Appendix D. Discussion on Evaluating Duct Openings When Penetrating 2-Hour Fire Walls

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Appendix D. Discussion on Evaluating Duct Openings When Penetrating 2-Hour Fire Walls

It is recognized by fire protection practices that fire dampers are not required in all cases when HVAC

ducting penetrates fire rated construction. In NFPA 90A, Standard for the Installation of Air Conditioning

and Ventilating Systems, 1989 Edition, Section 3-3.1, fire dampers are not required when ducts penetrate

fire rated barriers that have a resistance rating less than 2 hours.

However, NFPA 90A (Sections 3-3.1.1 and 3-4.1) requires 1 1/2-hour fire-rated dampers in ducts which

penetrate fire barriers of 2 hours fire resistance or greater (but less than 3 hours). Section 3-4.2 of NFPA

90A requires 3-hour fire-rated dampers in ducts which penetrate barriers having a fire resistance of 3

hours or more.

The listing criteria for fire dampers, specified in UL 555, requires fire dampers to be tested in an assembly

with a standard time temperature fire exposure. The criteria for a damper passing the UL 555 test

requires that the damper remains closed during the duration of the fire test following a hose stream test

where no flaming on the damper materials and no through openings that would allow flames to penetrate

the fire wall occur.

In the UL 555 test, no duct work is connected to either side of the fire wall where the damper is tested

because it is assumed that in a worst case situation the duct work will structurally fail, fall away from the

damper, and only the fire damper and housing will remain.

Using the passing criteria defined in UL 555, researchers4 5 have proposed equivalent protection of duct

openings with no fire damper installed where the duct remains intact near the wall opening creating a

barrier to flames passing through the opening at the end of a 2-hour fire test.

The research has demonstrated that the most important factors in maintaining the integrity of the ducting

that prevents flaming through the duct opening after a one hour fire exposure is the quality of the duct

construction and installation, a design which prevents gaps between the fire wall opening and the duct,

and the design and protection of the duct hangers so that the ducts are supported throughout the fire

period and hose stream test near the wall opening where the penetration occurs.

Full scale fire testing has demonstrated that specific size and design detailed for both rectangular and

round ducts, installed per HVAC Duct Construction Standards, Metal and Flexible, will remain in place

over a 2-hour standard time temperature fire exposure.

The cited research addresses other methods to analyze duct penetrations in fire walls where fire dampers

are excluded so that qualified engineers and designers can assess and qualify by engineering analysis

other design scenarios for ducts not tested in the full scale tests performed by the researchers.

The research did not rely on trade-offs such as sprinkler protection as a method for qualifying the ducts.

It was based on quantitative engineering equations and tools and fire test data. The research is not

applicable to ducts that contain combustible loading and did not address protection of openings in smoke

barriers.

Gewain, R., J. Shanley, P. DiNenno, J. Scheffey, B. Campbell. August 1991. Evaluation of Duct Opening Protection

in Two-hour Fire Walls and Partitions, Fire Technology, National Fire Protection Association, Quincy, Massachusetts.

Gewain, R. G., B. G. Campbell. J. H. Shanley Jr., J. L. Scheffey, May 1990. Protection of duct openings in two-hour

fire resistant walls and partitions, ASHRAE JOURNAL, American Society of Heating, Refrigerating and Air-Conditioning

Engineers, Inc., Atlanta.

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