GONZALES (AP) — An explosion and fire at a Louisiana chemical plant claimed a second victim Friday as federal authorities were piecing together the cause of the blast that injured dozens more.

Scott Thrower, 47, of St. Amant, died at Baton Rouge General Hospital’s burn center, said State Police Capt. Doug Cain. According to company officials, Thrower was an operations supervisor and had worked for Williams since 1999.

Zachary Green, 29, of Hammond, died in Thursday’s explosion at the plant in Geismar owned by Tulsa, Okla.-based Williams Companies Inc. He was an operator at the plant and started working for Williams last October. His body was found by hazardous materials crews moving through the site after the blast.

The U.S. Labor Department’s Occupational Safety and Health Administration is investigating. A department spokesman and company officials said the cause of the blast wasn’t immediately known, but the FBI ruled out terrorism. Plant officials said Friday that the fire was fueled by propylene and propane, highly flammable chemicals that are produced on site.

“Right now, it’s really too early to determine anything,” Labor Department spokesman Juan Rodriguez said Friday.

Williams Companies president and CEO Alan Armstrong said at a press briefing in Gonzales that the extent of the plant’s damage was unknown and it was unclear when operations would resume.

A crew of 21 employees and four contractors were working 12-hour shifts securing equipment at the facility and ensuring it was shut down properly, said plant manager Larry Bayer. Employees would continue to be paid.

Both men expressed sorrow over the events and empathy for the families of those injured. Bayer said he met with Green’s family on Thursday. Grief counselors have been made available to employees, they said.

“For Williams, this is a terrible and unprecedented tragedy, and an extremely difficult time for all of us,” Armstrong said. “I’ve talked with a few of our employees today and I know that they are hurting. However, I’ve also seen and been very inspired by their courage and compassion for one another.”

Armstrong said the company has a solid safety record and prides itself on maintaining accident-free plants. He said he was “shocked” to hear about the explosion.

“A lot of us in this industry have spent much of our careers working to make it safe to operate,” Armstrong said. “So when something happens like this, it really, honestly, feels like a big failure.”

At the time of the explosion, shortly after 8:30 a.m., there were 839 employees and contract workers at the plant, Bayer said. The plant is in the middle of an expansion project, but Bayer said he didn’t know if employees were working on a specific task when the explosion occurred.

On Dec. 18, plant officials reported a propylene leak to the state Department of Environmental Quality that apparently was caused while workers were attempting to tighten a valve during repair job on a pipe. The leak of the flammable gas started on the opposite end of the pipe. The facility’s control room was notified by radio and all “hot work,” was stopped such as cutting, grinding, welding and automobile engines.

While area officials were notified, the facility’s emergence response unit responded and contained the propylene vapors, according to the report.

The release didn’t exceed the plant’s permitted pollution release limits.

An inspection of the leak source revealed a “small isolated area of corrosion” specific to the connection of the small pipe nipple to the larger transfer line, the report stated.

According to the report, the repair was a routine job that’s commonly performed, generally without an emissions release.

Louisiana’s health department said 91 people were evaluated at hospitals after Thursday’s explosion and at least 84 had been released by Friday. Three remain hospitalized in intensive care.

Geismar is a Mississippi River community about 20 miles southeast of Baton Rouge. The plant is one of scores of chemical and industrial facilities dotting the riverside between Baton Rouge and New Orleans. It makes ethylene and propylene — highly flammable gases that are the basic building blocks in the petrochemical industry.

The state DEQ was testing the air around the plant for about 60 different types of pollutants.

“There have been no pollutant levels of any concern,” department spokesman Rodney Mallett said Friday.

Bayer said officials don’t know when operations will resume.

The deadly June 13 explosion and fire at the Williams Olefins chemical plant in Geismar released more than 62

Gerald Herbert