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The massive Garden Grove Evacuation continued into a fourth day Monday as more than 50,000 residents in Orange County remained under mandatory evacuation orders amid fears that a leaking chemical tank at an aerospace facility could explode or release dangerous toxic vapors. Emergency crews worked through the night attempting to stabilize a damaged storage tank containing thousands of gallons of methyl methacrylate, a volatile industrial chemical capable of triggering a catastrophic blast.

Officials with the Orange County Fire Authority said firefighters and hazardous materials experts conducted overnight operations to determine whether dangerous pressure was building inside the tank or whether the system had begun releasing pressure safely through a crack discovered over the weekend.

The emergency response has become one of the largest hazardous materials incidents in recent Orange County history, involving hundreds of firefighters, state emergency personnel, air quality specialists, federal agencies, and law enforcement investigators.

Crews Race to Begin Garden Grove Evacuations

Authorities said the central concern remains the possibility of a BLEVE — a Boiling Liquid Expanding Vapor Explosion — involving the damaged tank at the GKN Aerospace facility in Garden Grove.

Orange County Fire Authority Interim Chief TJ McGovern said firefighters were still trying to determine whether pressure inside the tank had stabilized.

“The BLEVE threat is the worst-case catastrophic event that we've been talking about,” McGovern said during an operational briefing. “The worst-case scenario is still possible.”

Emergency crews discovered a crack in the tank Saturday night, raising new questions about whether pressure was escaping naturally or whether vapor buildup was creating structural instability that could eventually lead to a rupture.

Initially, reports suggested multiple cracks had formed. However, the Orange County Fire Authority later clarified that there is only one confirmed crack. Officials explained that peeling weather stripping caused by continuous hose streams created confusion about additional structural damage.

OCFA Public Information Officer Wayhowe Huang said water being sprayed on the tank around the clock caused exterior material to peel away, making it appear as though multiple cracks existed.

Dangerous Chemical Crisis Causes Garden Grove Evacuations

Officials estimate the damaged tank contains between 6,000 and 7,000 gallons of methyl methacrylate, a highly flammable chemical used in plastics, coatings, and industrial manufacturing.

Fire officials reported that the internal temperature inside the tank climbed above 100 degrees Fahrenheit — far beyond what responders described as the chemical’s “happy place” or stable operating temperature.

Incident Commander Craig Covey said temperatures had been increasing by approximately one degree every hour, alarming hazardous materials experts monitoring the situation.

Authorities warned that the actual temperature inside the tank could be even higher because the tank gauge maxes out at 100 degrees.

Experts fear the chemical’s self-heating properties could trigger what is known as a “thermal runaway” event, where rising temperatures rapidly accelerate chemical reactions and increase pressure inside the container.