Solid 3-inch glass block units provide the greatest resistance to breakage and are ballistics-tested and qualified to UL levels 1, 2 and 6. Even greater resistance to forced entry can be achieved by using metal grid systems that accommodate the solid units. In the case of mortared systems, single blocks can be replaced at minimal expense compared to conventional glass, which requires replacement of the full pane or panel.

Hurricane resistance. Research following the devastation of Hurricane Andrew-the second most costly catastrophe in the U.S. after Hurricane Katrina-found that the most significant hurricane damage was from wind-blown debris made up of building parts. Studies also found that the most decisive cause of building frame collapse was the failure of doors and windows. Miami-Dade and Broward Counties consequently implemented changes in the Building Code relating to glazing systems. Many states have since adopted hurricane code requirements.

Hurricane-resistant glass block has a greater face thickness than standard glass block. It meets large missile tests referenced in the International Building Code in accordance with ASTM E-1886 and ASTM E-1996.

Earthquake resistance. Glass block panels inherently have two attributes that make them safe in earthquakes. One is their rigidity relative to a tall building's rigidity. When used in tall buildings, the glass block panels experience earthquake motions that cycle back and forth very slowly relative to the vibration frequency of the glass block. Thus, the glass block's ride during an earthquake is a smooth ride. The building acts like the soft shock absorbers in cars that soften passengers' ride from the irregular imperfections in the road.

The second attribute of the glass block is the rigidity of the glass block panel relative to the rigidity of short buildings or residences. The critical vibration frequency is greater than the more severe vibration frequency of the earthquake ground shaking. Therefore, the g-forces from the earthquake are not amplified or turned into the ground motion as other architectural items, such as chandeliers or bookshelves.

Lighting Design Considerations

Glass block has a dynamic relationship with both natural and artificial light. The affect of artificial light on glass block can vary dramatically with the type and intensity of light and the pattern of the glass block. In architectural applications, halogen, incandescent and fluorescent light sources are the most commonly used.

• In order to evenly light a glass block, use a "wall washing" technique by placing the light source 12 inches to 18 inches in front or behind the panel. Keep the light source parallel to the face of the panel in horizontal or vertical configurations.
• Using a "spotlight" technique of focusing directly on the glass block panel, the sidewalls and mortar will absorb the light differently from the central portion of the panel, thus producing an uneven look. To ensure an even lighting effect, place the light sources evenly every 12 inches to 18 inches along the ceiling or side walls.
• Curved or angular panels require both horizontal and vertical light fixture placements. When combining different types of light sources, the use of the same color spectrum will bring a more uniform effect. Alternatively, different colored lights can produce special effects.
• Neon tube lighting placed behind a glass block panel can create special "hot spots." For more even lighting, neon tubes may be placed directly behind the mortared course lines or along a panel's perimeter.