Generally, any type of glass that can withstand the fire test and therefore resist passage of smoke, flames and hot gases, is considered "fire-resistant glass". These glasses are then further categorised and related according to special criteria. Typically, the rating is based on how long a particular type and size of glass will withstand fire. Classifications range from 20 minutes up to 3 hours. Ordinary flat glass cannot withstand extreme temperature and may break at around 120 deg C. Fire-resistant glass must be able to withstand 870 deg C for a selected period of time and remain in its frame. Immediately following this extreme heat, the glass is exposed to "The Hose Stream Test" in which water is used to rapidly cool the hot glass to test its ability to withstand thermal change. More details are given here.
