YKK AP® ProTek® Glazing Systems for Blast Mitigation
What Buildings Need Blast-mitigation Measures?
YKK AP pioneered hurricane impact-resistant glazing systems and is leading the development of blast mitigation systems. These systems are designed to help protect building occupants from flying glass shards, the leading cause of injury in a blast event.
Any building that may be a target of terrorist attacks will benefit from the use of YKK AP ProTek storefront, entrances, curtain wall, and window systems as an integral part of the building envelope.
Current guidelines mandate that new buildings for the Department of Defense and the majority of other new federal buildings must be designed to afford the minimal level of protection from terrorist attacks. But any building near one of these facilities could also be at risk. As shown in the graphic below, a blast event is target-neutral. The destructive force of the blast radiates out from the point of detonation in all directions, so an unprotected building across the street from a targeted building may be as vulnerable, or more so, as the targeted building.
Studies show that up to 80% of injuries in a blast are the direct result of flying glass debris. In the 1995 bombing of the Alfred P. Murrah Federal Building in Oklahoma City, glass broke in buildings more than 10 blocks away. Broken glass alone accounted for 69% of the injuries outside the targeted building.
How To Protect Your Buildings’ Occupants From Blast-driven Glass Shards
The extent of damage caused by a blast is directly related to its peak pressure (measured in pounds per square inch) and its intensity, or impulse, which is a function of the blast’s peak pressure and the duration (measured in milliseconds). A firecracker and a stick of TNT both generate high peak pressure, but the TNT blast causes much more damage because it has a much larger impulse. The blast duration of a large explosive device is about 41 milliseconds—roughly one-eighth of the time it takes for an eye to blink.
According to blast consultants, laminated glass is a very effective way to protect building occupants from injuries that result when the glass breaks and razor-like shards explode into the occupied space. Laminated glass may break from the force of the blast, but the interlayer that is bonded to the glass will prevent the majority of the glass shards from entering the building. Products such as the family of YKK AP ProTek glazing systems are required to ensure that the sheet of laminated glass itself does not fly into the building.
Designing Buildings For Blast Mitigation
Buildings that are prominent potential targets require systems specifically designed to resist the destructive power of blast events with very high peak pressures and impulses. It is not necessary that all buildings be designed for this level of protection. The DoD, GSA, and AAMA rate the level of protection that a glazing system provides to building occupants based on its ability to mitigate injuries from flying glass.
The Department of Defense (DoD) has issued the Unified Facilities Criteria (UFC) that prescribes the minimum design requirements for all DoD buildings. This guideline enables architects to specify windows and entrances that are designed to help protect building occupants from serious injury in the event of a terrorist attack, even if these systems have not been tested. The UFC requires laminated glass and mandates that the majority of the glass remain in the framing system even when broken by a blast event. An interior seal of structural silicone, or a one-inch glass bite, is a requisite of the UFC to anchor the glass to the framing system. Glazing systems may be designed without these prescriptive requirements, but testing in accordance ASTM F-1642 is then required to demonstrate their ability to perform.
The General Services Administration (GSA), which manages over 9,000 federal facilities, also requires a minimum level of protection for building occupants from injuries resulting from a blast event. The GSA has published guidelines for glazing systems and their performance may be modeled with special computer programs or with actual testing in accordance with GSA-TS01-2003.
The American Architectural Manufactures Association (AAMA) has published a
voluntary design guideline, AAMA 510-06, in recognition that buildings in the
private sector may need to be designed to protect occupants from blast events
due to their proximity to a government building or a perceived threat. AAMA
510-06 requires glazing systems to be evaluated through dynamic analysis, using
government-approved software, or to be tested in accordance with ASTM F-1642