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Class B fire-resistant windows belong to the category of Class A insulated fire-resistant windows, with a fire resistance rating of A1.0. They can withstand a fire for one hour under standard combustion conditions while simultaneously meeting both fire integrity and fire-resistant insulation requirements. Compared to the 1.5-hour protection time of Class A windows, their fire resistance limit is slightly shorter, but their core insulation and blocking functions are fully preserved. This is fundamentally different from exterior fire-resistant windows that only block smoke and fire but do not control temperature. In the event of a fire, they can prevent flames and dense smoke from spreading through the window frame and can also control the surface temperature on one side of the interior, preventing curtains, boards, and packaging materials from being ignited by heat radiation. This is sufficient to support orderly evacuation and fire rescue operations, meeting the safety specifications of conventional fire compartments.
Regarding the fire resistance time of the product, there are some differences depending on different specifications and product configurations: Traditional specifications require that, in early or specific specifications such as the "Code for Fire Protection Design of High-Rise Civil Buildings," the fire resistance limit of Class B fire-resistant windows is usually specified as not less than 0.90 hours (54 minutes).
Current National Standards and Common Configurations
According to national standard GB 16809-2008, the mainstream fire resistance time for most models on the market is generally required to be no less than 1.0 hour (60 minutes). Some manufacturers also offer Class C or basic Class B products with a fire resistance time greater than 30 minutes, but the specific requirements depend on the project's fire protection design drawings.
Difference from Class A
Class B = 1.0 h (EI 60), Class A = 1.5 h (EI 90); frame wall thickness, glass thickness, and core density are often slightly lower, and the price is usually between Class C non-insulated windows and Class A.
Class B Fire-Resistant Window Installation and Acceptance Precautions
Integrity
The performance of fire-resistant windows depends on both the glass and the window frame. They must be equipped with qualified fire-resistant hardware (such as handles, door closers, smoke detectors, etc.) and certified by the China Fire Protection Product Conformity Assessment Center (CCCF) with a type test report.
Construction Specifications
After the steel window frame is installed, the gap between the window frame and the wall must be filled with cement mortar and cured for at least 24 hours; the gaps around the glass must be filled and sealed with fireproof cotton, and shoddy workmanship is strictly prohibited.
If you are purchasing or conducting project acceptance, it is recommended that you strictly verify the product's "3C certificate number" and accompanying "type test report" to ensure that its fire resistance time and all parameters fully meet the fire protection design requirements of your project, so as to avoid leaving safety hazards or failing fire protection acceptance.
The application of Class B fire-resistant windows (GB 16809, A1.0 / EI 60, 60-minute heat insulation type) mainly follows the "1-hour fire separation" requirement in building and fire protection codes. Common industries/scenarios include:
Residential buildings: External windows of "refuge rooms" in residences over 54 m in height (GB 50016 requires fire-resistant windows, but many regions implement Class B A1.0); adjacent external windows in residential stairwells, shared vestibules, and positive pressure ventilation shafts, with some local regulations requiring Class B; fire separation when there are insufficient external openings between residential floors.
In summary, Class B fire-resistant windows are the preferred fire protection component balancing safety performance and project budget. They avoid unnecessary performance enhancements, precisely match the fire separation needs of medium-risk indoor spaces, have transparent material standards, offer a wide range of styles, and are suitable for most overseas conventional building projects. They are a highly practical and cost-effective basic safety configuration in fire protection systems.
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