Spontaneous Glass Breakage due to a nickel sulfide inclusion. Spontaneous glass breakage might happen even when nobody is near the glass. Even though tempered safety glass breaks in small pieces, the pieces can remain interlocked with one another and come down in dangerous clumps. – See more at: http://chicagowindowexpert.com/#sthash.AKRHhZHv.dpuf
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Colorado Homeowner Blog 