by Lori Greene, CSI, AHC/CDC, CCPR, FDAI
For decades, traditional wired glass—with its crisscrossed wires creating diamonds or squares—was installed in buildings around the world. Thanks to its ability to remain intact even when broken, it was the first and, for years, only form of glazing available for fire door assemblies in schools, hospitals, and other buildings.
Over time, this glazing became known as ‘safety glass’—a name that would persist long after it was found to cause severe and often life-threatening injuries when subjected to human impact. Its reputation for safety has been reinforced by its appearance and the common misconception the wire mesh makes the glass stronger. In reality, the exact opposite is true.
The wire mesh actually weakens the glass to such a degree it is only half as strong as ordinary annealed glass. To make matters worse, when an adult or child’s arm, leg, or other body part projects through the glass due to impact, the initial injury is made significantly worse when the person instinctively pulls his or her injured limb back through the jagged shards of glass held in place by the wires. Severed arteries, nerves, and tendons are common injuries from impact with traditional wired glass.
Nowhere has this type of glass caused more injuries than in schools. In 2002, an epidemiologic study of Consumer Product Safety Commission (CPSC) injury data was conducted by Philip L. Graitcer of Emory University. Of the 2554 glass door injuries that occurred in U.S. schools in a one-year period, Graitcer stated he would “conservatively estimate that 90 percent of the 2500 glass door injuries seen each year in the CPSC system involved wired glass.” This works out to 2250 wired glass injuries in a single year. Taking into account the fact schools are only in session 180 days each year, it works out to a little more than 12 potentially debilitating and life-altering injuries—some resulting in death due to blood loss—every single school day.
Safety glass standards
As early as the 1960s, glass manufacturers recognized the need for industry standards even though building codes remained silent on the subject of safety glazing. A task group was formed and their studies found an average of 320,000 injuries per year from people impacting glass in doors and windows (all building types, including residential). In 1966, the standard developed by this task group was accepted as American National Standards Institute (ANSI) Z97.1, American National Standard for Safety Glazing Materials Used in Buildings.
When the Consumer Product Safety Commission was created in 1972, one of its first initiatives was to address the standards for safety glazing. CPSC 16 Code of Federal Regulations (CFR) Part 1201, Safety Standard for Architectural Glazing Materials, was developed as a two-tiered standard that went beyond the requirements of ANSI Z97.1, and became law in 1977.
ANSI Z97.1 has since been revised to include three levels of impact-resistance:
- Category A (similar to CPSC 16 CFR 1201 Category II);
- Category B (similar to Category I); and
- Category C (the original Z97.1 standard).
This third category will likely be removed from the next edition of ANSI Z97.1, as it has no equivalent in the CPSC standard. CPSC 16 CFR 1201 Category II and ANSI Z97.1 Category A provide the highest level of impact-resistance required by the safety glazing standards—the category required depends on the size and location of the glazing. ANSI Z97.1 Category C does not protect against human impact except for very young children, and is no longer allowed by the International Building Code (IBC) where safety glazing is required.
Code changes
When the CPSC standard was created, there were no glazing products that met both the impact-resistance and fire-resistance requirements. Traditional wired glass would withstand fire testing, including the hose stream test, but would not hold up to the impacts required by the new safety standard. In 1977, a 2.5-year exemption was granted for wired glass in fire door assemblies to give the glass industry time to develop glazing that met both fire and impact requirements. A court battle between Japanese wired glass manufacturers and CPSC ensued, and the commission was forced to abandon its efforts to regulate the product.
More than 20 years later, the 2000 edition of IBC (as well as the model codes prior) still contained the exception allowing traditional wired glass in fire door assemblies, even though by that time glazing materials—such as glass ceramic, specially tempered glass, and wired glass incorporating an impact-resistant film—had been developed able to withstand both fire and impact.