6 tips for hardening buildings against explosions

Building security experts discuss structural, procedural steps organizations can take to mitigate their risks

Last month, more than 70 people were killed in one of the worst terror attacks to ever strike Norway. Authorities say that Anders Behring Breivik is responsible for setting off a bomb in the country's capital of Oslo and carrying out a shooting rampage at a political youth camp on Utoya Island.

It is believed that Breivik used a fertilizer mixture similar to that of Oklahoma City bomber Timothy McVeigh and there are now efforts under way in the United States to place more regulations on the sale of ammonium nitrate fertilizers.

Though no building is ever immune from a terrorist bombing, there are several things that organizations can do to mitigate the threat and reduce the impact of a blast.

Tip #1: Understand what you're trying to protect against and understand what you're trying to protect.

Holly Stone, president of Stone Security Engineering: If you've looked at your facility and you've determined that a large-scale IED (improvised explosive device) is your biggest threat, then you would look at first and foremost protecting your perimeter and keeping vehicles as far away possible. The farther you can keep the explosive away from your structure or asset, the better off you're going to be, even without doing any structural hardening. If you are concerned about a suicide-type bomber or someone that would try to ram your building, then you would want to harden those perimeter barriers to an anti-ram capability.

Tip #2: Consider all of the elements of your structure in the hardening process including the exterior, interior and perimeter.

Stone: On the skin of the building or your building envelope, there are a couple of things to consider. The first is, when you look at injuries and fatalities from explosions in the past... once you get outside the blast zone most injuries are from flying glass debris. So, one of the first things you want to look at when hardening your building is the capacity of your skin or glazing systems. In new buildings, it's sort of a cleaner prospect. If you know that you have a threat and you know you have a protection criteria, you can build the protection into the design. Ninety-nine percent of the time in a new building, you will put in a laminated glass system that has been hardened. In existing buildings, it's not as straight forward. You have to take into account not only the capacity of your existing windows or facade system, but you also have to look at how it's attached to the building. You have to look at it systemically and you have to look at the supporting elements that go with it and I think that is one of the things many people don't do. Many times people come in and say 'oh, I'm just going to put it blast film,' and if you put it in where it's not touching the frame that's one thing, but if you start attaching your film to your framing system then you're loading up your perimeter walls and you have to make sure everything works as a system or you could be increasing your hazard.

The next thing you want to look at is the structure itself. Again, you want to start with what your threat might be, which when you start talking about hardening for blasts it's the number of pounds of explosives that you think a) someone would want to use against your structure, b) that could be delivered to your structure and c) all of your access restrictions, your vehicle and personnel screening, and where (the explosives) could get to. The structure has a hierarchy of importance, so you want to look at your primary vertical load carrying system first and make sure that is able to resist whatever threat you're looking at. You can provide protection by putting steel jackets on columns, you can add concrete, and you can add in additional columns. There are a lot of techniques that can be used to strengthen your existing structure, but before you start doing that you have to understand what the capacity is to begin with and where you need to be. After that you want to start to look at the other building elements you have. For instance, floor systems in a traditional building are designed to hold things up from a load acting downward, but all of sudden you add a blast force to it, your floor systems are being pushed upward and most existing buildings are probably not able to withstand a large force in the upward direction. So, you would want to retrofit your floor systems and your beams to resist that upward force and that might include providing better attachment between your slab and your beams or your beams and your columns. It might also include coming in on the top of your floor system, taking out all the existing flooring and putting in a fiber-reinforced polymer that would essentially add top layer reinforcement, which makes it able to resist that upward load.

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