Protecting buildings from blasts: How to integrate protective objectives and security layers through good design
Tuesday, 27 October, 2015
In our previous blog, “Anatomy of a blast: How explosions harm buildings and people”, we took a close look at the physical properties of explosions and how they actually cause damage to structures and the people within and around them. As we saw, the various methods of explosive attacks can present a serious threat to the wellbeing of personnel and critical assets.
In this blog, we examine some of the principles of physical protection relative to preventing bomb attacks and to mitigating their harmful effects through design.
Of course, buildings and people can be at risk from many other threats than explosions–not least burglaries and ballistic attacks–but that’s the stuff of future blogs!
Protection by design: the earlier the better
The physical protection of buildings against explosive attacks is vastly more effective, and cost effective, when protective considerations are part of the building’s basic design. While almost any structure can be retrofitted to improve its security, the design approach to physical protection – whereby protective features are an integrated part of the building’s architecture – is always to be preferred when possible.
The design approach enables architects and engineers to incorporate protective security alongside aesthetic, operational, environmental and productivity criteria. When balanced with these other key elements from the earliest project stages, such as definition of objectives and scope and conceptual or preliminary designs, physical security can be practically invisible, highly effective and relatively inexpensive.
Of course, this is not to say that the physical protection of existing buildings cannot be improved. It can and often is. Historically significant buildings that have been in use for centuries house many vital governmental and private sector activities; these buildings can be threatened by explosive attacks, too.
But whether the building to be protected is 200 years old or still on the drawing board, one thing is sure: the earlier in the design process protective security is considered, the better.
The multiple objectives of physical protection
Buildings have always been designed with the primary objective of protecting the people within them. Our ancestors used structures to shield themselves from the elements, predators, thieves and others who would do them harm. In an age where explosive attacks are a real threat to certain structures, however, architecture must now work in tandem with protection systems to prevent, delay, or mitigate the effects of a blast.
In the case of at-risk office or residential buildings, the highest protective design priority will always be the safety of employees and occupants. Loss of life must always be minimized; the building itself is seen as a secondary asset whose purpose is to remain standing as long as possible in order to allow the people inside to evacuate safely.
Critical infrastructure such as power plants, on the other hand, may have slightly different priorities. While preventing loss of life remains the most crucial protective objective, it may also be important to make sure that the building’s primary purpose (e.g., energy production, water filtering, communications services, etc.) continues to be served uninterrupted, or for as long as possible.
Regarding blasts, design criteria will include some or all of the following physical protection objectives:
- Stopping total collapse: Historically, this is the deadliest consequence of blasts against buildings. Engineers, architects and security professionals have to focus on structural integrity, structural resistance and protection measures so that, in the event of a successful attack, the building will remain standing.
- Stopping progressive collapse: Similarly, progressive collapse can lead to high casualties and damage to the building’s assets. Alternate-path methods can be used to stop progressive collapse, as can careful attention to the design of components for air-blast loading.
- Facilitating evacuation and rescue efforts: Good design also considers traffic flows after a blast, ensuring that emergency exits work optimally, and enabling first responders to access all parts of the structure and its occupants.
- Preventing or limiting flying debris: Glass and other building materials become lethal in nanoseconds after a blast, causing casualties within the building under attack as well as for blocks around. Much of this collateral damage can be prevented using simple methods.
- Equipment redundancy: While obvious for critical infrastructure, equipment redundancy can also be important consideration for architects and engineers whose primary concern is to protect people against the effects of a blast.
Whether the building to be protected is new or existing, a design approach will consider as many physical protection objectives as possible and balance these alongside all other considerations.
Using security layers to protect against blasts
The three primary layers of physical protection all play a role in preventing, delaying and/or mitigating the potentially deadly effects of an explosion targeted against a building.
Protection is maximized when the three layers are conceived as one system. Just as a chain is only as strong as its weakest link, a building’s physical protection is only as effective as the weakest point of every security layer.
Perimeter: The controlled access zone around the building is the first layer of protection, and is key to deterring and delaying bomb attacks. This can be done by using passive (e.g., fences and bollards) and active (e.g., surveillance and guards) barriers to protect and/or strengthen access points to the building and its immediate grounds. By increasing the stand-off distance from the perimeter to the building, placing a bomb close enough to the building to do it damage becomes more difficult. Perimeter protection can also provide valuable reaction time to intervene against attackers: even if the perimeter is ultimately breached, barriers can slow an attack and thereby improve other defensive responses.
Shell: The building’s exterior is the second protective layer. Architectural features can provide provide some protection against blasts, for example by angles of surface that don’t trap blast waves, and facades that reflect them. Similarly, materials can be chosen for their ability to absorb shock waves and/or for their propensity not to splinter into projectiles in case of a blast. Building shells can be retrofitted with specialized materials to improve their protective qualities. Of course, surveillance at the shell layer also plays an important role in detecting suspicious behavior.
Cell: Individual spaces, such as any offices along a given street up to a certain height, or server rooms, may also be the object of heightened physical protection against blasts. This can be done by blast-proof windows and materials that strengthen walls against penetration by flying debris. Other means, such as security sluices and/or guards may also provide a way to keep smaller explosive devices, such as personal-borne IEDs, from getting near their targets.
First prevent, then delay, and finally, mitigate
When thinking blast protection into building design – or retrofitting existing buildings to be more secure – it pays to employ three separate but connected mindsets: prevention, delay and mitigation.
Prevention: Stopping—or discouraging—the attacker at the perimeter, shell or cell is the ideal scenario, since no damage is caused to the building and none of its occupants is injured. In order to do so, the most obvious priorities are strong defensive measures and hard-to-bypass protection systems, both physical and operational.
However, there is a balance that needs to be achieved between a “fortress-like” design and aesthetics. While it can be a good idea to make a location appear secure, one must also keep in mind the symbolic meaning of visible protection. It could signal defensiveness, and that terrorists have achieved their goals of creating fear. It could also make the location even more tempting to attack. After all, if it weren’t valuable, why would it be protected so highly? Deception can be used to make a location seem less secure or less valuable than it actually is. But once again, it may have the opposite of the intended effect. This aesthetic balance is just one of the areas where physical protection professionals can add value to the design process.
Delay: Should prevention fail, the next priority is to delay the attack for as long as possible, allowing the building’s occupants to evacuate, and for further security measures (more guards, alarm systems, vaults shutting down, local security forces…) to be deployed.
Buffer zones are used to create this delay, either using the building’s architecture or its protective systems to effectively create a sort of security “maze” which attackers must navigate and defeat in order to reach their goal. In some cases, the attackers may even be forced to traverse through non-critical parts of the building. Ideally, the delay will help weaken the attack and save the maximum number of lives possible.
Mitigation: Should both prevention and delay fail to thwart attackers, the last resort is the mitigation of the attacks to weaken their effect. This step could be considered more “passive” than the other two, but that’s not the case.
As we have seen above, blast mitigation implies a solid design on both the architectural and security levels. A building’s ability to mitigate and withstand attacks should inform its core design—although that may not always be possible. For example, older buildings with historical value cannot be rebuilt from the ground up, and may inherit security flaws that can only be counteracted by retrofitting physical protection measures.
We hope this blog provides an overview of both the opportunities and challenges involved with protecting buildings against blasts—and look forward to your comments.