Glass
One of the weakest areas of building exteriors is the glazing. It is certainly the thinnest part of the wall and it often enables a potential intruder to see what is inside the building.

Glass itself comes in relatively few forms. We often talk about wired, toughened or laminated glass when we consider safety (anti-accident) and security (anti-intrusion)

Wired glass is commonly seen in many older buildings such as schools. It is not generally security rated as it is predominantly installed for fire resistance. While it has poor resistance to impact it can create a belief in the intruder that it is strengthened.

“Many building and fire officials are mistaken about the impact resistance of wired glass and believe it to be a safety product, in part because the wires give the appearance of increased safety.

The common misperception is that the embedded wires reinforce impact strength, when they do just the opposite. The wires actually weaken the glass and substantially reduce its impact resistance, so wired glass is in fact only half as strong as ordinary annealed glass. Wired glass is more dangerous than regular glass when it breaks because the exposed wires are razor sharp and catch a victim's body part in the opening, and increase the severity of the injury.”

Toughened glass is superheated glass that is quickly cooled with a cold air process. This process creates stresses on the glass surface which increase the strength by as much as 5 times that of standard glass.

Laminated glass offers different levels of safety and security protection from fire resistance through to bomb blast and bullet impact resistance. It is made up of two or more layers of glass with a layer of plastic or vinyl between each layer to create the finished laminated unit. The various combinations of thicknesses and different products produce various levels of protection.

Glass in this form provides a multi layered barrier to any attack. A lot of the impact can be absorbed by the interlayer which prevents the glass breaking. The potential to reduce serious harm accidents is why this product is used for many safety precautions.

If hit hard enough or long enough with a tool or implement the glass will break. However the interlayer will hold the glass together and, dependant on the layers and materials, ensure slow and noisy progress by the offender.

Glass sheets in this form are virtually indistinguishable from other forms of glass.

While it is possible to install glass which is completely resistant to forced entry the cost often outweighs the risk. It is essential to remember that an effective security plan must not be reliant on one security item or layer.

An uninterrupted offender with plenty of time will eventually get through most walls or windows.

Joinery
It is also essential to ensure that the window joinery frame in which the glass sits is suitable for security purposes. Other obvious aspects of the construction or equipment to be considered are the opening and closing devices, rubber bedding strips and the strength of security stays.

Security Bars
Security bars have been a successful method of securing windows and other areas of glazing for many years.  Bars need to be very securely entrenched to lessen the likelihood of them being popped. 
There are many different forms for covering windows and glass areas including a light but very strong expanded metal product, which can be less obvious but harder to penetrate. 

Windows and roof lights easily reached by offenders and/or not immediately visible by the public should be grilled to prevent attack.  Alternative mechanical ventilation and artificial lighting may be needed.  If window protection is required, the following minimum specifications are to be applied:

Bar grills
The sketch shows the alternatives, using flat iron or round iron. Horizontal cross bars for strength should be at least 600mm centres while vertical grills should have a maximum of 120mm centres.

Fixing:  Bolt to the window frame at a maximum of 200mm centres with  10mm diameter coach bolts. Burr over nuts to prevent tampering.

• Flat iron:  At least 40mm x 10mm in section.
• Round iron:  At least 16mm in diameter.
  

The sketch shows the minimum acceptable window grill specification.

NB:  Fit screens and bars inside the windows so that glass must be broken before the bars can be attacked.

Locking Devices  See container locks and  external  environment section

Printed from the GETBA Website www.getba.org.nz
on