As historic rainfall and flooding continue to pound America’s fourth-most populated city, residents of Houston’s industrial fence-line communities are reporting strong gas and chemical-like smells coming from the many refineries and chemical plants nearby. “I’ve been smelling them all night and off and on this morning,” said Bryan Parras, an activist at the grassroots environmental justice group TEJAS. Parras, who lives and works in Houston’s East End, on Sunday said some residents are experiencing “headaches, sore throat, scratchy throat and itchy eyes.”

Parras said there are chemical smells in the air all over the East End, but particularly in communities adjacent to Houston’s sweeping petrochemical industry. And residents can’t escape the smell, because flood waters have overtaken the city, and could reach over four feet in some spots. “Fenceline communities can’t leave or evacuate so they are literally getting gassed by these chemicals,” Parras said.

It’s still unclear exactly where the smells are coming from, but Parras suspects the source is the many oil refineries, chemical plants, and gas facilities nearby. Several of these plants have shut down or are in the process of shutting down due to Harvey’s historic flooding, and shutdowns are a major cause of “abnormal” emission events, according to a 2012 report from the Environmental Integrity Project. Short-term impacts of these events can be “substantial,” because “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.” The communities closest to these sites in Houston are disproportionately low-income and minority.