Glass is widely used at home and architectural application. In response to safety concerning the spontaneous breakage of tempered glass, the Bureau of Standards, Metrology & Inspection (BSMI) has revised CNS 2217 after referencing EN 14179-1 and added heat soak process to the national standard to reduce self-breakage rate from three in one thousand to one in 50 thousand. The revision is expected to effectively enhance the safe usage of tempered glass.
Self-breakage refers to automatic bursts without external forces. It is caused in main by the presence of nickel sulfide residues in glass and the phenomenon is exclusive to tempered glass, said the BSMI. Tempered glass is made by heating and fast cooling a piece of standard glass. When cooled rapidly, nickel sulfide, which is active in high temperature, becomes unstable and can make the glass break in room temperature. Nickel sulfide can be found in raw materials and heat soak process - exposing tempered glass to around 300 degrees Celsius for two hours - is used to induce a break in the oven. Glass with possibility of self-breakage is then eliminated after cooling.
Although tempered glass carries the risk of self-breakage, it is still considered "safety glass" by ISO and US and European standards because self-breakage only creates small debris without sharp corners to reduce the risk of human injury, said the BSMI. Consumers concerned about self-breakage are urged to choose tempered glass that has been heat soaked. Tempered glass must conform to CNS 2217 quality specifications before and after heat soaking, meaning that there is no difference in quality before and after heat soaking. For consumer identification, the BSMI noted that "Heat soaking toughened" labels must be attached. It also asked Taiwan Glass Manufacturer's Association and glass manufacturers to establish a self-management system for heat soaking toughened glass, which was launched on January 1, 2017. Under the system, a certified mark will be issued after inspection by an independent third party.
For more information, please visit CNS Online Service at http://www.cnsoline.com.tw
Agency in charge: Department of Standards (First Division)
Contact person: Mr. GUO-LONG WU
Telephone: (02)3343-5111