Despite its excellent performance, a phenomenon recognized for decades still exists: spontaneous glass breakage. Although rare, it is well documented in technical and scientific literature. Publications from Quebec (Prelco, Multiver), Ontario (Saand), British Columbia (Garibaldi Glass), the United States (Vitro Architectural Glass, National Glass Association), and Europe (EN 14179-1 and various scientific publications) all describe this phenomenon and the mechanisms behind it.

What Is Spontaneous Glass Breakage?

Spontaneous breakage occurs when a tempered glass panel fractures without any apparent impact, overload, or act of vandalism.

A panel may remain in service for months—or even years—before suddenly shattering.

Contrary to popular belief, such an event does not automatically mean the glass was defective or improperly installed. Several factors may contribute, and each incident should be evaluated individually.

The Primary Cause: Nickel Sulfide (NiS) Inclusions

The most widely recognized cause is the presence of microscopic Nickel Sulfide (NiS) inclusions trapped within the glass during manufacturing.

These inclusions are invisible to the naked eye.

During the tempering process, some inclusions may remain in a metastable state. Over time, they gradually change crystalline structure, expand slightly, and generate internal stresses that can eventually cause the glass to break spontaneously.

This phenomenon is almost exclusively associated with fully tempered glass and is generally not observed in annealed or heat-strengthened glass.

How Common Is It?

Fortunately, spontaneous breakage remains rare.

The most frequently cited industry references indicate that:

• Standard tempered glass presents an estimated spontaneous breakage rate of approximately 3 to 8 panels per 1,000, or 0.3% to 0.8%.
• Modern manufacturing processes, benefiting from improved quality control and production techniques, report significantly lower frequencies, ranging from 1 to 8 panels per 10,000, or 0.01% to 0.08%.

These figures represent published technical observations, not mandatory regulatory limits established by building codes or standards.

Heat Soak Testing (HST)

Primarily used in Europe and specified for certain projects in North America, the Heat Soak Test (HST) is an additional thermal treatment performed after tempering to reduce the risk of spontaneous breakage caused by Nickel Sulfide (NiS) inclusions.

Glass panels are held at elevated temperatures for several hours, allowing panels containing the most critical inclusions to fail in the factory before installation.

In Europe, this process is governed by:

EN 14179-1 – Glass in Building – Heat Soak Thermally Toughened Soda Lime Silicate Safety Glass. In Canada and the United States, the use of Heat Soak Testing generally depends on the project specifications, architect, engineer, or owner’s requirements.

Are Glass Railings Still Safe?

Absolutely.

Tempered glass remains one of the safest glazing materials available when designed, manufactured, and installed in accordance with applicable standards.

Its mechanical strength is approximately four times greater than that of annealed glass of the same thickness. When broken, it fractures into numerous small fragments, significantly reducing the risk of serious injury.

Our Approach at Rampes Avant-Garde

At Rampes Avant-Garde, every project is completed in accordance with the approved plans, specifications, and the requirements established by the project’s design professionals.

Whenever a glass breakage occurs, our approach remains consistent:

• objectively analyze the circumstances;
• document all relevant facts;
• collaborate with manufacturers and engineers;
• identify the most probable cause;
• recommend the appropriate corrective measures.

Because every project is unique, no conclusion should be reached without a complete technical investigation.

Frequently Asked Questions

Can tempered glass really break on its own?

Yes. Although rare, spontaneous breakage is a recognized phenomenon that has been documented by the architectural glass industry for decades.

Does spontaneous breakage mean the glass was defective?

Not necessarily. A fully compliant tempered glass panel may experience spontaneous breakage several years after installation.

Does Heat Soak Testing eliminate all risk?

No. Heat Soak Testing significantly reduces the risk but cannot completely eliminate it.

Are glass railings safe?

Yes. When properly designed, manufactured, and installed, glass railings fully comply with building code requirements and are safely used worldwide.

Technical and Scientific References

• Vitro Architectural Glass – TD-138: Heat Treated Glass for Architectural Glazing
  https://www.vitroglazings.com/media/acmdf3a5/vitro-td-138-heat-treated-glass-v8.pdf
• National Glass Association (NGA) – FB56-18: Heat Soak Testing of Tempered Glass for Architectural Glass Applications
  https://www.glass.org
• EN 14179-1:2016 – Glass in Building – Heat Soak Thermally Toughened Soda Lime Silicate Safety Glass (European reference standard for Heat Soak Testing)
  https://standards.iteh.ai
• Prelco (Quebec, Canada) – Technical documentation on tempered glass and Heat Soak Testing
  https://www.prelco.ca
• Multiver (Quebec, Canada) – Technical documentation on tempered glass and spontaneous glass breakage
  https://www.multiver.ca
• Garibaldi Glass (British Columbia, Canada) – Technical documentation on Heat Soak Testing in accordance with EN 14179-1
  https://www.garibaldiglass.com
• Saand Inc. (Ontario, Canada) – Technical documentation on tempered glass and Nickel Sulfide (NiS) inclusions
  https://www.saand.ca
• Kasper, A. – Spontaneous Cracking of Thermally Toughened Safety Glass, Springer Nature
  https://link.springer.com
• Karlsson, S. – Spontaneous Fracture in Thermally Toughened Glass
  https://www.semanticscholar.org
• Saint-Gobain Glass – Technical publications on Nickel Sulfide (NiS) inclusions and heat-treated glass behavior
  https://www.saint-gobain-glass.com