Volume 41, Issue 5 - May 2006

Sound Advice

Terrorism Acts and Hurricanes Guide Fenestration Trends
by John Arnold

“As a result, protective glazing material design and selection may 
not be simply a matter of following building code requirements. 
It may be a governing component of the building envelope, 
site or interior design, around which other building systems 
must be designed and integrated.”

Recent terrorism acts and dynamics surrounding the hurricanes in our country have caused the fenestration industry to focus its efforts on producing glass products that protect buildings and people.

Our awareness of both terrorist acts and hurricanes has increased significantly. Several major events in the past two decades, in fact, have led the Federal government to require blast-resistant designs for all new facilities. Blast loads happen quickly and require special fenestration solutions. Some high-level targets include:

• Government buildings;
• Federal, state and local agencies;
• Domestic and overseas operations;
• Military compounds;
• The city of Washington D.C.; and
• Buildings and homes nearby threat areas.

Most government entities now mandate blast mitigation for all new construction and most major retrofits. The fenestration industry is working with the government to actually establish standards that cover security and protective glazing. The General Services Administration has created several national standards and criteria for blast resistance such as the Window Glazing Analysis Response and Design and U.S. General Services Administration Standard Test Method for Glazing and Glazing Systems Subject to Air Blast Loadings. U.S courthouses, military barracks, federal buildings and airports are some applications affected. 

Protecting People
According to the Whole Building Design Guide (WBDG)1, while windows and glazing are important architectural and functional components of a building, glass fragments caused by accidents, disasters or intentional events (such as terrorist attacks) can lead to serious injuries to building occupants. In order to mitigate glass fragment hazards, designers must consider a multitude of factors, including a building’s occupancy, function and anticipated threats and risks to people and mission. As a result, protective glazing material design and selection may not be simply a matter of following building code requirements. It may be a governing component of the building envelope, site or interior design, around which other building systems must be designed and integrated.

Today, window systems must be designed to perform functions such as: 

• Preventing deadly glass shards from flying into a room;
• Keeping glass in its frame;
• Maintaining the frame from disengaging from the wall; and
• Stabilizing the wall intact to hold the frame.

According to Applied Research Associates Inc., in the past blast-resistant design was typically used for facilities close to explosive materials only or those that were well known targets of attack. Today, however, we are living in an environment of enhanced risk that requires protective designs and the management of risk for most facilities. 

According to WBDG, in any bombing attack, there are three basic types of effects that the occupants may experience. Primary effects include the human body’s response to direct blast loadings. These can be the result of exterior or interior detonations, which produce reflected, incident and possibly gas pressure loadings. The blast forces produced interact with the occupants directly causing injury or possibly death. 

Secondary effects include fragment and debris impacts. Heavy and/or high velocity fragments and debris interact with the occupants of the facility causing injury or possibly death.

Tertiary effects include loss of balance and subsequent impact of the person into his/her surroundings due to the passing blast wave or violent movement of a supporting structure. 

The debris generated (or the collapse of structures produced) during an explosive attack causes the majority of injuries and death in a bombing event. As an example, more than 5,000 people were injured by flying glass and debris in the bombings of two American embassies in Africa in 1998. The types of injuries that occurred included deep lacerations and eye injuries. Approximately 90 people were blinded in the attack on the U.S. embassy in Kenya.

When designing window systems to resist blast forces it is important that the glazing, framing and anchorage all be designed to withstand the required forces. Generally, the glazing should be the weak link (i.e., it is not desirable for the window system to prematurely fail and blow into occupied spaces due to failure of the frame or anchorage). This approach is commonly referred to as balanced design.

Impact Resistance
For blast products, protective glazing mitigates or reduces flying shards of glass. On the impact side, we worry about wind-born debris and the need to protect the building’s exterior and interior or a building can be destroyed from the inside out.

As the severity of hurricanes continues to increase, as with Katrina, the need for added protection to the most vulnerable parts of a structure, such as the doors and windows, becomes critical. Providing added protection to the envelope of a building or home should be a primary fenestration design requirement in new construction and renovation projects. There are a wide variety of protective glazing materials and systems available that will satisfy a project’s unique set of design conditions and needs. 

Selecting the most appropriate glazing hazard mitigation system will involve considerations of threat, vulnerability and risk, the envelope design, fenestration cost, lighting needs and other design objectives such as the need to balance security/safety and sustainability objectives. The type of protective glazing material selected may also vary within a building depending on the window’s or building’s location, size of the glazed opening, occupant load and criticality of functions and missions housed within the facility, as well as other considerations such as whether windows will be fixed or operable.

Impact-resistant glazing offers advantages that other mitigation devices do not offer. It stops wind borne debris and wind pressure and is visually pleasing and practical. 

the author
John Arnold is the manager of security products for TRACO based in Cranberry Township, Pa.

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1 The Whole Building Design Guide (www.wbdg.org) is offered by the National Institute of Building Sciences through funding from the NAVFC Engineering Innovations and Criteria Office, the U.S. General Services Administration, the Department of Energy (through the National Renewable Energy Laboratory) and the assistance of the Sustainable Buildings Industry Council.

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No reproduction of any type without expressed written permission.