Advances in fire-rated glazing have delivered new tools to designers working to maximize the amount of daylight reaching deep inside a school building. Forty years ago, traditional wired glass was the only fire rated glazing available. Today, there are safe wired glass products as well as clear, wire free and tint free alternatives that can be used instead of opaque masonry or gypsum in walls, doors, lobbies, courtyards, roofs and exit corridors, pulling in light from outside and from adjacent spaces. Not only do these new products give architects greater design flexibility, but they help bring light into deep interior spaces, reduce energy use, reduce noise and improve security. They can also provide the same level of passive fire protection as a solid wall.
Fire Protection vs. Fire Resistance Glazing
Depending on the composition and design of the fire rated glass, it can be either fire protective or fire resistive. Fire protective glass blocks smoke and flames, but not deadly radiant heat. Fire resistive glass blocks smoke, flames and radiant heat. Click here or the image on the left to see a video detailing the difference between fire protective and fire resistive glass.
Fire-protective glazing, such as wired glass, glass ceramics and specialty-tempered products, is only capable of stopping the passage of smoke and flames. These products are tested to NFPA 252 and 257 and are limited to 25% of the total wall area under current building codes. There are examples of fire-protective glazing products that have fire endurance ratings that exceed 45 minutes and yet fail to meet ASTM E-119 (the wall standard). Wired glass and glass ceramics have achieved fire endurance ratings of 90 and 180 minutes respectively, but neither can block radiant heat as required by ASTM E-119. Because of this, the use of these products is severely limited by building codes for applications requiring a rating beyond 45 minutes.
Fire-resistive glazing is designed to block radiant heat transfer from one building compartment to another. In order to specify the right type of fire rated glass, it is important to look beyond the fire endurance rating (20/45/60/90/120/180 minutes) and focus instead on the overall performance of the glass. Fire-resistive glass, in combination with fire-resistive framing members, is tested for both fire endurance and its ability to limit a rise in temperature on the surface opposite the fire per ASTM E119.
Fire Rated Glass Provides Passive Fire Protection
Thanks to code changes and fire-safety education launched in the 1960s, the number of fatalities from campus fires has dropped significantly. Still, school fires persist. K-12 school officials place nearly 15,000 calls a year for help in battling campus fires. While fatalities are rare, the rate of injuries from school fires is higher than in either homes or in non-residential structure fires. School property damage is estimated at over $100 million a year.
The next step in limiting injury and damage caused by school fires is to adopt a balanced fire protection approach that combines active and passive fire protection systems. Most people are aware of active fire protection measures, like fire alarms, sprinklers, and fire extinguishers that help detect and suppress fires. What many people do not realize is that often invisible, passive fire protection measures deserve a lot of credit for containing dangerous heat, smoke and flames, which is critical to safe egress.