Critical Factors in Specifying a Door Assembly that Withstands Blasts & Extreme Winds

Considerations in Specifying Door Assemblies to Protect Buildings,  Equipment and Occupants from Blasts and Hurricane-Force Winds

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Some buildings and spaces, due to the nature of their operations, are susceptible to blasts and explosions. Others, due to their proximity to coastlines, are vulnerable to hurricanes and gale-force winds. Some are at risk of both. Both blasts and hurricane-force winds result in flying debris that can prove dangerous, and sometimes fatal, to building occupants.

Blasts may be expected, for example, in a laboratory, where explosions are generated intentionally and are often repeated. They may be unexpected and unintentional, as the U.S. and other countries have witnessed when gas refineries, chemical storage or manufacturing facilities unexpectedly explode. Or they may be unexpected, isolated events, as in the case of a terrorist or sabotage attack.

How, then, can we ensure door assemblies remain in place and operable, maximize safety and minimize risk to personnel and equipment in environments that face exposure to both blasts and extreme hurricane-level winds?

This is accomplished in three ways.

First, by ensuring the door assembly, including the door, frame, anchorage, hardware and, in some instances, glass, is a comprehensive solution, designed to function collectively, and has been tested as such, either directly in a test setting or by application of established engineering calculations.

Second, by ensuring the door assembly meets or surpasses the unique specifications of the project, i.e., the wall type, size of opening, visions, etc., and that the door system, including locks, is compatible with the building’s security and access control systems.

Third, by specifying and installing a door assembly that has been judged to withstand  explicit dynamic and static pressure loads encountered during blasts and gale force winds.

Ensure the door assembly is supplied as a complete solution.

Many blast and wind-resistant door assemblies on the market are an assemblage of components (door, frame, anchorage, hardware, glass) from multiple suppliers and must be sourced individually and assembled on site. However, during standardized thirdparty testing, the door assembly is always evaluated as a complete unit.

One can imagine the potential margin of error caused by sourcing these components and visions separately and assembling them on-site. If the system is not assembled as originally tested, it can lead to discrepancies between the door response damage category experienced during testing and the door assembly’s actual performance when installed.

Because the door, its frame and accompanying hardware must all operate collectively, sourcing the assembly from a single supplier is advantageous. Such an assembly proves to be even more durable if it is not only fashioned from heavy-gauge steel but also engineered to include multiple latch points.

At the time of this writing, only one manufacturer is able to supply a comprehensive door assembly that addresses all levels of hurricane requirements and provides resistance to blasts.

Ensure the door assembly meets or surpasses the unique specifications of the project.

Each building project presents a unique set of challenges. This certainly holds true for structures that are required to withstand blasts and/or hurricane force winds. Blast loads are transient dynamic loads from the blast effects of an explosion and are usually stated in terms of peak pressure and impulse or duration.

To ensure door assemblies meet or surpass the unique specifications of the project, it is advisable to obtain shop drawings from the manufacturer. Such drawings rely on full-sized architectural plans and project specifications including the wall type, size of opening, visions, etc., and the requirements of the building’s security system to specify a door solution that has been directly tested or supported by engineering calculations to meet one of five ASTM Door Response Damage Categories (Categories I, II, III, IV or V).

Many manufacturers provide training for installers to ensure proper installation methods for their specific door opening. Some manufacturers will also assign a project manager to assist with tactical support, from the design/build phase to the end of the project. Project manager duties typically include assisting with spec writing and offering onsite and/or remote consultations with the project’s architect, contractor, product distributor and structural engineer to discuss the details of the project and installation of specific door assemblies and to verify proper installation.

In projects where blast resistance is required, the manufacturer’s project manager will typically communicate with the structural design engineer to understand requirements for peak pressure (or peak overload pressure) and impulse load.

Test acceptance criteria for blast events are divided into the following five categories which describe the level of structural damage present after the blast event. With respect to door and frame units, it signifies the operability of the door, and whether or not the door and/or frame become detached during the event, thereby presenting a flying debris hazard.

Ensure the door assembly has been tested to withstand the required load.

Testing standards for blasts and gale force winds differ significantly. The difference lies in the types of pressure applied; therefore, an understanding of pressure is important.

Pressure is the continuous physical force exerted on or against an object by something (a fluid such as air) in contact with it. Static pressure is the pressure one experiences if the fluid is stationary or if an object is moving in concert with the fluid. Dynamic pressure  is the pressure of a fluid that results from  its motion.

This distinction is an important one when testing building components to withstand high winds vs. blast forces. Static pressure loads are used to measure the effects of high winds while dynamic pressure loads are used to measure the effect of blasts.

As previously stated, blast resistant doors are designed to protect against the dangers created by a planned or accidental explosion or pressure leak, while wind resistant doors are tested to withstand the long-term effects of repeated applications of wind load as may result from a hurricane or other extreme wind event.

Testing standards for blast loads.

Blast loads are transient dynamic loads from the blast effects of an explosion, usually stated in terms of peak pressure and impulse or duration. The relevant test method for a dynamic load is ASTM F2927 (Standard Test Method for Door Systems Subject to Airblast Loadings). It is used to test complete door assemblies, including the door panel(s), latching hardware, hinges, post mullion  (if applicable), frame and frame connection  to a rigid reaction structure.

In addition, ASTM 1642 outlines the standard test method for glazing and glazing systems, and glazing retrofit systems, subject to airblast loadings. The data obtained from testing under this method is used to determine the glazing, glazing system, or glazing retrofit system’s hazard rating using ASTM F2912 (Standard Specification for Glazing and Glazing Systems Subject to Airblast Loadings). Knowing the hazard  rating provides the ability to assess the risk  of personal injury and facility damage.

In the search to understand the blast resistance of doors and frames, ASTM F2247 and ASTM F2248 are commonly mis-referenced. These standards apply only to static loads and not dynamic loads.

• ASTM F2247 (Standard Test Method for Metal Doors Used in Blast Resistant Applications) is the method used to test the structural performance of metal doors and frames and their restraining hardware (such as latches and hinges) used as a blast resistant barrier. However, this method involves applying static pressure based on the characteristics of the specified blast pressure and structural properties of the door panel design. This standard test method is not applicable to tests where the forces are created by explosive charges, forced air from a shock tube apparatus, or  any other method that produces a dynamic load.
• Similarly, ASTM F2248 (Standard Practice for Specifying an Equivalent 3-Second Duration Design Loading for Blast Resistant Glazing Fabricated with Laminated Glass) provides a design  load suitable for sizing blast resistant glazing comprised of laminated glass  or insulating glass fabricated with laminated glass.

Testing standards for extreme wind and hurricane conditions.

In regions prone to extreme wind events, door openings must meet High Velocity Hurricane Zone (HVHZ) requirements. This requires heavy duty anchors, steel reinforcement and hardware components engineered to firmly secure the door within the frame.

For building projects in Florida’s Miami-Dade and Broward counties, door assemblies must be tested and approved in accordance with the following test methods: TAS 201 Large and Small Missile Test Standards, TAS 202 Uniform Structural Load Standards,  and TAS 203 Uniform Cyclic Pressure  Test Standards. In other hurricane- prone regions of the U.S. mainland,  Hawaii and Caribbean Islands,  door assemblies must be tested  to standards ASTM E1886 and ASTM E1996. E1886 (Standard Test Method  for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Missile(s) and Exposed to Cyclic Pressure Differentials) considers windborne debris in combination with cyclic air pressure differential representing extreme wind events.7 Specification E1996 is the standard for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes.

Standards for buildings operated by the Department of Defense (DoD)

The standard UFC 4-010-01 DoD Minimum Antiterrorism Standards for Buildings establishes the minimum engineering standards that incorporate antiterrorism based mitigating measures where no identified threat or level of protection has been determined. The intent of these standards is to reduce collateral damage and the scope and severity of mass casualties in buildings or portions of buildings owned, leased, privatized, or otherwise occupied, managed, or controlled by or for DoD in the event of a terrorist attack.10 This standard references the following ASTM standards:

• ASTM E1996, Standard Specification for Performance of Exterior Windows, Curtain Walls, Doors, and Impact Protective Systems Impacted by Windborne Debris in Hurricanes
• ASTM F2247, Standard Test Method for Metal Doors Used in Blast Resistant Applications (Equivalent Static Method)
• ASTM F2912, Standard Specification for Glazing and Glazing Systems Subject to Airblast Loadings
• ASTM F2927, Standard Test Method for Door Systems Subject to Airblast Loadings

Standards for buildings operated by the U.S. Dept of Veterans Affairs

The U.S. Dept of Veterans Affairs outlines guidelines to protect the lives of VA patients, staff, and visitors in the event of an emergency. It distinguishes between design criteria and physical security standards for mission critical facilities, those facilities required to remain operational during a natural or man-made extreme event or a national emergency, and life-safety protected facilities, those required to safeguard lives in the event of an emergency, in its published manuals entitled Physical Security Design Manual for VA Mission Critical Facilities and for Physical Security Design Manual for VA Life-Safety Protected Facilities.

In addition to requirements for conventional structural design, including provisions for hurricane, earthquake, and any other extreme loading condition required by building codes, these standards mandate that all building components requiring blast resistance be designed using established methods and approaches for determining dynamic loads, structural detailing and dynamic structural response.

The manual for Life-Safety outlines requirements for doors and hardware in section 4.1.5.3 and 6.2.3. It states that all doors must be: designed using debris mitigating materials such as laminated glass and heavy gauge metal (14-gauge minimum); shall open towards the detonation; and the heavy duty frames and anchorages shall be capable of resisting the collected blast loads.

In a mission critical VA facility, vehicles may not be parked closer than 50 feet (15 m). Therefore, sections 6.2 and 7.1 of the Mission Critical Manual requires structures to be constructed to withstand the pressures and corresponding impulses produced by a threat vehicle located at the minimum standoff distance of 50 feet (15 m). The design must provide a level of protection for which progressive collapse will not occur, the building damage will be economically repairable, and the space in and around damaged area can be used and will be fully functional after cleanup and repairs.

Standards for process industries, including petrochemical and pharmaceutical

Testing standards for process industries are published by PIP, a member consortium of process industry owners and engineering construction contractors whose members collaborate to harmonize internal company standards and best practices for the design, procurement, construction, operation and maintenance of process facilities, including petrochemicals and pharmaceuticals.

The PIP STC 01018 Blast Resistant Building Design Criteria describes the minimum requirements for the design of permanent blast resistant buildings, including requirements for selection of structural systems, analysis methods, and design of ancillary items such as doors and openings.

Section 4.4.1 outlines the design criteria for blast doors. It requires that blast door manufacturer’s calculations or test data be provided to verify adequate blast resistance and door performance for the design load conditions. It recommends that door framing be provided by the door manufacturer.

This section also addresses the number and location of exit doors stating: In buildings large enough to require more than one egress door in accordance with local building codes, at least two doors shall be designated as egress doors for the purpose of limiting the damage to these doors if subjected to blast loads. Designated egress doors shall not be located on the same side of the building.

Conclusion

When specifying door assemblies to maximize safety and minimize risk to personnel, equipment and building structures, it is critical to ensure the opening is designed to withstand all potential external forces, whether an intentional blast, as in the case of a terrorist attack; an unintentional blast, as experienced in a testing laboratory or process facility; high-force winds created during hurricanes, or other weather-related occurrences.

In some cases, assemblies must be built to withstand both blast forces and gale-force winds. It is also necessary to ensure the solution is compatible with the building’s existing or planned security and access control system.

Ensure the door opening is manufactured using heavy-gauge steel, includes multiple latch points and can withstand the required dynamic and/or static pressure loads required. Independent, third-party testing   determines the door’s ability to withstand one of the five Door Response Damage Categories. For added assurance, source door openings from a supplier that furnishes the entire assembly as a complete solution, including the door, frame, anchorage, hardware and glass, as performance testing is always conducted on the entire unit.

Note that government institutions, such as the U.S. Dept. of Defense and the U.S. Dept. of Veterans Affairs, as well as many process industries, also publish their own guidelines for door opening standards.

Finally, as a best practice, rely on a manufacturer-appointed project manager to interpret the project’s requirements and furnish shop drawings, specify the appropriate door models, and verify that all door assemblies have been properly installed.

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