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Bomb Blast Film

• Introduction
• Research
• Conclusions

Introduction

• The principles underlying the design and installation of 'blast-resistant' glazing systems in new-build projects are now well-understood and some consensus has been reached within the industry. The Blast Resistant Glazing page provides some information on currently-accepted good practice.
• The principle of retro-fitting anti-shatter (aka 'safety', 'security', 'bomb blast') film to existing glazing is also a well-established industry practice. CWCT Technical Note No. 43, published in July 2004, is a recent authoritative statement on the subject. This document suggests caution in the use of applied films in a number of circumstances, including application to laminated glass.
• Architects are occasionally asked to apply anti-shatter film to Laminated Glass and there appears to be little industry guidance on the subject. This page is intended to provide that guidance.

Research

• The most authoritative guidance currently in the public domain is published by the Centre for the Protection of National Infrastructure. Start from the Anti-shatter film page of their website.
• Guidance on providing a degree of 'blast resistance' was previously available from several other UK Government websites but this advice has now been removed.
• The British Embassy in Riyadh website formerly stated:
  - 'Normal' anti-shatter film (ASF) is 100 microns thick and passes tests to BS 6206, Class B.
  - 'Enhanced' anti-shatter film is generally 300 microns thick and passes tests to BS 6206, Class A.
• The website also stated "It is not normally necessary to apply ASF to laminated glass ... The addition of anti-shatter film can, however, be justified where close-in detonations, fragments (grenades, mortars or nail bombs) are envisaged."
• Similar, but slightly less detailed, advice was provided on the MI5 website although this referred to 'normal' anti-shatter film as being 175 microns thick. This advice also suggested a minimum thickness of 7.5mm (2 x 3mm glass either side of a 1.5mm interlayer) for laminated glass to be considered 'blast resistant'.
• Tests were carried out in 1996, in the USA, to evaluate the performance of anti-shatter films compared with untreated annealed glass, and laminated glass. The tests were sponsored by a film manufacturer and seem to show very little difference between the filmed glass and the laminated glass although it should be noted that the laminated glass was of a much lower specification than would normally be used in the UK.
• There is some evidence that 0.38mm and 0.76mm PVB interlayers, typical in Laminated Glass available in the UK, are broken under the distortion produced in a blast situation, although they may be perfectly capable of holding the two panes together under "normal" breakage conditions.

Conclusions

• There seem to be no advantages, and some potential disadvantages, in applying anti-shatter film to laminated glass containing at least one PVB interlayer with a minimum thickness of 1.5mm and complying with BS 6206, Class A.
• There may be advantages in applying anti-shatter film to laminated glass with one 0.38mm or one 0.76mm interlayer but, for new installations, specifying a 1.52mm interlayer is generally preferable.

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