Scott Thrower, 47, of St. Amant, died at Baton Rouge General Hospital's burn center, State Police Capt. Doug Cain said.
Another worker, Zachary Green, 29, of Hammond, died in Thursday's explosion at the plant in Geismar owned by Tulsa, Okla.-based Williams Companies Inc. Dozens of others were injured.
Green 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.
"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.
Plant manager Larry Bayer said a crew of 12 people was securing equipment at the facility Friday and ensuring it was shut down properly after the explosion. Employees would continue to be paid.
Louisiana's health department said 88 people were evaluated at hospitals after the explosion and at least 81 had been released by Friday morning.
Baton Rouge General Hospital was treating three other people who were injured in the explosion. Kelly Zimmerman, a spokeswoman for Our Lady of the Lake Regional Medical Center in Baton Rouge, said two of the 16 blast victims it has treated remained hospitalized Friday. One was in critical condition and the other was in fair condition.
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.
More than 300 people were evacuated from the site Thursday, but some stayed behind, officials said. Ten workers stayed in an explosive-proof control center as the fire raged, Cain said. The workers performed vital tasks, including shutting valves that rendered the plant safe.
The state Department of Environmental Quality 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.