Fire Protection and Life-Safety Engineering for HVAC
Fire and life safety is where mechanical design meets GB 50016 and GB 51251. Questions usually concern boundaries, ratings and paths: where a duct crosses a fire compartment, how a stair is kept clear of smoke, and what the fan must survive.
Compartmentation
- Ducts crossing a fire compartment boundary need fire dampers rated 70 °C, with access panels and clear identification.
- Smoke exhaust ducts and dampers are rated 280 °C for 30 minutes, and the exhaust fan must be certified for that condition; a normal ventilation fan is not a substitute.
- Kitchen exhaust ducts must be non-combustible with the required fire resistance, and grease filters must be removable for cleaning.
Smoke control
- Pressurization: stairwell about 50 Pa, lobby 25–30 Pa, with a pressure-relief path so door-opening force stays under roughly 110 N.
- Smoke exhaust rates follow space type; make-up air at not less than 50% of exhaust, introduced low so it does not disturb the smoke layer.
- Control logic: detection starts the exhaust and pressurization fans, stops air-handling units serving the zone, and closes dampers; all fire systems on emergency power.
Worked example
A basement corridor of 60 m² with 3 m clear height at 60 air changes: volume flow = 60 × 180/3600 = 3.0 m³/s. Make-up air at 50% = 1.5 m³/s. Through a 1.5 m² opening the velocity is 1.0 m/s, acceptable; through 0.5 m² it is 3 m/s, which disturbs the smoke layer and fails review. The fan and duct are then selected at 280 °C, not at ambient.
Traps
Fitting 70 °C dampers on a smoke exhaust duct; designing exhaust without a make-up path; ignoring stack effect in tall stairwells, which can reverse pressurization at the top; using an ordinary centrifugal fan as a smoke exhaust fan; forgetting that dampers, fans and controls must all be on emergency power.