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By Elizabeth Chuck

The Texas plant that sent noxious black smoke into the air after Harvey flooded now faces a federal investigation and it said on Friday that it won't make public a detailed chemical inventory.

"We understand that the public is worried," Arkema Inc. CEO Richard Rowe told reporters Friday. But citing "security reasons from a terrorism perspective," he said the French-owned company — which has already released a list of the commercial products and raw materials on-site — wouldn't give specifics on quantities or where in the facility potentially hazardous chemicals are located.

A list with those details is called a Tier II filing and is submitted annually to state and federal officials, plus local emergency responders, said Dr. Marco Kaltofen, president of Boston Chemical Data and an engineering professor at Worcester Polytechnic Institute.

Related: Harvey Danger: How Toxic Is the Air in Texas Chemical Plant Explosion?

"What they ask chemical plants to do is give out a worst-case analysis, what's the worst accident can happen," he said. "And there's been a lot of pushback because people fear that that kind of information is useful for terrorists."

The flooded plant of French chemical maker Arkema SA, which produces organic peroxides, is seen after fires were reported at the facilty in Crosby, Texas, on Aug. 31.Adrees Latif / Reuters

But members of the public have asked for Arkema to share their Tier II. A petition asking for the company to "be transparent about what dangers this situation carries" had garnered more than 6,100 signatures as of Friday afternoon.

The crippled plant in Crosby, about 20 miles outside of Houston, lost refrigeration at around 2 a.m. Thursday as Harvey blew out its power system, degrading chemicals — including a highly volatile one called organic peroxide. The chemical is used in products such as paint, kitchen countertops, polystyrene cups and plates, and PVC piping.

Residents in a mile-and-a-half radius of the plant were evacuated before two explosions rocked it as unprecedented levels of water rushed in.

More than a dozen law enforcement officers who were guarding the plant complained of irritated eyes and throats from the smoke, and some went to the hospital. A large fire broke out at the plant again on Friday.

There were "at least four explosions" Friday, officials said. The chemical company said the storm's floodwaters swamped its backup generators and knocked out refrigeration needed to keep containers of organic peroxides from catching fire.

The Environmental Protection Agency said data from aircraft monitoring the explosions' aftermath showed there were "no concentrations of concern for toxic materials reported at this time."

Rowe insisted earlier in the week that there was "no way" to prevent an explosion, given Harvey's intense destruction.

But the U.S. Chemical Safety and Hazard Investigation Board, an independent federal agency, announced on Thursday it had launched an investigation into the explosions.

"Our team’s initial activities will include significant document requests to Arkema, Inc. to gain an understanding of the following areas: The chemical process used at the Crosby site; specific chemicals stored, used and produced onsite; and implications for emergency preparedness and response efforts," the agency's spokesperson, Vanessa Allen Sutherland, said in a statement.

Investigators would not deploy to the area until it was safe to do so, she added.

The Texas Commission on Environmental Quality (TCEQ) confirmed it had Arkema's Tier II filing on record but said it couldn't release it without a public information request.

"The company can release their Tier II report to anybody they feel like, and they're able to release it if they wish to," said a TCEQ spokesperson, Andrew Keese.

The Tier II filing process was centralized after the 2013 deadly ammonium nitrate blast at a West, Texas, fertilizer plant.

State Rep. Joe Pickett, D-El Paso, who was part of the legislative push, said Arkema should be transparent about the dangers of their chemicals, but he didn't think a Tier II would benefit the general public.

"I don't think we should have easy information for anyone to find out," Pickett told NBC News. "I do feel that the general public has enough to fall back on. There's enough there that if somebody really is concerned, all they have to do is contact first responders in the area they live in."