Heat-treated Glass

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Heat-Soaked Test

Heat soaked glass, HST, is tempered glass that is heated to eliminate any glass that is subject to spontaneous breakage, before installation.  The HST test identifies batches of glass that have a high incidence of nickel sulfide inclusions, a contaminant responsible for spontaneous breakage. This type of glass is suitable for difficult to access locations, high elevations or spaces that require extra protection, such as structural glass building facades.


  • During the manufacturing process, nickel sulfide inclusions are mixed into the batch material before being dissolved.  Measuring 3 to 15 mils in diameter, these inclusions are difficult to detect with the naked eye.
  • The HST treatment consists in heating the glass to a temperature of about 265°C for a given period of time and then allowing it to cool slowly.
  • This treatment, done in the factory before installation, causes the nickel sulfide inclusions to expand and spontaneous breakage to occur.
  • These inclusions, when located near the centre of the glass, may expand and produce sufficient stress to cause spontaneous breakage of the tempered glass.
  • Spontaneous breakage of tempered glass installed at high elevations could cause injury and in addition generate high replacement costs.  HST minimizes security and financial risks.


  • Structural glass, skylights, atriums
  • High value-added sealed units
  • Glass located in hard to reach locations


Consult the tools section for all our documentation.


*Certain conditions apply, contact us for more information.

Desjardins Complex