Flexible Duct Wrap As An Alternative To Fireresistance Rated Shaft Enclosures In The BOCA National Building Codes

by Steven R. Thorsell, L.A., CSI


The past few years have seen the development and introduction of flexible duct wrap materials which are intended for use in the enclosure of kitchen exhaust grease ducts and hvac air ducts. These flexible wrap materials typically consist of a lightweight flexible blanket comprised of non-asbestos, inorganic, fibrous refractory material encapsulated in an aluminum covering reinforced with a fabric scrim. These materials are typically produced in rolls of varying lengths and widths of 24 and 48 in. (610 and 1219 mm) and are intended for installation in direct contact with the exterior surface of the duct to be protected.

BOCA Evaluation Services, Inc. (BOCA-ES) has received requests from several manufacturer's to evaluate their products for compliance with the requirements of the BOCA National Building Code/1999 and the 1998 International Mechanical Code. The primary uses evaluated consist of (a) an alternative to a fireresistance rated shaft enclosure of a duct penetrating a fireresistance rated floor or wall assembly, (b) as an alternative for enclosure of kitchen exhaust grease ducts and (c) as a method of reducing clearance to combustibles for grease ducts. The materials have also been evaluated for surface-burning characteristics as an interior finish since the material is exposed and for noncombustibility to permit the use of the material in buildings of Type 1 and 2 (Noncombustible) construction.

In order to evaluate this type of material a set of criteria were developed and the following is an outline of these criteria:

1. For use of the material as an alternative to a fireresistance rated shaft required by Section 713.0 of the BOCA National Building Code/1999, it is necessary to establish equivalency with a traditional assembly tested in accordance with ASTM E119. The critical criteria here is the ability of the material to resist the penetration of fire and the transfer of heat under the time-temperature curve established by ASTM E119. To establish this performance, full-scale fire tests are conducted on a wall assembly constructed of steel of various thicknesses which are representative of the thickness of ducts the material is intended to be installed on. The maximum end point temperature criteria of ASTM E119 is used to establish the maximum hourly rating of the test specimen.

In addition, to determine the ability of the material to maintain the structural integrity of the assembly protected, full-scale engulfment testing performed in accordance with ASTM E119 is necessary to determine that the protected assembly does not suffer structural failure. Lastly, since the protected assembly is intended for installation on ducts which penetrate fireresistance rated floors or walls, the performance of the protected duct assembly in conjunction with a through-penetration fire stop system tested in accordance with ASTM E814 is evaluated. The F and T ratings of this testing, in conjunction with the hourly rating determined by the ASTM E119 testing, establishes the maximum hourly of the system.

It must be noted that the use of the material is limited to (a) the minimum thickness of the steel tested in the ASTM E119 testing, (b) the maximum size of the duct tested in the full-engulfment and through penetration fire stop testing, and (c) the lesser of the maximum hourly ratings determined by the three tests. The use of the material on duct sizes exceeding the maximum sizes tested may be permissible when additional testing and/or an engineering analysis is performed to determine that there will be no adverse structural effects, such as excess deformation or deflection, to larger ducts exposed to the ASTM E119 and ASTM E814 test criteria.

2. To evaluate the use of the material as an alternative method to reduce clearance to combustible materials, the UL 1978 test method is used. In this test a sample duct is constructed and wrapped with the material in accordance with the manufacturer's installation instructions and gas burners are installed inside the duct. A piece of plywood is placed in contact with the top surface of the wrapped duct and thermocouples placed between the plywood and wrapped surface, on the exterior of the wrap and between the duct surface and the wrap. The gas burner is lit and the internal temperature of the duct is brought to 500 degrees F. and held until equilibrium temperatures are attained on the grease duct surfaces and plywood. Next the internal temperature is increased until it reaches 2000 degrees F. and is held for 30 minutes. The pass criteria for this test is that the temperatures on the exterior surface of the wrap are maintained at or below acceptable levels and plywood must not show signs of combustion.

3. To evaluate the use of the material as an alternative to a shaft enclosure for kitchen exhaust grease ducts, as permitted by the exception to Section 506.3.12 of the 1998 International Mechanical Code, the criteria stated in Item 1 and 2 above are used. Additionally, the material is required to be listed and labeled by an approved agency. The requirements for the listing and labeling program requires that an independent third-party agency review and approve the manufacturer's in-house quality assurance program, perform random inspections and testing of the material at the manufacturer's plant(s), and label the material as conforming with the minimum performance requirements.

4. Finally, since the material is an exposed duct covering, testing in accordance with ASTM E 84 for surface-burning characteristics and testing in accordance with ASTM C 411 for hot–surface performance must be performed, as required by Section 604.3 of the 1998 International Mechanical Code.

Steven Thorsell is a Supervising Architect of Research and Evaluation with BOCA International, Country Club Hills, Illinois, and provides technical assistance to BOCA Evaluation Services, Inc. The specific products which have been evaluated to date by BOCA-ES are 3M/Thermal Ceramics FireMasterŪ Duct Wrap (BOCA-ES Research Report #94-70), Nelson Firestop Products FSB Flameshield Blanket (BOCA-ES Research Report #96-39, and Premier Refractories PyroscatŪ FP Duct Wrap (BOCA-ES Research Report #96-18). To determine the status of an existing report or to check on the issuance of any new reports for these materials refer to the products listed under Section 07250 "Fireproofing" in the BOCA-ES International Product Evaluation Listing, or on the BOCA-ES web site at "http://www.boca-es.org". To obtain copies of current reports contact BOCA Evaluation Services, Inc. at (708) 799-2305, through the BOCA-ES Fax-On-Demand System (708-799-2300, ext. 500) or on the BOCA-ES web site.
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