Like a cold-blooded animal—a lizard or a snake—the petrochemical hub that is the state of Texas went dormant during the deep freeze. Eventually, it’ll wake up again, and when it does the damage will be worse than if it never went to sleep. Filings submitted in recent days to the Texas Commission on Environmental Quality, or TCEQ, already show significant emissions related to stopping and restarting fossil fuel infrastructure. It’s an indication of what’s to come in a state that’s home to a quarter of U.S. natural gas production as well as half the oil production.

“This is an environmental disaster on top of a public safety and human health disaster,” said Luke Metzger, executive director of Environment Texas, an advocacy group.

Refineries must flare off or otherwise release trapped pockets of gas when starting up or shutting down. While weather-based shutdowns are often unavoidable and done in the interest of safety, they can result in emissions that go far above allowable levels. “These events are not exempt from pollution laws,” Metzger said. “It’s likely the events at these facilities could have been avoided.”

Exxon spokesman Todd Spitler emphasized that the shutdowns were due to the freezing weather and curtailment of natural gas supplies. “Any units that remain in operation are dedicated to exporting electricity back into the grid,” he said. Representatives from Valero didn’t respond to a request for comment; a spokesperson for Pioneer declined to comment.

This is the second time in less than six months the Texas oil industry has dealt with mass shutdowns due to extreme weather. The 12 hours after Hurricane Laura hit Port Arthur in August saw the release of more than 2,000 tons of emissions.

“I expect the oil industry is going to have numerous problems restarting, similar to what they encounter after a hurricane, such as damaged cooling towers and other equipment,” said Andy Lipow, president of Lipow Oil Associates in Houston. “The industry also has to be wary of water freezing and cracking pipes, which could release hydrocarbons into the atmosphere and cause an explosion and fires.”

The heightened risk of explosions are a grim reminder of what followed the onslaught of Hurricane Harvey in 2017. Floods at an Arkema SA chemical plant about 25 miles east of Houston knocked the refrigeration system offline, which imperiled the facility’s store of heat-sensitive organic peroxides. People living within 1.5 miles of the facility evacuated a day before trailers holding the chemicals “spontaneously combusted,” according to a Chemical Safety Board investigation. Arkema did not respond to questions.

The full scope of pollution from restarting petrochemical facilities following the freeze won’t be clear until next month. Companies must file final reports within two weeks, and TCEQ evaluates the disclosures against its rules governing emissions.

TCEQ is responsible for both the state’s air and water, the latter of which is also a concern for leadership. “We’ll examine what worked, what didn’t work so well, and what we can do to make things better next time—or, better yet, prevent it from happening again,” said Toby Baker, the agency’s executive director.