Page 80 - Build 152

Departments/Research By Colleen Wade, BRANZ Senior Fire Scientist
Fire behaviour of ducts
BRANZ recently investigated the re performance of HVAC ducting and pipe insulation, reviewing the re test methods that evaluate how they perform in a re.
Examples of exible insulated ducts with plastic or foil facings.
BUILDING CODE requirements for assessing the re properties of walls, ceilings, oor coverings and duct materials changed in April 2012.
A new classi cation system using group numbers for reaction to re was introduced, with further changes that a ected HVAC ducting made in December 2013. These allowed the fire test in AS/NZS 1530.3:1999 Methods for re tests on building materials, components and structures to be used for ductwork materials.
Ductwork re tested
The investigation included an experimental programme exposing ductwork installed in a small room to re. The duct materials were exposed to a gas burner to determine how the ducting performed when exposed to a re of a size similar to a burning wastepaper basket.
Flexible ducting is commonly used to connect air di user outlets to rigid ductwork in HVAC systems. It is typically limited in length, circular in cross-section and consists of an uninsulated sleeve or a sandwich construction with an inner lining, core insulation and an outer sleeve.
Sleeves are plastic or aluminium foil, and the insulation material is usually a lofted polyester.
Combustible insulation spread re
This type of exible ducting was found to readily ignite with a moderate aming re and burn quickly. Thin plastic facings burn through, with the polyester insulation melting and dripping to surfaces below. As the ducts melted and collapsed, they did not easily spread re along the length of the duct, helping to limit the total size of the re.
Combustible polyester insulation tted inside a rigid steel duct was also included in the test programme and performed poorly. The steel duct construction resisted collapse but allowed the burning insulation to spread re more easily inside the ductwork, eventually resulting in a bigger re.
78 — February/March 2016 — Build 152