Nickel Sulphide Inclusions & Spontaneous Broken Glass

What Building Owners & Managers Need to Understand

Spontaneous broken glass caused by Nickel Sulphide (NiS) inclusions remains one of the most widely misunderstood failure mechanisms in modern facade systems. While often attributed to material quality or country of origin, NiS‑related failures are a well‑documented, global manufacturing phenomenon that affects toughened glass used in buildings worldwide.

From a facade health and asset‑risk perspective, understanding NiS inclusions is essential for setting realistic expectations around glass performance, inspection regimes and long‑term facade care.

A Global Issue : Not a Country‑of‑Origin Problem

Nickel Sulphide inclusion is not linked to “cheap” or inferior glass, nor is it isolated to any single manufacturing region. It is an inherent risk associated with the production of toughened (tempered) glass, regardless of where that glass is manufactured.

In Australia, this distinction is particularly important. All architectural glass incorporating Low‑E or reflective coatings - which now feature in the vast majority of high‑rise and low‑rise developments - is imported. Domestic production of coated glass ceased in 2014 due to commercial and labour‑market realities, meaning that over 90% of new buildings use imported coated glass as standard.

As a result, the presence of NiS inclusions has no relationship to local employment outcomes, nor does it reflect a deviation from accepted global manufacturing practices. Consequently, NiS inclusions are not linked to any single manufacturing country or supply chain source. They remain an industry-wide phenomenon associated with toughened glass production globally.

What Is a Nickel Sulphide Inclusion?

Nickel Sulphide inclusions form during the early stages of the float‑glass manufacturing process. Molten glass is produced by floating liquid glass on a bed of molten tin, creating a continuous, uniform ribbon that is later annealed to relieve internal stresses.

During this process, trace nickel contamination - often originating from stainless steel components or raw materials - can react with sulphur in the glass melt, forming microscopic NiS inclusions. These inclusions are rare, but unavoidable with current manufacturing technology.

While many types of inclusions can exist in flat glass, the industry recognises Nickel Sulphide as the only inclusion type capable of causing spontaneous failure in toughened glass.

Why NiS Causes Time‑Delayed Broken Glass

Nickel Sulphide exists in two crystalline phases depending on temperature:

• Alpha phase (stable at high temperatures)

• Beta phase (stable at lower temperatures)

During the glass tempering process, the glass is heated above the phase‑transition temperature, converting NiS to its high‑temperature alpha phase. Rapid quenching during the tempering process does not allow sufficient time for the Nickel Sulphide inclusion to revert to its stable beta phase, effectively trapping it in the unstable high temperature alpha phase within the glass.

Over time - ranging from months to decades - the NiS attempts to revert to its stable beta phase. This transition involves a 2–4% increase in volume, generating extremely high localised tensile stresses within the glass core.

When these stresses exceed the residual strength of the glass, micro‑cracking propagates rapidly through the tension zone, resulting in the characteristic complete shattering of toughened glass, often without visible warning.

Why Failures Appear “Spontaneous”

NiS‑related breakage typically occurs without external impact, leading to the perception that the failure is random or unpredictable. In reality, the mechanism is time‑dependent rather than sudden — the final breakage is simply the point at which accumulated internal stress reaches a critical threshold.

Importantly, this behaviour is not a defect in installation, maintenance or building operation. It is a recognised delayed failure mechanism intrinsic to toughened glass, even when manufactured, installed and maintained correctly.

Implications for Facade Health & Risk Management

From a facade management perspective, NiS inclusions highlight several critical considerations:

• Spontaneous glass breakage is a known residual risk in toughened glazing systems

• Visual inspections cannot reliably identify NiS inclusions before failure

• Heat‑soaking reduces risk but does not eliminate it entirely

• Failures may occur many years after installation

This reinforces the importance of robust inspection regimes, risk‑based prioritisation of glazed elements, and clear response procedures when breakage occurs - particularly in locations where falling glass presents a safety hazard.

Managing NiS Risk in Practice

While NiS inclusions cannot currently be prevented at the manufacturing stage, their impact can be managed through informed facade‑care strategies:

• Designing facades with appropriate containment and redundancy

• Identifying high‑risk glazing locations during inspections

• Maintaining accurate defect and breakage records over time

• Ensuring rapid make‑safe and replacement procedures are in place

Digital defect‑management platforms such as Building Facade Manager (BFM) play a critical role in this context, providing traceability across inspections, incidents, replacements and long‑term facade performance tracking.

A Reality of Modern Glazing Systems

Nickel Sulphide inclusion is not a failure of standards, sourcing or workmanship - it is a known material behaviour within toughened glass systems worldwide. Recognising this reality allows owners, managers and consultants to move beyond blame and focus instead on risk awareness, facade health and long‑term asset resilience.

A well‑maintained facade is not one that never experiences defects, but one that identifies, manages and responds to them in a structured, informed and safety‑focused manner.

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Image: Characteristic butterfly fracture pattern caused by a nickel sulphide inclusion in toughened glass. Image © Wolfmann / cmglee, CC BY‑SA 4.0.