Where window systems require a level of blast resistance they should be specified by designers competent in the field of blast design.
The Centre of Protection of National Infrastructure – http://www.cpni.gov.uk/ have given guidance in April 2014. Of the protective methods available under two types:
1. Mitigating measures.
2. Protective measures.
Measures should be taken to mitigate the damage caused where the threat is less likely or far away. Where the design and building type such as a listed buiding does not allow for the replacement of building work in these areas only retro fit measures can be put in place such as:
- Anti-Shatter Film (ASF) (sometimes referred to as Anti-Fragmentation Film)
- Bomb Blast Net Curtains (BBNC)
- Laminated Glass Blast resistant glazing in normal window frames.
- Large panes of glass can be replaced with Toughened laminated glass. Especially applicable in ‘crowded spaces’ such as Shopping Centres and transport terminals.
In buildings/ areas where there is a s specified level of threat and where protection can be made a priority where the replacement of existing windows and incorporation of secondary glazing protective system can be put in place.
In these cases the building owner will need to agree the threat (charge mass and range or pressure and impulse) and the acceptable hazard level with the glazing designer.
In such situations the following measures are recommended by the CPNI.
- Blast Resistant Glazing in Blast Enhanced Frames
- Secondary Windows
- Blast Resistant Fixed Point Glazing
All Purpose Glazing secondary glazing systems also improve the sound insulation, thermal insulation and enhanced window security performance.
Where there is perceived to be a threat of damage caused by bomb or blast, we are recommended to put in place mitigating or protective measures where most applicable.