Fire damper

Fire dampers are passive fire protection products used in heating, ventilation, and air conditioning (HVAC) ducts to prevent the spread of fire inside the ductwork through fire-resistance rated walls and floors. Fire/smoke dampers are similar to fire dampers in fire resistance rating, and also prevent the spread of smoke inside the ducts. When a rise in temperature occurs, the fire damper closes, usually activated by a thermal element which melts at temperatures higher than ambient but low enough to indicate the presence of a fire, allowing springs to close the damper blades. Fire dampers can also close following receipt of an electrical signal from a fire alarm system utilising detectors remote from the damper, indicating the sensing of heat or smoke in the building occupied spaces or in the HVAC duct system.

Regulations and fire test regimes vary from one country to another, which can result in different designs and applications.

German fire damper in underground parking of a commercial building. Unlike its North American contemporaries, this damper addresses smoke migration through the damper's annulus.

North American fire dampers, ready for installation in Durasteel fire-resistance rated pressurisation ductwork.

Side view of North American fire damper, showing the closing mechanism that shuts the interior blades. An air gap of maximum 1/8" per linear foot of width facilitate installation and allows smoke migration through the assembly. European dampers conceal this mechanism, with exterior firestop mortar acting as both a heatsink and smoke seal.

European fire damper with interior fire-resisting board.

Fire damper in oversized hole in a 2-hour rated concrete slab. The annulus permits smoke migration.

Mechanical dampers shut the cross sectional area of a duct in the event of a fire either by means of pivoting a fire-resistant board (in Europe), or by means of steel shutters, similar to blinds on a window (in North America). In the European designs, the turning mechanism is fully contained, permitting the dampers (subject to type approval) to be grouted in place, which permits a heat sink effect to conduct heat from an accidental building fire, which impinges upon a duct and damper, to be conducted into surrounding structures. This also addresses the topic of smoke migration through the damper's annulus. In North American damper designs, the closing mechanism for the interior shutters resides on the outside of the damper, which is why NFPA 80 expressly prohibits the installation or presence of any materials in the damper's annulus, which are not mentioned in the manufacturer's instructions, which are governed by their certification listings. The closing mechanism must be allowed to operate, which necessitates that the annulus remain open, apart from an angle iron lip that surrounds the damper through-penetration in fire-resistance rated wall and floor assemblies. Maintenance efforts of mechanical dampers of both European and North American mechanical damper designs focus on the function of the mechanical shutting of the opening (which must be performed during inspection), as well as removal of any foreign objects that may otherwise impair this function.

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