MONACA — An explosion Thursday at a zinc smelting plant killed two people and injured at least one, authorities said.

A worker who initially had been reported missing was among the dead, Beaver County emergency dispatcher Kevin Joy said. The rest of the work force at the Horsehead Corp. facility was accounted for after the blast.

The explosion, which occurred around 4:30 p.m., involved a refinery column that produces zinc oxide, Horsehead spokesman Ali Alavi said. The facility has about 600 employees, he said. One worker complained of neck pain and was being checked out at a hospital, Alavi said.

County Coroner Teri Tatalovich-Rossi said the names and causes of death of the two victims would not be released until today, pending the results of autopsies and notification of families.

An investigation is under way to determine the cause of the explosion, Alavi said. Despite initial reports that a fire had broken out, he said: "My understanding was that there was no fire. There was an explosion, but no resulting fire."

Wesley Hill, director of Beaver County Emergency Services, said Thursday night that the explosion caused no risk to the public. The plant lies at a crossroads about a mile south of a shopping mall.

A half-mile down the road, workers at the World Famous Midway Bar & Grill, a regular hangout for plant workers, said emergency crews had used the bar's gravel parking lot as a staging area shortly after the blast.

According to its website, the U.S. Occupational Safety and Health Administration issued citations with proposed penalties of $186,750 in January 2006 at the facility. The results came after an investigation into why an employee stepped into an "uncovered condenser pit full of molten zinc" and suffered severe burns to his legs, according to the site.

OSHA also issued 27 "serious citations" for alleged violations that included a failure to use an approved safety platform, provide guardrails and protection barriers. The agency issued 14 "other-than-serious" alleged violations for "failing to maintain required records of employee exposures to lead and cadmium."

On its website, Horsehead said the electrothermic zinc smelter "operates as the country's largest."