An explosion and fire killed at least one person and injured 73 at the Williams Olefins chemical plant in Geismar, Louisiana, on Thursday, leading authorities to order people within two miles to remain indoors.
The blast at 8:37 a.m. (0937 ET) sent a huge fireball and column of smoke into the air at the plant along the Mississippi River just south of Baton Rouge and about 60 miles up river from New Orleans.
The fire, fueled by the petrochemical propylene, was still burning more than five hours later, though government monitors had yet to detect dangerous levels of emissions, Louisiana Governor Bobby Jindal told a news conference near the scene.
"There are no early detections of dangerous levels of VOC - that's volatile organic compound - but out of an abundance of caution both the company and the DEQ (Department of Environmental Quality) are doing testing not only at the plant site but miles away from the plant site following the direction of the plume," Jindal said.
Some 300 workers from the plant were evacuated and all the employees were accounted for, among them 10 who stayed behind in a safe room inside the plant, Jindal said .
"Emergency shut-down valves have been closed. The unit is isolated," parent group Williams Cos. said in a statement.
The company's own emergency response crews were assisting at the scene, Williams said.
At least five victims were being treated at Baton Rouge General Hospital, Dr. Floyd Roberts said.
"The next 48 to 72 hours is a critical time for burn victims, and as a team we're focused on stabilizing airways, replacing fluids ... and treating the wounds with antibacterial dressing to combat infection," Roberts said.
Authorities ordered people within a 2-mile (3-km) radius to remain in their homes, in part because of the toxic smoke, said Lester Kenyon, a spokesman for Ascension Parish.
That "shelter in place" order was later lifted for residents but remained in effect for four other plants in the area that scaled down their operations, Jindal said.
The U.S. Coast Guard said traffic on the Mississippi River went unaffected.
The plant produces approximately 1.3 billion pounds of ethylene and 90 million pounds of polymer grade propylene, according to the Williams website. These are used in the petrochemical process to make plastics.
Only propylene was burning, officials said.
"The chemical involved is a flammable, which is good in the sense that it is burning itself off, so there's no impact outside the fence line of the facility," Louisiana State Police Captain Doug Cain said.
Williams operates the plant and holds an 83 percent ownership interest in the Geismar facility, it said.
Shares in Williams Cos. fell as much as 3 percent shortly after the reports and were down about 1.5 percent in afternoon trade.
With massive equipment operating under intense pressure and high heat, the petrochemical industry is particularly prone to occasional fires and explosions, most of which are quickly brought under control with limited injury or damage.
Southern Louisiana is home to a large share of the country's petrochemical facilities and has seen at least two other blasts in the past two years.
Pressure on the industry to improve safety has increased since a blast at the Texas City refinery killed 15 people in 2005, among the worst such industrial accidents in decades.
An explosion at a fertilizer plant in West, Texas, that killed 14 people in April has also sharpened attention on handling of volatile chemicals.