In the event of a fire, most people believe that the flame is the main cause of death but in reality and confirmed by fire fighters and professionals, the main killer is the SMOKE!
Fire produces intense hear and hot smoke ranging from 760˚C to 1,000˚C in just 2 minutes on normal household material. Large volume of lethal smoke and hot combustible toxic gases produced during the fire will travel at high speed in enclosed buildings and endanger the lives of the people. The building will soon be blurred with thick smoke depleting oxygen and visibility rendering potential danger to panicking people trying to escape and loss of property. For this purpose, it is essential to provide a fire rated ductwork system designed to convey smoke, hot gases, fire and hazardous fumes and to supply air combustion in the fire area to ensure life safety.
It is important to emphasize on the proper design of smoke extraction systems and choice of material that has been tested. Fire resistant ducts are required to prevent fire inside and fire outside to reach other compartments and at the same time, prevent the fire from entering the duct. Bare steel duct are potentially more dangerous to be used as the lateral spread of flame causes the main fire to spread by radiation through the ducts to the potential compartment. Based on researches, steel tends to deform at the temperature of 300˚C and as temperature rises to 472˚C to 482˚C, there is a loss of strength and rigidity by 80%. In addition to the expansion of the material, the unprotected steelwork changes in structure resulting in bending and buckling, eventually leading to collapse of the ductwork. Hence, the fire is left to spread freely through other surrounded areas. This is a classic example which underline the fact that non-combustible material are not necessarily fire resistance if not proven in fire test. Thus, it is necessary to substitute the steel material but it would incur additional costs as steel is known to be highly economical and stable compounds. Alternatively, fire rated intumescent coating can be used on the steel material itself to provide necessary protection and fire rating.
To ensure that the Fire rated ductwork systems is capable of withstanding anticipated smoke temperature and satisfies fire resistance requirement, the system should be tested to comply with Australian Standard AS1530.4 or British Standard BS476 Part 24. Both standards have the same compliance criteria for performance as follow:
- Stability or structural adequacy; shall be deemed failure if the duct collapses.
- Integrity; shall be deemed failure when there are developments of cracks, fissures or other openings through which flames or hot gases can pass
- Insulation shall be deemed failure when the temperature at any point of the duct exceeds 180˚C or exceeds an average of 140˚C.
In addition, the ducts must maintain at least 75% of cross sectional area. The temperature should follow the ISO temperature curve for up to 1,100˚C and the ductwork systems can only be deemed complied with the standards when both Duct A (External fire) and Duct B (Internal Fire) passed all the performance criteria.
Once the fire rated ductwork systems have been tested to comply with the required standards, the system in the form of construction must be equivalent to that of the material tested. One should look at the test report to ensure that the Fire Rated Ductwork System has complied with the relevant standards for Duct A and Duct B. Failure of any one of these criteria for either Duct A or Duct B constitutes to the failure to comply with the standards and shall be deemed not in compliance with the standards. The test report will dictate the type of duct construction method (SMACNA or DW144) used including addition of fire rated gasket and sealant, rockwool insulation and other accessories installed during testing and the fire rated ductwork shall follow the same construction method as per tested to ensure that the systems are fully functional for its purpose for the required fire rating. Any deviation from the tested installation of the fire rated ductwork could subject the ductwork to failure to perform during the event of fire.
WinDuct® is a 2 to 4 hours fire rated ductwork system that is tested to Australian Standard AS1530.4 and British Standard BS476 Part 24. WinDuct® uses water-based intumescent coating to provide protection to the bare steel to below the critical temperature of 500˚C at which the temperature yield stress reduces to the permissible working stress to keep the ductwork cool. Intumescent coating protects the initial material by reacting to the heat exposure in a predictable, controllable manner by swelling controllably to many times its original thickness producing carbonaceous char which acts as an insulating layer for the substrate (duct). WinDuct® is also a green product with low volatile organic compound (VOC) rendering it safe and clean.
For more information, go to www.winduct.com