The Duct Through the Two-Hour Wall
In a two-story office tenant finish, the contractor runs a 16-inch by 10-inch galvanized supply duct through a 2-hour fire wall separating the suite from the adjacent parking garage. No fire damper is installed; the contractor argues the duct is 24-gauge steel and 'the wall is concrete on both sides, so nothing can burn.' The same job uses the ceiling cavity above a suspended ceiling as the return-air plenum; the cavity contains wood floor joists, kraft-faced fiberglass batts, and exposed foil-faced polyisocyanurate board. The building is sprinklered throughout. The drawings show a 20-inch by 12-inch return grille in the corridor ceiling but no return duct.
1. Is the duct penetration acceptable without a fire damper? What applies if a damper is needed?
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No. A duct penetrating a fire-resistance-rated assembly-here a 2-hour fire wall-must be protected with a listed fire damper installed in accordance with its listing. Duct gauge is not a substitute; the limited exceptions for steel ducts apply to specific 1-hour conditions with sealed annular spaces and no openings, not to a 2-hour wall. The damper must be set in the plane of the wall with the listed sleeve and retaining angles, the annular space sealed with an approved material, and the assembly identified. The inspector should also verify the damper is listed for the required rating and that the wall itself was not compromised by the oversize opening.
2. Can the ceiling cavity be used as a return plenum with those materials present?
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No. Plenum enclosures must be constructed of noncombustible or limited-combustible materials, and materials exposed to the airflow are restricted. Wood joists, kraft facings, and exposed foil-faced polyisocyanurate foam are combustible; foil facing does not convert foam plastic into a limited-combustible material, and foam plastic in a plenum is specifically restricted. The sprinkler system may permit certain limited combustible materials under the plenum exceptions, but exposed foam and kraft facing are not among them. The compliance path is to abandon the plenum return and install a ducted return, or to enclose the cavity with approved materials.
3. The contractor offers to add a fire damper but proposes to bury it above the screwed-down hard-lid ceiling with no access panel. Acceptable?
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No. Fire dampers must be provided with an approved means of access for inspection and maintenance, and they must be identifiable. A screwed-down ceiling with no panel leaves the damper uninspectable and un-resettable after a trip. The contractor must install a listed, labeled access panel of adequate size positioned so the damper can be seen, inspected, and reset, and must identify the damper. Until access is provided, the installation remains deficient even though a listed damper is present.