lives next door to his business, was listed in critical condition at the Portland hospital Wednesday night.

A second employee was inside the office and escaped injury.

Officials from the Maine Fire Marshal’s Office, the Occupational Safety and Health Administration and the Maine Solid Fuels Board, which inspects furnaces and heating units, planned to return to the business Thursday to pinpoint the cause of the explosion, McCausland said.

A fireball erupted in the explosion and blew out the office windows, but did not cause any of the buildings to ignite, McCausland said.

The explosion could be heard at least two miles away, he said.

Gordon Chapman, who owns an auto sales business and garage 200 yards away, heard the blast.