Features Glass
FGIA: Wired versus safety glass

First introduced some 130 years ago, wired glass represents the first attempt at developing safety glass by embedding steel wire mesh into annealed glass while it is still soft during processing. While it may appear to be strong, it typically only has about half the strength of regular plate glass. The wire is a weak link in the glass and it may be easily broken when impacted. In the mid-1970s, most North American codes and standards granted wired glass an exemption from strength requirements. This was because, at the time, it was the only type that slowed the spread of fire and smoke by retaining even shattered glass in the frame. Some of its more popular applications have been installations in stairwell doors, elevators, gymnasiums, hallway doors and sidelights in school buildings. 

This all changed when, after much discussion, the International Building Code Council removed the impact strength exemption in the 2003 IBC and subsequent editions for traditional wired glass when it is used in educational and athletic facilities, which meant it must comply with more stringent impact requirements. This effectively banned the installation of traditional wired glass from all areas subject to human traffic, meaning close to the floor or stairs in schools.

The impetus for this change has been the fact that, each year, hundreds of children and young adults are seriously injured in accidents involving wired glass. In the U.S., it has been estimated that 90 percent of the 2,500 glass door injuries seen each year involve wired glass. This is according to a 2002 epidemiologic study of the Consumer Product Safety Commission injury data. 

Wired glass is not a safety glass as it breaks into dangerous shards held together by the wires that snare victims, lacerating, maiming or even killing them. In general, it should not be used where safety glazing is required or where human impact is possible.

In Canada, NBC 2015 had still permitted unrestricted use of wired glass. NBC 2020 began to address this by adopting changes that require safety glazing in assembly occupancies to conform to the new safety glass standard CAN/CGSB12.1. Wired glass does not pass this standard. To reduce the hazard posed by wired glass, safety glazing is required in windows and doors where human impact is possible in assembly occupancies. Safety glazing is also required in shower and bathtub enclosures. 

While these code changes eliminate the use of traditional wired glass in areas where safety glazing is required, they do not constitute a complete ban on traditional wired glass, which can still be used in locations not ordinarily subject to human contact. Traditional wired glass can still be used in annealed glass applications — if it meets wind and thermal load requirements — and in fire-rated window assemblies that are out of reach of most human traffic, such as transoms.

Confusion still exists between the terms safety glass versus fire-rated glass. For example, references in the NBC to wired safety glass and the withdrawn standard CAN/CGSB12.11-M90 should be removed. For this reason, the CGSB Committee on Glass will be submitting a code change request to remove references to wired safety glass and CAN/CGSB12.11-M90 and replace them with references to CAN/CGSB12.1, which would apply to all occupancies where glass is subject to potential human impact.

Additional references in NBC to wired glass should be cleaned up. In cases where references to wired glass is used as an example of fire protective glass, the relevant fire standards should be referenced instead.

As glass safety has evolved, the need and desire for traditional wired glass has declined and other solutions have become available such as specialty tempered glass, heat reflective glass, specialty fire protective glass for 100-square-inch doorlites and filmed or laminated safety ceramics that block radiant heat. 

Several manufacturers provide wireless safety glazing products that are fire rated from 20 to 45 minutes. In essence, fire safety no longer needs to supersede impact safety.

Amy Roberts is FGIA director of Canadian and technical glass operations