nsi         normal vs tempered glass       nickel-sulfide-inclusion

NSI – Nickel Sulfide Inclusions Found In/Failure Concern: Tempered Glass, Curtain Walls Prevention: Glazing, Heat Soak Testing [a] NSI is a Failure Mechanism associated with glass breakage. Inclusions, also known as imperfections in the glass, are a common aspect of glass and appear in the production process of tempering glass. There are many types of imperfections; however NiS inclusions are extremely dangerous, and can cause extensive damage and overall failure in tempered glass[b] [c]. When glass is tempered it is cooled rapidly, however when NiS inclusions are present they remain in a high-temperature state and cool overtime. Thus the glass panels appear to be perfectly fine initially and then after placement or installment as the NiS cools it grows in volume, some 2-4%, causing the glass to crack and appear to explode due to the increase in internal tensile stresses[d].