BATON ROUGE, La. (AP) — Plants that were the sites of two chemical explosions  a day apart in south Louisiana remained closed, and it could be months before federal investigators determine the causes of the blasts that killed three workers and sent nearly 100 others to hospitals last month.
The Occupational Safety and Health Administration has sent teams to both sites to investigate the explosions.
OSHA has six months to complete investigations, spokeswoman Diana Petterson said in an email.
"It's difficult to say at this time how long the investigations will take," she said.
The blast happened June 13 at Williams Olefins in Geismar and June 14 at CF Industries in Donaldsonville, both located in Ascension Parish, southeast of Baton Rouge. Two people remain hospitalized with injuries, one from each blast, according to company officials.
Plant officials say they don't have damage estimates and are uncertain when operations will resume.
Both companies employ more than 300 full-time employees, and Williams Olefins has hundreds of contract workers as part of an expansion project that was underway at the time of the explosion. Company officials have said that Williams Olefins employees will continue to get paid while the plant is shut down.
The Williams Olefins plant, where one person was killed, produces ethylene and propylene, raw materials for common plastics used for such things as bottles, trash can liners and grocery store bags.
The Geismar plant explosion involved a distillation tower that left two people dead and sent 91 people to the hospital for treatment.
The U.S. Chemical Safety Board, an independent federal agency that investigates major chemical accidents, offered some insight into just how quickly danger developed at Williams Olefins, saying it took only seconds for a chemical vapor cloud to ignite into a towering inferno.
In recent testimony before a congressional committee, Chemical Safety Board chairman Rafael Moure-Eraso explained the early morning explosion started in the propylene fractionator area of the plant and involved a large distillation tower that processes propylene, propane and other highly flammable hydrocarbons.
The equipment was operating normally until 8:36 a.m., Moure-Eraso said.
"There was a sudden catastrophic failure involving a heat exchanger and associated piping attached to the distillation tower," he told the committee. "The steel shell of the heat exchanger ripped open, and piping detached where it connected to the tower. The exact sequence and cause of these events remains to be determined."
There was a "large-scale" release of propylene, propane and other hydrocarbons that formed a 200 feet high vapor cloud that ignited within four seconds, Moure-Eraso said. The fire burned for four hours.
Company officials have said there were 839 employees and contract workers at the plant at the time of the explosion as part of its expansion project.
Meanwhile, the blast at CF Industries happened in a section of the plant that was in "turn-around" mode, meaning the facility was shut down for scheduled maintenance, company spokeswoman Blythe Lamonica said.
The accident occurred in the evening, during a shift change. Lamonica said there were 25 to 30 employees on site at the time. It is unclear how many workers were in the immediate area of the explosion.
While that site is still closed, maintenance activity has resumed on a very limited basis, she said. The 10 other plants located on the complex are opened and are fully operational, Lamonica said.
The explosion happened when nitrogen was being pumped from an 18-wheeler truck via a hose attached to a nitrogen distribution header. For unknown reasons, the header ruptured or burst, killing one employee and sending seven others to the hospital for treatment. Authorities say there was no fire or off-site chemical release.
CF Industries manufactures ammonia and other nitrogen fertilizers at the Donaldsonville site for agricultural and industrial use.
Plants that were the sites of two chemical explosions a day apart in south Louisiana remained closed, and it could be months before federal investigators determine the causes of the blasts that killed three workers and sent nearly 100 others to hospitals last month. The Occupational Safety and Health Administration has sent teams to both sites to investigate the explosions.