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Consumer Reports Investigates why Sunroofs are Exploding

Glass in cars must meet minimum standards drawn up by the American National Standards Institute and SAE International, the society of automotive engineers. But those provisions haven’t been revised since 1996—long before supersized sunroofs became mainstream.

Tempered glass is nearly always used in sunroofs because it meets the existing standard. It’s the same kind of glass used in side and rear windows and is generally strong. Tempered glass, experts say, is sufficient when sunroofs are small and flat but not for those that are large and curved.

One problem is that modern designs are more three-dimensional and often involve bending glass to the curvature of the roof, notes Rob Vandal, senior director of research and development with Guardian Glass, a major American automotive glass supplier. That makes them more susceptible to impacts, even from very small objects, Vandal says, because they present a more vertical surface for an offending object to strike.

Russ Corsi, who worked nearly 32 years for Pittsburgh-based PPG, a global supplier of auto glass, says larger sunroofs are also more prone to weakening over time as the pane absorbs impacts from bumps in the road, twists and turns of the car’s frame, and “thermal shock”—the expanding and contracting from sudden temperature changes.

If sunroofs are “just breaking [on their own],” Corsi says, “it’s likely to be a manufacturing flaw,” noting “the larger the piece of glass, the smaller the margin of error.”

For example, Corsi says one quality-control issue involves the beveled edge that surrounds the perimeter of roof glass. A chip at that edge can make the glass vulnerable to failure, which, with tempered glass, means an explosion.

Corsi says one way to prevent exploding sunroofs might be to use a hybrid glass that has characteristics of both tempered and laminated glass.

Further complicating the safety equation are the pressures every automaker feels to reduce costs and to keep vehicles lighter for better gas mileage. Automakers generally use the thinnest glass they can—about half a centimeter thick.

Instead of calling for a specific type of glass, regulators could add performance requirements that windshields already must withstand.

https://www.consumerreports.org/car-...nger-overhead/