BW11 Fire Rated Ductwork
One of the most important factors to be considered when designing and constructing a building are effective zones to limit the spread of smoke and fire throughout the building via the ventilation ducts. Under normal circumstances this zoning is achieved by the use of fire dampers or fire/smoke dampers within the duct systems. However, under certain applications the use of fire dampers is inappropriate. In this case the ducts themselves must provide the same level of fire rating afforded by the wall or floor of the zone.
Systems, which would not be fitted with fire dampers under normal circumstances, are as follows but not exclusively:
- Pressurization Ducts
- Grease Ducts
- Non-Commercial Kitchen Exhausts
- Toilet Exhausts
- Dryer Exhausts
- Fire Smoke Emergency Exhaust
- Dual Ventilation/Smoke Exhaust Systems
- Exit/Escape Corridors and Lobbies
Any duct system that is intended to operate or has a special use under a fire condition and
cannot therefore utilize fire dampers will require to be fire rated.
Duct systems and applications, which have special or operational effect under fire conditions, are
as follows:
1. Pressurization Systems
Pressurization is a method of restricting the penetration of smoke into exit/escape routes,
protected stairwells, corridors and fire fighting shafts for deep basements by maintaining
pressure differential. Smoke contamination in these areas would jeopardize escape in the event
of a fire. NFPA 90A requires that pressurization ducts should be enclosed in a 2 hour fire rated
enclosure. The FLAMEBAR BW11 duct is classified by UL up to 4 hours Stability, Integrity and
Insulation without any additional enclosure.
2. Grease Duct Systems (see also our Grease Duct Pamphlet)
Exhaust systems serving commercial kitchen hoods are required, as per NFPA 96, to be separate
and independent of any other systems because of the polluted nature of the extracted air. Fire
dampers should not be installed in any exhaust duct systems serving kitchens. Any ducts which
penetrate fire resistive barriers should be fire rated to the same level of fire separation as the
wall or floor through which they pass. The fire rating should be for both type B exposure (fire on
the inside) and Engulfment: Type A exposure (fire on the outside). All penetrations require to be
fire stopped. Grease ducts pose a particular hazard in that they contain deposits of accumulated
grease on the internal surfaces. Fire in an adjacent zone through which the duct passes could
ignite the internal deposits and cause a flashback to the served kitchen hood. It is important
therefore that all grease ducts be insulated, to protect from a fire in an adjacent fire zone
igniting the accumulated grease. To minimize the build up of grease, fire rated access doors shall
be installed at maximum 10 feet centers to allow access for cleaning.
Grease duct installations shall be evaluated, tested and listed to the requirements of the IBC,
IMC and UMC and these require compliance with ASTM E-2336 or UL 1978 or UL 2221.
FLAMEBAR BW11 complies with ASTM E-2336 and UL 1978 and NFPA 96.
3. Non-Commercial Kitchen Exhaust Systems
NFPA 90A requires that non-commercial kitchen riser ducts on high rise apartments passing from
floor to floor up through the building, shall be protected in a 2 hour fire rated enclosure. Since the
FLAMEBAR BW11 duct system is a 2 hour rated assembly the need for a 2 hour enclosure is
eliminated. However, as defined in NFPA 90A all branches serving each floor shall be fitted with a
fire damper, fire/smoke damper or a SMACNA type (sub-duct).
4. Toilet Exhaust Systems
NFPA 90A requires that toilet exhaust riser ducts on high rise apartments passing from floor to
floor up through the building shall be protected in a 2 hour fire rated enclosure. Since the
FLAMEBAR BW11 duct system is a 2 hour rated assembly the need for a 2 hour enclosure is
eliminated. However, as defined in NFPA 90A all branches serving each floor shall be fitted with
a fire damper or a SMACNA sub duct.
5. Dryer Exhaust Systems
NFPA 90A requires that all dryer exhausts rising through a building passing from one fire zone to
the next be enclosed in a 2 hour rated duct/shaft. Since the FLAMEBAR BW11 Duct System is
a 2 hour rated assembly the need for a 2 hour enclosure can be eliminated. The Building Code
further stipulates that the internal face of the ducts be free from screws and protrusions which
could cause lint to be trapped.
6. Fire Smoke Emergency Exhaust Systems
If the duct system is intended to be used to remove hot smoke in an emergency ISO 6944 (1985)
requires that the duct maintains 75% of its original free area. If a duct crosses from the fire
compartment to an adjacent fire zone it must have the same fire resistance as the fire barrier it
crosses. Ducts used as smoke exhaust shall be rated for fire exposure type B (fire on the inside).
7. Dual Ventilation/Smoke Exhaust Systems
Serve as normal ventilation systems, but in an emergency are converted to provide smoke
exhaust in the event of a fire. Since the FLAMEBAR BW11 duct is already fire rated no
additional enclosures are necessary. By combining the two applications into one system
significant cost savings can be effected.
8. Exit/Escape Corridors and Lobbies
It is a requirement of the International Mechanical Code that any duct crossing an exit/escape
corridor or lobby must be fire rated for Stability, Integrity and Insulation, with the same rating as
the compartment through which it passes. It should be noted that with FLAMEBAR BW11
only one fire damper is required, if either side of the exit corridor is constructed with non-fire
rated ductwork.
Flamebar Applications Technical Manual (PDF)