Glass and Explosions
Glass that is able to protect an area from an explosive force is not new but has become a familiar requirement for the age we live in. Like fire resistance and manual attack the glass has to form part of a complete system and will not perform as required in isolation. Glass can be tested to the North American and European standards below.
ASTM F1642: Test method for glass and glazing subjected to air blast loadings
EN 13541 : 2000 : 'Glass in building - Security glazing - Testing and classification of resistance against explosion pressure'
Subject to blast waves generated using shock tube
Simulation of high explosive detonation
4 classifications (ER1, ER2, ER3 and ER4)
S (Splinters) or NS (No splinters)
The selection and application of blast resistant glass needs specialist advice and there are consultants who offer advice in this area. Like most threats it can be hard to determine the size of the explosion and the proximity to your location. The channeling effect of other buildings and street architecture can change the way the pressure wave effects buildings. Post examination of explosions can reveal some odd results. Unprotected buildings further away can sometimes have more damage than more immediate buildings. Although there is a pressure wave the result is glass being pulled out of buildings rather than being pushed in. Once the initial pressure wave of air has hit the building there is a vacuum left where the air has been violently moved out of position. It is the suction effect that can pull the glass outwards.
A common design is to use an outer pane of toughened glass and a fairly slim pane of laminated glass to the inside. The flexibility of the glass allows the energy to be absorbed even though the glass may break. It is important that the glass remains in its frame rather than becoming part of the problem. To make the glass stiffer can result in the energy being imparted to the frame or the building structure. Structural failure of the building is far worse that losing the glass panes.