Windows: The Security Threat in LEED Compliant Buildings

Government buildings account for 42 percent of new construction projects certified as compliant with Leadership in Energy and Environmental Design (LEED). For the government, the benefits of LEED compliance must be balanced against potential threats to the buildings’ physical security. The weak link? The windows.

At the February 12 luncheon meeting of the Federal Real Property Association, Trust Strategy Group’s Managing Partner Jeff Weiss explained the susceptibility of windows to forced entry and explosive blasts.

Explosive blasts create circular waves of energy, Weiss explained, like a pebble causing ripples in a pond, but in three dimensions. Blast energy finds the easiest path through the air. Windows are the weakest spot in a building, and therefore are a common point through which a blast can travel.

There are two main causes of damage to a building as well as personal injury resulting from an explosive blast. The first is from lacerations due to the fracturing of glass and the resulting shards that are propelled inward by the energy of the blast. The second is an internal pressure differentiation as the blast energy is carried inward – a pressure differentiation that can rupture eardrums and cause other similar injuries.

Fully 85 percent of fatalities from explosive blasts are related to window glass failures, Weiss explained.

Despite the inherent susceptibility of windows to physical security threats, Weiss noted that LEED compliance and certification is becoming increasingly important in Federal construction projects. According to the US Green Business Council, Weiss said, green buildings improve workplace efficiency and worker performance and can boost potential rental rates. Natural light, which is emphasized in LEED projects, also can improve productivity, Weiss said.

Organizations considering LEED compliance also must consider technology to mitigate glass intrusion and pressure changes resulting from explosions, according to Weiss. This technology must also be redundant enough to protect against the multiple blasts that are typical of terrorist attacks.

How can the Federal government afford LEED certification while maintaining safety and security? Weiss outlined several possible solutions, each of which has been tested in controlled situations, with varying degrees of success:

• Annealed glass: Blasts can still create numerous particles; therefore this solution does not reduce the threat of laceration injury.
• Catcher bar with filmed glass: A center bar in the window actually will cause a filmed glass window to bend around the bar before finally being fractured by the energy of the blast. This will not reduce the danger of glass shards created in the explosion. It also may exacerbate the pressure differential of the blast, as the window bending around the bar may cause additional energy waves.
• Filmed glass: While this may reduce the number of glass shards entering the work environment, there is the potential for an entire window to be blown into the space as a single immense projectile.

The optimal solution, Weiss said, may be a new technology of specially designed protective blinds, reinforced at their core with solid metal rods built into a metal frame. Due to principles of physics, this type of solution will cause the blinds to be closed by the initial force of the blast, preventing glass shards from entering. The metal reinforced core rods of each blind ensure both blast mitigation and reduced threat from forced entry.

According to Weiss, these reinforced blinds have been developed to accommodate standard GSA window dimensions (48 x 66 inches), minimizing the cost for retrofit or buildout of the facility or modification to the blind systems themselves.