In previous briefings, we discussed blast resistant film installations, blast basics, and the relationship between standoff distance and protection.
This post continues our information sharing by discussing the two basic types of specifications and specific types of information that we recommend be included when specifying blast resistant products.
Generally, there are two primary categories of specifications: Prescriptive and Performance.
Prescriptive Specifications: This type of specification is generally used for mitigation measure solutions which are fully designed and analyzed by the design team. These may include built-in-place solutions such as new concrete walls, installation of geotextile “catcher” solutions for non-structural walls, built-in-place anti ram barriers such as bollards, etc. Prescriptive requirements such as specific material types, strengths, and in some cases, installation requirements would be included in these specifications. The accompanying drawings would include specific details for installation.
Performance Specifications: Where built-in-place solutions are not feasible, manufactured systems may be specified. These systems are generally described by their performance characteristics such as providing a specified level of protection to a specific pressure and impulse. Blast resistant windows, doors and anti-shatter film are almost always specified in this manner. When using performance specifications, it is critical that all of the major performance characteristics are included. Equally important is that the specification includes a clear explanation of what the manufacturer must provide in order to prove compliance with the performance requirements. Without this, it is difficult to ensure that the building owner will receive products that meet their requirements. For instance, when specifying blast resistant windows, the following are some of the items that should be included in the specifications:
- Pressure(s) and Impulse(s) that the windows are to resist.
- Level of Protection the windows are to meet when subjected to the specified loading.
- Connection requirements to the supporting wall structure.
- Proof of Compliance. Proof of compliance may be based on explosive tests or analysis. Most often, proof of compliance will be accomplished through a combination of the two because in order for blast testing to be truly applicable, the tested systems must be of comparable sizes, installed on comparable substrates, and be tested to pressures and impulses at least as large as the ones under consideration. This rarely happens. Most often, blast testing needs to be augmented with project specific blast analysis that will customize the system to the building in question. Without this, blast testing is of almost no practical use in proving compliance with the specifications