In recent years there have been a number of sensational reports in the media about "spontaneous glass fracture", with stories relating to "glass raining down from high-rise buildings". These stories refer to incidents where toughened glass windows shatter without warning. Although it is only recently that this so-called "spontaneous" failure of toughened glass has come to public attention, it has been known about since 1960. These failures are due to the presence of nickel sulphide inclusions. In fact, nickel sulphide inclusions in glass are quite rare. In a typical glass batch there will be one 5ug inclusion per tonne of glass (an average concentration of 5 parts in 1012). This article takes an in-depth look at the nature of these inclusions and can be downloaded from www.glassonweb.com/articles/article/330/
