Coordination of smoke control zones with building spaces
The division of smoke control zones and their coordination with building spaces is the primary task in smoke control and exhaust system design. Reasonable smoke control zones both meet code requirements and accommodate building functionality. Maximum area of a smoke control zone—according to Article 4.2.4 of GB 51251-2017, for spaces with a clear height not exceeding 6m, the area of each smoke control zone should not exceed 500m², with a maximum allowable long-side length of 60m; for clear heights of 6–9m, the area should not exceed 2000m², with a maximum allowable long-side length of 75m. Smoke control zones should not cross fire compartments (a single fire compartment may be divided into multiple smoke control zones). Coordination of smoke curtains with structural beams: when the height of a structural beam projecting below the ceiling is not less than 500mm (referring to a distance from beam bottom to ceiling of not less than 500mm), the beam may serve as a smoke curtain (using structural beams to naturally divide smoke control zones), and no additional smoke curtain is required. When beam height is insufficient at 500mm, independent smoke curtains (fixed or motorized) must be installed, with a drop height from the ceiling of not less than 500mm. The gap between the smoke curtain and the structural beam should not exceed 500mm (to prevent smoke from spreading through the gap between beam and curtain). Smoke control zone division should make full use of natural separations in the building structure (structural beams, partition walls, etc.) to minimize the number of smoke curtains (each smoke control zone requires at least one smoke exhaust outlet; reducing the number of zones reduces the number of outlets, lowering system complexity and cost). Smoke control zone division must also consider: separation between guest rooms and corridors—doors between guest rooms and corridors should be Class B fire doors (effectively blocking smoke spread), with door gap spacing not excessively large (frame-to-leaf gap not exceeding 3mm); smoke separation between atria and surrounding areas—smoke curtains or structural beams (drop height not less than 500mm) should be provided between atria and surrounding areas, or fire rolling shutters (atrium fire shutters should descend in two stages: descending to 1.8m upon smoke detector activation, then to floor level upon heat detector activation).
Reservations and reinforcement for ducts penetrating structural elements
When smoke control ducts penetrate structural beams, shear walls and floor slabs, openings must be reserved and structural reinforcement implemented. Duct penetration through structural beams: when ducts need to pass through structural beams, openings (sleeves) should be reserved in the beams during the structural design phase, with opening locations avoiding the tension and compression zones of the beam (within the middle 1/3 of beam height), opening dimensions not exceeding 1/3 of beam height (and not greater than 300mm), and spacing between adjacent openings not less than 3 times the opening diameter. When openings cannot be reserved in beams, a duct routing scheme around the beam may be adopted (duct bends down below the beam then up around it), with duct width at the beam bypass not exceeding beam width + 200mm; the local resistance coefficient at the bypass increases by approximately 0.5–1.0, which must be considered in system design. Duct penetration through shear walls: openings (steel sleeves) should be reserved in shear walls, with sleeve diameter 100–150mm larger than duct outer diameter (for installation and firestop sealing), non-combustible material (rock wool or fire sealant) filled between sleeve and duct, and shear wall reinforcement around openings strengthened (adding 2 × 12mm diameter rebar at opening edges). Duct penetration through floor slabs: openings (rectangular or circular) should be reserved in floor slabs, with opening dimensions 100mm larger than duct outer diameter (50mm per side), upturned water stops (height not less than 50mm) provided at opening edges, and reinforcement strengthened at slab opening edges. Firestop requirements at all duct penetrations through structural elements: fire dampers (70°C fusible link closure) should be installed at firewall penetrations, fire dampers at fire compartment partition wall penetrations, fire dampers installed on ducts at floor slab penetrations (within 200mm below or above the slab), and gaps at duct penetrations sealed densely with fire sealant + inorganic firestop compound (seal thickness not less than 200mm).
Coordination of pressurized air supply systems with building doors
The coordination between the positive-pressure supply air system and building doors is a key factor affecting smoke control performance, especially the sealing performance of doors to stairwells and vestibules (normally closed fire doors), which directly affects the ability to maintain residual pressure. Door gap leakage calculation—the air volume loss of the positive-pressure supply air system mainly occurs through door gap leakage (the gap between the door and door frame, and the gap between the door and floor). The leakage air volume is calculated as the total door gap area multiplied by the air velocity (recommended air velocity 4-5 m/s). The door gap area of a single Class B fire door is approximately: the gap between the door frame and door leaf (3 sides) is about 0.03-0.05 m2 (based on door height 2.1 m and door width 1.0 m), and the gap between the door and floor is about 0.02-0.03 m2 (based on door width 1.0 m and gap 5-8 mm), giving a total door gap area of about 0.06-0.08 m2. When the design residual pressure is 25-30 Pa, the leakage air volume per door is about 0.06-0.08*4.5*3600=972-1296 m3/h. Balance between door opening force and wind pressure—when the positive pressure in the stairwell is too high (exceeding 30 Pa), the opening force of the fire door increases (opening force F = door area * residual pressure value / door axis force arm; generally the opening force should not exceed 100 N). Excessive opening force prevents people from normally opening the fire door for evacuation. Residual pressure control measures: install residual pressure valves (installed on the partition wall between the stairwell and vestibule or on the exterior wall of the stairwell), which automatically open to release pressure when the stairwell residual pressure exceeds 30 Pa (releasing to outside the stairwell or to the vestibule); VFD control of the supply fan (adjust the supply fan speed according to feedback from the residual pressure sensor to maintain residual pressure within the 25-30 Pa range); use electrically adjustable supply air outlets (adjustable outlet opening to control air volume distribution). Door sealing measures—to ensure the positive pressure effect, fire doors should be installed with sealing strips (intumescent fire sealing strips that expand to seal door gaps during a fire). The sealing strips should be installed continuously without interruption (continuously installed around the entire door frame), and the sealing strips should fit tightly against the door leaf (gap not greater than 1 mm).
Coordination between fan foundations and floor slab loads
The coordination between the installation foundations of smoke control and exhaust fans (including pressurization supply fans, smoke exhaust fans, and makeup air fans) and the loads on building structural floor slabs is a prerequisite for ensuring safe equipment operation. Fan load calculation—fan dead weight (weight of the fan body; generally 50-200 kg for axial fans and 100-500 kg for centrifugal fans), fan operating dynamic load (dynamic load factor 1.2-1.5, considering vibration during fan operation), duct load (weight of ducts connected to the fan, about 20-50 kg/m), and installation foundation dead weight (weight of foundation steel or concrete foundation). The total load should be included in the live load used for floor slab design (the standard live load value for fan rooms is generally 8-10 kN/m2; when the fan load is large, separate verification should be carried out). Vibration isolation foundation design—the fan foundation should adopt vibration isolation measures: install vibration isolators between the fan base and foundation (spring isolators or rubber isolators), with no fewer than 4 isolators (evenly arranged at the four corners of the fan). The compression of the isolators should be selected according to fan weight and speed (spring isolator compression 10-25 mm, rubber isolator compression 5-10 mm). Flexible connection between fan and duct: use fire-resistant canvas flexible joints (length 150-200 mm, fire-resistant canvas combustion performance Class A) to reduce transmission of fan vibration through ducts to the building structure. Connection between fan foundation and floor slab—the fan foundation (steel base or concrete foundation) should be reliably connected to the floor slab structure (fixed with chemical anchors or expansion bolts, bolts M12-M16, embedment depth not less than 100 mm), and a 10-20 mm rubber pad should be installed between the foundation and floor slab (for further vibration reduction and sound insulation). Structural load verification—fan equipment data (equipment weight, foundation dimensions, dynamic load factor) should be provided during the structural design stage, and the structural engineer should verify the floor slab bearing capacity (slab reinforcement and thickness meeting load requirements). If not satisfied, structural beams should be added below the fan foundation or the floor slab should be strengthened.