BS 5588 Part 9 suggests three methods to maintaining fire compartmentation where ductwork passes through compartment walls or floors.

Method 1 Protection using fire dampers
Method 2 Protection using fire resisting enclosures
Method 3 Protection using fire resisting ductwork

Good practice dictates that fire dampers should not be installed in certain circumstances and therefore fire resisting ductwork is used.

Smoke extraction systems
Dual ventilation/smoke extraction systems
Pressurisation systems
Car park extraction systems
Kitchen extraction systems

Fire resisting ductwork may prove to be a cost effective alternative to fire dampers in general ductwork systems (particularly over the lifetime of a building).

No capital/installation cost of fire/smoke dampers and associated access doors.
No reliance on mechanical fire dampers which may fail in time.
No regular testing regime.
No electrical wiring and control system associated with smoke dampers.

Technical Information

CASWELL FIRESAFE fire rated ductwork is manufactured from pre-galvanised sheet steel, mild steel and stainless steel to the exacting standards set by Firesafe Fire Rated Ductwork Limited.
CASWELL FIRESAFE fire rated ductwork has been tested and assessed by Warrington Fire and Research and satisfies BS476 Part 24: 1987, achieving the following fire resistance:
 
Duct Type A (Fire Outside)

Stability 240 mins
Integrity 240 mins
Insulation 120 mins
 
 
Duct Type B (Fire Inside and Fire Outside)

Stability 240 mins
Integrity 240 mins
Insulation 120 mins
 
CASWELL FIRESAFE is suitable for all fire resisting ductwork applications:
Smoke Extract / Kitchen Extract / Car Park Extract / Pressurisation
Full range of accessories available:
Supports, access doors, attenuators and volume control dampers to maintain fire resistance
throughout the whole system.
Rectangular, circular and flat oval ductwork constructions available.