Page 10 - Caswell Firesafe Manual 2018

TECHNICAL MANUAL

FFRDL / TM / BS / 01 / 2018

Dual Return Air / Smoke Extract Systems

In difference to car park and kitchen extract systems there will be situations where a dedicated extract
system is not required. It is possible to incorporate a fire resisting smoke extract or clearance system as
part of the general ventilation extract or recirculation system.

In normal operating conditions the system works with return air going back through the air handling unit,
however, in the event the fire fighting services wish to remove smoke from the affected area, a switch is
provided which closes the fire / smoke damper on the recirculation branch and opens a fire / smoke damper
on a separate branch attached to a high temperature smoke extract fan. This fan is switched on
automatically once the damper on the smoke extract branch has opened.

The ductwork is fire resisting from the point the fire compartment is breached and remains fire resisting
through to the point of discharge.

These systems are frequently used in shopping malls or large buildings with open spaces such as
concourses or atria. They are an effective and economical method of providing emergency smoke extract
in the event of fire.
BRITISH STANDARD VERSION
MECHANICAL VENTILATION SYSTEMS FOR
DUAL PURPOSE SYSTEM
METHOD 3 IN BS5588-9 & BS9999
NON FIRE RATED FAN
(NORMAL OPERATION) FIRE RESISTING DUCTWORK
FITTED WITH FIRESMOKE CONTROL DAMPERS
SUITABLY FIRE PROTECTED
PRIMARY & BACKUP FANS
PLANT ROOM
THE SMOKE CONTROL DAMPERS OPEN OR CLOSE
IN A FIRE CONDITION TO EXTRACT SMOKE FROM
THE AFFECTED ZONE, DEPENDING UPON THE
CONTROL PHILOSOPHY

SMOKE CONTROL DAMPERS
CLOSE FOR THE NORMAL EXTRACT
AND OPEN FOR THE SMOKE EXTRACT SMOKE CONTROL
IN A FIRE CONDITION DAMPERS

FIRE RESISTING DUCTWORK
& RELATING FIRE STOPPING
TESTED TO BS 476 PT24
FIRE
COMPARTMENT
WALL

PENETRATION
SEALS TO BS 476 PT24
FIRE COMPARTMENT FLOOR

FIRE RESISTING WALLS (for compartmentation) FIRE RESISTING SMOKE OUTLET DUCTWORK, RETAINING
FIRE RESISTING FLOORS (for compartmentation) CROSS SECTIONAL AREA OF MORE THAN 75 OF DUCT.
NON-FIRE RESISTING DUCTWORK STABILITY, INTEGRITY & INSULATION RATING EQUAL TO
COMPARTMENT WALLS, UNLESS SHAFT IS DEDICATED,
THEN STABILITY & INTEGRITY ONLY IS REQUIRED
DUCTWORK SUITABLE FOR CLEARING SMOKE.
ELEVATION OFTEN 1 HOUR INTEGRITY TO BS 476 PT 24 - ISO 6944
RETAINING A CROSS SECTIONAL AREA OF MORE THAN 75.

10 www.firesafeductwork.co.uk