On the 315 gala, a type of glass was exposed —防火玻璃 (fire-resistant glass).
Merchants with malicious intent used real fire-resistant glass to cheat the relevant department’s acceptance, then sold inferior fake products to cheat consumers of their money, deceiving the authorities and selling fakes, thus leaving hidden dangers for the safety of the society.
Counterfeit Fire-Resistant Glass Poses Safety Hazards (Source: 315 Gala Screenshot)
What is Fire-Resistant Glass?
Fire-resistant glass is a functional fire-rated material used to control fire spread and block toxic smoke. After undergoing special processing, fire-resistant glass can maintain its structural integrity and insulation properties in the event of a fire, offering enhanced protection for life and property. It is widely used in commercial buildings, schools, hospitals, industrial facilities, and other areas, especially in critical areas such as fire partitions, emergency exits, and escape routes.
Fire-resistant glass is rated into five levels based on its fire resistance performance, with fire resistance times ranging from 0.5 hours to 3 hours.
The fire resistance of fire-resistant glass is closely related to its fire resistance rating. The higher the fire resistance rating (duration), the better the fire resistance performance. This corresponds to better fire-rated insulation and structural integrity.
Why Does Glass Break at High Temperatures?
Before discussing why fire-resistant glass is fire-resistant, let's first consider why glass shatters at high temperatures. Glass breaks at high temperatures primarily due to its thermal expansion properties and physical structure.
When glass is heated unevenly, its thermal expansion is also uneven. Some parts of the glass may expand more than others, resulting in internal stress. If this stress exceeds the tensile strength of the glass, the glass will break.
Glass is poorly adaptable to temperature changes, and rapid temperature changes (such as thermal shock) can cause a temperature gradient between the surface and the interior of the glass, creating stress that is sufficient to break the glass.
The 315 Gala exposed a type of fire-resistant glass known as cesium-potassium fire-resistant glass. Cesium-potassium fire-resistant glass is a type of single-layer fire-resistant glass produced using an old-fashioned spraying method.
The spraying process involves spraying transparent fire-resistant liquid onto the surface of single- or multiple-layer flat glass substrates. The main components of the fire-resistant liquid usually include cesium (Cs) and potassium (K) salts. Under high-temperature conditions, through ion exchange, the larger cesium and potassium ions in the fire-resistant liquid replace the sodium ions on the glass surface. Physical tempering then forms a certain surface compressive stress on the glass surface, which can resist the thermal stress generated when the glass is heated, thereby giving the glass fire-resistant properties.
Fire-Retardant Liquid Coating on Glass
Essentially, cesium-potassium fire-resistant glass is produced by spraying only one side of the glass, which is an outdated technique. The coated surface can leave behind cesium-potassium chemical residue, potentially harming human health and the environment. Moreover, the transparent glass does not have a high light transmittance, and its fire resistance can weaken over time due to exposure to sunlight and rain.
Besides cesium-potassium glass, the broadcast also mentioned other types of monolithic fire-resistant glass: high-stress and high-borosilicate.
High-stress fire-resistant glass is created by heating a sheet of glass to its softening point and then rapidly cooling its surface, resulting in high surface stress that enables the glass to withstand the thermal shocks caused by temperature differences during a fire. Its fire endurance is around 1 hour, ensuring the integrity of the glass under high temperatures.
High-borosilicate fire-resistant glass is made by adding B2O3, Al2O3, and other raw materials to raise the softening point and reduce the thermal expansion coefficient of the glass. This allows it to endure extreme temperature changes without breaking, with a fire-resistance rating of up to 3 hours.
All three types of monolithic fire-resistant glass provide excellent fire protection. High-borosilicate glass offers superior stability, while high-stress glass is more susceptible to temperature fluctuations. Cesium-potassium glass has a declining market share.
Laminated Fire-Resistant Glass
In addition to monolithic glass, there is also laminated fire-resistant glass, which consists of two or more layers of glass or a combination of glass and organic materials that meet specific fire-resistance requirements. Laminated fire-resistant glass can be further classified as laminated composite fire-resistant glass and intumescent fire-resistant glass.
Laminated Fire-Rated Glass Diagram (Source: AI-generated by the Author)
Laminated fire-rated glass is made by bonding two or more sheets of single-pane glass together using an intumescent interlayer or by laminating a single pane of glass with an organic material.
In a fire, as the temperature rises, the gel decomposes, rapidly expanding to form an insulating layer that prevents the passage of flames and heat radiation, providing thermal insulation.
Insulating fire-rated glass is a frame sealed with two or more panes of single-pane glass, into which fire-resistant liquid is poured through a filling port and then cured by bonding and sealing.
When exposed to high temperatures, the transparent, gelatinous fire-resistant layer between the panes of glass quickly solidifies, forming an opaque fire-resistant and insulating panel. While preventing the spread of flames, it also prevents the transfer of high temperatures to the unexposed side.
Summary
As urban populations continue to grow, the density of buildings in cities is increasing, and the use of glass curtain walls in high-rise building façade designs is becoming more widespread.
In the event of a fire, fake and inferior fire-rated glass can make firefighting more difficult, and the spreading fire can cause enormous economic losses.
Therefore, it is crucial to select and use qualified fire-rated glass in the design and construction of high-rise buildings. There should also be strict standards and regulatory systems in place to ensure that all fire-rated glass products used are certified and meet national and international fire safety standards.
References
[1]Liu Zhixiang, Deng Pengfei, Pan Shihao, et al. "Classification and Research Status of Fire-Rated Glass"[J]. Guangzhou Chemical Industry, 2021, 49(15):16-18. (in Chinese)
[2]Xu Wenfei, Wang Yijie, Liang Runjie. "Research on Rapid Testing Technology for Single-Piece Fire-Rated Glass"[J]. Fire Science and Technology, 2022, 41(05):627-629+670. (in Chinese)
[3]Feng Yunxi, Cao Yanping. "Innovative Performance and Market Application of High-Borosilicate 4.0 Fire-Rated Glass"[J]. Building Materials World, 2020, 41(05):51-54. (in Chinese)
[4]Cheng Yousui. "Application Analysis of Fire-Rated Glass in Curtain Walls of High-Rise Buildings"[J]. Guangdong Building Materials, 2015, 31(12):21-23. (in Chinese)
Planning and Production
Author丨Denovo Team Science Popularization Team
Reviewer丨Cao Wangbei, Materials Engineer
Planning丨Ding Tian
Editor丨Ding Tian
Proofreading丨Xu Lai, Linlin
