The world of blast protection has been rapidly expanding and there are now numerous products and approaches to provide protection from explosive attack. Where there used to be two solutions, there may now be ten. It is critical that security and design professionals understand the strengths and limitations of the various mitigation measures, and how to select products appropriate for their project.
For exterior explosions, the most fragile and vulnerable elements make up the façade of the building: walls, windows, doors, louvers, etc. These elements are most often not critical for the structural integrity of the building (unless the façade consists of load-bearing walls), but they can represent significant hazards to occupants in the event of an explosion. For very large or close-in exterior or interior explosions, the structure of the building can be damaged as well.
The process of specifying blast resistant products can be simplified into 6 basic steps.
The following narrative provides a very brief description of each step.
Step 1: Is Blast Design Required?
While security consultants and blast engineers can make recommendations on this subject, it is the owner who must make the final determination. Project types that may require blast protection include:
- Government buildings.
- Data centers.
- Iconic buildings in urban environments.
- Multi-national corporate headquarters.
- Critical infrastructure.
- Crowded spaces (shopping malls, movie theatres, sporting arenas, etc.).
- Buildings located near any of the above.
- NGO compounds in high threat environments.
The types of threats to be considered in the design should also be identified at this juncture. This includes the delivery methods (vehicle, backpack, package, etc.). These delivery methods will lead to the establishment of the locations of the threats.
Step 2: Identify Vulnerable Elements
Based on the types and locations of the blast threats, the vulnerable building elements can be identified. These elements may include:
- Façade.
- Perimeter structure.
- Interior beams/columns/walls/slab systems (for internal or external threats).
- Roof systems.
- Emergency evacuation and rescue equipment.
Step 3: Develop Blast Design Criteria
For each type of building element, blast design criteria must be developed. The primary components of blast design criteria are:
- Blast load to use for design/analysis.
- Required response of the elements to the blast loads.
- Confirmation of compliance methods and requirements.
- Applicable existing blast design criteria documents (if any) to be used in the design.
Step 4: Identify Other Design Criteria
Other design requirements may be incompatible with certain approaches to blast resistance, and in other cases they may reduce the number of available products appropriate for a specific project. Other design criteria to consider may include:
- LEED.
- ADA accessibility.
- Fire resistance/fire egress requirements.
- Operability (e.g., with respect to windows).
- Historic preservation.
- Aesthetics.
Step 5: Supporting Structure Check
One of the critical things to remember when designing structures for blast resistance is that the individual building elements (e.g., door, window, wall, roof system) do not act alone. All building elements are supported in some manner, and those supportive systems must be able to withstand the blast loads transferred from the original building elements.
Step 6: Develop Specifications
Whether part of an overall construction document package or as a standalone document for one-off procurements, a well-written and complete specification is key to getting the proper blast resistant products. Specifications should include:
- Blast design criteria for the element being specified.
- Engineer/manufacturer/installer/testing facility qualification requirements.
- Other design criteria (or reference to other specification sections).
- Blast design guidelines/standards/testing standards.
- Calculation/test report submittals.