According to the requirements of building fire protection regulations such as the "Code for Fire Protection Design of Buildings", fire doors are used in openings of firewalls, stairwell entrances and exits, evacuation corridors, and pipe shaft openings to serve as fire-resistant partitions. Based on material, fire doors are generally divided into two main categories: steel fire doors and wooden fire doors.
Wooden fire doors are characterized by their light weight, easy installation, and good decorative effect, and are widely used in various civil buildings and some industrial buildings, such as guest room doors in star-rated hotels and restaurants, and ward doors in large hospitals. After nearly 20 years of rapid development, there are currently 372 wooden fire door manufacturers nationwide.
The research and production of wooden fire doors have played a positive role in protecting people's lives and property and improving the decorative effect of buildings. However, due to loopholes in product technical standards, certification, and management, the wooden fire door industry as a whole is sluggish, which greatly restricts its development and makes it difficult to guarantee the quality of fire doors used in projects. This paper summarizes the problems existing in my country's wooden fire door technical standards, testing, licensing, production, and industry management, and proposes countermeasures to solve these problems.
1. Technical requirements and certification for wooden fire doors
1.1 Technical requirements for wooden fire doors
The technical specifications for wooden fire doors consist of two parts: "General Technical Conditions for Wooden Fire Doors" and "Fire Resistance Test Methods for Doors and Roller Shutters." The main contents of the General Technical Conditions for Wooden Fire Doors include material selection standards, permissible manufacturing deviations, installation gap widths and permissible deviations, etc. Furthermore, wooden fire doors should possess sufficient overall strength, maintaining good integrity after a sandbag impact test, and the internal filling material should not crack or detach; they should open and close flexibly, requiring no more than 80N of force to open, and have a self-closing function.
The fire resistance rating of wooden fire doors is classified into Class A (≥1.2h), Class B (≥0.9h), and Class C (≥0.6h). The "Fire Resistance Test Method for Doors and Roller Shutters" specifies the test equipment, test conditions, specimen requirements, test procedures, and fire resistance rating determination criteria for fire doors.
1.2 Certification
Manufacturers of wooden fire doors must obtain production and sales licenses from the Fire Protection Product Conformity Assessment Center of the Ministry of Public Security (hereinafter referred to as the Assessment Center) before they can engage in the production and sales of their products. The certification is based on the "Implementation Rules for Type Approval of Fire Protection Products - Fire Door Products".
2. Existing Problems
The following are the main problems in the technical standards, production, certification, testing and management of wooden fire doors.
2.1 Material Selection
The "General Technical Conditions for Wooden Fire Doors" specifies the "Selection Standards for Timber Used in Wooden Fire Doors." To eliminate defects such as live knots, dead knots, pith, cracks, diagonal grain, and oil spots, boards sawn from first-grade logs are used. The timber utilization rate from board to finished product is generally less than 20% for door frames and cladding strips, and less than 28% for door leaf skeletons. This low timber utilization rate increases product costs and wastes resources. Furthermore, most timber is difficult to impregnate, and impregnation is even more challenging for timber with cross-sectional dimensions larger than 50×100mm. Therefore, developed countries generally use flame-retardant engineered wood for the door frames and door leaf skeletons of wooden fire doors.
2.2 Flame retardant treatment of wood and engineered wood products
Fire protection regulations such as the "Code for Fire Protection Design of Buildings" stipulate that firewalls must be made of non-combustible or flame-retardant materials; the "Code for Fire Protection Design of Interior Decoration of Buildings" stipulates that all building wall decorations, except for ordinary residential buildings, must be made of non-combustible or flame-retardant materials.
As a component of firewalls, wooden fire doors, in addition to their fire resistance rating, should also be made of flame-retardant materials. However, the "General Technical Requirements for Wooden Fire Doors" does not specify any requirements for the door's finishing material.
Article 3 of the Supplementary Rules for Type Approval of Steel and Wooden Fire Doors stipulates that wooden fire door manufacturers must be equipped with wood flame retardant treatment equipment. However, since some manufacturers have stated in their technical documents that the wood has not been flame retardant treated during factory certification and type inspection certification, a consensus has been formed that when using broadleaf wood to produce fire doors, the wood does not need to be flame retardant treated. This statement is extremely harmful to the quality supervision of wooden fire doors and fair market competition. It can be said with certainty that if the wood is not flame retardant treated and is not protected with fireproof coatings or non-combustible materials, the fire resistance limit of the fire door will definitely not meet the requirements of Class A fire doors. The basis is as follows: In Europe, the average burning rate of wood used in the calculation of the strength of wood structure is 0.7 mm/min for structural wood, 0.5 mm/min for broadleaf wood for interior decoration, and 0.6 mm/min for coniferous wood (the fire-exposed surface is vertical)[8]. The carbonization rate of wood used in Japanese architectural design is 0.6 mm/min[9]. The thickness of the frame material for fire doors is typically around 35mm. At a carbonization rate of 0.6mm/min, it would burn completely within 60 minutes. Fire doors are tested under positive pressure and bear their own weight; when the wood thickness is less than 10mm, the fire door loses its integrity and insulation. The author used untreated ash wood to make a fire door with a fire resistance rating of 47 minutes. Japanese data indicates that when the door structure and thickness are the same as domestic wooden fire doors, fire doors made of untreated wood meet the 0.5-hour fire resistance requirement, while fire doors made of flame-retardant engineered wood meet the 1.0-hour fire resistance requirement.
2.3 Manufacturing and Installation Deviations
According to the "Permissible Deviations in the Manufacturing of Wooden Fire Doors," the permissible deviations for the height and width of a Class I wooden fire door are 0/-1 for the door frame and +1/0 for the door leaf. Assuming the nominal size of the door leaf is X, the actual size of the Class I door leaf can be X to X+1 mm, and the actual size of the inner opening of the door frame can be X-1 to X mm. If the inner opening of the door leaf or door frame is not further processed during installation, the fit will be too tight, and the door will not close. According to the "Gap Width for Installing Wooden Fire Doors," the gap width for installing wooden fire doors is 1.5–2.5 mm for the door leaf butt joint and the vertical gap between the leaf and the frame, and 1.0–1.55 mm for the top gap between the frame and the leaf. To ensure a single-sided vertical gap of 1.5–2.5 mm between the leaf and the frame, the additional cutting allowance for the door leaf during installation is 3.0–7.0 mm.
