Fire Dampers/Fire Wall

Penetrating Firewalls with Exhaust Ducts

THE NATIONAL FIRE PROTECTION ASSOCIATION (NFPA) has addressed the issue of fire protection of exhaust ducts penetrating firewalls in specialty manufacturing facilities, such as semiconductor and related facilities, where poisonous gases, severe caustic or concentrated acid fumes are transported through the ducts neutralizing scrubbers. To protect the occupants in these facilities, it is important that these hazardous fumes are continued to be exhausted in the event of a fire. For example, fire codes stipulate that there must be an auxiliary power source that will operate the exhaust fans at a minimum of 50% of the designed system velocity, in the event the main power source is interrupted from a fire.

NFPA 318-15 STANDARD for the PROTECTION of CLEANROOMS states the following:

9.3.4 Exhaust ducts penetrating fire resistance–rated construction shall be contained in an enclosure of equivalent fire-resistive construction. Fire resistance construction and enclosures with equivalent fire-resistive construction shall extend 1.8m(6 ft) or a distance equivalent to two times the duct diameter, whichever is greater, on either side of the rated construction.

9.3.5 Fire dampers shall not be installed in exhaust ducts.

Effectively, a 12-foot (3.65 meter) or longer box must be built around the duct, which has the fire resistance of the firewall itself. If a fire occurs on either side of the wall, the duct will be protected and will not be able to collapse, preventing the fire from spreading from one side of the wall to the other. The type of duct does not matter. This same protection concept is desired on metal ducts penetrating fire walls, as well as rated nonmetallic materials which are approved for use without automatic sprinklers. It is recommended that this design concept be reviewed by the “Authority having Jurisdiction” over the specific project.

The “NFPA 318 Standard for the Protection of Cleanrooms – 2015 Edition” may be ordered by visiting the NFPA on the Internet at

See page 194 for additional information on NFPA.