Hence, as concrete is a very poor conductor of heat and an inert material; it can be useful in avoiding a fire from spreading and emitting toxic fumes thus preventing deaths and reducing injuries.
Figure 1 Figure 2
Effect of heat on concrete after 2 hours of exposure to 1000°C Fire
(1) Fibre reinforced concrete and
(2) Ordinary reinforced concrete
(Takenaka Co, 2000)
Clay bricks
Brickwork is normally a very good fire-resisting material. Clay bricks can withstand temperatures up to 1000 o C or even more. It can resist prolonged and severe fire up to 4 hours without damaging itself. This stability is owing to the high temperatures to which clay bricks are normally subjected when being manufactured. However, in some rare cases, the heating surface of the brick may fuse. Fortunately, this does not create much problem to the strength of the brickwork.
Gypsum plasterboard
Paper – faced gypsum plasterboard is a commonly used dry wall in most buildings these days. Apart from being a flexible partition, it is also a very good material to resist fire. Pure gypsum consists of calcium sulphate and water of crystallisation. Other materials such as glass fibre and vermiculite also exist but in small quantities. These products improve the durability of the gypsum and also its performance. When gypsum is heated during a fire, temperatures on the exposed face will increase gradually until 100 o C. At this temperature, the water of crystallisation is evaporated and as the heating continues the heat progresses and it eventually dehydrates the entire board.
Complete dehydration occurs at an approximate temperature of 210 oC – 300 oC. This process is called calcination. It is very dangerous as the gypsum will tend to crack. Hence, glass fibre and vermiculite are used to provide a much better resistance to fire. Glass fibre tends to expand when exposed to high temperatures. The role of vermiculite is to lowers the rate of calcination.
Thus, this process prevents the plasterboard from shrinking and gives it more strength. These addictives can help to save many people from getting injured or losing life during a fire.
Steelwork
Unprotected steelwork normally reduces its strength by half when subjected to temperatures of 500 o C – 550 o C. Therefore, it is very vulnerable to fire. Steel is also known for its good thermal conductivity, which is a very dangerous property when a fire breaks in a building. However, steel is vital in construction. To sort out the problem of conductivity, steel structural assemblies are protected by insulating materials. Other structural materials such as brick or concrete can be used; however this is a very expensive method. The most commonly used insulator is intumescent paints. These are available in liquid form and are usually sprayed using airless spray equipment. Smaller areas are rolled or brushed. Only a thin layer is to provide insulation and they are durable materials.
Intumescent materials react to heat by expanding more than 29 times their initial thickness and foam is developed as the insulating layer. This foam provides protection for about 20 to 120 minutes depending o the thickness of paint applied. However, this does not provide full protection of life but it plays a major role in safety during fire.
Timber/wood
Wood and timber have been used for years as fire separating elements. Timber burns at a low rate and resists thermal conduction by forming a self insulating char as shown in the diagram below. It can resists fire up to 1 hour. This process is called pyrolyis. Since timber has a low thermal conductivity and charred layer has a much lower conductivity, the access of oxygen to the timber surface is reduced.
A) Original size
B) Section of a member after a half an hour of fire testing
C) One hour of fire testing
http://www.benfieldatt.co.uk/technical_information/timber_frame/fire_performance
However, the ignition point also depends on the characteristics of the species of timber being used. To deal with this process, timber is treated with fire retardant chemicals to provide adequate safety. It can be costly but when the safety of a person is concerned, the cost hardly matters.
Plastic
Plastic is another product that is widely used in construction these days. However, it is a highly combustible material and produce toxic fumes when catches fire. About 80 % of deaths during a fire are caused by inhalation of toxic fumes rather than by direct burning. To deal with problems such as easy ignition, high combustion rate and smoke formation, phosphorus containing retardants are used to produce fireproofing polymers, which can resist up to 500 o C and since rate of decomposition is higher, toxic fumes are produced for a longer period of time. This new product is quite expensive but efficient, as it can reduce the number of deaths caused by inhalation of toxic fumes during a fire.
Glass
Normal glass is a low resistive fire material and is also very brittle. Exterior fire can penetrate buildings through windows and other glazed openings that have been formed by the effective heating of the fire. However, there exist some heat resistant glasses. These are ceramic glasses and normal glasses which are conducted with protective treatments such as vinyl film sun shades and aluminium foil. The application of aluminium foil in the exterior panel of glass is a very effective treatment, as the shiny surface of the aluminium foil reflects the radiant heat, hence keeping the window relatively cool. Compared to aluminium foil, ceramic and vinyl glasses are not that effective. They can nevertheless be used for windows in the upper floors of buildings.
Conclusion
Hence, for the maintenance of safety during a fire, fire - resisting materials should be used either in their natural or reinforced form. Construction materials such as concrete, clay bricks, gypsum plasterboard, steel, timber or wood, plastic or glass must be thoroughly used. Also some of these stuffs such is timber as quite costly, however when the question on safety arises, someone’s life is seemed to be more precious than these materials. Thus, taking all these materials and their fire-resisting properties into account, they must be used in the construction of buildings as they provide adequate safety.
Reference List:
- B. H. Jones, Performance of Gypsum Plasterboard Assemblies Exposed to Real Building Fires, University of Canterbury.
- A.C Parnell and E.G Butcher, Smoke Control in Fire Safety Buildings, E. & F. N. Spon, 1979.
-
G J Langdon-Thomas, Fire Safety In Buildings Principle and Practice, A. & C. Black,1972.
Malhotra H.L, Design of Fire -Resisting Structures, Surrey University Press, 1982.
- W. Grosshandler, Fire Resistance Determination and Performance Prediction Research Needs Workshop: Proceedings, 2002.
