Why does the escape route window break in a bus or something when they are hit with those tiny orange hammers (emergency hammer?) with metal tips. I mean you can’t even get much force to the hit because the handle is so small you can’t use do a good swing.
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its more about concentration of force onto a very small area. the glass is tough but brittle, and it;s designed to shatter in a manner than doesnt leave dangerous shards. you use the hammer to shatter it, then pull it out of the way and escape
a larger hammer might work just as well, its just they want a smaller one thats easier to use inside the (wrecked) vehicle, and something they can install and secure right next to the window so a panicking (and potentially injured) passenger, working in a restricted space and poor angles, can pull it out and pummel the panel of glass to escape.
the glass is hardened so it has has a lots of tension inside, you only need to make a small nick in the surface in the glass to make it shatter
Tempered glass is made in a special way so that the outer layers of the glass are in compression, and the inner layer is in tension. That is, the outside is being squeezed really hard by the inside that is being stretched really hard.
Normally glass can’t take high tension (stretching) loads without cracking. But the outer layers in compression prevent a crack from starting in the inner tension layer. The sharp point of little hammer is just enough to put a small chip in the outer protective layer. This lets a crack start in the inner inner tension layer. Once the crack starts, its all over. The crack runs (**very** fast) throughout the entire piece of glass.
You want the pressure on a tiny area of the glass to cause it to break. Those hammers and spring loaded automatic center punches will shatter glass without much trouble.
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