In late May, a chemical storage tank containing over 7,000 gallons of methyl methacrylate (MMA), a toxic chemical used in the production of plastics, began heating up at a GKN Aerospace facility south of Los Angeles. The tank, owned by GKN Aerospace—a company that supplies parts to the aviation industry, including aircraft windows—reached a temperature of 100°F (38°C), raising concerns of a potential explosion. This prompted the evacuation of over 50,000 residents in Garden Grove and efforts by fire crews to cool the tank. At one point, the tank "actually bulged," according to the local fire chief. Fortunately, no explosion occurred. Months later, GKN and local authorities announced a $100 million (£74 million) compensation program for residents affected by the evacuation. However, production of aircraft windows at the site, which had been halted, is still not fully restored, currently operating at about 50% of normal capacity, according to statements from its UK parent company, Melrose Industries. The goal is to fully restore production by 28 September. GKN is one of the few companies in the world that manufacture aircraft windows—highly engineered, safety-critical components for planes. The incident has caused a minor disruption in the aircraft manufacturing industry. Production at GKN's Garden Grove facility remains affected. Boeing told the BBC it is "taking steps to mitigate any potential impacts," describing the production shortfall as an "industry-wide" situation. "We are supporting our supplier," a spokesman added. An Airbus spokeswoman said, "We are closely monitoring and are seeing positive progress toward a return to normal." Aircraft manufacturers are increasingly ordering larger cabin windows to offer passengers a wider view of the outside world. This requires additional testing to ensure the larger windows are as durable as the smaller ones. The oval-shaped windows in the cabin, next to passengers' seats, are typically made of plastic-based materials. "You start from a sheet of acrylic," says Jean-Eric Vermont, general manager of French company Saint-Gobain Aerospace. "Then you cut to size, [to] give the shape." Saint-Gobain tests its windows by exposing them to pressures many times higher than those encountered on an aircraft at altitude. These acrylic-based cabin windows are usually made of two layers, and Saint-Gobain also performs tests to confirm whether the window will survive if one of those layers is damaged. Cockpit windows, Vermont says, are "totally different." They are generally made of glass, which is chemically reinforced by adding potassium to it. This process involves replacing smaller sodium ions with larger potassium ions, which helps to strengthen the molecular structure of the glass. When the glass cools during production, it compresses into an extra strong, tight formation. Some of the latest aircraft feature curved cockpit windows to improve fuel efficiency by making the plane more streamlined. However, curved cockpit windows are challenging to manufacture—any distortion or defect is clearly visible to the pilot. Quality control checks are used to ensure that no such issues exist in the final product.