Safety glass must be used in doors and low-level glazing to comply with Building Regulations. It is designed to break safely to prevent injury from sharp shards of glass. Safety glass is usually stronger than normal float glass.
There are two main types of safety glass.
Laminated glass: This is made by sandwiching sheets of glass together with interlayers in between. The interlayers hold the glass together when it breaks. Laminated glass is very difficult to break through, so it is often used for security. It is also a key part of a noise reducing window, so choosing noise reducing windows can also improve security.
Toughened glass: Normal float glass is modified by heating the glass, so that it breaks into small fragments. Toughened glass is unlikely to break when hit by a blunt object (e.g. a hammer), but will break relatively easily if the force is concentrated onto a small point (e.g. using a centre punch).
In order to comply with the Building Regulations, where safety glass is required, the glass must be marked to show that it complies.
The diagram below shows where safety glass is required: