Blast Doors 101
Primitive forms of blast protection doors have been around ever since the invention of gunpowder. Commercially manufactured blast doors, however, were only introduced to the market in the mid 1950s. It was the cold-war era and for obvious reasons the scientific communities took a real interest in the physics of explosions. Since then, the study of blast hazards and the means to mitigate them has expanded rapidly. So fast in fact, it has spawned an entire engineering field dedicated to developing protection against blasts and explosions.

So what exactly are blast doors and how do they work? While the physics explanation would overwhelm even the most intellectual of minds, a workable understanding can be achieved by examining three simple topics: pressure ratings and the basic mathematics involved; the components and construction of a blast-door assembly; and the standards that guide the industry.

Pressure ratings are specified by certified engineers expertly trained in calculating the anticipated trajectories, distances and blast forces expected from various types of hazards. Typically given in PSI (pounds per square inch) or PSF (pounds per square foot), pressure ratings determine the construction and design of a blast assembly. Blast doors with PSI ratings of 6 or higher are referred to as high-range blast-door assemblies. Medium-range blast assemblies offer PSI ratings 4-5 and low-range blast assemblies are those that offer PSI ratings of 1-3.

To illustrate how PSI ratings translate to the total pressure a door is expected to withstand, let's examine an assembly specified 36" by 84" in size with a PSI rating of 3. For the purpose of this example, we will consider the pressure "static," meaning the pressure is continuous and uniformly applied to the entire door. Because the total pressure is arrived at by multiplying the square-inch surface area of the door by the PSI rating, this particular assembly would have to be constructed to withstand 9,072 pounds of pressure (3024 sq.in x 3). If the dimensions of the door increase just slightly to 48" x 96" with the same specification of 3 PSI, the door would now have to be constructed to withstand 13,824 pounds of pressure.

The door, frame and hardware all work together to achieve a designated PSI rating. To ensure a solid working unit, the exterior of a blast door is manufactured out of cold- rolled steel sheets, while the interior support systems are comprised of either "hat sections" or "structural tubing," constructed out of carbon steel. "Hat sections" are in the shape of a hat and "structural tubing" is in the shape of a square or a rectangle. Determining which interior structural shape to use depends on the size of the door, the PSI required and the blast engineer's specifications.

Frames too are manufactured out of steel and their configurations are determined by door thickness and the specific wall anchors utilized. Because frames must transfer blast pressure to the walls, low to medium blast rated frames are engineered to be anchored to typical wall materials such as a tube stud, block or concrete. High blast ratings, on the other hand, will likely require the frames be anchored to embedded steel channels or installed within the wall during the concrete pour with anchor bars of various diameters.

Blast-door hardware then takes into consideration whether the pressure will seat the door into the frame or unseat it against the hardware, and whether latching will be required to hold all or a portion of the pressure. (This is determined by considering the rebound scenarios set forth in the specifications). Typically, the rebound resistance of the hardware is 1/2 of the peak pressure the door is expected to withstand. High blast ratings typically require custom-designed hardware but "off-the-shelf" hardware can be modified for use with low and medium ratings. Locksets can then be specified as either manual- or power-operated depending on the blast hazard anticipated.

When it comes to visual design, blast doors could theoretically be made in any shape because the pressure dynamics remain the same. Even concave and convex designs are possible-though tremendously expensive. Singles, pairs, sliders, vertical lift and swinging configurations are also possible. (Only overhead coiling doors might not be possible due to their limited internal structures).

Plus, blast doors can be veneered to be aesthetically appealing when needed in office and retail settings such as banks, embassies, consulates, court houses, etc. Even blast-Resistant vision lights can be incorporated as long as the glass has the appropriate PSI rating. Pretty much the only component a blast door assembly typically avoids is the threshold. After all, a bump in the road is the last thing you want when operating in the presence of explosive materials and other blast hazards.

Mathematics and design aside, the remaining intriguing element of blast door assemblies are the limited standards, requirements and regulations that dictate the use of blast doors. In 1991, the U.S. General Services Administration (GSA) developed some initial "security criteria" for the construction of government buildings. The Interagency Security Committee (ISC) adapted GSA's criteria in May 2001 and released its own Security Design Criteria for New Federal Office Buildings and Major Modernization Projects. GSA-ISC's combined guidelines now apply to all federal buildings except those under the jurisdiction of the Department of Defense (DOD).

DOD's own requirements are published under Unified Facilities Criteria 4-010-01, the most recent version of which is dated October 2003 and titled Minimum Antiterrorism Standards for Buildings. More stringent than the GSA-ISC Security Criteria, UFC 4-010-01 outlines 23 prescriptive standards in four major categories including site planning, architectural, structural and electrical-mechanical. For practical reasons, security and engineering consultants currently use both documents to help architectural teams develop designs that lower the risk of loss of life and damage to property exposed to blast hazards.

As far as blast door testing and certification goes, several industry and government bodies are working towards the standardization, but nothing concrete currently exists. "Shock tube testing," a process that utilizes airbursts at controlled levels, can be utilized to test low and medium PSI ratings. High-range blast assemblies can undergo "destructive testing," but these tests are typically costly and produce the same results as mathematically expected.

In most cases it is safe to assume that if the calculations done by the blast engineer are correct, then the doors should perform to the level required. This means that in order to get the blast protection desired-you better make sure you use an experienced, certified blast engineer, and ask him to check his math twice.

Carefully choosing your blast door manufacturer is also just as important. In the US there are only a handful of manufacturers that build commercially produced blast-door assemblies. And of those, there are even fewer that do it with quality. When evaluating your candidates, look for experience, reputation, past client references, blast engineer recommendations, and clear documentation of the blast characteristics of the materials and processes used.

Krieger Specialty Products has been manufacturing blast-resistant door assemblies for over 30 years now. Our client references include the Pentagon, Texaco Refineries, Sinclair, US Bank, United States Postal Service and hundreds more. Our reputation for qualify customer service, helpful information, fast turnaround times and accurate estimates is unsurpassed in the industry. Available from 1 PSI to over 30 PSI, all our blast-door assemblies are "Professional Engineer Calculations" stamped. To find out how we can help you with your next blast and pressure door assembly, give us a call. We're always happy to answer any questions you have regarding your special-purpose door needs.
If you have questions please call us at 562-695-0645
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