Fire Rated Duct Products

The Massachusetts Board of Building Regulations and Standards (BBRS) meets once a month to discuss topical building code and other related issues. The BBRS relies on a number of advisory committees to assist with carrying out its mission and one of these committees is the Fire Prevention and Fire Protection (FPFP) advisory committee. Most recently, the FPFP committee took up the topic of fire rated duct products to determine how these products comply with the code.

The discussion focused on whether fire rated ducts or similar fire wrap products were being used in a code compliant manner. While not a comprehensive list, examples of such products include 3M’s Fire Barrier Duct Wrap, Conquest Firespray’s FlameBar fire rated duct system and Caswell Firesafe Fire Resisting Ductwork.

Using these types of products for grease ducts is well established and clearly defined in the code; however, these products are being used for performance-based applications with increased frequency. One example of alternative uses includes using fire rated duct products to separate stair pressurization duct work from interior building spaces prior to it reaching the stair shaft enclosure. See 780 CMR 909.20.6.1 (3). Another example where fire rated duct products are used is where ducts penetrate a fire barrier and the use of fire damper is prohibited such as hazardous exhaust.

Fire rated duct products are frequently used as an alternative means of protection to the fire damper in smoke control and laboratory exhaust applications. The common argument for these alternative approaches is that the duct work maintains the fire resistance rating of the wall being penetrated as the duct itself provides continuity of the fire rated separation until the duct terminates at the exterior or it reaches an area where protection is no longer required.

The common question is, how can the duct work maintain the fire rating afforded by a wall when the fire rated duct product has not been tested to ASTM E119? ASTM E119 is a standard used to test the fire ratings of walls, columns, floors and other building members under fire exposure conditions and does not include test requirements or pass/fail criteria for fire rated ducts. Should the same fire rating test requirements used on a wall even apply to a duct? Is it important for the duct to have been tested in the installed orientation or is it important for a duct to have been tested for fire exposure from both inside and outside the duct?

The International Building Code (IBC) does not recognize fire rated duct products as an equivalent to the ASTM E119 test standard and therefore these products must rely on alternative testing methods. This in itself is not a show stopper; however, it does mean that the use of these products cannot be used as of right. These products must be approved by the building official as a modification (780 CMR 104.10), an alternative material, design and method of construction (780 CMR 104.11), as a compliance alternative in an existing building or through the MA state building code appeal process.

Duct products that have been tested to ISO 6944 or ASTM E2816 for horizontal and vertical orientations as well as for fire exposure inside and outside the duct could gain approval through 780 CMR 104.11 as the available test data more closely aligns with testing conducted under ASTM E119. This is a common approach used by manufacturers of foreign products that have been tested to standards that are not yet recognized by US building codes. Justification for using an alternative testing method generally requires drawing parallels between the alternative test methods proposed and those which are recognized by the building code.

Using a modification (780 CMR 104.10) is more likely to be used where the available testing of a product does not completely align with the test standards of the IBC. In these instances, an analysis must be completed on the product in its proposed application. Similar to the approach used for 780 CMR 104.11, parallels between available test data and that required for compliance with the building code must be evaluated. Where gaps exist between code required test standards and those not recognized by the code, a hazard/risk analysis would be necessary to substantiate the use of a product that would otherwise not be permitted as of right. Depending on how a fire rated duct product is being used (stair pressurization, hazardous exhaust, orientation, proximity to hazards, etc.) the appropriateness of using these products can be presented to the building official for approval under 780 CMR 104.10.

The biggest take-way from the efforts of the BBRS and FPFP committees is that with the exception of specific applications identified in the mechanical code, there are no tests recognized by the Massachusetts State Building Code that outright permits carte blanche use of these products as an alternative to fire rated wall, floor or ceiling construction.