To minimise the risk of tempered glass spontaneously breaking, due to inclusions in the glass, customers can request glass be subjected to a Heat Soaking Treatment (HST). This treatment involves subjecting the tempered glass to a temperature of 260°C and holding it there for a time depending on the regulations specified. This treatment causes the rapid phase change in the existing inclusions in the glass, leading to the breakage of glass with these inclusions. HST treatment is recommended where stability and maintenance of the enclosure or façade and the safety of users would be affected by breakage of the tempered glass. It should be stressed that, although the Heat Soaking treatment reduces the likelihood of such a spontaneous occurrence, it does not eliminate it completely. Therefore, there is always some possibility of failure, and this should be taken into account in the design and use of the tempered glass.