Nickel Sulfide Failure

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Nickel sulfide failure, or commonly referred to as Spontaneous Breakage of Glass is a rare situation that can occur where glass in a building breaks for no obvious reason. There are a variety of potential causes for this type of unexpected breakage, but typically it can be attributed to glass edge damage, or surface damage from handling or glazing. When the glass is further stressed by high wind, vandalism, building or framing movement the glass may incur breakage.

True nickel sulfide failure, however, is a bit more complicated. Sometimes during the manufacturing process of tempered glass nickel sulfide stones can form in the central tension zone due to nickel contamination. After the glass has been installed and it undergoes temperature variations, this microscopic sized stone (0.003-0.015), can grow in size and cause the glass to shatter.

This unusual type of glass breakage occurs only in tempered glass, not in annealed or heat-strengthened glass. There is no current means for completely eliminating nickel sulfide stones and they are undetectable to the human eye. ASTM guidelines allow for certain blemishes including nickel sulfide stones but limit them to 0.020-0.100 of an inch is size depending on the size of the glass and level of quality. This of course is much larger than a typical nickel sulfide stone.

Most glass manufacturers employ methods to greatly reduce the incidence of nickel sulfide stones including the exclusion of nickel in the primary batches and the use of magnetic separators.