Window Safety Film, Anti-spall and Bomb Blast Glass
Safety film is a clear high quality polyester film designed to make glass safer, both by strengthening it against breakage and by containment of dangerous shards travelling at high velocity in situations where breakage does occur.
175 micron film, also known as "bomb blast film" is a 2 ply film and suitable for most applications where the safety of staff or the general public is a concern. High-risk areas, with the potential threat of terrorism, or near a petrol station or chemical plant for example would benefit from the use of the film. The film provides a protective barrier by holding broken glass in place, thus reducing the injuries and damage that could otherwise occur, and in some cases might contain flying masonry.
Consider using 300 micron film for panes over 6 square metres area, or over 8mm thick, or for ground floor windows of over 3 square metres. The specification can be lowered to at least 100 microns if bomb blast net curtains are also used.
The film must be fixed in clean and dust-free conditions. On new windows or areas being re-glazed, apply film to the glass to its extreme edges before fixing the frames. If, however, there is to be extensive building work after installation - in which case dust and debris may cause unacceptable scratching - it may be better to postpone fixing the film until work is complete. In this case the film should be applied as close as possible to the putty of glazing bars with an edge gap of less than 3mm. 5mm can be tolerated along particularly irregular putty edges.
Butt joints are acceptable if the film is insufficiently wide to cover the glass in one piece.
With double glazed windows consisting of two separate frames, in which the inner frame can be opened independently of the other, treat both panes. If the inner pane cannot be opened independently, or a "sealed unit" is fitted, applying film to the inner panel is sufficient. Sometimes inner frames are only lightly fitted; if so, they should be fully secured. The film cannot be applied to the patterned side of frosted, figured or reeded glass.
After the PIRA bombing of Bishopsgate, London in 1993, British security force MI5 issued the following advice to window film specifiers including architects and structural engineers.
"Modern buildings make much greater use of glass than older buildings, which means that most bomb casualties nowadays are caused by flying glass."
There are three main methods of protection against flying glass:
Applying transparent polyester anti-shatter film (ASF) to the glass and providing bomb blast net curtains. This is a retro-fit upgrade to existing glass in order to reduce fragments and splinters. In timber-framed Georgian-style windows bomb blast net curtains should be used in conjunction with the ASF.
Installing blast resistant glass (i.e. laminated glass) in new buildings or refurbished windows.
Installing blast resistant secondary glazing inside exterior glazing.
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