Blast resistant glass is a range of glass constructions aimed at preventing and reducing injury in the event of a bomb or similar explosive attack.
The majority of injuries sustained after an explosive attack on a building are caused by flying glass or falling glass, this is known as spawl. The purpose of blast resistant glass is to reduce or stop this flying glass after an explosive attack, therefore reducing injury.
Layers of toughened glass are laminated together using PVB interlayers or Sentry Interlayers to create a strong toughened laminated panel of glass. Using this glass construction the interlayer absorbs the energy of the blast, allowing the glass panels to break and expand without flying glass being emitted from the surfaces.
The thickness and type of interlayer used as well as the thickness of glass and number of layers required will depend on the level of bomb or blast resistance required to the glass installation.
The classification of glass in terms of blast resistance is determined using testing method EN 13541. In these controlled tests the glass unit is placed within a shock wave tube, explosive detonations of 10kg to 2500kg TNT are detonated at distances ranging from 35m to 50mm away from the glass face.
The tests take into account the amount of deflection in the glass under the explosive pressure as well as the amount of spawl emitted. Glass units are then given a blast resistance classification of ER1 to ER4.
Of course these tests and classifications only refer to the glass units to be used in these high security installations. For a full understanding of the security and safety of a glass installation the framing and fixings to be used also need to be considered.