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What Causes Glass Shower Doors to Explode

There’s nothing like a nice, hot shower after a long, busy workday. But just as you’re rinsing away the stress of the day … CRASH! Your glass shower door explodes into what seems like millions of tiny pieces. Why did your glass shower door explode without warning?


Cases of glass shower doors—and even other types of glass, such as tabletops (—exploding for what seems like no reason, aren’t unheard of, but they are extremely rare. According to a Tempered Glass Safety Alert published in 2018 by the U.S. Consumer Products Safety Commission, nationwide there are about 500 emergency department visits associated with shattering glass shower doors every year. This means it’s only about twice as likely as getting struck by lightning; about a 1 in 7,500 chance during your lifetime. Your chance of evening knowing someone who knows someone that had a shower door exploded is exceptionally slim. However, the question remains—what causes these shower doors to break, without reason or warning? Keep reading to get to the bottom of what causes these glass shower doors to explode.

Understanding Different Types of Glass

The first step in unraveling the causes of why glass shower doors explode, seemingly without reason, is understanding glass itself. Different types of glass are produced for different applications. By code, applications that could be hazardous to human impact, such as someone tripping and falling into a glass door, must be constructed with safety glass. A shower door is such an application. Safety glass is produced in such a way that if it does break, its threat level is minimal compared to non-safety glass. Here’s a look at the most common types of glass.

Annealed Glass

Annealed glass is probably the simplest form of glass. Annealed glass is left to cool naturally after the manufacturing process. It is also known as untreated glass. When broken, it will break into large, sharp pieces. These pieces often have jagged edges and can cause significant injury to people or damage to property nearby. For these reasons, building codes restrict or prohibit the use of annealed glass in applications that could be subject to human impact, including shower doors.

Heat-Treated Glass

Heat-treated glass describes glass that has been processed to alter its strength. There are two main types of heat-treated glass: heat-strengthened and tempered glass. Heat-treated and tempered glass are processed on the same type of equipment. In both processes, the glass is heated to approximately 1,200 degrees Fahrenheit, then force-cooled to create surface and edge compression, which increases its strength. However, there are also important differences.

Heat-Strengthened Glass vs. Tempered Glass

During heat-strengthening, the cooling process is slower than during tempering. Heat-strengthened glass is approximately twice as strong as annealed glass. Tempered glass, on the other hand, is about four times stronger than annealed glass. When it is processed, it is cooled very quickly to increase its strength. Tempering changes the property of the glass, so when it breaks, it shatters into small pieces, rather than sharp shards, which can cause significant injury. Tempered glass is considered a safety glass, while heat-strengthened glass is not. However, when heat-strengthened glass breaks, the pieces are closer in size to annealed glass and tend to stay in the opening longer than tempered glass.

Laminated Glass

Laminated glass is also a type of safety glass. It is fabricated with at least two pieces of glass and one plastic interlayer, though it can be made with more layers if needed. It’s essentially a glass sandwich. The plastic interlayer, usually made of polyvinyl butyl (PVB), holds the glass together when it is broken. This helps keep the glass from flying and causing injuries or damage.

Why Did My Glass Shower Door Explode?

Now that you understand some of the different types of glass, we can address some of the issues that can cause it to break. Keep in mind that the majority of shower doors are made from tempered glass.

Spontaneous Shower Glass Breakage

You may have seen reports on the news about glass breaking spontaneously. But what causes this breakage? In some cases, it’s due to the inherent nature of the tempering process. Spontaneous breakage can occur due to nickel sulfide inclusions in the glass. The inclusions can sometimes grow over time and cause stress, which can then break under heat or other external stresses. These occurrences are uncommon and should not deter you from having a glass shower installed in your home.

Some glass manufacturers conduct what’s called heat-soaking. Because spontaneous breakage can happen when nickel sulfide is in the glass, heat soaking is done in a chamber. It exposes the glass to higher levels of heat than the nickel sulfide can withstand. This allows the glass to break in a safe environment rather than during installation or while in the end customer’s possession. Because this is a destructive, pass-fail test, not all companies choose to do it.

Another side effect from heat-treating is that while the glass becomes more resistant to a direct impact, it is more susceptible to side impact. A small side-edge chip in the glass, for example, could eventually make the whole door shatter.

Improper Shower Door Installation

In some cases, glass shower doors can break due to incorrect installation. If not installed properly, the door could slip out of the hinges or off its track when opened. Likewise, damaged parts and pieces, such as rubber stoppers or runners on the bottom, can also contribute to eventual glass breakage.

To protect yourself and your family from the possibility of breakage, be sure to assess your shower door glass regularly. Check the hardware and frame to make sure fasteners and fittings are secure. Also, check the glass edges for chips and cracks that could lead to spontaneous breakage. It’s also important to avoid slamming the shower door and avoid using door handles or towel bars as a safety grip, as that could also put added pressure on a glass door.

And in the event that your glass shower door does break, you can rest assured knowing that experts are here to help. We can connect you with installers right in your area who can assist you with your shower door glass needs. Whether you choose to replace the broken glass or perhaps decide you want to upgrade to a brand new glass shower enclosure, affiliates can help. Visit our website to find a professional in your area, and you’ll soon be enjoying your new and improved glass shower enclosure. attempts to provide accurate information but cannot be held liable for any information provided or omitted.  You should always work with a licensed, insured, and reputable glass shop that can assess your specific needs and local building codes and offer professional services. Never attempt to cut, install, or otherwise work with glass yourself. All content is provided on an informational basis only.

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  • We came home from vacation to find our shower door shattered, with glass and hardware strewn everywhere. I am soooo upset. We had these doors custom made, 6 years ago, and they were NOT cheap. One in 7,500 sucks when you’re the ONE!

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