As Featured in GGP Magazine - 11/18
Phil Brown, European regulatory marketing manager at Pilkington United Kingdom Limited, part of the NSG Group, explains how specifiers can choose the right glass to protect against attempted break-ins.
As designers look to fill the interior of buildings with natural light by glazing greater areas of external walls, the role of glass as a line of defence against potential intruders has grown.
But a key challenge faced by those specifying security glass is assessing what level of resistance it needs to provide, given the wide range of methods of attack it might be subjected to. An attacker might try to use hands or feet, for example, or they might use a tool found nearby such as brick or item of street furniture. Alternatively, they might come equipped with a hammer, a crowbar or axe.
This makes it difficult to quantify exactly how much force will be applied to the glass in the event of a break-in attempt.
To approximate the onslaught of a manual attack, the European Committee for Standardization (CEN) has developed a test scheme that models impact in a simplified way. The test methods specified in this Standard do not reproduce the conditions of real human attack but are intended to give a classification of comparative resistance.
The tests – which glass needs to pass to achieve a classification under BS EN 356 –introduce eight different classes for the level of resistance to attack.
For classes P1A to P5A, the tests involve subjecting the glass to impact from a steel sphere weighing 4.11kg dropped three times from heights ranging from 1.5 metres to 9 metres, but with an extra six impacts for P5A. For classes P6B to P8B, the glass needs to resist penetration from between 30 and 70 strikes with a mechanical axe.
How much protection is enough?
The level of resistance a pane of laminated glass can deliver depends largely on the type and thickness of the interlayer. There is no one-size-fits-all solution when it comes to protecting buildings, as the level of resistance required varies significantly from one application to another.
Since 1st October 2015, Approved Document Q in England has set security requirements for new dwellings in England. The approved document sets out reasonable standards for doors and windows to resist physical attack by a casual or opportunist burglar by being both sufficiently robust and fitted with appropriate hardware.
A window that has been tested to meet the security requirements of PAS 24 would be considered a secure window. Where windows contain glass and non-key unlocking hardware, each glazed area must include at least one pane of laminated glass meeting the requirements of BS EN 356 Class P1A or higher.
Pilkington Optilam™ 6.8mm, for example, which features two panes of 3mm float glass and a 0.76mm pvb interlayer, achieves BS EN 356 Class P2A – one class higher than P1A – so would satisfy this requirement.
As the threat level increases, thicker glass with a greater number of interlayers may become appropriate. So, a shop window might require a higher EN 356 classification than would be needed for a domestic application, and areas where the threat is even higher, such as Government buildings, may call for much thicker laminated glass.
The whole system counts
When it comes to resisting manual attack, it is not only the glass that needs to be resistant, but also the frame, the method of fixing the frame to the structure and the method of fixing the glass in the frame. These all need to be designed to resist a similar level of attack as the glass.
This includes any doors or other means of access into which the glass might be installed.
The way the edges are fixed into the frame is particularly important. A 50mm-thick sheet of laminated glass that might be able to stand up to an attack with an axe won’t protect a building if an attacker is able to lever it out of its frame, so ensuring rebates are deep enough to prevent this is essential.
One of the major benefits of appropriately designed laminated glass is that the interlayers retain their integrity even if the glass is fractured, so any would-be intruder won’t be able to enter the building even if they attack the glass hard enough to break it. But this only holds true as long as the glass is properly locked in place by clamping pressure or a sealant.
It’s vital for specifiers to be aware of the way in which different types of glass reacts to impact, whether from deliberate attacks or accidental incidents. If there is any doubt as to whether a glazing system will deliver sufficient protection, consulting a specialist is always a good idea.
Ultimately, as glass increasingly forms the barrier between buildings and the outside world, choosing the right level of security is critical in keeping people and property safe.