"Dave Liquorice" wrote in message
ll.co.uk...
On Fri, 18 Jul 2014 09:45:39 +0100, harryagain wrote:

I'm amazed about the roof panel.
Only the lower panels need to be toughened glass.
You might ask about this aspect.

Does seem odd.

They are here as a safety thing, ie if someone/child accidently breaks
one, less chnce of getting cut up.

By falling/pushed against it. You don't want to do that with ordinary
glass that breaks into loads of razor sharp daggers. You#ll stil get
cuts from the toughend granuals but you won't sever arteries of
ligaments.

They are allegedly harder to break than normal glass.

It's funny stuff toughed glass, it's understress all the time and
when it goes it goes. The trigger can be pretty small, a nice sharp
automatic centre punch can do it. But I've also witnessed a Special
Effects guy having quite some difficulty shattering a toughed car
windscreen. He started very cautious with gentle taps from a small
hammer and cold chisel, end up with a lump hammer and really giving
it some...

When I was buying my toughened glass patio doors for the house
in the early 70s, the operation flogging them made a big play of the
fact that they are very difficult to get thru even with a sledge hammer.

What they didn't mention is that a sharp stone can do them in.