Hurricane Harvey, which has since been classified as a tropical storm, has claimed the lives of at least eight people. Millions continue to struggle in the dangerous floods plaguing the city of Houston, and as they hold on for survival, they face yet another threat.

Harris County, Texas, is home to roughly 40 percent of the nation’s petrochemical capacity.

At least 10 refineries have shut down, but whenever a refinery has to close or be restarted–especially in emergency situations–its emissions far exceed what is usually allowed.

“Upsets or sudden shutdowns can release large plumes of sulfur dioxide or toxic chemicals in just a few hours, exposing downwind communities to peak levels of pollution that are much more likely to trigger asthma attacks and other respiratory systems,” a 2012 study cited on the Huffington Post stated. “The working class and minority populations typical of neighborhoods near refineries and chemical plants bear the brunt of this pollution.”

Some Houston residents are already feeling the effects of the refineries. Bryan Parras is a nonprofit worker who visits the area. He told the Houston Press that he was certain the pollution was affecting him.

“It was weird because I was getting a heartache and a scratchy throat, like the one I get when I take people on toxic tours of Manchester, but I was sitting at home,” Parras said. “The stuff was getting sucked into my house through the window air conditioning units.”

President Donald Trump is scheduled to visit the state, but will not stop in Houston so he won’t “be getting into harm’s way or interrupting the evacuations or emergency response.”

“He most likely will be going closer to where the hurricane hit land,” Texas Gov. Greg Abbott said during an appearance on Cbs The Morning.