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As you will probably know there are several types of glass and glazing materials used in domestic doors and windows and some types are more secure than others.  The following paragraphs provide descriptions of glazing materials and their uses and make some suggestions about what to ask for when you replace your doors and windows.  Although I do not think it necessary for you to run to the expense of replacing your window and door glazing there is sufficient information in this section should you wish to do so.

ESSENTIALS

  • Do replace broken panes of glass or broken double glazed sealed units and if these are located in doors or accessible windows then consider using 6.4mm laminated glass.
  • If the door or window is not properly secured then upgrading your glazing to a security glass isn’t going to help
  • If you are going to replace your doors and (accessible) windows get ones that are certified to PAS 24 and BS 7950 respectively.  For the windows specify the use of 6.4mm laminated glass for the sealed glazed unit’s inner pane

PLEASE NOTE: At the time of writing this note (January 2012) we are awaiting publication of PAS 24 2012 for both enhanced security doors and windows.  I will update this information as soon as the new standard becomes available. 

Make the thief break the glass

By making a glazed door or a window resistant to kicking or levering open we increase the likelihood that the burglar will either give up or will have to break glass or remove it to get in.  By breaking glass the thief may increase his chance of being detected for the following reasons, which are all related to each other:

Noise

Breaking ordinary float or plate glass makes a familiar sound that can at least travel to the third or fourth house along the street in both directions.  A tiny minority of burglars have used suction cup glass cutters or newspaper and syrup to avoid making the noise, proving that they are very concerned about someone hearing ‘the sound of breaking glass’ and calling the police.

The noise generate by breaking glass differs from one glass type to another.  Toughened glass, which is commonly used in replacement doors and windows for safety reasons, makes a sort of dull ‘thud’ noise, which doesn’t travel.  Laminated glass, used in enhanced security doors and windows, again makes very little noise when broken because of the plastic interlayer that is designed to hold the glass together.

Another way to avoid making noise is to remove the glass sheet or sealed glazed unit from the door or window in its entirety.  This was a very common method of intrusion against traditional freshly glazed windows using putty or windows using external wooden glazing beads, and against the earlier designs of replacement aluminium and PVC-U windows, where the external glazing beads were simply popped off (often during the dead of night when the occupants were in bed).  It was this latter example that led the police to work with industry, the Glass and Glazing Federation and the British Standard Institute to develop a security standard for doors and windows.

Time

Breaking though any type of glazing will take time and the longer the time it’s going to take the greater the chance that the thief will give up.

The time it takes to break through a pane of glass that is big enough to reach the catch of an unlocked window or the turn knob on the inside of a door will again depend on what type of glass is being broken.  Sheet, float and cast glass (see below) will break very easily.  Toughened safety glass, although very resistant to blows by blunt objects, will break easily and quickly if hit by something sharp, such as a centre punch.  Ordinary 6.4mm laminated glass will break in the same way as float glass but the shards will be held together by the tough plastic interlayer, buying you quite a few valuable seconds.  In some cases the thief has to push the entire sheet through the door or window, because it is so well held together.

If the thief has to climb through the gap left by the smashed out glass he has to carefully remove the shards or otherwise risk injury, thus gaining you a little more time.

Injury

Most thieves would want to avoid injury when smashing glass and use various techniques to do this.  For example, many thieves (but not all) will avoid breaking very large panes of glass for the simple fact that a large expanse of glass, with some possibly above their body height may be more likely to injure them.  That said, some now realise that very large panes of glass reaching to ground level will often be toughened, which has been designed to prevent injury (See below).

Forensics

Smashing glass will always produce microscopic particles of glass that will get into the burglar's clothes and if the thief is subsequently caught by the police the forensic people can sometimes match the glass fragments to the scene.  Likewise, crawling through broken glass can leave other valuable forensic evidence behind, such as clothing fibres, shoe prints, fingerprints, leather glove prints and possibly blood, the latter of which could lead to DNA identification.

The important issue here is to make sure that your doors and windows are very secure so that the thief has no choice other than to break through the glazing.

Types of glass – a brief description

Sheet

Sheet glass is not totally distortion free, but it’s cheap and is often used for greenhouses and sheds.  It has no real security value other than the fact that it makes noise when broken and can cause injury

Float

Float or plate glass is relatively distortion free and is used as glazing for windows and doors.  No security value, except for the noise it makes when broken and the danger of injury.

Cast

Cast or patterned glass is used in doors and bathroom windows where light and privacy are required.  It breaks in the same way as float glass and has no security value other than the noise it makes and the risk of injury 

Wired (Georgian wired)

Usually made from float glass this is usually seen in fire doors.  The wires help to hold the glass together in fire situations.   Although there are hybrids using special glazing materials the normal type has no security value and, unlike ordinary float glass, is less likely to make noise and cause injury. 

Toughened

Made from specially treated float glass it is used as a safety glass both in the home and in commercial premises.  The use of safety glass is required by Building Regulations in areas where there is a high chance of a collision, such as a person running into a glazed door or low level window.  It is often used in sealed double glazed units in replacement doors and windows.  Each pane is marked in the corner with either BS 6206 or BS EN 12600.  It is made-to-measure at the factory and cannot be cut on site.   It has no security value at all as it can be broken with a sharp implement, makes very little noise and causes little, if any injury. 

Laminated  

The type used in domestic applications is usually 6.4mm thick and consists of two sheets of float glass with an interlayer of polyvinyl butyral (PVB) or Ethylene and Vinyl Acetate copolymer (EVA).  6.4mm laminated glass is sold as safety glass, but because the PVB will hold the glass together when broken it is also useful for security.  The actual entry level for a security rated laminated glass used to be 6.8mm, but security glazing is now being performance tested to BS EN 356: 2000 and so should be selected by its performance rating rather than its thickness.  In practice, however, most domestic enhanced security doorsets will still use 6.4mm laminated glass as will enhanced security windows if laminated glass is specified.

If you have laminated glass in any of your doors or windows it may be marked 'Laminated' or 'BS EN 14449:2005'.  BS EN 14449 is an evaluation of conformity and product standard. 

When replacing your doors and windows please specify the enhanced security types, quoting PAS 24 and BS 7950 respectively, and ensure that the glazing used in ground floor and otherwise accessible windows has at least one sheet of 6.4mm laminated glass in the sealed unit (PAS 24 doors use laminated glass as a matter of course).   If you are interested in using 6.8mm laminated glass or need to specify a glass that has a performance rating against BS EN 356: 2000 you will have to ask your supplier at the beginning of your negotiations.  This is because 6.8mm laminated glass may require a deeper rebate and if you quote a performance security grade for the glass, such as BS EN 356: 2000 P2A (See table below) the window supplier will have to source the glass and make sure that it can be used in their windows.  Also note that the energy ratings of windows can be affected by the glazing material and the ‘air’ gaps between the glass and these matters will have to be taken into consideration.

In the future it is possible that window and door manufacturers will use EN 356 security rated glass in all their enhanced secure doors and windows and P1A or P2A will become the normal standards for most domestic risks.  If you consider that your risks are much higher, then I would suggest looking at door and window products manufactured to higher levels of security using the Loss Prevention Certification Standard (LPCB) LPS 1175 Issue 7.  There are very few manufacturers making the very high security domestic doors and windows and I recommend you contact the LPCB on 01923 664100 or take a look at their listings for manufacturers by clicking here   

Laminated glass is available in many different thicknesses with multiple laminations using different interlaying materials, including polycarbonate.   It has many uses including noise control and the provision of anti-bandit, anti-blast and bullet resistant screens.  It’s also available using toughened glass to combine the benefits of safety and security glass when a very large sheet is required.

Security glazing film

Films of various thicknesses can be applied onto window and door glass to improve its security, but needs to be applied behind the glazing beads or bars to be fully effective.   I therefore recommend a professional installation.  The film acts a little like the PVB interlayer in laminated glass and holds the glass together when it’s broken.  Another security use, which you may have seen at your workplace, is to mitigate the effects of a bomb blast, by preventing shards of glass flying around the inside of a building and causing injury or falling onto the pavements below. 

Other non security applications for glazing film include the provision of privacy, the reduction of solar heat gain, which saves money on air conditioning, the reduction of glare, the reduction of fading (such as tables and chairs in a conservatory), the conversion of ordinary float glass into a safety glass to meet building regulations and the provision of window graphics.

Further information about window films can be found at the following organisations:

Glass and Glazing Federation

Applied film group

54 Ayres Street,

London,
SE1 1EU

Tel: 0207 939 9101

European Window Film Association

22-24 Rue du Luxembourg

B-1000 Brussels Belgium

Tel:        + 32 2761 6664

Polycarbonate

This very strong plastic glazing material can sometimes be found in access controlled doors and surrounding glazed panels on local authority and housing association estates.  Its use usually indicates that either there has been vandalism in the past or there is a concern that if ordinary glass was used it would be regularly broken.   It is best used in small panes and through fixed into its rebate.  By that I mean that the fixing screws for the glazing bars go through pre drilled holes in the polycarbonate sheet and then into the fabric of the door.  The size of the panes will of course be determined by the design of the door.  Unfortunately the material does get scratched, can be burnt with lighters and might turn a little ‘milky’ over time.

Security standards for glazing

BS EN 356:2000 Glass in building. Security glazing. Testing and classification of resistance against manual attack

This graded standard provides an entry level for domestic security at level P1A and then increases to levels of resistance to suit all sorts of domestic and commercial risks.  The glass could in theory be quite thin and pass at P2A, but in reality 6.8mm is the thinnest available at the moment. 

The glass is tested in a horizontal test bed and a hard body impactor weighing 4.11kg is dropped onto it from various heights.  As the heights or numbers of drops increase the security grades increase.  The highest three grades are resistant to various numbers of axe blows.

BS EN 356: 2000 Resistance to manual attack categories 

CATEGORY OF RESISTANCE

DROP HEIGHT mm

TOTAL NUMBER OF STRIKES

CODE DESIGNATION OF RESISTANCE CLASS

P1A 

1500 

3 in a triangle 

BS EN 356 P1A 

P2A 

3000 

3 in a triangle 

BS EN 356 P2A 

P3A 

6000 

3 in a triangle 

BS EN 356 P3A 

P4A 

9000 

3 in a triangle 

BS EN 356 P4A 

P5A 

9000 

3 X 3 in a triangle 

BS EN 356 P5A 

P6B 

N/A 

From 30 to 50 

BS EN 356 P6B 

P7B 

N/A 

From 51 to 70 

BS EN 356 P7B 

P8B 

N/A 

More than 70 

BS EN 356 P8B 

 

LPS 1270: Issue 1 - Requirements and Testing Procedures for the LPCB Approval and Listing of Intruder Resistant Security Glazing Units

View standard here 

Glass certificated to this alternative standard published by the Loss Prevention Certification Board is generally destined for commercial uses, although occasionally glazing tested by this standard has ended up in someone’s home where the occupants had been the subject of a terrorist threat.  This standard is used in conjunction with LPS 1175, which is a security standard often used for testing security doors and windows.  It is unlikely that the glass you fit to your home will have been certificated to this standard.

BS EN 1063: 2000 Glass in building. Security glazing. Testing and classification of resistance against bullet attack

This standard will be discussed in Commercial Security when published 

BS EN 13541: 2001 Glass in building Security glazing. Testing and classification of resistance against explosion pressure

This standard will be discussed in Commercial Security when published

BS 5357: 2007 Code of practice for installation and application of security glazing

Recommendations for installing framed security glazing and unframed bullet resistant glazing for internal use.

Safety standards for glazing

BS 6262-4:2005 Glazing for buildings. Code of practice for safety related to human impact

BS EN 12600:2002 Glass in building. Pendulum test. Impact test method and classification for flat glass. 

This European standard has replaced BS 6206: 1981, but glass in your home may well still be marked with the old standard number.

BS EN 14449:2005 Glass in building. Laminated glass and laminated safety glass. Evaluation of conformity/product standard

Building Regulations

England and Wales

The Building Regulations 2000 Glazing – safety in relation to impact, opening and cleaning

Approved Document N, N1 Protection against impact. Published 3rd May 2006.  

Scotland

Building Standards(Scotland) Regulations 1990

Part P ‘Miscellaneous hazards’

Northern Ireland

Building Regulations (Northern Ireland) 2000

Part V: Glazing

A bit of history

Roman times saw the first use of window glass in Britain, but only in the homes of the wealthy.  It was formed by splitting and rolling an elongated balloon of blown glass.  This was then cut up and the pieces were joined together using lead strips.  You couldn’t look through it particularly well, but it was translucent and so let in light and kept the bad weather out.  The quality of the glass made in this way gradually improved, but by the 13th century it was replaced by a much more superior ‘crown glass’ imported from France.  Crown glass was made by blowing a sphere of glass and then cutting the end opposite the blowpipe.  It was then spun into a circular sheet.  The glass made in this way, although not perfect, was optically far superior to anything before.  The circular sheets produced by this method would be thicker in the middle and thinner at the edges.  The sheets were cut up and formed into leaded lights with the thickest part of the glass piece at the bottom.  Some pieces of glass would be from the centre of the blown sheet and retain the concentric circles (bull’s eye) created during spinning, a familiar sight in the windows of some old buildings, and a feature often picked out in traditional Victorian Christmas Card scenes.    Glass was only found in wealthy people’s homes right up to the middle of the 17th century.  The abolition of glass tax at this time increased the demand and new production techniques meant that even the average earner could have it in their windows.