How Can Fire Spread Between Buildings - Assignment Example

1. Give a definition of fire, include an appropriate diagram. Fire is the heat and light energy released during a chemical reaction (in particular, a combustion reaction). Depending on the substances alight, and any impurities outside, the color of the flame and the fire's intensity might vary. Fire in its most common form can result in conflagration, and has the potential to cause physical damage through burning. 2. Identify the different stages of fire growth, include an appropriate diagram. The first stage of fire growth is the smoldering stage. When heat is applied to a combustible material, the heat oxidizes the material’s surface into combustible gases. The oxidation process is exothermic, meaning that the oxidation process itself produces heat. The second stage of fire growth is free or open burning. When the temperature of a fire gets high enough, visible flames can be seen. The visible burning at this stage is still limited to the immediate area of origin. The combustible process continues to release more heat, which heats nearby objects to their ignition temperature, and they begin burning. The third stage of fire growth is called flashover. It is the most significant moment of any structure fire. As combustible gases are produced by the two previous stages they are not wholly consumed. They rise and form a superheated gas layer at the ceiling. As the volume of this gas layer increases, it begins to bank down to the floor, heating all combustible objects regardless of their proximity to the burning object. In a typical structure fire, the gas layer at the ceiling can quickly reach temperatures of 1500 degrees Fahrenheit. 3. Explain the difference between pre-mixed and diffusion flames, and provide some practical examples of each. A premixed flame is a flame in which the oxidizer has been mixed with the fuel before it reaches the flame front. This creates a thin flame front as all of the reactants are readily available. If the mixture is rich, a diffusion flame will generally be found further downstream. Diffusion flames, smoothly flowing (laminar) or turbulent, belong to the class of flames whose ingredients are not mixed prior to entering the burning zone. Molecular or turbulent diffusion is responsible for the mixing of the gases in such flames. The distribution of the combustible material and of oxygen over various flame cross sections is regular in laminar flames. 4. What are the 5 functional requirements of Approved Document B? Requirements Means of warning and escape B1. The building shall be designed and constructed so that there are appropriate provisions for the early warning of fire, and appropriate means of escape in case of fire from the building to a place of safety outside the building capable of being safely and effectively used at all material times. Internal fire spread (linings) B2. (1) To inhibit the spread of fire within the building the internal linings shall: (a) adequately resist the spread of flame over their surfaces; and (b) have, if ignited, a rate of heat release or a rate of fire growth, which is reasonable in the circumstances. (2) In this paragraph 'internal linings' mean the materials or products used in lining any partition, wall, ceiling or other internal structure.  Internal fire spread (structure) B3. (1) The building shall be designed and constructed so that, in the event of fire, its stability will be maintained for a reasonable period. (2) A wall common to two or more buildings shall be designed and constructed so that it adequately resists the spread of fire between those buildings. For the purposes of this sub-paragraph a house in a terrace and a semi-detached house are each to be treated as a separate building. (3) Where reasonably necessary to inhibit the spread of fire within the building, measures shall be taken, to an extent appropriate to the size and intended use of the building, comprising either or both of the following: (a) sub-division of the building with fire-resisting construction; (b) installation of suitable automatic fire suppression systems. (4) The building shall be designed and constructed so that the unseen spread of fire and smoke within concealed spaces in its structure and fabric is inhibited. External fire spread B4. (1) The external walls of the building shall adequately resist the spread of fire over the walls and from one building to another, having regard to the height, use and position of the building. (2) The roof of the building shall adequately resist the spread of fire over the roof and from one building to another, having regard to the use and position of the building. Access and facilities for the fire service B5. (1) The building shall be designed and constructed so as to provide reasonable facilities to assist firefighters in the protection of life. (2) Reasonable provision shall be made within the site of the building to enable fire appliances to gain access to the building.  5. There are two broad standards for the design methods of fire resistance of buildings: prescriptive and performance-based. Explain the difference between them. A prescriptive method defines a structural fire design fairly precisely in terms of the materials used, shape and size of structural elements, thickness of fire protection materials and construction details etc. Traditionally, the design recommendations are mainly based on the experience with identical or similar standard fire tests. This concept works very well in a static situation but inhibits innovation and development of construction industry. It can become very restrictive in situations where designs need to evolve to meet architectural or aesthetic requirements. For these reasons, the prescriptive designs have been evolving for many years towards the performance-based designs. A performance-based method for structural fire design is analogous to the process of designing structures to wind loads and seismic effects. The function of a structural element will be defined and a set of objective tests will be given that allows the evaluation of fire performance in relation to the key functional criteria: Is it strong enough to sustain the working load? Does it last long enough before it collapses or causes the collapse of structural components connected to it? 6. What are the two categories of fire testing? Explain the difference between them. Fire testing generally falls into two categories: 1. Tests to measure ignition and the spread of flames from one area to another, and 2. Tests to measure fire resistance. Fire resistance tests measure a material's ability to continue to serve its structural role during a fire. 7. Why is it important to carry out more than one experiment to test the same parameter? Various test methods have its own parameters to test fire and highlight the highly scalable results based on its testing. By doing more than one test with same parameter will help us to choose the best way to test the fire. More than one fire test leads us to have more choices to choose the best way of testing fire with the given situation. 8. What factors influence the severity of a fire within a compartment? A compartment fire is defined as the fire resulting from the ignition of a fuel contained within an enclosure, normally as a result of a liquid fuel spill or solid fuel spread on the floor of the compartment, which is ventilated through wall openings. The growth of these fires occurs in two phases, namely pre-flashover during which only the original fuel is burning and the fire is localized close to the primary fuel source, and post-flashover, during which all combustible items within the enclosure are engulfed in flames, and the fire is thought to be fully developed. 9. How is heat transferred in a compartment fire? Include a diagram. Heat transfer models most often used in fire engineering practice to predict the temperature of structural elements exposed to fires in compartments adopt a radiation component which assumes that the fire is separated from the surrounding surfaces by perfectly transparent media. As a result the predicted temperatures usually differ significantly from the measured values. 10. Explain the term “flammability limits”. Flammability is the ease with which a substance will ignite, causing fire or combustion. The degree of difficulty required to cause the combustion of a substance is subject to quantification through fire testing. (chemistry) A measure of the extent to which a material will support combustion 11. Draw a graph/ diagram to illustrate the flammability limits of flammable vapours. 12. Define the term “limiting oxygen index”. A numerical index, the ‘LOI’, is defined as the minimum concentration of oxygen in an oxygen – nitrogen mixture, required to just support downward burning of a vertically mounted test specimen. The Limiting Oxygen Index (LOI) test is a widely used research and quality control tool for determining the relative flammability of polymeric materials. 13. What does it mean if a sample has a high LOI or a low LOI? Higher LOI values represent better flame reentrancy. The test method is generally reproducible to an accuracy of + 0.5% and although originally designed for testing of plastics, the method has been used extensively for evaluating the relative flammability of rubbers, textiles, paper, coatings and other materials. LOI values of different materials Polyethylene (PE) 17,5 % Crosslinked PE (XLPE) 19,0 % Polypropylene (PP)       17,5 % Nylon™    20 % Soft PVC 24-35 % Rigid PVC    40-45 % Teflon™     95 % Flamastic KBS COATING™    100 % Flamastic KBS SEALANT™ 100 % 14. Explain the ignitability test? In the harmonization of the European test codes in the context of preventive fire-protection techniques for buildings, this test is to be adopted as a European test method. This method is used to evaluate the fire behaviour of a building material subjected to an impingement by a small flame, e.g. the flame of a match. 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 modern device used to study the fire behavior of small samples of various materials in condensed phase. It is widely used in the field of Fire Safety Engineering It gathers data regarding the ignition time, mass loss, combustion products, heat release rate and other parameters associated with its burning properties. Device usually allows the fuel sample to be exposed to different heat fluxes over its surface. The principle for the measurement of the heat release rate is based on the Huggett's principle that the gross heat of combustion of any organic material is directly related to the amount of oxygen required for combustion. This instrument is equipped with additional facilities thereby providing detailed information about ignition behaviour, mass loss, and generation of smoke and toxic gases, during sustained combustion of the test specimen. 16. What are the criteria for when flashover will occur? The criteria for when flashover will occur: reading the fire situation and having an attack plan (with alternatives) having adequate resources available and ready before initial attack recognizing the tell-tale signs that "announce" the possibility of a forthcoming flashover having charged hoselines with adequate pressure and flow capacity wearing reasonably clean bunker gear and adequate SCBA knowing when, where, and how to dilute the fire gases and reduce temperatures inside the confined space 17. Once ignition has occurred what is required to maintain combustion? Once ignition has occurred there are two factors which dictate whether combustion takes place. That is for the system to be transformed from a stable mixture to a rapidly reacting combustion process. The first is that there should be sufficient energy to allow initiation of the reaction. This may be supplied by any of a number of methods: electrical spark, heat addition, radical addition. Second is the propensity of a system to burn is dependent on many factors: fuel type, calorific value, mixture, pressure, velocity, turbulence, enclosure geometry. 18. What are the basic two types of uncertainty found in measurements? Give an example of each. The two major types of uncertainty that are found in measurements are (1) Model uncertainty, which arises when the emission and/or removal estimation models used in developing the inventory estimates do not fully and accurately characterize the respective emission and/or removal processes (due to a lack of technical details or other resources), resulting in the use of incorrect or incomplete estimation methodologies and (2) Parameter uncertainty, which arises due to a lack of precise input data such as emission factors and activity data. 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 Mean = 43.545 Median= 43.67 Standard deviation = 1.16779 Uncertainty in mean = +/- 0.001 Uncertainty in standard deviation = +/- 0.00001 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 21. What are the four main classes of ignition? Four main classes of ignition: 1. Natural Phenomena(e.g. Lightning) 2. Human Carelessness (e.g. Smoking materials, matches, cooking) 3. Technological failure (e.g. electrical wiring and appliance faults) 4. deliberate fire raising (e.g. suicide, vandalism) 22. In relation to the characteristics of building materials give definitions for the following terms: • Combustibility, Able or likely to catch fire and burn. Able to react vigorously with oxygen to produce heat and light, seen as flame. A substance or material that is able or likely to catch fire and burn • Fire propagation, To move or transmit fire forward through a medium such as air. • Fire resistance, The property of acting as a barrier to fire. Acoustical ceiling systems form a membrane to contain fire within a room. The ability of a building component to act as a barrier to the spread of fire and confine it to the area of origin. • Surface spread of flame When a flame spreads across a liquid surface confined by a parallel sided channel it achieves a steady rate of spread. When the liquid’s initial temperature is less than its closed flash point this rate of spread is controlled by the preheating of the liquid ahead of the flame. 23. Explain what the two major mechanisms of burning are. Combustion or burning is a complex sequence of exothermic chemical reactions between a fuel and an oxidant accompanied by the production of heat or both heat and light in the form of either a glow or flames. Permanently damaging a metal or alloy by heating to cause either incipient melting or intergranular oxidation. See also over-heating. Heating a Material beyond Allowable Temperature Limits. This Causes Melting Or Intergranular Oxidation. It May Appear As Brown Or Blue Marks On The Metal. 24. How can fire spread between buildings? Once a fire had reached very large proportions involving say, a whole city block, the level of radiation issuing from it was so great that materials 100 m (300 ft) away could be ignited. At this stage, containment of the fire might no longer be possible. The most important reason why such catastrophes are now less frequent is probably the general adoption of the rule that any fire should be contained within the building of origin by the use of fire-resistant building components, by spatial separation, and by firefighting. Design recommendations concerning spatial separation generally involve the assumption that firefighting will reduce the risk of ignition of adjacent buildings, both by wetting them down and by playing water on the primary fire, and thus reducing the fire's level of thermal radiation. Fire-resistant construction is sometimes adequate, but often firefighting is essential if a fire is to be contained by the construction. 25. Define the term “fire plume”. Identify and explain the different regions within a fire plume. The fire plume is the single most important object of study in fire science. It provides the radiant energy source that generates the gasified fuel from the condensed phase needed to sustain the fire. It also serves as the heat pump which both entrains air into the active combustion zone and then circulates the combustion products through the surrounding enclosure. The central role of the fire plume has been recognized for some time, there are still some uncertainties about the plume structure. Read More