Exploding Glass Shower Doors: the Causes

Foot and Shattered Glass

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Over the years, a small but significant number of homeowners have reported a strange, frightening, and potentially dangerous issue: glass shower doors that seemingly "explode" into small pieces spontaneously, often with no apparent provocation or stress. In many instances, it happens in the middle of the night, awakening the homeowners suddenly as a glass panel first bursts then crash to the floor and bathtub or shower pan.

The Phenomenon

Contractors and glass door manufacturers initially reacted with understandable disbelief and skepticism: Glass does not explode all by itself. Surely, they argued, homeowners were actually reporting glass doors coming free from their frames or mounting hardware and crashing to the floor. The glass panels were not actually exploding spontaneously.

But enough homeowners reported the same experience that gradually this phenomenon was acknowledged. An internet search for "exploding shower doors" produces dozens of results, including reports in major newspapers and trade magazines. Though extremely rare, there were even instances of residents experiencing the glass spontaneously exploding while they were showering. Certain characteristics were common to most of these experiences.

  • The glass did not simply crack, it shattered explosively. The breakage was never a crack that progressed into pieces of glass tinkling to the floor. One minute the shower door was completely intact; the next minute it was fragmented into minute pieces, and the noise of the shattering was very loud—sometimes described as deafening.
  • The explosion was spontaneous. This was not a case of shower panels falling out of frames and crashing to the floor, or of door brackets coming loose and causing the entire door to fall. Instead, the glass panels were shattering from the center outward all on their own, often with no one even in the room.
  • It frequently happened at night, often very late or past midnight. Homeowners were in bed and sometimes were first woken up by an initial crack, followed by the explosion. Most episodes happened between midnight and 3:00 am.

One homeowner's report is typical of what many people describe:

The middle of it blew clean apart leaving glass shards inside the frame. We were awakened by a very loud explosion upstairs . It was pretty scary. My daughter who sleeps upstairs said that she heard two noises. The first was like a big crack noise. Minutes or an hour later the thing 'exploded.'

The Industry Reaction

Some retailers, when confronted by concerned and sometimes angry homeowners, have argued that the report of an "explosion" is exaggerated—that homeowners are probably hearing it this way because the small space and hard surfaces in a bathroom make any falling glass sound like an explosion. But it is hard to discount the people who actually witness such events and describe the explosion occurring first, followed by the falling glass. The retailers who sell the glass shower doors usually argue that improper installation is to blame.

For their part, the installation contractors will point to the fact that the frames, hinges, and brackets often remain in place and undamaged after such mysterious glass explosions occur. In their view, the problem lies in the tempered glass

The Consumer Products Safety Commission (CPSC), on its self-reported board, Safer Products, lists plenty of instances of shattered shower doors. One entry regarding a Kohler Clear Glass Bypass Bath Door reads much the same way as the above-mentioned incident. To its credit, Kohler Co. does respond to the complaint.

In the specific case of shower doors, all doors are manufactured with tempered glass in compliance with Consumer Product Safety Commission (CPSC) and American National Standards Institute (ANSI) standards. To ensure this is the case, newly tempered glass is fractured and tested on a regular basis every day at our plant. In addition, Kohler voluntarily submits its glass to an independent entity for testing, to ensure consistency with and adherence to these standards.
Although tempered glass in general is stronger than non-tempered glass, especially when it comes to direct impacts to the face of the glass, it can still break. By design, tempered glass completely shatters into thousands of small pieces when stressed beyond its capacity and serves as a safety feature which helps avoid more serious injuries from the larger, sharper shards often seen in non-tempered glass.

In other words, neither the door manufacturers nor the installation professionals acknowledge any responsibility for exploding glass doors.

Theories About Cause

A number of theories about the cause of exploding glass have been offered.

  • Does the temperature change, from warmer to cooler, affect tempered glass? A Seattle Times article reports contractor Jerry Filgiano as saying that temperature extremes can affect tempered glass, though the slow lowering of temperatures from day to night likely does not count as "extreme." 
  • The same article says that nicked glass edges caused by a screw or bolt can cause the entire panel to shatter and that framed doors may be less apt to shatter than frameless doors.

Mark Meshulam, a Chicago building consultant who has testified as an expert on the subject says that although such instance appears spontaneous, there is always an underlying cause.

"Spontaneous is a relative term. Maybe it's spontaneous, but it really had a reason."

Meshulam described tempered glass as being "like a tightly wound spring" that can reach an apparently spontaneous breaking point for one of two reasons: an internal flaw, or damage to the glass.

  • A tiny, almost invisible chip or crack can occur if a door is nicked by a misaligned screw or is bumped along the delicate outer edges. Such damage does not cause the door to break immediately, but may suddenly give way as temperature changes cause the glass to expand and contract, or even due to vibrations caused by noise.
  • More rarely, doors can break due to nickel sulfide inclusion, a defect that occurs during the manufacturing process. When a piece of foreign material gets trapped inside the glass when it is manufactured, over time it can cause the glass to shatter for no obvious reason.

The Tempered Glass Connection

It's important to note that actual injuries from exploding shower door glass are very rare. That's because the tempering process used to create safety glass causes it to break into very small pieces rather than large, sharp shards. But while this is the greatest strength of tempered glass, it is also a weakness. The heating process of tempering causes the tensile strength of the glass to be altered, and while this makes it much more resistant to direct impact, it also becomes more susceptible to side impact. A piece of tempered glass may withstand a baseball crashing into its face, but it may shatter easily if struck with a mild blow on the edge.

A hanging glass shower door that falls from its track, for example, may shatter quite easily. It is conceivable that some of the exploding shower doors occur because one of the top rollers loosens, causing the door to fall an inch or two, shattering on impact. There have also been cases of shower doors on sliding tracks that shatter if the rubber bumpers are missing and the door strikes the side track during operation.

Should your shower door spontaneously explode, you can rest assured that you are not alone. It has happened to hundreds if not thousands of people, and the phenomenon is well documented. And you can also be quite sure it is not caused by poltergeists. Although the causes are not immediately obvious, there are perfectly rational explanations for why shower doors explode.

Serious injuries are very rare, but it does make sense to periodically inspect your glass door to make sure that all hardware and brackets are in place, and that the glass panel contains no small nicks or cracks. If you spot damage, repair or replace the components immediately.