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A double-steel fire-resistant door consists of two door panels, a frame, a fire-resistant lock, a door closer, and a sequencer. The most crucial component is the sequencer: when both doors are opened simultaneously, the sequencer controls their sequential closing - usually closing the secondary door first, then the primary door, preventing the two doors from interfering with each other and leaving a gap. In the event of a fire, the fire-resistant expansion seals along the door edges rapidly expand when heated, filling all gaps between the door and frame, and between the doors themselves, completely blocking hot smoke.
Unlike ordinary single-leaf doors with their narrow passageways, the biggest advantage of double-leaf doors is their ample opening space. Whether it's large-scale daily pedestrian traffic or the movement of large equipment, medical devices, or goods, there are no restrictions. This is why double-leaf steel fire-resistant doors are almost always the first choice for evacuation stairwells in shopping mall underground passages, hospital wards, industrial plants, and large office buildings. This combination of practicality and emergency response capabilities is difficult for other types of doors to match.
To meet the needs of large spaces and equipment passage, Double Steel Fire-Resistant Doors are typically large in size:
Standard Width
The most common standard sizes on the market are 1500mm × 2100mm or 1500mm × 2300mm. For high-traffic areas such as shopping malls and hotel lobbies, the width usually reaches 1500mm - 1800mm.
Maximum Size
According to relevant regulations, the overall width of a standard steel double fire-resistant door generally does not exceed 2100mm, and the height does not exceed 2300mm. If a factory or warehouse requires an extra-large opening (e.g., over 3 meters wide and 3 meters high), it is considered a non-standard custom product, and reinforcing ribs must be added inside the door leaf to ensure stability.
Door Type Classification
In addition to two equally sized "double doors," there are also "mother-and-child doors" (one large and one small, usually in a 3:7 ratio). Generally, double doors are used for door openings wider than 1.2 meters, while mother-and-child doors can be used for openings within 1.2 meters.
Structural and Material Requirements
Symmetrical load-bearing structure: Double Steel Fire-Resistant Doors typically employ a symmetrical load-bearing design. Each door must independently meet fire resistance standards to achieve an overall fire resistance rating of Class A (≥1.5 hours) or Class B (≥1.0 hour).
Steel Plate Thickness
The door frame steel plate thickness is typically no less than 1.2mm, and the door panel thickness is no less than 0.8mm. For industrial doors used in large spaces, thicker steel plates are used to enhance wind pressure resistance and load-bearing capacity.
Sealing and Smoke Prevention
Fire-resistant expansion sealing strips are also required at door seams. These strips rapidly expand and seal gaps under high temperatures, effectively preventing the penetration of toxic fumes.
Key Points for Selection and Acceptance
Verify 3C certification and dimensions: Inspect the permanent label on the door on-site to confirm that the model, specifications, and inspection report are consistent. Many projects fail due to "substituting large for small" - using a narrow door as a wide door in the inspection report, a major problem area in fire safety inspections.
Check Installation Quality
The door frame must be grouted (cement mortar fills the cavity), which is crucial to prevent heat deformation. After the doors are closed, the overlap between the two door panels should be no less than 15mm, with no obvious gaps allowing light to pass through.
Test Hardware Linkage
Manually test the closing process to see if the door closer allows the two doors to close in the correct sequence, without jamming or rebounding. The force of the door closer should be moderate - too loose and it won't close properly, too tight and it could cause injury.
Double Steel Fire-Resistant Doors are never just tools for passing inspections. Normally, it's just an ordinary passageway, inconspicuous and unassuming; but in the event of an emergency, it's the last line of defense separating danger and protecting people. If you are planning a project and struggling to decide which type of fire door to install in your passageway, considering the overall passage experience, durability, and fire resistance, a double steel fire door is definitely a high-quality choice that you can't go wrong with.
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