Why Can Tempered Glass Break Spontaneously?
Understanding a Recognized Phenomenon in the Architectural Glass Industry
Glass is one of the most widely used materials in modern guardrails, balconies, curtain walls, and architectural buildings. Depending on the application, it may be used as fully tempered glass, laminated glass, or laminated tempered glass. These products are valued for their mechanical strength, transparency, durability, and safety performance when properly designed, manufactured, and installed in accordance with applicable codes and standards.
Despite their excellent performance, one rare phenomenon has long been recognized within the architectural glass industry: spontaneous glass breakage. This phenomenon is documented in technical publications from Quebec, including Prelco and Multiver, Ontario’s Saand, British Columbia’s Garibaldi Glass, as well as by Vitro Architectural Glass and the National Glass Association (NGA) in the United States. It is also discussed in European references, including EN 14179-1, and in numerous scientific publications.
What Is Spontaneous Glass Breakage?
Spontaneous glass breakage occurs when a glass panel fractures without any apparent impact, excessive loading, or act of vandalism. A panel may remain in service for months—or even years—before suddenly breaking.
Such an event does not automatically indicate that the glass was defective or improperly installed. Several factors may contribute to a glass failure, including previous impact damage, edge damage, installation stresses, structural movement, thermal stresses, or internal inclusions. For this reason, every incident should be evaluated individually based on its specific circumstances.
The Most Commonly Recognized Cause: Nickel Sulfide (NiS) Inclusions
The cause most frequently associated with spontaneous breakage of fully tempered glass is the presence of microscopic Nickel Sulfide (NiS) inclusions. These tiny particles may become trapped within the glass during the manufacturing process and are invisible to the naked eye.
During the tempering process, some inclusions may remain in a metastable condition. Over time, they gradually transform to a more stable crystalline structure, increasing slightly in volume and creating internal stresses that, under certain conditions, may be sufficient to fracture the glass.
This phenomenon is primarily associated with fully tempered glass and is much less common in annealed or heat-strengthened glass. In the case of laminated tempered glass, one tempered lite may still experience spontaneous breakage; however, the laminated interlayer—typically PVB or SGP—helps retain the broken fragments and maintain the integrity of the panel until it can be replaced.
How Common Is It?
Fortunately, spontaneous breakage remains uncommon.
The technical references most frequently cited within the industry indicate that standard tempered glass may present an estimated spontaneous breakage rate of approximately 3 to 8 panels per 1,000 (0.3% to 0.8%). More recent production methods, benefiting from improved manufacturing processes and enhanced quality control, have reported significantly lower frequencies, generally in the range of 1 to 8 panels per 10,000 (0.01% to 0.08%).
These figures should be understood as published technical observations rather than mandatory regulatory limits. Actual frequencies may vary depending on the origin of the glass, manufacturing processes, quality control procedures, service conditions, and the criteria used to classify and record breakage events.
Heat Soak Testing (HST)
Heat Soak Testing (HST) is an additional thermal treatment performed after tempering to reduce the likelihood of spontaneous breakage caused by Nickel Sulfide inclusions. During the process, glass panels are held at elevated temperatures for several hours, allowing panels containing the most critical inclusions to fracture 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 is generally determined by the project specifications or the requirements of the architect, engineer, or owner.
While Heat Soak Testing significantly reduces the probability of spontaneous breakage, it does not completely eliminate the risk. To date, no manufacturing process or testing method can guarantee the complete elimination of spontaneous breakage associated with Nickel Sulfide inclusions.
Are Glass Guardrails Still Safe?
Yes.
When properly designed, manufactured, and installed, glass guardrails fully comply with applicable building codes and are widely used in residential, commercial, and institutional projects throughout North America.
Fully tempered glass provides exceptional mechanical strength and breaks into numerous small fragments to reduce the risk of serious injury. Laminated glass, on the other hand, incorporates an interlayer that helps retain broken fragments, improving the post-breakage performance of the glazing system and maintaining the panel in place until replacement.
Our Approach at Rampes Avant-Garde
At Rampes Avant-Garde, every project is completed in accordance with the approved plans, project specifications, and the requirements established by the design professionals.
Whenever a glass breakage occurs, our approach remains consistent: we document the facts, evaluate the circumstances, collaborate with manufacturers and engineers, identify the most probable cause based on the available information, and recommend the appropriate corrective measures.
Because every project is unique, no conclusions should be reached before a complete technical evaluation has been carried out.
Frequently Asked Questions
Can tempered glass really break on its own?
Yes. Although rare, spontaneous glass breakage is a recognized phenomenon that has been documented by the architectural glass industry for several decades.
Does spontaneous breakage mean the glass was defective?
Not necessarily. A fully compliant tempered glass panel may experience spontaneous breakage months or even years after installation.
Does Heat Soak Testing prevent all spontaneous breakage?
No. Heat Soak Testing significantly reduces the risk of spontaneous breakage caused by Nickel Sulfide (NiS) inclusions, but it cannot completely eliminate the risk.
Are glass guardrails safe?
Yes. When properly designed, manufactured, and installed in accordance with applicable building codes and standards, glass guardrails are safe and are widely used in residential, commercial, and institutional projects throughout the world.
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
