Scientific Principles for Fire Professionals - Assignment Example

Scientific Principles for Fire Professionals Name Institution Date A. i) What is the “Fire Tetrahedron”? Describe its components. A fire Tetrahedron is a four-sided geometric figure that represents the four components necessary to sustain combustion. These components include heat, fuel, oxidizing agent and uninhibited chemical reaction chain (Brett & Brett 1997). Heat This is the energy sufficient enough to release vapor from fuel and finally cause a fire ignition. Any heat generation can supply this component of the tetrahedron. For instance, heat can come from direct flame impingement, an electrical source or an arcing electrical source. This tetrahedron component can get transferred easily through direct contact, convection or radiation, and that is why firefighters use the application of cooling water to extinguish a fire. Fuel Fuel makes up the most variable component of the tetrahedron in that variety of both natural and manmade substances can burn making a fuel source. Firefighters find this variable very important because they get to determine the approach of distinguishing a fire by the type of burning material. Fuel always exists in the form of a solid, liquid or gas. Oxidizing Agent The first and most crucial component of the tetrahedron is the oxidizing agent; also commonly known as air. Air is made up of roughly 21% oxygen, which makes the perfect combustible element that supports fire ignition. Although most people perceive oxygen as inflammable, it remains one major component necessary for combustion to take place. Fuel is the part of the fire tetrahedron with the broadest variable content -- many natural and manmade substances burn. This variable is important to firefighters because the type of material burning often dictates the approach that must be taken to extinguish it. Fuel may take the form of a solid, liquid or gas. Chemical Chain Reaction A chemical chain reaction is the most recent segmented added to the tetrahedron and it represents the right mixtures of the other three components, in the right proportions; in the ignition and sustenance of combustion. For combustion to take place a sufficient and uninhibited exothermic energy reaction must take place. The ratio of fuel to air must exist in flammable limits for this reaction to occur; otherwise the removal of the same will prevent combustion as well as suppress a fire (Klinoff,2007). ii) Compare the “Fire Tetrahedron” with the “Fire Triangle.” The Fire Tetrahedron and the Fire Triangle make up the basic fire model that firefighters use to extinguish most fires. For years, the model existed as the Fire Triangle because it only constituted of three components which include fuel, oxidizing agent and heat. However, with continuous studies into fire applications and principles, a fourth element; the chemical chain reaction got added to the Fire Triangle to make up the Fire Tetrahedron. Therefore, the Fire Triangle exists as the simple model that explains the combustion process through the existence of three basic and important fire components; oxidizing agent, fuel, and heat. On the other hand, the Fire Tetrahedron is the new model that has partially replaced the Fire Triangle. It explains that fire naturally occurs through the combination of four elements; fuel, heat, oxidizing agent and a chemical chain reaction; combined in the right mixture and proportionality. iii) Discuss how the “Fire Tetrahedron” can be used to understand the combustion process. In order to comprehend and learn how fire extinguishers work and the entire process of extinguishing one must first know the chemistry of combustion. The combustion chemistry emanates from the Fire Tetrahedron, which explains the complex chemical and physical processes that cause a fire. The Fire Tetrahedron also referred as the Triangle of combustion represents the three components fuel, oxygen, and heat; that must exist in the right proportion for combustion to take place. The three elements together with the fourth element, the chemical chain of reaction present for combustible elements that adequately sustain combustion or the combustion of any combustible material. The tetrahedron explains how combustion takes place in that oxygen must readily be available for combustion. If oxygen is available and then sufficient heat is subjected to a material, that will raise the ambient temperature of the material or the fuel; causing an exothermic chemical energy reaction in the material. This process described above is what scientist refer to as the combustion process. All these factors existing in the right mixture and proportionality symbolize the Fire Tetrahedron; which finally leads to the combustion of the material. Fire extinguishers help put out fires by eliminating one or two of the basic components of the Fire Tetrahedron (Carter, 1990). In other words, the combustion process is normally associated with the oxidation of a fuel, in the presence of oxygenated air, with the emission of heat; leading to a chemical process where electrons get lost. Using the oxidation perspective, the Fire Tetrahedron explains the combustion process in the sense that for oxidation to occur, a reducing agent, fuel and an oxidizing agent, oxygen must be present. When the heat gets added to these two components, the molecular energy gets transferred from the fuel to the oxygen molecules causing an exothermic chemical chain reaction that ignites and sustains combustion; hence a fire. Slow oxidation, such as rust produces slow heat such that combustion does not occur. However, self-sustained combustion takes place when sufficient excess heat from the exothermic reaction radiates back to the fuel; resulting to vapors and leading to ignition in the absence of the source of a fire ignition. The Fire Tetrahedron also explains that the combustion process can also occur through solids by two mechanisms: flaming and smoldering. The flaming combustion process is when the fuel in gas or vapor form, oxygen, and heat interact in an exothermic chemical energy reaction causing combustion of gasses. On the other hand, smoldering is a surface burning phenomenon that involves solid fuels burning under a lower rate of heat, in the presence of oxygen and with no visible flame. The combustion process in smoldering fires eventually transitions to flaming in the presence of sufficient energy; when the flow of the oxidizing agent is constant to speed up the rate of combustion. iv) Describe how the knowledge of the Fire Tetrahedron can be used to prevent fires. How can knowledge of it be used to extinguish fires? The Fire Triangle or the Fire Tetrahedron exist as a simple model that helps firefighters understand the ingredients that cause most fires. The Fire Tetrahedron replaced the triangle that illustrates that; in order for a fire to get ignited the four components must mutually correlate in the right mixture. Therefore, it is clear that if one of the four components gets removed from the tetrahedron; that can promote fire prevention or extinguishing of the same. For instance without the sufficient supply of heat a fire cannot get ignited or continue. The elimination of heat can only happen by applying a substance that inhibits fire reaction or reduces the amount of heat available for the entire process. Normally, the firefighters use this knowledge by applying water cooling that introduces the water agent in the heating phase, hence reducing the amount of heat available for fire reaction or combustion. Introducing the right amount of types of inflammable gas or powder into the fire also helps reduce the amount of heat; for the chemical reaction, thereby suppressing the fire. Looking at fuel, as one of the components of the tetrahedron, removal of the same also helps significantly in the prevention and suppression of fires. For example, applying this knowledge to the removal of the scraping embers from a burning building or structure may help remove the source of heat enhancing the fire; hence help stops the fire. Fuel can be removed mechanically or naturally as fuel separation remains an important factor especially in the suppression of wildfires (Nichols, 2010). The removal of the oxidizing agent; air which contains oxygen can also help tremendously in fire prevention or suppressing the continuation of the same. This is because without sufficient oxygen or with a decreased oxygen concentration the combustion process slows down; causing a fire to stop or the whole combustion process does not occur at all. In most cases, when a fire goes down, there is plenty of air left, therefore we can conclude that having the knowledge of how the air proportionality influences combustion, in the Fire Tetrahedron; can help significantly in fire prevention and extinguishing. B. i) Describe all of the important fire properties of a material. Combustible; this material fire property describes the material’s ability to burn or readily ignite. The majority of construction materials have this fire property; such materials include wood, wood-plastic composite and other plastic products. Noncombustible; this property describes a material’s inability to catch fire, combust or ignite when exposed to heat or fire. Certain materials exhibit this property when subjected to certain combustible conditions. This property can be assessed through the ASTM E 176 standardized test. Fire-resistance; this property explains the capability of a material to contain a fire or withstand fire without burning down. This property normally gets assessed using the fire ratings and fire-resistance tests to determine if the material used in construction can contain the fire; hence allow time for evacuation in case of a fire. Ignition-resistant; according to the International Code Council’s International Wildland-Urban Interface Code, this property describes materials that meet the minimum flame spread rating; after a specific duration subjection to the wetting-drying weathering cycle. The only test that can evaluate the fire behavior of such materials is the horizontal flame fire test. Most wood and wooden products treated with fire retardants qualify for this property (Quarles, 2013). ii) Choose two properties you consider to be the most important in evaluating the fire behavior of a material. Describe why you think they are the most important, and give an example of a test method that is available to assess that property. Discuss the suitability of the method as well as any major limitations of the method. The fire behavior of a material describes the material’s physical or chemical response when subjected to heat or fire. The combustible property is very important when determining which class ratings of materials to use for building or construction, for example, when renovating one’s home. The probable ratings and relative combustibility of a material determine which category and combinations of Class A and fire-resistant materials should get incorporated into the overall structure of a building. This property ensures that this balance is created in construction so to make the building more sustainable in case of a fire. Various tests exist that help evaluate this material fire property and thereby determine the fire performance of combustible materials. The two properties that undergo evaluation in determining the combustibility of a material include the flame spread index and heat release rate. The method for assessing the flame spread rating of a material is the gas flame test. This test involves subjecting the material to a gas flame; whereby the material gets placed in a horizontal tunnel under a very high gas flame. A combustible material with the lowest flame spread qualifies as a Class A while the rest get the Class B and C categories based on their performance in the test. This method is suitable for classifying the commercially used materials because it rates the materials based on their highest level of performance. However the numeric rating process is subject to human error, hence may result in result biases; leading to major anomalies during construction. On the other hand, the heat release rate of a material can undergo the assessment through mass loss measurement method. This method measures the weight loss of a burning material to determine the rate of energy the material will likely release when burning. This method has suits evaluating this property because it has high approval ratings in the criteria of materials that comply with the Chapter 7A building code. The method has a limitation in that the test works on the assumption that a material has to burn to a gaseous state in order to test the heat release rate. Also, the heat release rate in this method remains constant for most of the materials tested which means that this test may not present conclusive results about certain materials. On the other hand, the non-combustibility property can get measured through a standardized method known as the ASTM E-136. This method determines the fire behavior of a non-combustible material through subjecting the material to a 750 degree C, of fire in a vertical tube furnace. In order for a material to qualify as noncombustible the material specimen must meet the following specifications: • The material’s temperature should not exceed 30°C (54°F) above the measured apparatus temperature. • After the first 30 seconds of testing the specimen should not show any flaming. This method and criterion suit most construction materials that exist in the solid state. However for materials that exist in gaseous or liquid state this method does not apply because such materials flame immediately in the first 30 seconds of testing (Quarles, 2013). References Brett, Y., & Brett, J. (1997). Why are you like that?: Understanding the four elements tetrahedron of behaviour. Auckland, N.Z.: Learnology Publications. Carter, H. R. (January 01, 1990). Chemistry of fire - the basics. Voice. Nichols, J. (2010, April 17). Industrial Fire Prevention. Retrieved May 11, 2015, from http://industrialfireprevention.blogspot.com/2010/04/fire-triangle-and-fire- tetrahedron.html Information about the Fire Triangle/Tetrahedron and Combustion. (2011). Retrieved May 11, 2015 from http://www.firesafe.org.uk/information-about-the-fire-triangletetrahedron-and- combustion/ Klinoff, R. W. (2007). Introduction to fire protection. Clifton Park, NY: Thomson Delmar Learning Quarles, S. (2013, March 13). Fire Ratings for Construction Materials - eXtension. Retrieved May 11, 2015 from . Read More