The capability to detect NiS inclusions in
fully installed glass represents a significant
advancement in preventative maintenance
and risk assessment for high-rise buildings.
While these nondestructive testing
methods—comprising ultrasound imaging,
laser scanning, and refined photometric
analysis—offer efficacious means to identify
potential defects, they are not devoid of
challenges. Each approach has limitations
concerning accuracy, environmental sensitivity,
and implementation feasibility, thereby
necessitating meticulous consideration prior
to widespread adoption. Industry professionals
continue to evaluate their practicality, with
the objective of refining detection techniques
and integrating them into comprehensive
glass assessment protocols. A review of the
advantages and disadvantages of each of these
NiS analysis methods for in-place construction
is presented below.
Ultrasound Imaging
Ultrasound imaging sends high‑frequency
acoustic waves through glass and analyzes
reflections from discontinuities to infer internal
defects. While it can penetrate the full thickness
and detect larger flaws (for example, voids or
delaminations), typical NiS inclusions are near or
below practical resolution limits, yielding weak,
indistinct signals.
Glass type utilized: Multiple types of glass were employed in this project, with both tempered and heat-strengthened (HS) glass integrated into the assembly. It is noteworthy that HS glass exhibits a significantly lower failure rate attributable to inclusions. • Historical information: The property owner disclosed that the design team did not mandate HST. This omission was attributed to value engineering decisions made during the design process, wherein the scope for such testing was removed for cost-saving considerations. Cause of Failure (Laboratory Findings and Material Considerations) The collective evidence for the Nashville project indicated that NiS inclusions constituted the primary cause of the observed spontaneous glass breakage. NiS particles, typically ranging from 0.002 in. to 0.004 in. (0.05 mm to 0.10 mm) in size, are inadvertently incorporated during glass manufacture. Under conditions of thermal fluctuation, these inclusions undergo expansion when the glass experiences significant temperature changes. Due to the constrained flexibility of the glass core, the expanding NiS inclusion generates sufficient internal stress to initiate cracking from within, thereby producing the distinctive “butterfly” fracture pattern. The report provided by the glass testing laboratory confirmed NiS inclusion as the cause of the breakage. It was pertinent to point out to the client that NiS inclusion-based breakage occurring in HS glass is exceedingly rare, if indeed possible. This observation supports the inference that the installed glass was not HS but rather tempered glass, which was subjected to higher thermal stress than HS glass and facilitates the NiS phase transformation, leading to particle size increase and subsequent cracking of the glass from within. Industry Context and Other Notable Factors from the Case Study While the occurrence of NiS-induced breakage at the time of the investigation was statistically rare, the consequences in terms of safety and maintenance remained substantial to the owner as well as the occupants of the building. Cost implications also represented a major concern for spontaneous breakage in the buildings for the remainder of the complex that were not only occupied but also featured multiple systems integrated into their exterior cladding, such as mechanical vents, steel accessories, or other adjacent construction elements. It was explicitly explained to the client and owners of the complex that estimating the potential breakage of NiS inclusions is a probabilistic calculation and is not intended to serve as an accurate prediction of future glass breakage on any given building. Although frequencies of breakage on projects globally may fall within a similar range, the industry has yet to establish an agreed-upon average against which breakage can be precisely quantified. Furthermore, not all breakages can be quantified with ease, given that these events often result in a multitude of shattered glass pieces, rendering cause analysis challenging. Conclusion: Investigation (Specific to Nashville Case Study) The investigation into the spontaneous glass breakage in Nashville underscored the complex nature of glass performance within modern architectural systems. Evidence derived from on-site inspections and laboratory analysis strongly supported NiS inclusions in the tempered glass as the root cause of these failures within this particular glass facade. In the case of the Nashville project, the removal of HST played a crucial part in the presence of the NiS throughout the exposures of the building. The time elapsed between each of the breakage occurrences indicated that the phase changes were not just attributable to the thermal differences, as the south, west, and north facades all experienced breakage at varied times. Given the unpredictable nature of NiS inclusion breakage, the following proactive steps were recommended to the Nashville development team and client: • Immediate stabilization: Secure any compromised glass units using heavy-duty film or reinforced tape to mitigate public hazard until a permanent fix is applied. • Detailed documentation: Record the exact date, time, and ambient conditions (both interior and exterior) at the time of each breakage to better understand potential triggering factors. • Glass replacement strategy: (1) Promptly remove and replace affected units. (2) Preserve broken samples for ongoing technical analysis to further validate the root cause. • Manufacturer engagement: (1) Notify the glass manufacturer regarding the confirmed defect and discuss potential revisions in their production process to reduce the risk of NiS inclusions. (2) Where possible, consider additional HST or enhanced screening methods before installation. • Long-term monitoring and maintenance: (1) Implement a regular inspection regime that includes detailed documentation of environmental conditions to track any subsequent occurrences. (2) Adopt updated industry best practices to minimize the likelihood of future incidents. Furthermore, breakage also occurred on the ground-floor atrium glass, which is largely shaded by the adjacent buildings, reducing the possibility of causality to a primarily solar-exposed condition. In general, although such breakages are statistically rare when compared to the sheer number of glass-clad buildings, the impact of glass breakage on safety and property maintenance unequivocally warrants proactive intervention. By incorporating immediate stabilization measures, the suggestions of maintaining thorough documentation, engaging manufacturers, and planning for long-term monitoring offer the stakeholders of the development the ability to effectively manage risks and uphold building safety standards. HST should be given due consideration by project teams at the early stages of the design process. While ensuring proper fabrication and minimizing the risk of spontaneous breakage can entail significant expense, early awareness of these potential risks enables owners and clients to plan accordingly. By addressing these costs up front, they can be integrated into the overall project budget or offset through strategic adjustments in other areas, thereby ensuring a more judicious allocation of resources. IMPLICATIONS FOR BUILDING OWNERS AND DESIGNERS The unpredictable and delayed nature of NiS-induced spontaneous breakage presents significant implications for building owners and designers. For building owners, these failures can lead to substantial liabilities, pose safety concerns for occupants and the public, negatively impact asset value, and potentially damage
