CHEYENNE, Wyo. (AP) — State regulators issued three safety citations, including fire prevention and fire equipment maintenance violations, against the Sinclair oil refinery in Wyoming where a flash fire recently injured four workers.

Two fires occurred at the refinery while a routine safety inspection was being conducted last year, Ken Masters, compliance supervisor with the state Occupational Safety and Health Administration, said Friday.

A spokesman for Salt Lake City-based Sinclair Oil Corp. was out of the office Friday and not available for comment.

The state OSHA is investigating a flash fire that occurred Tuesday at Sinclair's refinery about five miles east of Rawlins.

Three workers were injured and remained hospitalized at North Colorado Medical Center's Western States Burn Center in Greeley, Colo. Their condition improved to fair Friday, according to a medical center official. A fourth worker was treated at Memorial Hospital of Carbon County in Rawlins and released Tuesday.

Masters said he couldn't speculate on when OSHA's investigation will be completed. New citations against Sinclair could be issued as a result of the investigation.

Sinclair has released little information about the fire but has said that it also is investigating and that its main concern is for the welfare of its injured workers.

The three citations issued in March listed serious violations with paperwork, maintenance, training and fire prevention. The state has proposed more than $45,000 in fines, which Sinclair can appeal and negotiate with the state.

Masters said the citations resulted from OSHA inspections of preventive maintenance operations and procedures at the refinery.

"If the management of those maintenance programs is not right, you can have some serious consequences," he said.

Inspectors consider violations to be serious when "there's a lack of proper maintenance practices that could result in a fire or it could result in somebody getting seriously injured," Masters said.

When OSHA inspectors were at the refinery in October and early November, two fires occurred at the facility, he said. It was the first time in his eight years with Wyoming OSHA that fires broke out while inspectors happened to be on site, Masters said.

Several other fires occurred at the refinery last year, but Masters said companies aren't required to report incidents in which fewer than three workers are hospitalized. Any incident in which a worker dies must be reported.

Sinclair has already corrected some of the violations reported in the March citations, and Masters said the company has been cooperative with the state agency.

There are five oil refineries in Wyoming, and OSHA does a thorough inspection of each about once every three or four years, Masters said. It takes about six months for such inspections, he said.