From Wired Glass to Clear Solutions

This article talks about moving from wired glass to clear solutions. For over 100 years, traditional wired glass was the only fire rated glass product available. It is unsafe. Now, clear fire rated glass solutions are both fire and impact safe.

by Diana San Diego

FOR WELL OVER 100 YEARS, traditional wired glass was the only fire rated glass product available. It was mistakenly perceived as “safety glazing” because the embedded wires gave the illusion of increased strength and impact resistance, when in fact, the opposite is true. Wire actually weakens the glass, making it half as strong as ordinary window glass. It breaks easily on human impact exposing razor sharp wires that can trap a victim’s limb in the opening and increase the severity of the injury. Alarmingly, traditional wired glass is still the most commonly used fire-rated glass product found in educational facilities, leading to more than 2,500 wired glass impact injuries among students every year.

Historical Background and Code Development

In 1997, the Consumer Product Safety Commission (CSPSC) enacted a federal safety glazing standard (16 CFR 1201) to protect people from injury due to accidental impact with glazing. The building codes apply the CPSC standard to require that glazing used in hazardous locations, such as doors and sidelines, must meet minimum Category I and II impact standards, depending on the size of the glazing panel. Smaller glazing panels in sizes up to 1,296 square inches must meet the Category I impact test of 150 ft. Lbs. Larger glazing panels must meet the higher Category II standard impact test of 400 ft. Lbs. of impact resistance.

However, at that time that the new CPSC requirements were enacted, the wired glass manufacturers alleged that they lacked the technology needed to manufacture a product that could meet the CPSC standard. Since traditional wired glass was the only fire-rated glazing product at that time, it was granted a temporary exemption from meeting the CPSC standard. This exemption meant that traditional wired glass only had to meet the lesser ANSI Z97.1 standard, which stipulates 100 ft. Lbs. Of impact resistance. However, independent testing performed on traditional wired glass demonstrated that it fails with as little as 50 ft. Lbs., a force easily created by a five-year-old pushing on the glass.

This all changed in the 2003 IBC, when traditional wired glass lost its exemption from meeting safety glazing standards when used in educational and athletic facilities.

In the 2004 IBC Supplement and the 2006 IBC, traditional wired glass became no longer exempt when used in any hazardous location for all new construction and in all types of occupancies. Replacement glazing up to 1,296 square inches must also meet the minimum CPSC Category I requirements. Furthermore, all glazing used in gymnasiums or athletic facilities must meet the more stringent Category II requirement.

While these code changes eliminated the use of traditional wired glass in areas where safety glazing is required, it did not constitute a ban on wired glass. It still may be used in fire window assemblies that are not in hazardous locations. However, it is limited to 25% of the wall area. This size limitation applies to all fire-protective glazing products.

Industry Innovation Leads to Improved Impact and Fire Safety

Industry innovation was the main driving force behind IBC changes to strengthen safety glazing requirements. Between 2000 and 2002, a filmed wired glass product was developed that met both the fire and the CPSC impact safety requirements of the code. Although it looks like traditional wired glass, this new safety wired glass product is able to successfully pass both the fire test requirements and the stringent CPSC Category II impact safety standard.

Before that innovation, the same manufacturer also introduced clear, non-wired-fire- and safety-rated glazing options in the U.S. Market. These fire-protective, specialty tempered products met all the fire and safety requirements of the code while outperforming wired glass in many ways. For the ultimate in design flexibility, clear fire-resistive options became available, enabling architects to combine large clear view areas with maximum fire and impact safety. Before, the only option for 1- and 2-hour walls wound have been a conventional solid wall. With advanced fire-resistive glazing able to perform just like a brick wall or traditional fixed stud-framing, designers, can now have large areas of clear fire-rated glass that increases security, provide lighting, reduces noise, and allows aesthetic design flexibility.

Alternatives to Wired Glass: Fire-Protective and Fire-Resistive Glazing Choices

While the advent of advanced fire-rated products used in lieu of traditional wired glass have given architects the opportunity to design with glass like never before, there is still a lot of confusion about their correct and code-approved use.

The key to understanding fire-rated glass products and their applications lies in distinguishing between the two fire performance categories in the IBC: fire protective and fire resistant. Each category has its own set of performance features, test standards and allowed applications. Simply relying on the fire endurance rating (20,45,60,90,120 and 180 minutes) or whether a product is “thick” or “thin” can lead to faulty specifications and misapplications of the product.

Fire-protective glass is designed to compartmentalize smoke and flames and is subject to application, area and size limitations under the IBC. Fire-protective glass is typically used in doors and openings up to 45 minutes and cannot exceed 25% of the total wall area because it does not block radiant heat transmission. These products are tested to NFPA 257/UL 9 for windows and NFPA 252/UL10C for door assemblies.

It is important to note that while there are fire-protective products rated from 60 to 180 minutes, their application is limited to door vision panels, and size limitations may apply. For 180-minute doors, fire-protective products may be listed for 100 square inches, although the IBC does not permit any vision panel in a 3-hour rated fire door. For 60- and 90-minute doors in exit enclosures and exit passageways, fire-protective products are limited to 100 square inches, whether or not the building is fully sprinklered. More information on the code change and the 2012 IBC are discussed in following sections.

In addition, fire-protective glass, have limited use in 1-hour walls and are prohibited altogether as sidelites, transoms and windows in 2-hour interior walls because they cannot block radiant heat. These limitations are recognized in the IBC, and recent revisions to the 2012 IBC give end users clear guidance in applying those limits.

Fire-resistive glass is not limited in application or size. This type of fire-rated glazing compartmentalizes smoke and flames and blocks the transmission of dangerous levels of radiant heat through the glazing. As a result, it can be used in wall and door applications 60 minutes and above without the size limitations that apply to fire-protective glass. These products are tested to ASTM E-119/NFPA 251/UL 263.

These standards apply to all fire-resistive wall materials where teh temperature rise on the non-fire side cannot exceed an average of 250 degrees Fahrenheit. The intent is to block the dangerous transmission of radiant heat, which can cause paper, drapes, clothing, and other combustible materials within 20 feet to ignite without coming into contact with the actual fire. Imagine the devastating effect unrestricted radiant heats has on building occupants attempting to exit past a large glazed area during a fire. By effectively compartmentalizing smoke, flames and radiant heat, fire-resistive glass ensures safe egress, no matter how large the glazed area.

Clear, Fire Rated Glazing Offers Additional Benefits

Aside from increased fire safety, today’s clear fire-rated glass products offer other benefits as well. Recent studies confirm that when school spaces are brighter, students learn faster, teacher morale improves, and energy costs are reduced.

Today’s school designers are incorporating advanced fire-rated glass in stairwells, lightwells, corridors, wall partitions, indoor courtyards, exterior walls, and other places where masonry, gypsum or other opaque, conventional, fire-resistant wall materials were once used. Fire-rated glass allows light to pass through from one area to another, blending natural and artificial lighting into spaces deep within the building. Schools can save energy and create a sense of openness, and the additional visibility between spaces contributes to enhanced safety.

Source:  First appeared in Doors & Hardware, May 2012