Applied Knowledge

Blast Resistant Retrofit Concepts

When leasing space in or buying an existing building, chances are that the building was not designed and constructed with blast resistance and protection in mind. As such, buildings located in high threat environments (see our previous post) most likely require some type of blast resistant retrofits.

The scope and selection of retrofits varies depending on the type and size of the threat. However, the basic concepts underlying the majority of blast resistant retrofits are simple and generally fall into one of the following categories:

  • Vacate the premises and move personnel to a more secure location,
  • Keep the threats as far away as possible from the people and buildings,
  • Install specially designed systems to catch hazardous debris,
  • Upgrade the capacity of structural members to reduce the amount of hazardous debris,
  • Upgrade connections securing building elements to each other (tie the building together better).
  • Protect the building using a shield structure,
  • Position personnel away from hazards within the compound and within the buildings, or
  • A combination of the above approaches.

An example of this can be seen in window retrofits. Most existing windows are not designed to resist blast loads and can create significant flying glass hazards to people, in the event of an explosion.   These existing windows require upgrades to reduce hazards to people who are occupying the buildings. One retrofit approach is to install Shatter Resistant Film (also known as Blast Film or Anti-Shatter Film) to the inside face (protected side) of the window glass. While this is a good first step, it really only provides a baseline of protection.   Where the threat is larger, the distance to the threat is smaller, or the amount of required protection is higher, the film can be combined with a catch system to provide additional protection.  There are many types of catch systems for windows, two typical systems are horizontal catcher bars or vertical cables. See the figure below for before-and-after photos of a window with film and a catcher bar.

catch_film

In looking at these photos, you can see significant damage. At first glance, this may seem to be a failure of protection. However, in many instances, this would be considered to be successful protection. Why? The Post-Blast photo shows that the shatter resistant film has held the shattered glass together as a single sheet rather than multiple shards that could cause serious injury. Additionally, the catcher bar has stopped the glass/film sheet from being thrown into the protected space. Thus, the hazard is isolated to the area directly in front of the windows and the potential for injury has been greatly reduced.

Another retrofit concept to remember is that when upgrading a building element (i.e., a window, a door, beams, etc.), the capacity of the connections and structure supporting that element must also be checked to ensure that they can resist the blast loads. The system is only as strong as its weakest link.

For example, if the glass of an existing window is strengthened to resist a specific blast load, but the existing connection between the window frame and the supporting wall is only designed to resist conventional wind loads the weakest link has been moved from the glass to somewhere else. In this example, if an explosion occurs, the glass might not fly out, but the window frame might break free from the structure and fly into the room.  Below is a picture of a room after a blast event.

catch_system

In this case, the existing windows were retrofitted with shatter resistant film in combination with a catch system consisting of cables spanning the full floor-to-floor height, at the interior side of the windows. The blast caused the glass to break, but not shatter. However, the anchors connecting the window to the wall failed, and the entire window frame was thrown into the occupied area. Fortunately, the catch system was able to stop the frames before they could fly very far into the room. As a result, the hazard was isolated to the area near the windows. This also highlights the importance of personnel location during a blast event. Hazards can be significantly reduced by locating people away from exterior walls and windows.

For information like this, and more, check out our upcoming face-to-face course: Protective Knowledge – Protection in High Threat Environments.   This course is being offered in New York City from May 23 – May 25, 2016, and is focused on security and design professionals, owners, and contractors who work in high threat environments.

What Is A High Threat Environment?

We talk a lot about the need for protection, the changes in our world that have increased the threats, and the requirement to be ‘ever vigilant’.   But what are we really protecting against, and why? This article focuses on blast threats, but can be extrapolated to other attack modes.

Decisions about whether to provide blast protection, what type of protection, and how much blast protection should be provided, are difficult to make and should be reviewed on a regular basis. The decisions are difficult because:

  • Threats change rapidly and unpredictably.   Prime examples are the recent incidents in Paris and Brussels. Even though the intelligence services of France and Belgium may have had information that could have indicated a potential threat, it was not deemed sufficiently credible to take appropriate preventative action.
  • Changes in the types of work or projects undertaken by an organization can dramatically alter the threat profile. For instance, an organization feeding children in Afghanistan may have a relatively low threat profile, but if they start providing Polio vaccinations, the threat will markedly increase.
  • Changes in the immediate environment of a facility can also heighten (or lower) the threat. For example, the re-location of the US Embassy in the United Kingdom from Grosvenor Square to Nine Elms will change the threat landscape for both locations – for better or for worse.

In making protection plans and decisions, the first question people often ask is “Is this a high threat environment?” This is not an entirely straightforward subject.   When you ask yourself this question, the first places that probably pop into your mind as ‘high threat’ are Afghanistan, Yemen, Syria, Somalia, and Iraq, etc., and you would not be wrong, these are indeed areas with high threat and a high tempo of attacks.   The map below shows the number of explosive attacks around the world between January 2016 and March 2016 (Note that the background compilation of data for this map is from Wikipedia. While we do not generally use Wikipedia as a source, this particular page has compiled a fairly comprehensive list of information about terrorist attacks using various different news sources and each attack in the list has an associated news source referenced. We are therefore comfortable sourcing this list from Wikipedia.).

A glance at the map would tend to confirm that first thought regarding high threat environments. There were 23 attacks in Iraq, 12 attacks in Afghanistan, and 7 in Yemen. However, a closer look also reveals that there were more explosive attacks in Turkey than Somalia, which is counter-intuitive based on events in the past few years.   Also indicated on the map are the recent bombings in Brussels. Brussels is the heart of the European Union government and the home of NATO headquarters. Until last month this city would not have made the Top Ten list of high threat locales and yet now it is the focus for counter-terrorism activities throughout Europe. Additionally, information regarding the efforts of Al-Qaeda and the Islamic State to export terror to western countries calls into question our more ingrained thoughts on ‘high’ versus ‘low’ threat environments.   While there is no question that the active conflict zones around the world will continue to be at higher risk of explosive attack, we need to expand our definition to include crowded spaces, high profile targets, and buildings with high profile occupants; regardless of region.

2016 Q1 Attack Map

So, rather than thinking of high threat environments in terms of countries, organizations (be they public or private) should consider the following questions:

  • Do our operations place us in a higher probability target category?
  • Are we located near higher probability targets?
  • Do we have high profile employees or visitors who increase our target attractiveness?
  • Would we be considered to be a crowded space?
  • What attack modes are most likely to occur in our facilities?
  • What are our assets that need to be protected?
  • What is the current standard of care in our location and our industry?

For information like this, and more, check out our upcoming face-to-face course:  Protective Knowledge – Protection In High Threat Environments.

Four Critical Characteristics Of Blast Waves

An explosion is a rapid release of energy in the form of light, heat, sound, and a shock wave.   From a protection perspective, the shock wave is what we are most concerned about.   However, as a security professional or an architect, or a procurement official, you may be asking yourself, why do I care?   Well, you really don’t.  What you care about is how this shock wave affects people and property and how to best mitigate the potential hazards.   In order to better understand the hazards and mitigations, it is useful to understand some of the fundamental characteristics of the shock waves.   The following are some of the primary characteristics that are of interest:
  • The shock wave expands outwards in all directions.  Which means that just because you aren’t the target does not mean that your building won’t be damaged.  So whether the target is across the street, around the corner, or two blocks away, there will be some effects on your building and it’s occupants.
  • The duration of the shock wave is very short, measured in milliseconds rather than seconds (think of a blink of the eye), and the energy imposed on anything it its path are enormous – many times greater than hurricanes.  The short duration gives engineers a fighting chance to develop designs of new buildings and retrofits of existing buildings to resist the enormous energy.  The short duration allows engineers to design blast resistance buildings differently than buildings only subjected to more continuous loads such as gravity, so not all blast resistant buildings need to end up looking like bunkers.
  • The energy of the shock wave decreases exponentially with distance.   This means that every foot (or meter) counts, especially closer to the detonation.   So if you are laying out a new building or compound, think carefully about where explosive attacks might come from, and locate your occupied buildings as far as possible from those locations.
  • The amount of energy imposed on a person or structure is dependent on the angle at which the shock wave hits.  A straight-on (or perpendicular) approach transfers more energy than a parallel approach, this is one of the reasons that bomb damage can often look like a bite was taken out of the building.   As you go farther down (or up) a building from the detonation, the angle gets closer and closer to parallel, thus decreasing the amount of energy imposed on the building elements.
Again, why do we care about these characteristics?  Because they translate to how be smart about increasing protection.
For information like this, and more, check out our upcoming face-to-face course:  Protective Knowledge – Protection In High Threat Environments.