Debunking the Top 3 Myths About Blast Hazards
Extreme Loads and Structural Risk
Blast hazards are present industry-wide, commonly linked to sources such as vapor clouds, bursting vessels, and in extreme instances, acts of terrorism. While there are general rules of thumb that guide our knowledge about blast hazard effects and assessments, there are also common misconceptions. These often stem from misinterpretation, partial understanding or new information superseding previous knowledge. Discover the most common blast hazards misinformation organizations will encounter and should promptly address.
Myth #2 - Overpressure Below 1 PSI is Safe
Injuries can be caused by non-structural items at overpressures below this threshold. Several blast assessments guides and technical manuals suggest that conventionally designed structures with predicted overpressures of 1 psi or less will cause very little damage and no injuries. While this can be the case for some structures, there are certainly exceptions to this type of broad generalization. Items such as windows, bookshelves or storage racks placed against exterior walls, light fixtures and overhead HVAC equipment can become flying or falling debris after being disconnected or impacted by the exterior structure movement during an explosive event.
Pre-engineered metal buildings, self-framing insulated metal panel buildings and lightweight trailers are examples of structural systems constructed so efficiently that there is little to no reserve capacity for even a small amount of additional loading. Significant damage and potential injuries are possible under relatively low blast loads.
Facility and safety managers should carefully consider the type of structures and their use when deciding that blast hazards are low enough to not be a potential risk. Many industry guides now indicate that both pressure and impulse should be utilized to perform blast assessments for the protection of personnel. The use of pressure limits/asymptotes alone are highly discouraged.
Myth #3 - The Bigger the Building, the Safer We Are
Heavy steel or reinforced concrete structures do not symbolize blast resistance. The goal of a good blast design is to create structures that are capable of absorbing blast energy without a catastrophic failure overall. Structural systems and members that are designed to respond in a ductile manner (i.e., bend before break) are essential in absorbing blast energy. It is equally as important that supports and connections be capable of transferring the full ultimate capacity of a structural member. The loss of support or connection often results in a sudden failure (i.e. break before bend) and potential catastrophic collapse. However, this does not mean every blast design should resemble a bunker or bomb shelter.
Designers that are not familiar with blast design techniques tend to increase the size of structural systems and members to add a safety margin. This can produce structures that are oversized, uneconomical, unbalanced and many times unwarranted. At worst, heavier designs will transfer higher loads to supports which can be overlooked and result in potential risk for a non-ductile response and failure.
Facility and safety managers should be familiar with blast design philosophy and intended performance. It is highly important to engage design teams with blast considerations that are familiar and directly experienced in blast design and philosophy.