The Occupational Safety and Health Administration has proposed penalties of $40,300 to the operator of a Smith County oilfield where three workers died in an explosion.

Another worker was injured in the June 5 blast at the Partridge-Raleigh LLC oil field about six miles southwest of Raleigh.

OSHA said Tuesday that the accident occurred as employees welded pipes connecting used oil storage tanks. The federal agency said vapors in one tank that contained oil residue traveled through the piping and sparks ignited the vapors.

Clyde Payne, director of OSHA’s Jackson office, said the agency’s regulations require purging of containers and piping before welding.

Payne said Stringer Oilfield Services was cited for allowing welding in an explosive atmosphere, failing to ventilate or take steps to prevent heat or sparks from entering the piping and tanks, failing to protect employees working on the tanks and failing to provide written safety programs for employees working in confined spaces.

The company has 15 working days to appeal the OSHA citations and proposed fines.

Those killed and injured were employees of Stringer Oilfield Services.

Cody Scarborough, 18, and Nicholas Pounds, 23, both of Foxworth, died at the scene of the explosion, officials said, while George Ben Jefferson, 53, of Columbia, died later.