Many Texans are turning to dangerous heat sources amid widespread power outages caused by the winter storm, leading to more than 900 carbon monoxide poisoning cases in the state.

The Houston Fire Department reported over 300 calls related to carbon monoxide poisoning as of today. Across Memorial Hermann Health System hospitals, there’s been 100 such emergency room cases. 

“With that number of patients going in, it’s turning into a mini mass casualty event,” Samuel Prater, MD, UTHealth emergency physician who works with Memorial Hermann, said.

More than half of the patients treated at Memorial Hermann’s emergency rooms were children. 

Ben Taub Hospital, Lyndon B. Johnson Hospital and Baylor-St. Luke’s Medical Center, all based in Houston, have also treated a number of carbon monoxide poisoning cases since Feb. 15, according to the Houston Chronicle. Several deaths in the Houston area are also suspected to be caused by carbon monoxide poisoning. 

Many of the cases have been linked to unsafe use of heat sources such as grills and space heaters, Memorial Hermann Health System said in a Feb. 15 statement.

“If you’re using generators to supply power, the generator needs to remain outside,” Dr. Prater said. “Also, under no circumstances should barbeque pits be used inside the home to create warmth.”

The health system also warned against leaving a gas range or oven running, among other uses of unconventional heat sources.

“They’ve been going without heat for over 30 hours now and trying to protect their families by doing the best way they know how,” Rachel Netzler, a spokesperson for the Harris County Fire Marshal’s office, told the Chronicle. “Unfortunately, all these carbon monoxide poisonings are preventable.”