Thermal fracturing in glass

Thermal fracturing in glass occurs when a sufficient temperature differential is created within glass. As a warmed area expands or a cooled area contracts, stress forces develop, potentially leading to fracture. A temperature differential may be created in many ways, including solar heating, space heating devices, fire, or hot and cold liquids. Sloping glass surfaces are subject to greater solar radiation than vertical surfaces and so are more prone to solar thermal fracture. In framed window glass, the edges are relatively cooler than the exposed areas, so space heating devices in very close proximity may cause thermal fracture.
References.
"Thermal Stress And Thermal Fracture in glass" - Viridian Glass