How does the tempered glass blew?

The difference between the steel blew and the tempered glass external force crushing is mainly due to the difference of "starting point". Tempered glass blews generally in the center of the glass. Initiation point of the center there are obvious fragments were butterfly-like, commonly known as: "Butterfly spot."

Tempered glass external impact crushing generally visible in the crushing point traces, no butterfly spot. The glass is broken from the impact point of the radioactive distribution.