The Role of Radiation in Fire Spread between Neighbouring Buildings - Coursework Example

Name : xxxxxxxxxxx Institution : xxxxxxxxxxxx Title : xxxxxxxxxxxx Tutor : Dynamics of Fire Course : xxxxxxxxxxxx Date : xxxxxxxxxxxx Radiation Introduction Radiation refers to the transfer of heat through space. Thermal radiation is usually produced when heat that is as a result of the movement of charges within a material is changed into electromagnetic radiation (Siegel, Howell & Howell, 2001). This energy then radiates travelling in straight lines towards different direction through space heating other surfaces through ionization. Thermal radiation normally occurs at an extensive range of frequencies that are determined using the law of radiation developed by Max Planck (Siegel, Howell & Howell, 2001). The overall amount of radiation produces usually increases directly with the increase in temperatures. In addition, the velocity of thermal radiation produces by any electromagnetic wave is directly proportional to the quantity of absorption that the wave experiences. The main radiating gases produced during combustion are carbon dioxide, nitrous oxide, methane and water vapour. Also referred to as the green house gases, they are responsible fro the green house effect in the atmosphere. These gases absorb the heat that has been radiated by the earth’s surface and radiate it in all directions. Some of the heat is thus radiated downwards back towards the earth’s surface resulting into higher temperatures below. An increase in the amount of the green house gases directly leads to the amount of head absorbed as well as the heat radiated back leading to more temperatures in the earth’s atmosphere. The role of radiation in fire spread between neighbouring buildings In the event of a fire breaking out in a building, the fire could radiate heat that could ignite combustible materials found within the neighbouring buildings. The flames burning through opening like windows and doors could allow radiation to occur as radiating compounds and gases emit heat which is then transferred across to the adjacent buildings leading to the spread of the fire and more risk of loss. As such, there is need for space separation between buildings to prevent such potential transfer of heat (Furness & Muckett, 2007). Assessments should be carried out so as to know the extent to which a potential fire could spread from a building and get into the neighbouring buildings and the risks involved if such a spread occurred. There is need for adequate space to be left between buildings so as to prevent a fire from spreading as well as limiting the amount of combustible materials used in the lining of walls and decorations that could be ignited as a result of absorbing radiated heat from adjacent buildings (Wilder, 1997). This space is determined by calculating the length to the boundary between the two buildings divided by two. The effect of enclosure ventilation on combustion and the composition of smoke Enclosure ventilation systems allow free air flow within a building allowing proper filtration of air into the various rooms within the building. Adequate provision of oxygen during the combustion process leads to the complete burning of combustible material resulting into fewer products as compared to burning that occurs ion limited amount of oxygen. The combustion process produces both heat and smoke. Smoke is normally described as the solid and liquid particles as well as gases found in the air that are formed during the process of pyrolysis or combustion (Wilder, 1997). The nature and composition of the smoke produces as a result of both pyrolysis and combustion depends on several factors such as the quantity of the product burning, amount of oxygen present during the burning process, as well as the distance the product is from the fire (Wilder, 1997). The basic composition of smoke is carbon dioxide, carbon monoxide, hydrogen cyanide, nitrogen oxides and ammonia, halogen acids such as hydrogen fluoride and hydrogen chloride, and organic irritants such as formaldehyde, isocyanates, and unsaturated aldehydes. The presence of sulphur and phosphorus leads to the formation of sulphur and phosphorus oxides respectively (Furness & Muckett, 2007). Hydrocarbons produced may include methane, acetylene, benzene and ethane with the heavier ones condensing to form soot and/or tar. Functions of smoke control Smoke control is important as it helps prevent the loss of life due to the amounts of toxicants present in smoke such as asphyxiants that cause narcosis and upper respiratory irritants. These toxicants could be in large amounts which could potentially lead to toxicological effects when inhaled over short incidents of exposure (Wilder, 1997). Smoke, which normally has its own heat, could lead to flashovers since it includes a considerable concentration of flammable compounds which could become ignited when in contact with atmospheric oxygen resulting to burns (Craighead, 1995). Sulphur oxides and halogen acids in smoke form corrosive acids when they come into contact with moisture in the atmosphere that harms both living and non living things. In addition, smoke leads to poor visibility that could result in accidents. Methods of smoke control Pressurized exits Pressurization refers to the utilization of fans that introduce pressure differences between barriers that have a high resistance to the flow of air (Craighead, 1995). These fans help to prevent the further movement of smoke between the rooms in a building. Pressurization is normally utilized in high rise stairs that are separated using rated fire construction. These exists are usually pressurized with the pressure serving to avert any smoke from going into the stairs. The pressurization system installed is activated when smoke is detected by a smoke detector that is situated at the opening of the stairs. Bathroom exhausts Bathroom exhaust systems usually have opening between floors in a building. In addition, the bathroom exhausts for a group of rooms in a building are normally joined on vertical risers. As such, exhaust fans are installed as additional components within the subduct system. These fans should function continuously in order to prevent smoke from spreading from one floor to another. Dampers should be added as precautionary measures to prevent the smoke from spreading in the event the fans do not work properly (Furness & Muckett, 2007). Operable windows A building design that is founded on pressure disparities between the floors could be prone to smoke if the building has numerous openings to the outside. If the weather becomes too windy and the windows located in the windward side are closed while those in the leeward side are open, the building will be prone to smoke as it will not be driven out. Operable windows help to bring in air from outside that potentially drives the smoke out of the building in the direction of the wind. Dilution This involves the use additional air that is used to dilute the smoke that is present in a building. The air that is added removes the smoke from the non fire spaces that are within a building so as to maintain the necessary levels of air (Furness & Muckett, 2007). This additional air makes the smoke to be diluted reducing its amounts as well as effects. Buoyancy This refers to a process where hot combustion gases are passed through passive vents that are fitted with powerful fans. These vents are located on the roof and ceiling within large spaces. These vents assist in removing the smoke that could be inside a building at rates that are faster that the smoke is being produced enabling easier evacuation activities. The use of standard fire curves for determining fire resistance Standard fire curves have been used to model a real fire based on temperature-time interaction (Craighead, 1995). The type of fire that could arise depends on several factors such as the amount of ventilation present, the building materials used and any fire resistance that could be present. Fire curves have been used to determine the fire resistance that a building can have against a fire by testing the building materials to be used in constructing a building. The disadvantages of using fire curves is that they do not represent the real fire since several factors such as the intensity of the fire in a real and standard fire are hardly the same (Furness & Muckett, 2007). They also are unable to model the most severe fire situations that occur in life that contain several combustible materials, adequate amounts of oxidants, and the lack of adequate disaster preparedness. The approach to standard fire curves is usually varied on both onshore and offshore applications since the factors involved in these two types of fire accidents are not the same. Fires that occur on offshore structures are very different from those that occur on structures that are found onshore. The kind of fire behaviour exhibited onshore is different from that exhibited offshore. The availability of fire protection materials, high winds and tides and the exposure to jet fires complicate fire resistance offshore as compared to onshore fires. Bibliography Craighead, G. 1995, High-Rise Security and Fire Life Safety (2nd Ed). London: Butterworth-Heinemann. Furness, A., & Muckett, M., 2007, Introduction to fire safety management. London: Butterworth-Heinemann. Siegel, J. R., Howell, R., & Howell, J., 2001, Thermal radiation heat transfer. New York: Taylor & Francis, Inc. Wilder, S., 1997, Risk Management in the Fire Service. New York: Penn Well Books. Read More