On safety of Heat-Soak tested thermally toughened glass

NiS inclusions are found everywhere in the raw glass; their repartition is visibly influenced by gravitational settling (Author’s presentation GPD 2017). We explain this physically, applying STOKES’ settling theory. Further elaboration with more parameters allows to understand the observed nickel sulphide inclusion size spectrum. Obviously only a minority of the original NiS population (c.15%) arrives finally in the glass; also size-depending decomposition (“digestion”) and self-destruction (“explosion”) due to composition evolution in the glass melt are playing a rôle in this size separation process. Comparing this with the size spectrum of inclusions really having caused breakages reveals a “breakage ratio” curve that can be used to quantify how dangerous a given nickel sulphide inclusion population really is. This will help to solve the actual key problem of spontaneous breakages on buildings, namely to quantify the residual breakage risk of HS-tested toughened glass (acc. EN 14179-1). Real breakages on buildings are very seldom; therefore, quantification is difficult. We present an example from Saint-Gobain, revealing that the residual risk is much lower than previously estimated. Instead of 1 breakage in 400 t, it seems closer to 1 in 6000 t. Therewith, it reaches a component safety comparable to concrete or steel.

Andreas M Kasper

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