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DUCT DESIGN
3.7 UV light
Some polymeric materials used to manufacture nonmetallic flexible ducts may degrade with prolonged exposure to ultraviolet (UV) light radiation. UV radiation occurs naturally in sunlight or can be artificially generated by specialized lamps. The outer barrier (jacket) may degrade if ducts are installed outside in direct sunlight or within attics, crawl spaces, etc. where direct sunlight enters, e.g. turbine vents, sky lights, canopy windows, etc. The inner core (liner) may degrade if ducts are positioned near a bio - treatment lamp (UV emitter) installed within the HVAC system. Unless the product is specifically designed to withstand exposure to UV radiation from sunlight or from specialized lamps, special care shall be taken to ensure the outer vapor barrier and inner core material are shielded from the direct path of such radiation. Reference the manufacturer ’ s recommendations for specific product information related to UV exposure.
3.8 Fire Safety
Flexible ducts cannot be considered “ noncombustible ”, except metallic non - insulated ducts, but they are generally regarded as “ limited - combustible ”. The UL 181 Safety Standard for “ Factory - Made Air Ducts and Air Connectors ” is used to investigate safety performance as referenced in the applicable International Codes (ICC), Uniform Mechanical Code (IAPMO), the applicable National Fire Protection Code/Standard (NFPA), and various other state and local codes. The UL 181 Standard has been used for more than 40 years for evaluating duct safety. The testing procedures were developed by taking a wide range of safety related installation situations into consideration, including structural integrity and flammability characteristics. Four (4) fire tests are used to investigate the flammability and burning characteristics of flexible duct as follows:
3.8.1 Surface Burning per UL 181 Section 7
The Surface Burning Characteristics (Flame Spread and Smoke Development) for both interior and exterior duct using the 25 ft. [7.6m] tunnel test method that is published in UL 723, the American Society of Testing and Materials (ASTM E84), the National Fire Protection Association (NFPA 255) and the American National Standards Institute (ANSI)
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3.8.2 Burning Test per UL 181 Section 11
Ease of ignition/burning test using a Bunsen burner on both the inner core and outer jacket of the duct.
3.8.3 Flame Penetration Test per UL 181 Section 10
Flame penetration test using a specifically designed test apparatus to evaluate the retardation of flame passage from exterior to interior of the duct.
3.8.4 Flame Resistance Test per UL 181 Section 8
Component flame resistance test conducted on tapes, fabrics, adhesive, and related components that are exposed direction to the air system.
3.9 Fire Resistance - Rated Assemblies
A fire - resistance rating refers to the period of time an assembly is able to contain a fire and perform its intended structural function. UL ’ s product category for Fire - resistance Ratings (BXUV) covers fire - rated assemblies for floor - ceilings, roof - ceilings, beams, columns, walls and partitions based upon the test method and acceptance criteria in UL 263 (ASTM E119), "Fire Tests of Building Construction and Materials." The ratings are expressed in hours (i.e. - 1 hour fire rating). When an assembly complies with the test criteria, a detailed description of the assembly, its performance in the fire test, and other pertinent specifications for materials, certification coverage and alternate assembly details are included in the fire resistive assembly report. These assemblies are published on UL ’ s Online Certifications Directory Product iQ, www.ul.com/PiQ. Many designs allow the use of Class 0 or Class 1 flexible air ducts and air connectors. This directory of fire - resistance designs should be consulted to determine the requirements for air ducts within a particular assembly design.
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