Engineering Design Practice - Assignment Example

Name: Course: College: Tutor: Date: 1. Give a definition of fire, include an appropriate diagram. Fire is the heat and light energy that is given out when a combustion reaction takes place. Fire in its most common form can result in conflagration. The fire has the potential to cause physical damage through the burning. 2. Identify the different stages of fire growth, include an appropriate diagram. Fire has several stages in its growth and the stages can be divided into three distinct stages these being the; a.) Growth Stage (incipient) During the stage fire increases in size from small flames to full fire that extends to the entire room. This may take several seconds or several hours to happen to occur. Fire is dependent on combustible content oxygen supply which maybe from the ventilation openings. b.) The fully developed stage also referred as free-burning stage In the fully developed stage, a room and contents are involved in fire. Where no efforts are made to put off the fire the fire continues to burn until the available fuel and/or oxygen in the room or area is consumed. c.) The decay stage As the available oxygen is consumed in the decay stage, the fire slowly gets to the decay stage. Far much as some oxygen remains in the fire area, most of the visible flames start to diminish, and the fire continues to smolder. The high heat and smoke conditions remain this creates the probability for there being a back draft. 3. Explain the difference between pre-mixed and diffusion flames, and provide some practical examples of each. The main difference between the pre-mixed and diffusion flames is that they follow opposite directions due to the different influences of temperature. In pre-mixed flames as the temperature rises the rate of oxidative attack on the soot precursors increases faster than the rate of precursor formation through pyrolysis. Thus the higher the temperature the less is the tendency to soot. In the pre-mixed flame all aliphatic form some acetylene which is the mono-element for precursor formation and all fuels essentially follow the same nucleation route. 4. What are the 5 functional requirements of Approved Document B? 5. There are two broad standards for the design methods of fire resistance of buildings: prescriptive and performance-based. Explain the difference between them. 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 and the performance-based approach affords the design team greater flexibility than the prescriptive code requirements. The prescriptive methods use a single fire scenario to evaluate all structural members and neglecting other fire factors. 6. 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; a.) 7. Why is it important to carry out more than one experiment to test the same parameter? More than one experiment to test the same parameter is done to ensure that the results are correct and to and that the parameter is effective for use. 8. What factors influence the severity of a fire within a compartment? Compartment fire is any fire within a structure that has a roof (ceiling) and at least two enclosing perimeters or sidewalls. The severity of fire within a compartment is influenced by conditions like the fire being constantly ventilated, receiving a continual renewal of oxygen while at the same time expelling the smoke and fire gases. (NFPA, 2007) 9. How is heat transferred in a compartment fire? Include a diagram. Transfer of heat in a compartment fire (completely enclosed space) 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) 10. Explain the term “flammability limits”. Flammability limits, also referred as explosive limits, flammability limits is the proportion of combustible gases in a mixture, between which limits this mixture is flammable. 11. Draw a graph/ diagram to illustrate the flammability limits of flammable vapours. 12. Define the term “limiting oxygen index”. Limiting Oxygen Index (LOI) is the evaluation of a product’s capacity to support combustion. 13. What does it mean if a sample has a high LOI or a low LOI? When a material has a high Limiting Oxygen Index, this means that it will not support combustion. When it shows a Low Limiting Oxygen Index it means that it supports combustion. 14. Explain the ignitability test? The ignitability test establishes the ignitability of a vertically oriented test specimen which when exposed to a small flame, either at the edge or the surface of the specimen. In the ignitability test, checks the burning behaviour of the specimen being tested for flame spread, and the occurrence of burning particles. 15. The cone calorimeter can be used to measure a number of different parameters from experimental fires, what are they and which one is the most important in determining the fire hazard performance of materials? A cone calorimeter is used to collect data regarding the ignition time, mass loss, combustion products and heat release rate. The principle measurement being the heat release rate, in this principle, the gross heat of combustion of any material is directly related to the amount of oxygen required for combustion. 16. What are the criteria for when flashover will occur A flashover is the event of a given source of ignition which results in the sudden and sustained transition of a growing fire to a fully developed fire. In simple terms, a flashover is a term used to describe the theory of a fire's growth up to the point where it became fully developed. For a total flashover to occur in its real form there has to variables such as thermal influences where radioactive and convective heat flux are assumed to be the driving forces although 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. 17. Once ignition has occurred what is required to maintain 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. 18. What are the basic two types of uncertainty found in measurements? Give an example of each. There are two types of uncertainty in measurements; fractional uncertainty is given by the ratio of the uncertainty divided by the average value. For this example, (1) 19. 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 = = 20. 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 21. What are the four main classes of ignition? 22. In relation to the characteristics of building materials give definitions for the following terms: • 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. 23. Explain what the two major mechanisms of burning are. 24. How can fire spread 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 radiative heat transfer. Through these methods fire can spread between buildings and cause damage. 25. Define the term “fire plume”. Identify and explain the different regions within a 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) Works Cited Grimwood, P. (2003). Read More