Security of Glass – blast mitigation & terrorist attack

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The threat of explosion, whether by accident or design, will create fear. Often out of all proportion to the actual risk.

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The source of blast pressure impact can be varied. Most cases result accidentally. Some are born out of error or neglect. A few are deliberate and are called terrorism.

A common factor means that the event is quite unexpected. In terms of both the timing and of the place. Hence the chaos and panic which may ensue.

Blast mitigation covers a wide field. Just glass alone is a major weakness in the defence of any building. It demands careful consideration. A rehearsed plan of action is essential.

Glass can break into sharp pieces, fly and kill. Toughened glass is deemed safe for human impact, yet can break into millions of tiny granules and become lethal shrapnel.

As soon as any pane of glass breaks under blast pressure, the force enters the building in general and is free to rampage at leisure. The same effect can result if a window were to be left open.

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Blast mitigation works simply to absorb or reject a blast pressure wave. Its main aim is to reduce risk of injury and death. A secondary aim is to reduce damage to the premises.

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A risk assessment of a set of premises is needed and with a full report submitted. That will cover in general all external panes of glass. It must also consider the status of each entrance and exit to a building.

It must review all internal glass closely. These panes will inflict injury when breaking. But when protected can stop blast pressure from circulating further. And so lives can be saved.

The key to success is to prevent blast getting into ducting, stairs, lift shafts and atria. If this can be achieved, casualties in other areas of a building can be kept to a minimum.

As with any assessment of risk, there is no replacement for experience and independence of thought. A client under threat needs to be told the bald truth. Not just something he might like to hear.

A risk assessment should not confine itself just to the glass. The frames holding each pane should provide a secure grip around the perimeter. And how secure is the fitting of the frame into the building structure? Failure of the glazing method or of the frame will affect safety badly.

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Accidental blast from gas explosion or petro-chemical incident is better understood and can be more easily planned for. The terrorist is another kettle of fish.

Recent experience shows that cars, skips and almost any type of container may be used to leave a device prior to detonating. A warning might be given; it might not.

Defence against a ballistic attack is more difficult to combat, but the number of injuries are often far less. Specialist glass is required, but it would not be considered for an average commercial building.

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The need under such circumstances is for the proactive involvement of each staff member.

Apart from the physical upgrade of security, glass and other parts of a building, the staff can operate a policy of care. Keeping doors and windows closed at all times. Reporting unusual events in the area of the building, including unwarranted parking of cars or other vehicles.   

A proper policy for self protection within a company should be developed, discussed, implemented and enforced.

Avoid sheer lunacy. AITCo Consulting was witness to such an example when carrying out a risk assessment on a major Central London government office during the Irish Republican Army (IRA) attacks.

A statutory fire door was seen to be wedged open. This was for the convenience of staff using the office.

The door was kept open by the pulling back of a weighted bomb blast curtain guarding an adjacent window and draping it over the top of the door.

Fire and smoke protection compromised. Blast ingress into the office now guaranteed. And the added bonus? Blast now had a free run down the corridor and up the main staircase.

Such criminal lack of care must be avoided at all costs.

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In new premises, fitting blast resistant glass is an option. But in most other cases existing glass is treated in situ.

Ordinary annealed glass is too fragile. Toughened and wired glass granulates. Laminated glass will resist blast better, but can suffer rear face spalling – a mass of minute glass fragments flying from the back face of the unit, which can inflict fatal injury.

Window film has been used widely to keep breaking glass together for 30 years. It acts rather like flypaper and has been very successful.

The first true blast film was developed in London in time for the first IRA bombing offensives. Its success in the face of blast bombing, petrol bombing and physical attack was quite astonishing.

It was tested by North Atlantic Treaty Organisation (NATO) and the Federal Bureau of Investigation (FBI) as a means of defying Palestinian bomb attacks upon United States military bases throughout the NATO area. Onlookers were shocked by the result achieved under controlled testing. A grenade exploded just in front of the test pane failed to penetrate the glass. One exploding on the glass itself tore a small hole and the plug of filmed glass was found on the ground beneath the test rig.