Smoke Control. Stand-Alone
Ductwork used in smoke extract systems should normally be rated for stability, integrity and insulation at least equal to the compartment wall through which it passes; as stated in Approved Document B Fire Safety, Notes to Table A1, Appendix A.
Smoke Extract ductwork must be able to retain a high percentage of its cross-sectional area in the event of fire.
This percentage varies between 75% and 90% – depending on which test standard is referenced – and applies equally to ductwork in the fire compartment and adjacent compartments. In order that this free-area criteria is maintained, fire resisting ductwork should be used within the service shaft requiring Stability and Integrity ratings. If there is combustible material within 500mm of the duct, then insulation is required.
All buildings will have escape routes within their design. In the event of fire these protected routes need to be kept clear of smoke to assist the occupants to escape and also allow safe entry for the fire-fighting services to bring the fire under control.
Two types of control systems are often used to achieve this:
Smoke Extract – to remove smoke from escape routes, malls and stairways etc. for a given period.
Pressurisation – to provide fresh air at a higher pressure than the air within the escape route, lobby or stair case to prevent the ingress of smoke.
Smoke Control. Dual Purpose
These systems are used in conjunction with a series of fire / smoke dampers.
Under everyday operating conditions, the smoke ventilation system works as normal by supplying
or extracting air from designated areas.
In a fire condition, however, the dampers on the standard system close and automatic dampers on the emergency system open
to allow the system to function as either a smoke extract or pressurisation system.
The ductwork must be fire resisting to satisfy the compartmentalisation plan of the building.
As with Stand-alone systems, Dual-purpose Smoke Extract ductwork must retain a minimum cross-sectional area both in the fire compartment and in adjacent compartments.
