Heat Soaked Clear Tempered Glass (HST) – Certified Facade Safety
When tempered glass is specified for high-rise curtain walls, overhead canopies, glass fins, or public balustrades, spontaneous breakage caused by Nickel Sulfide (NiS) inclusions poses critical safety and replacement liability. DeShen Glass provides certified Heat Soaked Clear Tempered Glass (HST) conforming to EN 14179-1 to virtually eliminate the risk of in-service spontaneous failure.
The Nickel Sulfide (NiS) Problem and HST Solution During standard glass tempering, rapid quench cooling freezes microscopic nickel sulfide inclusions into their high-temperature α-NiS phase. Over time on a building facade, solar radiation and ambient heat cause these inclusions to transition back to their stable β-NiS phase, accompanied by a ~4% volume expansion. If an inclusion is located in the central tensile stress zone of the glass pane, this expansion triggers catastrophic spontaneous shattering.
In our calibrated HST chamber, glass panes undergo a rigorous 3-stage thermal cycle: 1. Heating Phase: Controlled heating from ambient to 290°C ± 10°C. 2. Holding Phase: Maintaining 290°C for a minimum of 2 hours, forcing any NiS inclusion to complete its phase expansion and fracture defective panes inside the oven. 3. Controlled Cooling Phase: Gradual cooling back to room temperature to preserve glass flatness and structural integrity.