Smoke kills more people in fire than heat, flames or structural collapse every year. Often, smoke incapacitates so quickly that it reduces the oxygen level or replaces it with other toxic gases causing a respiratory hazard to its victim, either by suffocation or burning of the respiratory tract (National Fire Protection Association, 2019). In its killing fumes, people find it hard to make it out to the exit in time and most often, being overcome by the quick spread of smoke.
The early warning of heat and fire becomes an important factor in the operation of the building. From the concept of fire services, separation and segregation is one of the principles of fire extinction, for example, removal of limitation of oxygen to allow combustible materials to continue burning and to build walls and compartmentation to reduce the size of the fire load.
There is a need to balance between active fire protection and passive fire protection systems. The fire protection industry operates in heavily regulated environment with specific standards, qualifications and demonstrated competencies to work. Licensed companies carry the burden of liability, indemnity and insurance to the building operations and its users.
Steel is an alloy comprising of a mixture of iron and carbon, and sometimes other elements. Widely used in construction, infrastructure and building, steel is one of the most stable material that is high in integrity, rigidity and strength. Steel can support large amount of weight, but however, like other materials, steel loses its stiffness and strength when exposed to high temperatures (Kodur, et.al.,2010). Steel starts to lose its conformation at 299°C and when the temperature reaches between 470°C to 500°C, steel will start to lose its strength and rigidity up to 80% and coupled with expansion due to heat exposure, steel will suffer changes in its structure such as bending and buckling, eventually leading to collapse (Mohamad, et.al., 2013 & Ullah, et.al., 2013).
Steel is also catagorized as a non-combustible material as it tends to deform when treated and exposed to high temperature exposures. Non-combustible materials are materials that do not aid combustible or additional heat when exposed to an ambient fire, in other words, non-combustible material are endothermic (absorb heat) and when oxidized, tends to deform and decomposition. At this time, fusion and loss of strength by the materials occur leading to loss in the integrity of the structure. Therefore, it is important to keep the temperature of steel to maintain its properties during incident of fire.
The use of passive fire protection materials acts to insulate the steel substrate from the sudden spike of elevated temperatures and maintain its structural integrity. Intumescent coating is a type of reactive material that is widely accepted in the world of fire protection for the its substantial properties and behaviour as an excellent insulator for its base material (Ullah, et.al., 2013).
Fire rated ductwork systems
Fire rated ductwork systems are a part of the passive fire protection systems. A fire ductwork system is designed to convey smoke, hot gases and flame from area to areas to supply air combustion in the fire area. For this purpose and reason, it is essential to provide fire protection of a duct system to ensure life safety and protection of the building and property.
- The standard set by fire department is intended to prescribe minimum requirement which are intended to:
- Restrict the spread of smoke through duct system in building or into a building from outside
- Restrict the fire through duct systems in a building
- Permit the air duct system in a building to be used for additional purpose of emergency smoke control
- Ventilation duct systems intended solely for the evacuation of smoke, which are intended to maintain their integrity and cross-sectional area within the fire compartment in order to enable maximum quality of smoke to be extracted throughout the fire period.
Ductwork are used for smoke extraction and are required to meet two requirements in which it has to be at a standard whereby it is capable of withstanding anticipated smoke temperature and have satisfied fire resistance requirements if the ductworks are to be passed through a fire resisting barrier. Fire resistant ducts are required to prevent fire inside or outside the duct to reach other compartment and prevent the fire from entering the duct. Using base duct of 1.2mm, there are potentially more dangerous. When there are no air spaces behind them, the hazard is particularly great in the case of air conditioning duct as the lateral spread of flame cause the main fire to spread by radiation through the ducts to the potential compartment. Therefore, due to safety reasons, most of the ducts are required to be fire resistant externally and internally.
As an important component or system to provide safety in the smoke control system, the fire rated ductwork system design must be tested by the Accredited Laboratory to the required standard and to be certified by the local fire service department. For smoke control as determined under the law. Where the ductwork is used for fire and smoke control, it should be tested according to A.S. 1530.4 and BS 476: Part 24 or its equivalent for external fire exposure (Duct A) and internal fire exposed (Duct B). The criteria for testing include structural adequacy, integrity and insulation.
By Michael Chang
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