Fire rated ductworks are used to guarantee the fire compartmentation. More precisely, fire rated ventilation ducts can avoid fire and heat spread between two compartments.
It is possible to prevent fire spread from one fire compartment to another, along stairways, rooms and general access corridors, only if all building materials and structural elements share a common fire classification and fire resistance rating.
Compartment walls and floors must have a certain fire resistance, which means that the performance criteria of load-bearing capacity (stability), integrity and insulation have been met for a duration of 30 to 240 minutes. It is therefore extremely important that, where compartmentation boundaries are penetrated by services, the fire separation criteria for the penetrated elements are maintained and, in particular, that ducting should not become a conduit along which fires, or hot smoke, may spread to other areas.
The view on risk of smoke spread in ventilations systems varies throughout Europe. In some countries smoke spread via the ventilation system is not considered to be a problem at all, in other countries smoke dampers or fire/smoke dampers are always required where there are more than one fire compartment supplied by the same system. Finally, there are countries where the regulations in addition to fire/smoke dampers also allow performance-based design.
In any case, the fire performance of a duct which penetrates a fire resisting/separating element must requires careful consideration by specifiers. Typical metal sheet ducts fail to meet internationally accepted fire protection requirements. They heat and deform rapidly from the effects of fire. Under specific circumstances they can even accelerate the spread of flame and smoke.