Window Security – Types of Glass
Glass – Types of Glass
Any type of glass can be considered a useful barrier against the burglar, because whenever it is broken, the offender risks leaving evidence behind him. Clothing fibres, blood, sweat and fingerprints are the obvious clues to be looked for, but small pieces of glass can also get into the clothing of the person who broke it and anyone standing nearby, and forensic scientists have techniques that enable them to match glass fragments to the scene of a crime. So by fitting good window and door locks, you can force a determined burglar to break glass, and in doing so, you can increase the likelihood that he will be caught. In other words, crime prevention techniques directly assist detection, a factor that sometimes is not appreciated even by the professionals.
Another advantage of some types of glass is the familiar noise it makes when broken, a noise that attracts the attention of people when heard late at night. Another advantage that may not be quite as obvious is that glass contributes towards the powerful crime deterrent of ‘natural surveillance’. Because of great advances in glass technology, architects now are able to design buildings with glass walls, and you can often look right through a building and out the other side. This severely hampers burglars, since there are few places to hide.
A variety of glass types are used in the home; all have good and bad points in security terms.
Ordinary Sheet Glass
Although this glass can be used in windows, the manufacturing process sometimes causes distortion, so it tends to be used for greenhouses and sheds. It can be cut to any size with an ordinary glass-cutter.
This type of glass breaks noisily into dangerous shards, and therefore could cause injury to an intruder. However, it’s easy to break and has little security value as a barrier.
This is a distortion-free glass, which is sometimes called plate glass. It is made by floating molten glass on to molten tin. It’s commonly used in domestic windows and also in some shop windows. Gradually, however,glass in shop windows is being replaced by laminated or toughened glass.
This glass breaks noisily into dangerous shards, and therefore it could cause injury to an intruder. However, it’s easy to break and has little security value as a barrier.
This is used as a safety glass (BS 6206) in a wide variety of applications, including all-glazed doors, glass walls and wherever there is low-level glass in buildings. It is made to measure from specially treated float glass and can’t be cut with a glass-cutter.
Toughened glass breaks relatively quietly into tiny fragments. It can withstand a soft body impact, but it only has to be nicked with a sharp tool to shatter. Because it breaks into such small pieces, it is less able to capture forensic evidence. It has low security properties.
This is made from two or more sheets of glass (normally float) or plastic, sandwiched together with one or more inner layers of polyvinyl butyral (PVB). It is used as a security and safety glass, and sometimes as a fire break.
Laminated glass will break fairly quietly, but will be held together by the tough PVB inner layer. Consequently, it presents less danger to an intruder than float or sheet glass. The thicker laminates (7.5 mm and above) are used as security barriers, but even the safety laminates of 6.4 and 6.8mm thickness resist easy penetration and will delay entry. If the glass is simply cracked, it can be left in place until a new piece has been cut to fit.
Normally made from float glass, this glass contains a thin wire mesh that is intended to hold it together if it is broken. It is often used in fire doors and as roofing glass in commercial premises. Most types are not regarded as either a safety glass or security glass.
Wired glass breaks more easily than laminated glass and does present a danger of injury to an intruder. It resists intrusion, but not to the same extent as laminated glass.
Applied Safety and Window Security Film
If you want to improve safety, instead of replacing sheet glass with toughened, or toughened glass with laminated, you can apply a film to the inside of a glass pane (see How to Apply Window Security Film to Windows). Some films reduce UV light damage (which may fade furniture and carpets in a ), while others help keep a conservatory cooler in the summer. Some suppliers will apply the film for you, while others provide DIY kits. For the best results, the film should be applied to the entire sheet of glass. This will require the removal of the glazing beads which are refitted after the film has been applied.