Engineering Solutions in Fire Technology - Assignment Example

ENGINEERING DESIGN PRACTICE 8th DECEMBER, 2008 1. Give a definition of fire, include an appropriate diagram. Fire is the result of an action whereby heat and light energy are unconfined during a course of chemical reaction, combustion being specific to fire. The color of the flame and the intensity of the fire flame depend upon the external substances that combine together during the chemical process. Fire is also defined as a speedy but continual chemical reaction which is convoyed by the emanation of light and heat. The outcome of such chemical process is self-sustaining, unless extinguished till the limit that the fuel strength falls below a certain required value. 2. Identify the different stages of fire growth, include an appropriate diagram. The different stages of fire growth are Incipience (Ignition), Growth, Flashover, Fully developed fire and Decay. The ignition stage is the initial phase where an exothermic reaction takes place with an increase in temperature above the required limits. In the growth stage, the fire may get more intense or slow down depending on the type of combustion and the exposure to oxygen etc. In the Flashover stage there is a transition from the growth to the fully developed fire and is taken to be a mechanism where there is a presence of thermal instability. In the fully developed stage energy release is at maximum and the process is constricted by the availability of oxygen. The final stage is the decay phase where the fuel becomes consumed and the energy release is reduced and thereby the gas temperature decrease. 3. Explain the difference between pre-mixed and diffusion flames, and provide some practical examples of each. The most distinct difference among the two kinds of flame is that in diffusion flame the fuel oxidizers proportion keep fluctuation throughout the flames, example candle flames, match flames etc whereas in the case of premixed flames , the fuel oxidizer ratio is constant throughout the fame. For instance, a uniform combustible mixture stored inside a tube which is ignited through a spark and creating a flame is a perfect example of premixed flames (Johnson E A, Miyanishi K, 2001). 4. What are the 5 functional requirements of Approved Document B? The requirements are: 1. Means of Warning and Escape so that appropriate provisions for the same in case of fire from the building to a place of safety can be made. 2. The internal fir spread (Lining) B2, aims to identify those areas within the building that should be furnished as per the standard classifications 3. Internal fire spread structure should define the load bearing element of the structure and the nature of fire resisting compartmentation 4. External fire structure should provide guidance for fire resistance of external walls and the roof coverings 5. Excess and facilities for the fire service when attending fire at the building. (Furness A, Muckett M) 5. There are two broad standards for the design methods of fire resistance of buildings: A prescriptive method is used to define a structural fire in accordance with the materials used, shape and size of structural elements, thickness of fire protection materials and construction details etc best for a static situation but on the other hand a performance-based method for structural fire design is adaptable to the process of designing structures to wind loads and seismic effects. More emphasis is given to the evaluation of fire performance in relation to the key functional criteria which has made it more apt for situations which need aesthetic requirements. 6. What are the two categories of fire testing? Explain the difference between them. Falls testing generally falls into two categories firstly the test to measure ignition and the spread of flames from one area to another and secondly to measure fire resistance. The difference between the two is that Fire resistance tests identify the material’s ability to sustain it and serve its structural role during a fire while Fire ignition test helps to identify the spread of fire, the intermittent flame and the burning brand (BSI, retrieved on 8th December, 2008). 7. Why is it important to carry out more than one experiment to test the same parameter? It is important to carry multiple experiments in order to confirm the pre identified results under various circumstances. Multiple experiments for testing same parameters help in eliminating any ambiguities or chances of any variations or conflicting results which can be challenged in the future. Multiple experiments help in testing all possible situations and roles of various elements which can affect the results in some or the other manner and thus helps in getting on to a common and verified consensus. 8. What factors influence the severity of a fire within a compartment? The factors that influence the severity of fire within a compartment are 1. Fire load type and its density and distribution 2. Combustion behaviour of the load of the fire 3. The compartment size 4. Ventilations conditions 5. The thermal properties of the compartment boundaries (IStructE, retrieved on 8th December, 2008). 9. How is heat transferred in a compartment fire? Include a diagram. In a fire compartment, an area of a building is completely separated from the remainder of the building. This areas could be a single room, a series of rooms or an entire floor. The heat can be transferred through flames issued from the from a broken window or a door opening tend to revert back and touch the wall and window above The flow and intensity of the heat is often too high to move on to the other compartment of the building (Sultan A M, 1990). When an object in a room starts to burn, after some time confinement begins to influence fire development. The smoke produced by the burning object rises to transform itself into a hot gas layer below the ceiling; the thermal radiation produced from the hot layer, ceiling, and upper walls begins to heat all objects in the lower part of the room and increase the rate of flame spread to the other areas as well. 10. Explain the term "flammability limits". Flammability limits are also called as flammable limits which express the ratio of combustible gases in a mixture, that’s sets up a range between which , the mixture id regarded to be flammable. The lower flammable limit (LFL) (lower explosive limit) describes the least required or ranged mixture that is still flammable while the upper flammable limit (UFL) (upper explosive limit) gives the best possible flammable mixture. 11. Draw a graph/ diagram to illustrate the flammability limits of flammable vapors. 12. Define the term "limiting oxygen index". The limiting oxygen index is a widely used term for research and quality control, and identification of the flammability of polymeric materials. In other words LOI is also defined as the minimum concentration of oxygen in the oxygen and nitrogen mixture. The test for LOI is conducted in accordance with the National and International standards. However, higher the value of LOI the better it represents the flame retardancy factor. 13. What does it mean if a sample has a high LOI or a low LOI? If a sample attains a higher Limiting Oxygen Index rate, it signifies that there is a better flame retardancy factor or possibility however if the LOI is low in a sample it indicates that the flame reduction or extinction possibility is quite low. A high LOI reveals that a material burns with difficulty or is highly incombustible whereas low LOI reveals vive versa. The LOI indicates the flammability of the plastic material, high LOI is always beneficial. 14. Explain the ignitability test? The ignitability test is used to determine the glow fire ignitability temperature. The test emphasizes on three main areas which are the test criterion, the highest temperature at the end of the glow wire at which there is no sign of ignition that is the time where ignition lasts for longer that 5s at the time of contact and thirdly the ignition temperature which is 25 °C higher (30°C higher if between 900°C and 960°C) in comparison to the highest temperature measured at the end of the glow wire. 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 a device meant to identify the behavioral changes of small samples of various different materials in a condensed phase especially meant for Fire Safety Engineering. The parametres which are measured by the use of cone calorimeter are ignition time, mass loss, combustion products, heat release rate and other para,eters which are significant to burning. The calorimeter exposes different itself to different heat fluctuations over its surface. 16. What are the criteria for when flashover will occur Flashover is probably the final event or the stage which can lead to maximum hazards in the building. This point needs certain set criteria as every place does not reaches flashover. There has to be a point where the place is completely filled with flames and heat fluctuations are such which could ignite other combustibles as well. The gas temperature in the upper part of the fire place should reach a temperature of 550-650 degrees (Babrauskas V, 1980). The adiabatic flashover induction period is an important criterion for occurrence of flashover. 17. Once ignition has occurred what is required to maintain combustion? Once the ignition has already occurred, it is very important to sustain the combustion. Once the ignition has begun, the vapors get ignited and the flames in turn heat the fuel and enhance the rate of production of flammable vapors. The combustion process helps the flame to exist at the surface of the fuel. Proper combustion could be maintained by the ration gas valve that has the ability to sense the blower suction pressure and adjusts the gas flows depending upon the requirement. 18. What are the basic two types of uncertainty found in measurements? Give an example of each. The two types of uncertainties found in measurements are Type A and Type B. Type A is random uncertainties indicated by repeating measurements. Statistical methods can reveal of random uncertainties by analyzing series of observations. The importance of the random component of uncertainty becomes higher if there exists a considerable spread in a sample of measurement results. For instance, when an electrical measurement is concerned, random uncertainty components are generally present due to electromagnetic interventions and other kinds of electrical disturbances affecting the system. Systematic or Type B components of uncertainty errors are those which remain consistent when a sample of measurements is taken. Type B elements are identified on the basis of scientific judgment using all the available information including manufacturer’s details, data provided in calibration reports and knowledge of the measurement process. 19. 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 Range 41.62 - 45.10 Mean = 43.54 Standard Deviation 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 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 21. What are the four main classes of ignition? The four main classes of ignition are 1. Natural phenomenon: Natural ignition source is lighting, apart from it earthquakes, forest fires, volcanic activity etc are few of the natural hazards which may cause ignition. 2. Human carelessness: continuous human awareness, encouragement of good human safety norms is some measures which can be taken to avoid human carelessness. 3. Technological failure: can result in ignition. Areas such as plant rooms, labs, boiler houses, kitchens etc need to be under constant vigilance to minimize threat. 4. Deliberate fire raising: by anti social elements such as terrorists etc can be a major threat to fire ignition which needs to be monitored and controlled. (Stollard P, Abrahams J, 1999) 22. In relation to the characteristics of building materials give definitions for the following terms: Combustibility: is the quality of being capable of igniting or burning the building material. Fire propagation: is the proliferation of the materials used at the time of ignition Fire resistance: The materials which can protect themselves from the fire for certain duration or can withstand a fire resistance test. Surface spread of flame: is affected by the moisture content of the material. It is the speed with which a lining material spreads flame that determines the size of the fire. 23. Explain what the two major mechanisms of burning are. Two mechanisms of burning are gas phase flaming combustion and solid phase glowing combustion. In the former the gases and vapors being produced from the liquid or solid fuels are heated from the flames of fire itself. Flaming is a gas base combustion process while glowing is a solid base combustion process. 24. How can fire spread between buildings? The fire can spread through Flying brands may result in secondary fires from a considerable distance from a primary fire, Convective heat transfer cab cause fire in case the temperature of the gas stream is very high to several degree Celsius and Thermal radiation levels from buildings with highly flammable linings or are affected by wind directions etc. Fire can also spread by direct contact or spontaneous ignition, piloted ignition and branding. 25. Define the term "fire plume". Identify and explain the different regions within a fire plume. REFERENCES Johnson A E, Miyanishi K, 2001, Forest Fires: Behavior and Ecological Effects, Published by Academic Press, 2001 Furness A, Muckett M, 2007, Introduction to Fire Safety Management: The Handbook for Students on NEBOSH and Other Fire Safety Courses, Published by Butterworth-Heinemann BSI, Fire Testing, retrieved on 8th December, 2008, http://www.bsi-global.com/en/Standards-and-Publications/Industry-Sectors/Fire/Fire-Testing/ IStructE, IStructE Guide to the advanced fire safety engineering of structures, retrieved on 8th December, 2008, http://www.istructe.org/publications/files/Advanced_fire_safety-Sample_pages.pdf. Sultan A M, 1st August,1990, Reducing Fire Hazards in Small Buildings, retrieved on 8th December, 2008, http://irc.nrc-cnrc.gc.ca/pubs/bsi/90-2_e.html Babrauskas V, 1980, Engineering, Estimating Room Flashover potential, Fire Technology, Vol 16(2): 94-103 Stollard P, Abrahams J, 1999, Fire from First Principles: A Design Guide to Building Fire Safety, Published by Taylor & Francis, 1999 Read More