Shatter Surprise: Why is the Glass in Some Oven Doors Suddenly Exploding?

A suburban mother is shaken when her glass door shattered into hundreds of pieces during the self-cleaning process

NBCUniversal Media, LLC

Like many Americans who were stuck at home during early days of the COVID-19 quarantine, Cheryl, who considers herself more of a cook than a baker, decided to make brownies. 

“I took them out of the oven, they were like, very done around the edges and soggy in the center,” the suburban mother said.    

A head scratcher since her new Bosch 30” Double Oven was just three months old. But when she made a second batch, she discovered that her oven temperature was off by about 25 degrees. 

So once COVID restrictions were lifted, she called for a service appointment. 

“I thought I'll clean the oven before I have someone come look at it,” Cheryl said.

So she set the self-cleaning timer and walked away. But towards the end of the cycle, there was a loud explosion. 

“It was pretty scary. I didn't really know what it happened until I walked over and I peered inside and thought something doesn't look right at all," she said.

The inner glass of her top oven door had exploded, and the glass was shattered into hundreds of pieces.

“It almost looked like a bath of glass in there," she said.

The explosion was shocking and scary for Cheryl, but apparently she wasn't alone in her experience. There are hundreds of videos posted online showing the aftermath of explosions that occurred during the self-cleaning process - and not just for Bosch appliances. There are videos posted affecting every major appliance manufacturer.

“There are two scenarios of why oven glass can break spontaneously,” says Mark Meshulam of Chicago Window Expert. “There's one family of oven glass that is soda lime glass, which is window glass, and it's heated and cooled rapidly so that it becomes tempered. That's one type of glass that is used in oven doors. Another type is borosilicate glass. It more used in laboratory glassware or the old time Pyrex glass, and that one tolerates heat and cold very well. So, the shift to soda lime glass has brought about an increase in these types of breaks because it's not as tolerant of the thermal cycles that the glass will go through."

But the more plausible scenario for homeowners is something they can’t even see, or prevent. It’s a nickel sulfide inclusion, or small flaw in the glass, not visible to the naked eye.

“It's only about a tenth of a millimeter in diameter. That little ball has some strange properties.” Meshulam said, adding, “over time it's fighting to get out. And sometimes the high heat event like oven cleaning event can bring about that finally that spontaneous failure that was in there.”

But Meshulam says while the explosions are becoming more common with the use of soda lime glass, there is no need to fear the self-cleaning feature on your oven. 

“Most people will survive their whole lives using the self-cleaning feature and not really encounter this problem,” he said.

NBC 5 Responds reached out to Bosch, asking what type of glass was used in their 30” double oven. We did not get a response, but they did agree to replace Cheryl’s oven, saying:

“BSH Home Appliances is committed to the highest standards of safety, quality and craftsmanship, and has a long-standing history of providing consumers with appliances that uphold the highest safety and quality standards.”

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