Windows and Facades
Windows and glazed façades are important elements of a building, but they can be vulnerable to:
- Visual observation/overlooking
- Surreptitious attack
- Forced entry
- Ballistic attack
- Blast and associated fragments from explosive devices
Windows comprise of a number of components and their security resistance is linked to how these components perform as a system. The components include for example:
- Seals and/or anchorage to the support structure/frame
- Supporting structure/frame
- Anchors connecting the support structure to the building frame/walls
- Hardware associated with openable windows, e.g. hinges and locking systems
Consequently, when specifying the level of protection required of the window, it should relate to the whole system, not just the glass.
When identifying glazing there are various types of glass to select from, each of which has different properties:
Annealed/float glass – traditional window glass which forms sharp glass shards when broken. It is not recommended for use in any security solution.
Toughened glass, also known as tempered glass – the production process produces glass that is approximately five times stronger than annealed glass. It will break into small chunks instead of glass shards.
Heat strengthened glass – this is similar to toughened glass but is only twice the strength of annealed glass.
Laminated glass sandwiches – an interlayer between layers of glass designed to hold together when the glass shatters.
Polycarbonate – significantly stronger and lighter than glass and hard to break.
Laminated glass is the preferred option for most security applications because of its unique properties. Care should be taken to ensure that the correct type of laminate is specified and used. It is also important to ensure that the rest of the glazing system, e.g. support structure and fixings, is specified correctly
Anti-shatter film and bomb blast net curtains may be used in conjunction with any of the types of glazing.
Additional measures such as bars and grilles may also be incorporated to provide enhanced security. Thought should be given to whether these are placed inside or outside the glazing.
Obscuration measures can be used to mitigate both the threat of ballistic attacks and unauthorised observation. In the case of ballistic attacks, such measures will prevent aimed shots but may not stop un-aimed fire. Therefore, the construction details of glazing need to be considered to determine whether they will withstand bullets from the selected threats (i.e. pistols, rifles or shotguns).