Why Does Laminated Tempered Glass Matter For Your Design?



Nelophobia is the fear of glass. More specifically, its fragility.

The image in the minds of most people is the hazard presented by shards of glass when broken.

As such, there is a tendency in the U.S. to avoid glass in architectural applications due to nelophobia. After all, we are a litigious society, the perceived fragility of glass and the risks involved will often result in a designer choosing to avoid glass as a design element.

However, when properly selected, glass may be specified

With a spate of glass railing failures in the 2010s, a change was made in the building codes in the 2015 cycle. All glass used in glass railing must now be laminated tempered or laminated heat-strengthened glass.

Learn more about types of glass.

Spontaneous Glass Breakage

Some of the failures were attributed to spontaneous breakage.

Spontaneous glass breakage may occur without any obvious cause. It could be due to:

  • Glass edge damage or impact
  • Surface damage from handling and glazing that then weakens the glass during high winds,
    building or framing system movement
  • Vandalism
  • An inclusion inside the glass

There are more than 50 types of inclusions in float glass. The most widely discussed is a nickel sulfide stone.

Nickel-sulfide stones can form during the production of float glass due to contamination. It can end up in the center tension zone of tempered glass. After that glass is installed and exposed to varying temperatures, this tiny stone may grow in size and cause the glass to shatter.

Spontaneous breakage caused by nickel-sulfide inclusions occurs only in tempered glass.

There is no known technology to completely eliminate nickel-sulfide stones in float glass. And because they are so small, there is no practical way to inspect for them.

Most North American glass manufacturers have controls in place to prevent nickel-sulfide formation. Heat soaking after fabrication may destroy some flawed glass panels. But, heat soaking cannot guarantee the 100% elimination of nickel-sulfide inclusions.

Heat soak testing is a destructive test for nickel-sulfide inclusions. Tempered glass is put into a heat soak oven and brought to, and held at, a temperature of 555 degrees Fahrenheit for two hours.

Most glass containing nickel-sulfide will shatter during this process and be eliminated from the glass project. But, heat soaking cannot guarantee the 100% elimination of nickel-sulfide inclusions.

Glass Breakage Video

But, there are differences in laminated glass. This video compares the performance of monolithic tempered glass, polyvinyl butyral (PVB) laminated glass, and ionoplast laminated glass.


The first test is for monolithic tempered glass. When the glass shatters, the resulting opening presents a continuing hazard.

The second test shows the effect of an impact on polyvinyl butryl (PVB) laminated glass. PVB is a spongy material. It was developed for the auto industry and its purpose is to prevent passengers from passing through the windshield in an accident. If both plies of glass break, the panel will remain intact but it will drop like a wet blanket resulting in a void. In recent years, rigid PVB layers have been developed to provide a safer alternative.

The third test is for glass with an ionoplast interlayer. Ionoplast is rigid. When both plies break in this test, the panel remains in place providing a safer end result.  Learn more about ionoplast interlayers. For more information contact us.

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