From the earliest times, protecting the perimeter has been always been the first requirement for a secure defence.
Today, in the post 9/11 world, the threat from armed criminals and terror groups has never been higher. To deny access to groups such as these, specialist security doors can provide considerable protection. John Bowden of Safeguard Doors reports.
<br><br>
The idea of a secure door to restrict access and protect a perimeter has been with us for thousands of years. Castles and other fortifications long sported a drawbridge and portcullis for just such reasons but, in today’s world, the requirements of the security door have changed dramatically over the last 30 years. Modern security doors to assist with perimeter protection can now be easily integrated into any building project from new construction through to security retrofit, and one single doorset can now be expected to perform a multitude of tasks. These can range from resisting sledgehammer attacks up to an assault with automatic weapons and fragmentation explosives.
<br><br>
If we are to believe Newton’s third law of physics, which states: when an object exerts a force on another object, it experiences a force in return, we must ensure that our doorset offers more resistance to that which is going to be applied against it. Typically this may on occasions mean the fitting of a door that provides physical protection at LPS 1175 Level 4, has one hour fire resistance and that can protect against 7.62 NATO rifle rounds. It must also protect against the explosive blast properties from fragmentation devices such as pipe bombs and will have been tested for resistance against car bombs. But whom you ask would need perimeter protection like this?
<br><br>
Fortunately, not many. Some people, however, live with this level of protection as a matter of course. At government, diplomatic, military and sometimes even celebrity level, there can be a constant threat of physical harm, theft, or kidnap and ransom as a motive. Take the recent decision to provide a bullet-proof glass shield to protect the Prime Minister in the House of Commons. Such a device will now be placed in front of the Strangers gallery where members of the public sit to protect against threat. It will seal off MPs in the chamber below, although the spectating public will still be able to see proceedings and hear them via a loudspeaker. The shield is being installed in response to the current security climate and the anti Iraq war disturbances in the gallery following the Hutton report. It joins the electronic key based security systems being fitted to many doors throughout the Palace of Westminster and the X-ray machines and metal detectors already in place.
<br><br>
But while all such precautions do help, it can remain difficult to determine an exact threat. It could take the form of anything ranging from a determined terrorist attack, an arsonist, a stalker or quite simply an opportunist thief who happens to be in the right place at the wrong time. Typically therefore to provide perimeter protection against such a threat, security doors are increasingly found in government offices, prisons, police buildings, courthouses, military facilities and installations, banks, specialist IT suites, high value retail establishments and any place where ballistic and attack resistant security against criminals or terrorists is required.
<br><br>
The idea of a perimeter security door is all about control. The control can be to keep things in or keep things out. To refine this statement further, we need to achieve this objective in a manner that is user friendly, reliable and aesthetically pleasing. This latter point may not seem so important if the doorset is perhaps protecting equipment within a military compound but this level of protection has now reached public buildings and even some high value domestic properties. So how can we go about designing a modern doorset that meets these demands'<br>
There is no ‘high tech’ solution in the modern security doorset. To achieve these levels of performance we need to keep the ‘onion skin’ principle in mind. That is to say there is no’ one layer solution’. It is important to combine layers of materials which each have their own propensities. For example, a steel door can be cut quite cleanly with a petrol driven disc cutter. However, the introduction of a timber core can have a dramatic effect on the cutting ability of this powerful machine ‘ timber simply clogs the cutting blade and dramatically degrades its efficiency. Surreptitious entry with power tools and drill bits are another threat and this can be arrested by the inclusion of a layer of manganese steel. This material hardens very quickly and becomes harder than the intruding drill bit itself.
<br><br>
What about plastic
<br><br>
Well, if there’s enough layers of it, it can stop anything from pump action shotguns and 9mm pistols up to NATO rounds from a 7.62 rifle travelling at nearly 1,000 meters per second! But while no material can ever be ‘bullet-proof’, we can design systems capable of withstanding attack from specific type, calibre and velocities of ballistic threat. Extensive tests which measure the spacing or pattern of impacts and any penetration (or spalling) in relation to the number of impacts, help us to identify the best possible materials for the ballistic type threat.
<br><br>
Following on from this, there is also a link between bullets and bombs. The detonation of a fragmentation device such as a pipe bomb has a two-fold effect. Firstly there is a blast wave. This is the explosive charge expanding rapidly at many times the speed of a rifle bullet. However, with respect to a device such as the pipe bomb this element of physics is only the catalyst for the primary intention, which is to fragment the pipe in which it is contained. These shards of metal project and spin quite randomly. When placed at the foot of a door the doorset must do its job by either repelling or capturing and retaining these highly charged fragments.
<br><br>
The final test for our doorset is the car bomb. In this instance the charge is many times greater than that of a pipe bomb. Because the blast from this type of device will usually begin at a point further away from the door (usually known as the stand off distance) the chances of fragmentation hitting the door compared to a pipe bomb type device is less. However, if the engine block happened to be the part that hit the door then there are other equations to consider. The greater part of this device is the blast pressure, which it exerts upon the door and the length of time for which the pressure remains applied.
<br><br>
So how far do we go with all this’ In the case of blast doors for example do we make a doorset whereby after a large explosion the doorset has been so heavily fabricated that the door remains in place and the remaining fabric of the building has been turned into rubble’ Or do we perhaps manufacture a high security doorset, which is so secure it is easier to break through the adjacent wall’
<br><br>
With all these things in mind, there has to be an element of common sense. The high performance door set must help protect the perimeter but must also compliment the building structure in both looks and integrity. There is also one more consideration, sometimes the most important – cost. Sometimes security officials will decide they must have bullet or blast resistant security doors fitted, that is until they discover how much such devices cost! Then suddenly they feel that they can downgrade their specification. This can be a tough call, but if the perceived threat against a building or someone in it is real, then the bottom line is quite simple – can you put a price on a life?
