The Glass and Glazing Federation also offer advice on mitigating blast damage through the use of bomb protection anti-shatter window films applied by specialist installers like Pabro Window Films in Kent.
The document is offered over the next few slides in full, looking at safety and anti-shatter films in particular and highlighting the correct application and installation of them to reduce risks of flying glass in the event of a bomb blast or other impact. This is especially crucial advice for businesses in major cities such as London, Birmingham, Leeds, Sheffield, Bradford, Liverpool, Manchester, Bristol, Wakefield, Cardiff, Coventry, Nottingham, Leicester, Sunderland, Brighton, Plymouth, Southampton, Westminster, Portsmouth and Salisbury.
Glass and Glazing Federation advice for blast mitigation using adhesive performance window films.
This document gives recommendations for the use of adhesive backed polymeric safety film applied to glass for reducing the risk of injury from glass shattered in an explosion.
The Glass and Glazing Federation offer detailed advice and recommendations on utilising a range of safety, security, bomb protection and anti-shatter window films to reduce damage and injury from flying glass.
2. Definitions and Description
2.1 Adhesive backed polymeric film
One or more layers of polymeric film laminated together, with an adhesive on one external face. It may also incorporate one or more of the following: colouring, UV absorbers, UV inhibitors, metal layer(s), metal alloy layer(s), metal oxide layer(s), scratch or abrasion resistant surface, release liner.
2.2 Safety film
Adhesive backed polymeric film designed so that when applied to a glass pane the final product can be classified in accordance with BS EN 12600 “Glass in building – Pendulum test – Impact method test and classification for flat glass”. Safety film is also known as ‘Anti-Shatter film’ or ASF since it is intended to retain broken glass fragments and hence reduce shattering of glass over a wide area.
2.3 Anti-Shatter film
See section 2.2 ‘Safety film’.
The total thickness of the safety film is the sum of the thicknesses of the polyester film layers in the finished safety film, excluding the thicknesses of adhesive and other coatings.
Note: Glass substrates may include:
Basic soda lime silicate glass products according to EN 572-1 to 8; Special basic products –Borosilicate glasses according to EN 1748-1-1; Special basic products – Glass ceramics, according to EN 1748-2-1; Special basic products – Alkaline earth silicate glass, according to EN 14178-1; Silvered float glass, according to EN 1036; Thermally toughened soda lime silicate safety glass, according to EN 12150-1; Heat strengthened soda lime silicate glass, according to EN 1863-1; Chemically strengthened soda lime silicate glass, according to EN 12337-1; Heat soaked thermally toughened soda lime silicate safety glass, according to EN 14179-1; Thermally toughened borosilicate safety glass, according to EN 13024-1; Thermally toughened alkaline earth silicate safety glass, according to EN 14321-1; Laminated and laminated safety glass, according to EN ISO 12543-2, -3; Coated glass, according to EN 1096-1, wired glass according to EN 572-3
2.5 Cure time
The time required for the adhesive backed polymeric film to achieve its expected adhesion level and for visual effects due to water haze/water bubbles/etc. to disappear.
Note: Cure time should not be confused with performance time. Safety film will, with correct installation procedures, achieve good performance before complete cure.
3. Risk Reduction
3.1 Risk Reduction with Safety Film
3.1.1 Systems of Hazard Rating of the risks from shattered glass in an explosion have been developed by the UK Government and other organisations based upon decades of explosion testing, and are being incorporated into international standards.
3.1.2 The Hazard Rating system from ISO draft standard DIS 16933 (publication expected shortly) is shown in Figure 1; DIS 16933 includes a range test which uses 3 metres deep test cubicles with defined areas within the cubicle for different hazard levels. Safety films on annealed glass are intended to reduce High Hazard to Low Hazard or Very Low Hazard. Safety film on annealed glass with specifically designed retention systems can further improve the performance to Minimal Hazard or No Hazard.
3.2 Risk Assessment
A professional Risk Assessment is required to establish the risks from an explosion for a particular building. This will be dependent upon criteria including the glazing and glass types, size and thickness, the assessed threat, the building location, the building environment, and the usage of the building. The Risk Assessment will also help to identify the measures required for reducing the risks from an explosion. Installation of safety film is only a part of the overall strategy for protecting people and property in an explosion. For specification of safety film, building owners and managers very often select the appropriate safety films based upon a High Threat (see section 4.2), partly because many at risk buildings are in major cities and are close to potential ‘targets’. In addition, the cost penalty for the increased protection of higher performing is relatively small.
4. Threat Levels
4.1 Explosion Properties
It can be difficult if not impossible to define exactly the specific properties and effects an explosion may have on the buildings and structures around it. However, extensive research has developed substantial practical and theoretical understanding of explosions, allowing protective measures in order to reduce the effects of explosions to be taken with confidence.
4.2 Threat Levels
Two levels of the potential threat of an explosion have been established: High Threat and Low Threat.
-High Threat is for buildings where there is a significant risk of an explosion of approximately a van bomb size.
-Low Threat is for buildings where there is a significant risk of an explosion of approximately a satchel bomb size.
4.3 Recommendations for the use of safety film at these threat levels are given in section 5
5. Recommended safety films for reducing risk of glass shattered in an explosion
5.1 The recommendations given below are the minimum levels of protection required to protect against both High Threat and Low Threat (section 4.2). They are based upon the current Home Office Scientific Development Branch recommendations and publications and the current understanding of the effects of an explosion on glass at the time of publication.
5.2 Safety films for reducing the risk in an explosion of injuries from shattered glass are recommended based upon their performance. This generally means that as film thickness increases, so does film performance, although the expectation is that technology improvements may result in higher performing products without always an increase in thickness.
5.3 These recommendations are not intended to substitute for a professional Risk Assessment but can be used to quickly decide the minimum specification of safety film required for the threat level (section 4.2).
5.4 Recommendations for High Threat buildings
5.4.1 The recommendations for use of safety film where a High Threat from an explosion exists and where pane size = 3m² and pane thickness = 6 mm are given in Table 1.
Table 1. High Threat: Safety film recommendations for panes = 3m² & = 6 mm
|Ground - 11th||Safety film at least 150 microns thick and meeting BS EN 12600 Class 1B1|
|12th and over||Safety film at least 100 microns thick and meeting BS EN 12600 Class 2B2|
Table 2. High Threat: Safety film recommendations: panes > 3m2 and/or > 6 mm
|Ground - 1st||Safety film at least 275 microns thick and meeting BS EN 12600 Class 1B1|
|2nd - 11th||Safety film at least 150 microns thick and meeting BS EN 12600 Class 1B1|
|12th and over||Safety film at least 100 microns thick and meeting BS EN 12600 Class 2B2|
Table 3: Low Threat: Safety film recommendations for all pane sizes and thicknesses
|All Floors||Safety film at least 100 microns thick and meeting BS EN 12600 Class 2B2|
5.6 Internal Glass Partitions
Internal glass partitions should be treated with 100 micron thick safety film meeting BS EN 12600 Class 2B2. For internal double glazing it may be necessary to treat both sides of the glazing panel.
5.7 Secondary Glazing
The recommendations for use of safety films where the window consists of two separate frames and where both frames can be opened independently (e.g. as in secondary glazing) are given in Table 4.
Table 4. Secondary and similar glazing Safety film recommendations for all pane sizes and thicknesses
|Primary||As in sections 5.4 to 5.5|
|Secondary||Safety film at least 100 microns thick and meeting BS EN 12600 Class 2B2|
5.8 It is possible to obtain a higher classification for safety film on one thickness of float glass than for the same film on a different thickness of float glass. Therefore, classification to BS EN 12600 for safety film means that:
-The specific safety film has been independently tested as a safety film + float glass lamination and meets the stated BS EN 12600 classification, where glass thickness is the same as that to be treated,
-The exception to the above is that occasionally thicker glass than is normally encountered may require protection, and independent testing to BS EN 12600 may not have been carried out for the thicker glass. In these cases, it is normal to accept that testing on thinner glasses is sufficient evidence to demonstrate adequate performance; note that a film of at least 150 microns thickness is preferred. However, the client must decide whether further testing is needed to demonstrate EN 12600 performance for the particular film + glass thickness combination.
5.9 These recommendations are generally for monolithic glass; laminated glass may be treated with safety film to reduce spalling. Insufficient testing has been done at the time of publication to state whether safety film on laminated glass gives any performance increase for explosion protection.
5.10 It is important to check whether there are any other requirements when installing safety film, e.g. marking of safety glazing required in BS 6262.
6. Additional Notes
6.1 Independent testing has shown the efficacy of safety films for protection in an explosion. As with all safety products, correct installation is essential. It is therefore very important to use a professional installation company with an appropriately trained and experienced labour force.
6.2 Installations of safety film use water-based detergent solutions during the cleaning and application processes. The detergent solution must be adequately squeegeed out from between the safety film and glass, but this always leaves a small amount of water behind. Some visual effects during cure that may be observable include haze and the occasional small water bubble; these are not installation defects and should decrease and disappear as cure proceeds.
6.3 The cure time should not be confused with time to achieve a level of performance. For example, with good installation, performance against impact to BS EN 12600 “Glass in building – Pendulum test – Impact method test and classification for flat glass” can be achieved within one or two days of installation for many safety films.
The Home Office Scientific Development Branch (HOSDB) has provided valuable assistance and advice in preparation of these recommendations
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