Existing stress, changing temperature and shifting building structure. Any and all of those can cause it
this post was submitted on 06 Mar 2025
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There could have been a defect that caused immense stress in the glass. Alternatively, there could have been microscopic cracks caused by mishandling. Or both. Either way, a tiny temperature fluctuation was probably the final straw that broke the camel's back. The actual root cause probably happened several years ago.
Tempered glass, the type which is used for stuff like shower screens or car windows is under constant tension against itself. The inside of the glass wants to be bigger than the outside. Normally this makes it harder to break as the bonds on the outside are so strong and uniform they prevent it from bending or shearing as easily as normal glass.
The problem is that if you manage to break those bonds, the outside can very rapidly tear itself apart as it finds a way to relieve that tension. It basically pops like a balloon. The reason it breaks into small pieces is because anything bigger is still under tension and once the surface is damaged the crack will spread to ease it.
So your glass could have had a defect or damage which broke a few of those bonds, and heat cycles eventually pushed it to break the next bond along and start a chain reaction which destroyed the whole thing.
Edit: it could even be that some grit fell in the housing or something. The reason spark plugs break car windows is because the edges are sharp enough to cut the glass with very little force.
Today I learned
So you don't have to whack a car window hard with the spark plug? You only need to scratch at it a lil bit?
You smash the spark plug, and toss the shards at the window. After that, the window is easy to shatter.
The spark plug example is popular because presumably you find both old sparkplugs and spare car windows at junk yards. What it really is that the ceramic that they're made out of hard and sharp enough when broken to damage the surface of the glass which causes the chain reaction.
This can happen if you tighten any screws/knuts that hold it in place too much. It creates enough stress that when there is enough of a temperature change, the weakeness presented by the fixture can cause it to shatter.
Ha ! That happened to me last year actually. Showered in the morning everything was fine. Came back from work to the thing in pieces on my floor. It can happen with tempered glass due to manufacturing defects. I think what actually triggers it to break apart isn't even well understood. And good luck explaining that shit to your landlord because it's pretty rare.
we own the house so we had to explain it to the person that fitted the shower and bathroom. Which luckily they understood because it’d happened before to another of their customers and they sorted the issue out for free.
I guess you feel the pain lol. It’s a weird situation to be in.
Definitely ghosts. Shower ghosts. Clean shower ghosts. Clumsy clean shower ghosts.
This is ectoplasm!
;)
Seems like you got your answer, but I’d also like to say sorry that your shower broke! I’m sure it was nasty to clean up and now it has to be replaced which is likely either an unexpected cost or your landlord’s problem, in which case I hope you have a responsive landlord.
I appreciate it and we own the house, so we had to explain it directly to the person who fitted the bathroom with the shower and what not, they understood the situation and they cleared it up for free but we decided to not have another glass pane fitted and instead use a shower curtain
My tempered glass sunroof blew apart while I was driving. Manufacturing defect. A woman had the same problem the same week (2015 glass, around 2019).
It was insanely loud. Like a shotgun going off by your head. :p
Very loud especially when it’s nighttime and everyone is in bed and it’s quiet, like I literally went into defence mode thinking there was someone breaking in through a window or something lol
They rarely shatter on their own. The damage was probably done earlier but you didn’t see it, and it took a while before it finally spread enough it broke.
Maybe, I didn’t notice any cracks or chips in the glass and that was about 2 hours earlier. But maybe It was a hairline crack or something
Glass can and will break for no apparent reason, even tempered glass.
During manufacturing the glass can take on stress that is not visible but is a ticking time bomb. Temperature differential alone can push that stress past its breaking point.
Other people have good answers already, but could also be nickel sulphide inclusion in poorly manufactured glass.