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.

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