Fire dampers are not required at penetrations of shafts where the penetrations are in parking garage exhaust or supply shafts that are separated from other building shafts by not less than how many hours of fire-resistance-rated construction?

Fire dampers are critical safety devices installed in ducts and air transfer openings to prevent the spread of fire and smoke within a building's ventilation system. In the context of penetrations through fire-resistance-rated construction, regulations usually specify where these fire dampers are necessary to maintain the integrity of fire separations.

In the case of parking garage exhaust or supply shafts, building codes provide allowances stating that fire dampers may not be required if the penetrations are made in shafts that are separated from other building shafts by a fire-resistance-rated construction of at least two hours. This is because two hours is deemed sufficient for preventing the passage of fire and smoke from one area to another in the event of a fire incident, assuming other conditions of the building system are adhered to.

This standard reflects a balance between safety measures and practical construction considerations, recognizing that if a sufficient barrier exists, the need for additional fire dampers may be less critical. It ultimately ensures that fire safety is maintained while allowing for certain flexibility in design and construction practices, particularly in specialized environments like parking garages.