The federal Environmental Protection Agency is on the scene of a  dangerous chemical leak at a Garden Grove aerospace facility that led officials to evacuate roughly 50,000 residents over an explosion threat, the agency told The California Post.

At the request of Orange County Health Care Agency, the EPA is providing air monitoring support and vital air quality information to local authorities.

“EPA has monitors located throughout the area and in the community, and all air monitors are currently showing non-detect. EPA is working closely with state and local authorities, including Orange County Fire Authority (OCFA), the lead for this response,” it said in its statement.

The monitoring comes after a pressurized storage tank holding 7,000 gallons of methyl methacrylate, a highly flammable liquid used in plastic manufacturing, began heating up after the cooling mechanism stopped working.

Fire authorities said there were two scenarios that could happen: A catastrophic explosion or a major spill of the liquid.

Thanks to a crack in the container and cooling attempts by fire authorities, the explosion was ruled out earlier in the week. And on Tuesday night, Orange County Fire Authority Chief TJ McGovern told reporters that all public evacuation orders have been lifted.

“To the residents, we thank you again,” he said. “We understand the inconvenience and the difficulties and the challenges that this has all brought to you.”

A street closure remains in effect, Garden Grove Police Chief Amir El-Farra said. Western Street from Garden Grove Boulevard to Chapman Avenue is closed.

Crews are checking the temperatures of the tank and mitigating any issues. Orange County Health Officer Dr. CK said air monitoring would continue to ensure fumes from the chemicals don’t pose a threat.

Exposure to the chemical can have serious health consequences.

“It’s a respiratory irritant, so it can start off very mild, but it can progress to a point where, yes, you would probably require hospitalization, if not more,” Division Chief Nick Freeman of the Orange County Fire Authority told ABC7.

Exposure can occur through inhalation or direct contact. Short-term exposure may irritate the skin, eyes and respiratory system, while longer-term exposure can cause “severe respiratory distress.”

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