Many office and residential buildings use large glass curtain walls for their appearance. Occasionally, glass breaks spontaneously without an obvious external impact. To achieve the required strength, curtain-wall glass is generally toughened. Heat treatment in a tempering furnace creates strong surface compression, which helps counter external forces. This gives toughened curtain-wall glass high strength and impact resistance; greater surface compression generally corresponds to greater strength.

This is an unbalanced state that tends to return to equilibrium when the opportunity arises. The release of this imbalance causes toughened glass to break into small particles. Breakage can result from either external or internal factors.

External causes include overloading, impact from hard objects, insufficient clearance, and edge damage. Internal factors include defects in edge processing, sharp corners, and holes, which can create stress concentrations, as well as excessive internal stress and nickel sulfide impurities.

The first two elements are caused by process control in the toughened glass process, and the nickel sulfide element is produced in the glass-on-slide process. The fragmentation caused by internal factors is called self-detonation. The toughened glass of self-explosion is not to be avoided completely, it is also without warning, the probability of its generation is usually 3‰ , but our country is relatively high.

Glass may contain small nickel sulfide crystals that do not normally cause damage. During reheating for tempering, these impurities change phase. The high-temperature alpha phase is retained as the glass cools, and it may take years to revert to the beta phase. As the low-temperature beta-phase impurities expand, they can create localized stress concentrations and cause spontaneous breakage. However, this occurs only with sufficiently large impurities located in the tensile-stress zone.