GKN methyl methacrylate leak: what lessons can be learnt?

On May 21, a thermal runaway inside a tank of methyl methacrylate (MMA) at GKN Aerospace’s Garden Grove, California, aerospace manufacturing facility triggered a vapor release from the tank into the atmosphere. The continuing thermal event subsequently clogged the pressure-relief valves, causing pressure in the tank to expand, leading to several days of uncertainty about whether the tank would crack or explode and what the risks might be to surrounding communities if either occurred.  

The tank is one of three clustered together outside the southeast corner of the GKN facility (see map). The capacity of each tank is 34,000 gallons (128,700 liters). Tank #1, the source of the leak, held about 7,000 gallons (26,500 liters) of MMA. Tank #2, which contained an unknown quantity of MMA, did not leak. The contents of the third tank, referred to as Tank #4, are unknown and the tank was not a focus of concern throughout the incident. 

Without functioning valves on the tank, the only recourse authorities had was to douse the tank with water in the hope of slowing the reaction and preventing an explosion — what is called a Boiling Liquid Expanding Vapor Explosion (BLEVE).  

At the peak of the crisis on May 22 and into May 23, state and local officials, fearing the health impacts of a cloud of MMA wafting over neighboring communities – particularly in the event of a BLEVE — ordered evacuation of 50,000 residents from communities surrounding the GKN facility, with the closest homes and neighborhoods located due east of GKN and approximately 1500 feet (460 meters) from the company’s property. 

By May 25,2026 thanks to a combination of cooling water from firefighters and a leak in the tank that relieved the growing pressure, evacuations were partially lifted. By May 26, the reaction was quelled and the threat of explosion had passed; all residents were allowed to return to their homes. 

In the wake of this chemical accident, much attention has been paid to chronic material handling problems at the GKN facility, with community leaders and residents voicing concern about the risk of another accident and the responsibility GKN bears. 

GKN, for its part, worked closely with local governments and hazardous chemicals professionals to mitigate and manage the accident. GKN Aerospace senior vice president Steve Carlin, in a statement on May 26, said, “On behalf of the team at GKN Aerospace, I want to say how sorry we are for the uncertainty and disruption this situation has caused. I recognise how challenging this has been, particularly over the Memorial Day holiday. We are committed to understanding what occurred and identifying ways we can support those affected.” 

On June 4, GKN Aerospace announced it has funded $3 million to Orange County United Way’s OC Community Resilience Fund to provide assistance to those affected by the recent evacuation of areas surrounding GKN’s Garden Grove facility. The company is also committing another $1 million to support broader community initiatives across Orange County. GKN earlier funded $1 million to the American Red Cross to support residents directly impacted by evacuation orders when those orders were in effect. 

“By working with a trusted local organisation with the infrastructure to mobilise resources quickly, we hope to help expedite assistance to those most in need,” said Carlin. “We will continue to engage with community leaders, work with the authorities, and help the community move forward.”

Public discontent and questions regarding compliance with federal laws:

Whether the $5 million spent and pledged is enough to satisfy local authorities and community members remains to be seen. Initial reporting from local news outlets in Orange County show that discontent is high among citizens and leaders. Also an open question is whether the storage of large quantities of MMA so close to a densely populated residential area complies with state or federal regulations.  

The MMA at GKN’s Garden Grove facility is used to produce polymethyl methacrylate (PMMA) for the manufacture of transparencies and canopies for the F-35 fighter jet, the Boeing 787, the Airbus A350, the Airbus A220, and HondaJet. Although the application is not a composite, MMA is a component of some common resins used in composites manufacturing. Other polymers, like epoxy, cyanate ester, unsaturated polyester, and bismaleimide can also polymerise prematurely and trigger a thermal event. 

Whatever the cause, the GKN accident in Garden Grove is a good reminder of the best practices for storage of highly reactive resin systems — careful tracking of material volume, use of inhibitors to mitigate premature polymerisation, regular verification of pressure relief valves. 

source : Jeccomposites

cover photo: GKN Aerospace