The breakage of tempered glass caused by internal factors is called self-explosion. For tempered glass, self-explosion is inevitable without warning, and its occurrence probability is usually 2 ~ 5 ‰, which is relatively low in western countries and relatively high in China.
The glass may contain nickel sulfide impurities in the form of small crystals. Under normal circumstances, the glass will not be damaged. However, due to the reheating of tempered glass, the phase state of nickel sulfide impurities is changed. The high temperature α state of nickel sulfide is frozen when the glass cools rapidly, and it may take several years for them to return to β state. Because the low-temperature β state of nickel sulfide impurities will increase in volume, local stress concentration will occur in the glass, thus the self-explosion of tempered glass will occur. However, only relatively large impurities will cause self-explosion, and the self-explosion of tempered glass will only occur when the impurities are at the core of tensile stress. Nickel sulfide can occur at any time after the completion of production, and the most typical time to cause the self-explosion of tempered glass is 4 ~ 5 years after the completion of production.
The above are the common causes of broken glass. You can also ask the merchants who sell glass to you if there is any problem with the quality of their glass products.