Engineering Design Practice - Assignment Example

Engineering Design Practice Insert Name University Module Tutors Name 6th December 2008 Definition of fire Fire can be defined as the rapid relentless chemical change that releases heat and light which comes with the accompaniment of flame, especially the exothermic oxidation of a combustible substance. As the chemical change takes place “fire” it grows in several stages. The incipient stage This is what may commonly be referred as the growth stage. This stage which can take a few minutes to happen and its characterized by fire growing, increasing in size from small flames to full fire that extends to the entire room. The free-burning stage Also the fully developed stage, this is when the fire is fully charged and the fire continues to burn until the available fuel and/or oxygen is consumed. The decay stage This is the stage where the fire dies out and most flames that were visible diminish. As the available oxygen is consumed in the decay stage, the fire slowly gets to the decay stage. Pre-mixed flames and diffusion flames differ in that the flames follow opposite directions due to the different influences of temperature. As the temperature rises in pre-mixed flames the rate of oxidative attack on the soot precursors increases faster than the rate of precursor formation. Thus the higher the temperature the less is the tendency to soot. What are the 5 functional requirements of Approved Document B? There are two broad standards for the design methods of fire resistance of buildings: prescriptive and performance-based. The difference between the two is that in the Performance-based design method of fire resistance in buildings starts with an analysis of fire scenarios to determine which design alternatives will meet those fire safety goals while the prescriptive design apply single fire scenario to evaluate all structural members and neglecting other fire factors. 1. What are the two categories of fire testing? Explain the difference between them. Fire testing is used as a means of determining if the fire protection products meet the minimum performance criteria as per the applicable legislation. There are two categories of fire testing; Carrying out more than one experiment on the same parameter It is important to carry out more than one experiment to test the same parameter; this is always done in order to reduce the margin of error. Fire within a compartment is influenced by ventilation receiving which helps it with the continued renewal of oxygen and helping in the expelling the smoke and fire gases. (NFPA 2007) 2. How is heat transferred in a compartment fire? Include a diagram. Transfer of heat in a compartment fire the combustion consumes the oxygen while potentially flammable gases remain within the space accumulating from the ceiling downward. When the temperature inside this space reaches the ignition temperature of these gases and the oxygen's concentration is within the flammable range, a generalized ignition may well happen, enveloping the entire space in a sudden deflagration. (NFPA 2007) Flammability limits Flammability limits, this is the proportion of combustible gases in a mixture, which limits this mixture is flammable. Limiting oxygen index Limiting Oxygen Index (LOI) is the assessment of a product’s capacity to support combustion. High LOI or a low LOI Having a high Limiting Oxygen Index means that a given material will not support combustion while as a Low Limiting Oxygen Index means that it supports combustion. Ignitability test The ignitability test is the test tat is carried out to identify the ignitability of a test specimen which when exposed to a small flame, either at the edge or the surface of the specimen. The purpose of the test is verifying the burning behavior of the specimen being tested for flame spread, and the occurrence of burning particles. The cone calorimeter The cone calorimeter collects data regard the ignition time, combustion products and heat release rate. The most important of the parameters is the heat release rate. Occurrence of a flashover A flashover is a term used to describe the theory of a fire's growth up to the point where it became fully developed. A flashover occurs where there are variables such as thermal influences, radioactive and convective heat flux. Also in the ventilation conditions, compartment volume and geometry, fire location and the chemistry of the hot gas layer also serve to influence any potential for a compartment fire progressing to flashover. Requirement for maintaining combustion Oxygen; for combustion to take place, the presence of the component of air that supports burning must be available for the burning to take place at the same time for the continuity for the same. The two types of uncertainty found in measurements There are two types of uncertainty in measurements; Fractional uncertainty FU= Fractional uncertainty is calculated by finding the ratio of the uncertainty to that of the average value. Relative uncertainty RU= Presented below are 10 heat release rates for a piece of laminated wood at 25.00kW/m2. Calculate the range, the mean, the standard deviation and then the uncertainty in the mean and the uncertainty in the standard deviation. Test 1 2 3 4 5 6 7 8 9 10 Heat Release Rate @ 25.00kW/m2 44.80 42.15 42.97 43.60 43.88 44.80 42.79 45.10 41.62 43.74 x f fx fx² 44.8 1 44.8 220.04 42.15 2 84.3 3553.245 42.97 3 128.91 5539.2627 43.6 4 174.4 7603.84 43.88 5 219.4 9627.272 44.8 6 268.8 12042.24 42.78 7 299.46 12810.898 45.1 8 368.8 16632.88 41.6 9 374.4 15575.04 43.74 10 437.4 19131.876 55 2400.67 102736.594 = = 3. In the table below there is a set of results obtained from the “Bang Box” experiment. Plot a graph which will best show your results and state what the results show. Fuel Acetone Test 1 Test 2 Test 3 Test 4 Test 5 Test 6 Test 7 Test 8 Number of Drops 2 6 10 12 14 16 18 20 Height attained by lid (cm) 0 20 40 80 120 150 110 90 X F fx fx² 0 2 0 0 20 6 120 2400 40 10 400 16000 80 12 960 76800 120 14 1680 201600 150 16 2400 360000 110 18 1980 217800 90 20 1800 162000   98 ∑fx9340 ∑fx²1036600 What are the four main classes of ignition? 4. characteristics of building material Combustibility, this is the state of a building material being combustible, or support burning, in building the combustible materials use should be reduced. Fire propagation, this is a class of algorithms use to simulate the spread of fire that fall under dynamic systems. Fire performance characteristics of lining material used in building are of considerable significance for they can propagate to the spread of fire. Fire resistance in building is the use of materials that do not support combustion when constructing. This is done to ensure that the materials will continue to support imposed loads during a fire and in the case of walls and floors, they are used to hinder the propagation of fire to adjacent compartments or buildings either by the conduction of heat or by the flow of hot gases. Explain what the two major mechanisms of burning are. Fire spreading between buildings Fire spreads from one building to another separated from it by a vacant space through the aid of flying brands, convective heat transfer, and radioactive heat transfer. Through these methods fire can spread between buildings and cause damage. Fire plume A fire plume is the column of hot gases, flames, and smoke rising above the fire. The flame and its column of hot combustion products rise because of a buoyancy force that is caused by the differences in density or temperature. If the hot gases cool to ambient temperature, the buoyancy force becomes zero and the plume will no longer rise. The air being drawn in at the bottom of the flame is called entrainment. The speed of this entrainment flow will have a pronounced effect on the flame height. A fire plume is dependant on fresh air, for the faster the fresh air source is moving into the flame, the higher it will rise. (NFPA 921, Ch1.3.92) Bibliography Junger, B. S. (2001). Fire. 224. Potter, G. H. (2006). fire protection system installation. Read More