The working principle of composite smoke exhaust ducts primarily involves the collaborative function of smoke control and exhaust systems. It prevents smoke from fires from entering safe areas through mechanical pressurization and expels the smoke outside the building.

Composite smoke exhaust ducts play a crucial role during fires, mainly in the following aspects:

Smoke Control System (Positive Pressure Supply): Delivers air from the outside to prevent smoke from entering stairwells, vestibules, and refuge floors, ensuring that the evacuating population does not suffocate from smoke.

‌Draught System (Negative Pressure Extraction): Directs smoke generated to the outside of the building through ducts, effectively reducing smoke accumulation indoors, improving visibility, and providing better sightlines for evacuation and rescue operations.

‌Make-up Air Duct‌: Supplements the air volume of the exhaust system to maintain system balance and efficiency.

Additionally, the design and material selection of composite exhaust ducts must meet specific requirements and standards, such as:

Material Requirements: The composite smoke and exhaust duct material should be made of non-combustible materials, with fire resistance ratings in compliance with design specifications to ensure structural integrity and thermal insulation during a fire.

‌Fire Resistance Limit: The fire resistance of the duct must meet the requirements of integrity and insulation, including maintaining the structural stability and insulation properties within the specified fire resistance test period.

Pressure Resistance Requirement: The duct strength must meet various working pressure requirements, including the standards for low-pressure, medium-pressure, and high-pressure ducts, ensuring no cracking at joints under high pressure and no overall structural deformation or damage.

‌Airtightness Requirement‌: Under the corresponding working pressure, the air tightness of the duct connections must meet the standard, not exceeding the air leakage limit, to ensure the sealing performance of the duct.

In summary, composite smoke exhaust ducts, through their specific design and materials, as well as their synergy with smoke control and exhaust systems, effectively enhance the safety of buildings during emergencies such as fires.