Window fracture mystery

[ThisPlumPlayer]

There was a loud bang and this is what happened. The place is in a safe neighbourhood and it was the middle of the day. Only the outer window glass was damaged, inner glass was intact. The window was installed many years ago. Outside temperature was mildly warm, so no extreme temperatures. Do you know what could have happened and what would cause such an odd fracture pattern?

Probably a flaw in the glass and it has shattered. Happened to our shower screen in the middle of the night!

It's just there was a hidden flaw in the glass, we had a pane in our conservatory go like that. Weird but not unknown. You can get the double glazed panel renewed, it's not too expensive.

Maybe a bird flew into the window or a driver hit a stone that flew up

Thanks for your replies. You guys mentioned the same happened to you. My windows are probably a decade old. Just wondering if your shower screen/conservatory pane was newly installed when it happened?

Our glass kitchen table looked fine about 3 years old and one day recently it just shattered all over the kitchen still dont know why

When our conservatory pane shattered it was over 10 years old . We also had the glass door of a washing machine shatter during a wash - that was a couple of years old.

Heat

Someone threw a stone?
Bird flew into it?
Small flaw in glass

Pressure changes can do it. We had one go after about 2 years.

Glass can have inbuilt stresses that cause it to fracture.

I don't see that an impact caused that.

Did you examine outside to see whether there was anything lying around that may have hit the glass and bounced off ? Maybe if so there would be a dent in the outside panel.

Our lounge window did that a couple of years ago. Massive bang then the whole outer pane disintegrated. It wasn't too expensive to replace the glass but the shock of the bang took me a while to come down off the ceiling from!

Happened to me once on my patio doors- gave me a fright! Glaziers said it can happen- pressure, change in temp, flaw in glass etc. Mine was about 10 years old.

There's an impact mark, something has hit the window (I work in glazing)

There's a strip of grass and a public pathway outside. We did find a piece of metal on the grass not too far from the window but that could have been lying there for a long time. Good idea about the outside panel - I will examine the frame more closely for any marks.

I don't have much experience with glazing so correct me if I'm wrong but I always thought an impact mark would leave cobweb-like lines going in all directions from the point of impact. Have you come across a fracture that leaves a circular pattern before? Thanks

It's more likely to have the cobweb pattern when it's laminated glass. Thermal breaks are usually where the pane on the outside has heated and cooled quicker then inside. Sometimes toughened glass will spontaneously break because it's actually quite brittle. But if you look at the right hand side of the glass that looks like an impact mark, we've seen a lot if breaks lately with BB guns, catapults etc but the most common is a stone flicked from a car or a lawnmower we've even seen it where the neighbours have mowed the lawn and a stones flicked over and hit a window

What did the bit of metal look like ?

Rusty ?

Heavy ?

A bright edge where it has just broken off something ?

It could be a deformed air rifle pellet, but it won't be rusty if so. If it is something that has sheared off and flown through the air it should have a bright edge where it sheared off. If it has been out there for a long time it will probably be rusty if it is mild steel.

If a bit of metal hits it at any speed I am sure it will leave a dent in the glass and cracks will radiate out from that as you say.

Looks like a football has hit it to me.