HOUSTON >> At least 2 tons of highly volatile chemicals used in such products as plastics and paint exploded and burned at a flood-crippled plant near Houston early today, sending up a plume of acrid black smoke that stung the eyes and lungs.

The blaze at the Arkema Inc. chemical plant burned out around midday, but emergency crews continued to hold back because of the danger that eight other trailers containing the same compound could blow, too.

No serious injuries were reported. But the blast added a new hazard to Hurricane Harvey’s aftermath and raised questions about the adequacy of the company’s master plan to protect the public in the event of an emergency in the flood-prone Houston metropolitan area of 5.6 million people.

“This should be a wake-up call (for) all kinds of plants that are storing and converting reactive chemicals in areas which have high population densities,” said Nicholas Ashford, a Massachusetts Institute of Technology expert.

The Environmental Protection Agency and Texas environmental regulators called the health risks minimal in Crosby but urged residents downwind to stay indoors with windows closed to avoid inhaling the smoke.

Arkeda had warned earlier in the week that an explosion of organic peroxides stored at the plant was imminent because Harvey’s floodwaters engulfed the backup generators and knocked out the refrigeration necessary to keep the compounds from degrading and catching fire.

All employees had been pulled from the plant before the blast, and up to 5,000 people living within 1½ miles had been warned to evacuate on Tuesday.

Two explosions in the middle of the night blew open a trailer containing the chemicals, lighting up the sky with 30- to 40-foot flames in the small farm and ranching community of Crosby, 25 miles from Houston, authorities said. Aerial footage showed a trailer carcass, its sides melted, burning in a flooded lot.

The Texas environmental agency called the smoke “especially acrid and irritating” and said it can impair breathing and inflame the eyes, nose and throat.

Fifteen sheriff’s deputies complained of respiratory irritation. They were examined at a hospital and released.

The U.S. Chemical Safety Board, an independent federal agency, launched an investigation into the accident.

The plant is along a corridor near Houston that contains one of the biggest concentrations of refineries, pipelines and chemical plants in the country.

Andrea Morrow, a spokeswoman for the Texas Commission on Environmental Quality, said the agency had not received any reports of trouble at other chemical plants in the hurricane-stricken zone.

Texas A&M chemical safety expert Sam Mannan said the risk management plan that Arkema was required by state and federal law to develop did not address how it would deal with power and refrigeration failures or flooding.

A 2016 analysis he did with university colleagues ranked the Crosby plant among the 70 or so facilities with the biggest potential to cause harm in greater Houston, based on such factors as the type and amount of chemicals and the population density.

Arkema, which is headquartered in France, did not immediately return calls on the plant’s contingency planning.

Rachel Moreno, a spokeswoman for the fire marshal of Harris County, which encompasses Houston, would not discuss details of the risk management plan, such as how high the plant’s backup generators were placed.

Arkema officials did not directly notify local emergency managers of the generator failure, Moreno said. It came, instead, by way of the plant’s workers, who told the Crosby Volunteer Fire Department about it when they were rescued during the hurricane, she said.

On today, Rich Rennard, an executive at Arkema, said the chemical compounds were transferred to refrigerated containers after power was lost. But he said those containers failed too, causing the chemicals in one unit to burn. Rennard said more explosions were expected from the remaining containers.

In February, the U.S. Occupational Safety and Health Administration fined Arkema nearly $110,000 — later reduced to just over $90,000 — over 10 serious safety violations found during an inspection at the Crosby plant, according to agency records.

Records obtained by AP show that Arkema had kept using some equipment even when safety systems weren’t working properly, and didn’t inspect or test it as recommended. In one unit, the company also didn’t ensure equipment there was safe or keep employees up to date on their training.