HOUSTON (AP) — A tank holding a flammable chemical caught fire at a Texas plant Tuesday, killing one worker, critically injuring two others and sending panicked employees fleeing over a fence to safety.

Harris County Sheriff Ed Gonzalez confirmed the fatality in a tweet and said the two injured had been taken by helicopter to a hospital. The two injured were in critical condition, said Rachel Moreno, spokeswoman for the Harris County Fire Marshal’s Office.

Authorities shut down a roadway near Tuesday’s fire at a KMCO chemical plant in Crosby, about 25 miles (40 kilometers) northeast of Houston, Gonzalez said.

All residents within a one-mile radius of the plant were ordered to stay indoors or shelter in place. The fire sent a large black plume of smoke into the air.

The fire erupted about two weeks after a March 17 blaze at a petrochemical storage facility in Deer Park , located about 20 miles (32 kilometers) south of Crosby. That fire at a facility owned by Intercontinental Terminals Company burned for days and triggered air quality warnings. Crosby also is where an Arkema’s chemical plant was inundated by water during Hurricane Harvey in 2017. Some chemicals eventually caught fire and partially exploded.

“It is disturbing and it is problematic that we’re seeing this incident in a facility, especially on the heels of” the fire in Deer Park, said Harris County Judge Lina Hidalgo, the county’s top administrator.

Gonzalez said a transfer line at the KMCO plant ignited in the area of a tank of isobutylene — a flammable colorless gas used in the production of high octane gasoline — which then caught on fire. First Responders were trying to contain the fire, Gonzalez said.

The fire spread to a nearby warehouse where dry chemicals are stored. Officials were working with KMCO to get a list of what chemicals were in the warehouse, Moreno said.

Moreno said the Environmental Protection Agency has been testing air samples from the area around the plant and has not found any harmful readings.

Worker Justin Trahan told Houston television station KPRC that he heard “some panic on the radio” but no alarms sounding before the plant caught fire.

“We didn’t think anything of it — we didn’t think it was anything severe,” he said.

Trahan said employees began running after “the tank ignited.”

He said that he and other colleagues had to jump over a fence to escape because all the gates were locked.

John C. Foley, chief executive of KMCO, said in a statement that the company had activated its emergency response team and set up a command center.

“We are working with local first responders to extinguish the fire,” he said.

KMCO is a chemical company that offers coolant and brake fluid products and chemicals for the oilfield industry.

The Crosby, Sheldon and Channelview school districts asked students and staff to shelter in place at all their campuses. But later Tuesday afternoon, Crosby and Sheldon lifted those orders to shelter in place.

The Texas Commission on Environmental Quality said that it has dispatched emergency response personnel to conduct an initial assessment of the fire.

KMCO has had environmental violations in the past, according to a review of records.

In 2016, KMCO’s corporate agents pleaded guilty to a federal criminal charge of violating the Clean Air Act. A plea agreement document stated that a plant employee made false entries in logs of air testing of tanks that were known to be leaking chemicals. Another employee then used those falsified logs to submit reports to the federal and state environmental authorities. The document says the violation went on between 2008 and 2012.

A year earlier, the EPA cited KMCO for failing to comply with regulations on its risk-management plan for the plant, but settled with the plant for a $2,700 penalty.

Texas has served the plant with three notices of violation of a federal clean-air law since last August, the EPA website shows.