Arkema SA's U.S. arm failed to relocate chemicals made at the Crosby, Texas, plant ahead of 2017's Hurricane Harvey and every prior storm, charged prosecutor Michael Doyle.

Arkema, its U.S. chief executive, Richard Rowe, and the plant manager, Leslie Comardelle, are charged with the toxic releases. Former logistics chief Michael Keough who helped coordinate the response was charged with assault over injuries to emergency workers who inhaled the fumes.

The plant outside of Houston in 2017 became waterlogged and lost power needed to cool volatile chemicals after Hurricane Harvey dumped more than 50 inches (1.27 m) of rain on the area. Twenty-one people sought treatment for exposure to fumes from three chemical fires that erupted.

"The question is not when should it be removed, but should it be kept there when severe weather is threatening?" Doyle told a jury of nine women and three men. The plant is in a flood plain and had never removed its chemicals ahead of storms.

The executives face up to five years in jail on an endangerment charge and the company could be hit with a fine of up to $1 million. All pleaded not guilty in court on Thursday.

Defense attorneys accused the state of criminalizing "an act of God," and insisted no one could have foreseen the flooding that led the volatile organic peroxides to ignite, releasing toxic fumes.

The plant had never previously flooded and never lost power, said Arkema attorney Letitia Quinones. It would have been more dangerous to residents to move the chemicals through city streets, she said.

"No one knew it was going to be like this," said Quinones. She said law enforcement officials determined the area to be evacuated, not company officials. Two of the deputies that were injured entered the exclusion area without taking proper precautions, she said.

Judge Belinda Hill rejected defense motions for a mistrial after Doyle cited testimony given under immunity that the judge had ruled was not permitted in court.

The trial began after a series of petrochemical fires in the region last year fouled the skies over several cities, raising worries about chemical industry practices. The state's top environmental regulator called for a compliance review after businesses and schools were evacuated by fires at sites making gasoline, rubber, resins or storing petrochemicals.

The Crosby plant produced organic peroxides that are used to make plastic countertops, consumer goods and automotive parts. More than 350,000 pounds of the chemicals ignited and burned during three separate fires, a report by the U.S. Chemical Safety Board found.

By Erwin Seba