Southern California chemical tank crisis: Explosion risk eliminated — But the emergency isn’t over

A potentially catastrophic chemical emergency in Southern California eased significantly on Monday (May 25) after firefighters confirmed that pressure inside an overheating industrial tank had been relieved through a crack in the container, sharply reducing the risk of an explosion.

The incident unfolded at a manufacturing facility operated by GKN Aerospace in Garden Grove, California, where a large storage tank containing thousands of gallons of methyl methacrylate — a highly flammable industrial chemical used in plastics manufacturing — overheated and began venting vapors.

Although authorities say the immediate explosion risk has diminished, evacuation orders affecting roughly 50,000 residents remain in place while crews continue monitoring the site.

The tank contained between 6,000 and 7,000 gallons of methyl methacrylate (MMA), a chemical commonly used to produce acrylic plastics and transparent components for commercial and military aircraft.

As temperatures inside the tank increased, the chemical began releasing vapors — a warning sign that pressure was building within the sealed container.

Firefighters responded by continuously spraying the tank with water to cool it down and prevent what experts feared could become a massive industrial explosion.

By Sunday, officials said the interior temperature had climbed to about 100°F (37.7°C), increasing concern that the tank could rupture violently.

As MMA warms, it can transition from liquid to gas, causing pressure to build rapidly inside a confined container. If pressure rises beyond what the tank can withstand, the vessel can rupture explosively.

Engineering experts compared the scenario to an overheated soda can.

A crack discovered in the tank turned out to be unexpectedly beneficial because it allowed pressure and gas to escape gradually rather than accumulate to explosive levels.

By Monday morning, officials said the tank temperature had dropped to 93°F (33.9°C), and the pressure release dramatically reduced the likelihood of a catastrophic blast.

Orange County Fire Authority Division Chief Craig Covey described the overnight findings as “incredibly positive news.”

At night, cooler ambient temperatures reduced risks to firefighters and allowed teams to safely approach the container, conduct thermal readings, and confirm that the crack was relieving pressure.

Drones were also deployed to monitor the tank every 10 minutes for temperature spikes.

Officials additionally installed containment barriers around storm drains and waterways to prevent environmental contamination if a leak occurred.

It is highly flammable and can pose serious health risks when inhaled in significant concentrations.

Potential health effects include:

-Respiratory irritation and breathing difficulty

-Eye, skin, and throat irritation

-Neurological symptoms such as headaches or dizziness

-Nausea and chemical sensitivity

MMA has a strong odor and may be smelled over wide areas even at concentrations below harmful levels.

-The tank still contains hazardous material

-The structural integrity of the container remains uncertain

-A chemical leak remains possible

-Conditions could change if temperatures rise again

The emergency has nevertheless disrupted thousands of households and businesses across the region.

The lawsuit argues that regardless of whether an explosion occurs, the emergency itself could reduce nearby property values and expose residents to long-term environmental stigma.

GKN Aerospace has apologized to residents and said it has been “working around the clock” to reduce risks.