Engineerin Design - Assignment Example

Q1. Give the definition of combustion. Ans. Combustion is a complex sequence of chemical reactions which are exothermic in nature. Essentials for combustion are fuel or a combustible substance and an oxidant. Outcomes of the reaction are heat or both heat and light. Q2. Fire safety in buildings is concerned with achieving two fundamental objectives, name them. Ans. Two fundamental objectives of fire safety in buildings are the safety of life of the occupants and protection of the property from damage. Additionally, objectives are ensuring continuity of operations and environmental safety. Q3. What are 5 fundamental requirements of approved document B? Ans. The fundamental requirements of approved document B are: Means of warning & escape: The building should have appropriate provisions for early warning about fire, and in case of fire there must be means of escape from the building to a safe place outside the building which must be safe and usable at all times. Internal linings for restricting fire spread: The internal linings should be of such material which can resist the spread of fire over its surface, and if ignited the rate of heat release and rate progress should be less. Internal structure for restricting fire spread: The building should be designed such that its structure should remain stable for reasonable period of time in event of fire. The building should also be sub-divided so as to resist fire spread. The building should be designed such that unseen fire and smoke accumulation within confined spaces is inhibited. Fire suppression systems should also be installed in the building. External fire spread: Buildings should be designed such that fire should not spread from one building to the neighboring building. The roof of the building should also resist the spread of fire over the roof. Facilities and access for the fire service: Design of the building should provide appropriate facilities to firefighters in life protection. Provisions should be made in the structure so that fire fighting equipment can gain access. Q4. Give the definition of the term “Means of escape from fire”. Ans. Means of Escape from fire is defined as the structural means, whereby a safe route is provided for people to escape from the building in case of fire, from any point in a building to a safe place, clear of the building, without outside assistance. Q5. What information do you need to know when designing means of escape? Ans. When designing means of fire exit, following information is required: Time of Evacuation: The average time a person gets to come out of the building safely after fire is started is the time of evacuation. It depends on the type of building structure and occupancy of the building. Travel Distances: Travel distance is the distance measured from any point in the building to a place of relative or ultimate safety. Travel distance will depend on how fast people will react to escape and how long it will be before the fire prevents that movement of people to the escape route. Exit width: The width of exit required depends upon the rate of flow of people, number of occupants and the flow time. It is calculated by: Where, U = width required N = occupants count 40 = STD flow rate T = flow time (depends on the type of building) Minimum number of exits: The minimum number of exits depends on the minimum width of exit required and maximum available size of any particular exit. It is calculated by: Where, E = No. of exits, U = width of exit required Q6. Why is it important to perform fire tests? Ans. By performing fire tests, properties of a material being used in construction can be known. Properties pertaining to burning and oxidizing are of importance when testing for fire safety. Fire testing are of two types: tests to measure speed of flame and ignition speed from one area to another, and tests to measure resistance to fire. Fire resistance tests finds out a material's ability to continue to serve safely its structural role during a fire. Q7. Why is it important to carry out more than one experiment to test the same parameter? Ans. There are different types of fire. Fire occurred due to different reasons and depending on the burning material, treats the material used for construction differently. The temperature range and variation can be different. Testing the material in more than one experiment ensures that the structure will remain stable during different conditions of fire. Q8. Explain the term “Trench Effect”. Ans. The trench effect can be depicted as mixture of circumstances that causes fire to grow vertically with pace on a slant surface. The trench effect is observed when there is a fire near inclined surfaces. The flame heats up the surface of material causing the flames to rise up; these gases reach auto-ignition temperature and catch fire. This fire again heats the higher surface and the cycle continues. Q9. Define the terms “upper and lower flammability limits”. Ans. Lower flammability limit: LFL is defined as the lowest concentration of vapor air mixture at a given pressure and temperature conditions that can ignite. The air vapor mixture will not catch fire if vapor concentration is less than LFL. Upper flammability limit: UFL is defined as the highest concentration of vapor air mixture at a given pressure and temperature conditions that can ignite. The air vapor mixture will not catch fire if vapor concentration is more than UFL. Q10. There are five main factors which will affect the development of fire growth within a compartment. They can be divided in two categories: those that are concerned with the compartment itself and those which are concerned with the fuel. Please name four of these factors. Ans. The factors are: The structure of the compartment The size of the compartment The burning rate of fuel The nature and amount of fuel. Q11. Discuss and explain the stages of fire development. Ans. Following are the stages of fire growth: Ignition: This is the initial point when the source catches fire and shows sustained flames. Growth: the initial growth depends not on the material in the compartment but the fuel itself. The fuel source will continue burning at an increasing rate and raising temperature till the time fuel and oxygen are available. Flashover: Flashover is the point when all the material in the room in involved in the fire. At this point a rapid growth is seen in the temperature. Fully developed fire: This is the point when the flames and the temperature are at its highest level. Decay: Finally when all the combustible material in the room is consumed, the fire starts decaying. Q12. Combustible and flammable fuels involved in fire have been broken down into five categories, identify them. Ans. Combustible and flammable fuels involved in fire belong to following five categories: Class A: Normal combustible like garbage, wood, paper, etc. Class B: Most flammable substances like petrol, diesel, paint, etc. Class C: Energized electrical machines like pump, transformer, etc. Class D: flammable metals like sodium, potassium, etc. Class K: grease, cooking oil, fats, etc. Q13. Name four parameters you can determine using cone calorimeter. Ans. Following parameters can be determined using cone calorimeter: Ignition time Mass loss Combustion products Heat release rate Q14. Explain what is meant by “ignitability” of a material. Ans. Ignitability of a material represents ability of a material to catch fire during routine handling. Generally such materials have flash point of less than 140oF. Q15. Explain what is meant by “positive pressure ventilation”. Ans. Positive pressure ventilation means pressurizing a structure with ventilation blowers or fans before attacking fire. This method helps in venting out smoke and high temperature combustible material. Q16. What is difference between heat and temperature? Ans. Difference between heat and temperature is that heat is the total amount of energy stored is a particular object. Both kinetic energy and potential energy combined represent the heat. On the other hand, temperature of that object is represented by the kinetic energy only, faster the molecules of the object move more will be the temperature of that object. Q17. Why is it important to investigate cause of fire? Ans. The cause investigation of fire is very important because it helps in developing methods to avoid future occurrence of fire. In most cases the cause of ignition and the fuel (combustible substance) are present at the same place, causing fire. Identification of the two helps in eliminating one of them or both to improve the fire-safety of a design. Q18. Explain the difference between a diffusion flame and premixed flame. Ans. The primary difference between diffusion flame and premixed flame is the point of creation of fuel and oxidizer. In diffusion flame the fuel and oxidizer are initially separate and are mixed only at the time of combustion, whereas in premixed flame fuel and oxidizer are mixed completely before ignition. Q19. Explain what flashpoint of a fuel is. Ans. The flashpoint of a fuel can be defined as the minimum temperature at which the air vapor mixture of the fuel is ignitable. At this temperature the mixture may stop burning if the source of ignition is removed. Q20. Why are vapors important to the burning process? Ans. Vapors are important in burning process because vapors are formed by initial heat applied and it is not the original substance, but the vapor which catches fire and burns. If the vapor was not to be formed, the material will not catch fire. Q21. Explain the limiting oxygen index test. Ans. In this test, a flame is placed in a vertical transparent tube and a mixture of oxygen and nitrogen is forced upwards. The concentration of oxygen is gradually reduced and at a point where the flame is no longer sustained due to lack of oxygen. This concentration of oxygen gives the volume percent. Q22. What are the limitations of limiting oxygen index test? Ans. The limitations of limiting oxygen index test are that the result has a variation of ±5% and also the test can not be applied to all kind of materials. It is limited to materials like plastic, wood, paper, etc. Q23. Explain the terms “pilot-ignition” and “auto-ignition”. Ans. For a flame to be produced, an ignition source is required. In case of pilot-ignition, the ignition has to be provided externally to start the flame, whereas in case of auto-ignition, the flame starts by itself without an outer source. Q24. Presented below are 10 heat release rates for a piece of laminated wood at 25kW/m2. Calculate the range, the mean, the standard deviation and then the uncertainty in the mean and uncertainty in the standard deviation. Ans. Range = Highest value – lowest value = 45.10 – 41.62 = 3.48 Mean = Sum of all values/no. of values = (44.8+42.15+42.97+43.88+44.80+42.79+45.1+41.62+43.74)/10 = 43.545 SD = 1.1079 Uncertainty = , where, t = SD and n = no. of values = = 0.35 Q25. In the table below, there is a set of results obtained from “bang box” experiment. Plot a graph which will best show your results and state what the results show. Ans. Here we can see in the graph thatas the ratio of acetone air misture increases, the burning is more effective, highest energy is released when no. of drops are 16. After that increasing the acetone amount will require more oxygen which will not be available and the effectivity of reaction decreases. Referances: 1. Fire Properties of Polymer Composite Materials By A. P. Mouritz, A. G. Gibson 2. Forest fires: behavior and ecological effects By Edward A. Johnson, Kiyoko Miyanishi 3. www.communities.gov.uk/fire/firesafety/firesafetylaw/ Read More

It is calculated by: Where, E = No. of exits, U = width of exit required Q6. Why is it important to perform fire tests? Ans. By performing fire tests, properties of a material being used in construction can be known. Properties pertaining to burning and oxidizing are of importance when testing for fire safety. Fire testing are of two types: tests to measure speed of flame and ignition speed from one area to another, and tests to measure resistance to fire. Fire resistance tests finds out a material's ability to continue to serve safely its structural role during a fire. Q7. Why is it important to carry out more than one experiment to test the same parameter? Ans. There are different types of fire.

Fire occurred due to different reasons and depending on the burning material, treats the material used for construction differently. The temperature range and variation can be different. Testing the material in more than one experiment ensures that the structure will remain stable during different conditions of fire. Q8. Explain the term “Trench Effect”. Ans. The trench effect can be depicted as mixture of circumstances that causes fire to grow vertically with pace on a slant surface. The trench effect is observed when there is a fire near inclined surfaces.

The flame heats up the surface of material causing the flames to rise up; these gases reach auto-ignition temperature and catch fire. This fire again heats the higher surface and the cycle continues. Q9. Define the terms “upper and lower flammability limits”. Ans. Lower flammability limit: LFL is defined as the lowest concentration of vapor air mixture at a given pressure and temperature conditions that can ignite. The air vapor mixture will not catch fire if vapor concentration is less than LFL.

Upper flammability limit: UFL is defined as the highest concentration of vapor air mixture at a given pressure and temperature conditions that can ignite. The air vapor mixture will not catch fire if vapor concentration is more than UFL. Q10. There are five main factors which will affect the development of fire growth within a compartment. They can be divided in two categories: those that are concerned with the compartment itself and those which are concerned with the fuel. Please name four of these factors. Ans. The factors are: The structure of the compartment The size of the compartment The burning rate of fuel The nature and amount of fuel. Q11. Discuss and explain the stages of fire development. Ans. Following are the stages of fire growth: Ignition: This is the initial point when the source catches fire and shows sustained flames.

Growth: the initial growth depends not on the material in the compartment but the fuel itself. The fuel source will continue burning at an increasing rate and raising temperature till the time fuel and oxygen are available. Flashover: Flashover is the point when all the material in the room in involved in the fire. At this point a rapid growth is seen in the temperature. Fully developed fire: This is the point when the flames and the temperature are at its highest level. Decay: Finally when all the combustible material in the room is consumed, the fire starts decaying. Q12. Combustible and flammable fuels involved in fire have been broken down into five categories, identify them. Ans. Combustible and flammable fuels involved in fire belong to following five categories: Class A: Normal combustible like garbage, wood, paper, etc.

Class B: Most flammable substances like petrol, diesel, paint, etc. Class C: Energized electrical machines like pump, transformer, etc. Class D: flammable metals like sodium, potassium, etc. Class K: grease, cooking oil, fats, etc. Q13. Name four parameters you can determine using cone calorimeter. Ans. Following parameters can be determined using cone calorimeter: Ignition time Mass loss Combustion products Heat release rate Q14. Explain what is meant by “ignitability” of a material. Ans.

Ignitability of a material represents ability of a material to catch fire during routine handling.

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