SECTION 2

[Audio] SECTION 2 Basics of Fire and Fire Science.

[Audio] Learning Outcome Physics and chemistry of fire Physics of fire configuration Fire hazards of materials and Products Introduction to Compartment Fire Basics of fire containment Fundamentals of fire growth Theory of fire extinguishment Explosions Duration:1:45.

[Audio] 2-4 Physics and Chemistry of Fire Temperature Units Celsius. A Celsius (or centigrade) degree (°C) is 1/100th of the difference between the temperature of melting ice and boiling water at standard atmospheric pressure (101.3 kPa). On the Celsius scale, zero (0°C) is defined as the melting point of ice, and 100°C as the boiling point of water. The Celsius unit is approved by the International System (SI) of units. Kelvin. A Kelvin degree or Kelvin (K) is the same size as the Celsius degree but the zero on the Kelvin scale is -273.15°C. Zero on the Kelvin scale is the lowest achievable temperature, known as “absolute zero”; thus, the Kelvin scale provides us with so-called absolute temperatures. Fahrenheit. A Fahrenheit degree (°F) is 1/180 of the difference between the temperature of melting ice and boiling water at standard atmospheric pressure (101.3 kPa). On the Fahrenheit scale, the melting point of ice (0°C) is taken as 32°F; thus, 212°F is the boiling point of water (100°C). Rankine. A Rankine degree (°R) is the same size as the Fahrenheit degree, but on the Rankine scale, zero is –459.67°F (–273.15°C).The Rankine scale provides us with absolute temperatures. Fahrenheit and Rankine degrees are not approved SI units.

[Audio] 2-4 Temperature Measurement Liquid Expansion Thermometers These thermometers consist of a tube partially filled with a liquid. The tube measures expansion and contraction of the liquid by changes in temperature. The tube is calibrated to permit reading the level of the liquid in degrees of a temperature scale. The most common example is the mercury-in-glass thermometer. Bimetallic Thermometers Bimetallic thermometers are made from strips of two metals that have different coefficients of expansion. They are laminated together so that, as the temperature changes, the strip deflects because the metals expand or contract to different extents. The amount of deflection is measured on a scale that is calibrated in degrees of temperature. Thermocouples Thermocouples consist of a pair of wires of different metals or alloys welded together at a point to form a junction. A voltage is generated across this junction, the magnitude of which depends on the nature of the metals and the temperature. Pyrometers Pyrometers measure the intensity of radiation from a hot object. Because intensity of radiation depends on temperature, pyrometers can be calibrated to give readings in degrees of temperature..

[Audio] 2-4 Heat Units Joule (J). the joule is defined as the energy(or work) expended when unit force (1 newton) moves a body through unit distance (1 m). The joule (J) is an approved SI unit. Watt (W). The watt is a measure of power or the rate of energy release (or consumption). One watt is equal to 1 joule per second (1 W = 1 J/sec) Calorie. One calorie is the amount of heat required to increase the temperature of 1 g of water by 1°C (measured at 59°F [15°C]). One calorie is equivalent to 4.183 J. British Thermal Unit (Btu). The amount of heat required to raise the temperature of 1 lb of water by 1°F (measured at 60°F [15.5°C]) is called the British thermal unit. One Btu equals 1054 J (252 calories) or 1.054 kJ. Btu and calories are not approved SI units..

[Audio] 2-5 Specific Heat the amount of heat it absorbs as its temperature increases. It is expressed as the amount of thermal energy required to raise unit mass of a substance by 1 degree, and its units are J/kg·K. Water has a specific heat of 4200 J/kg·K Specific heats vary over a considerable range from 460 J/kg·K for steel to 2400 J/kg·K for oak. Latent Heat A substance absorbs heat when it is converted from a solid to a liquid or from a liquid to a gas. This thermal energy is called latent heat. Heat of Gasification. heat of gasification is used to describe the amount of energy that is required to produce unit mass of flammable vapor from a combustible solid that is initially at ambient temperature. Density. The density of a substance is the ratio of its mass to volume (expressed as g/cm3 or kg/m3). Specific Gravity. Specific gravity is the ratio of the mass of a solid or liquid substance to the mass of an equal volume of water. (At 15°C, the mass of 1 cm3 of water is 1 g.).

[Audio] 2-5 Gas Specific Gravity. Gas specific gravity is the ratio of the mass of a gas to the mass of an equal volume of dry air at then same temperature and pressure. Buoyancy. Buoyancy is the upward force exerted on a body or volume of fluid by the ambient fluid surrounding it. If the volume of a gas has positive buoyancy, then it is lighter than the surrounding gas and will tend to rise. If it has negative buoyancy, it is heavier and will tend to sink. (2-6) Conduction: Heat transfer through a solid (e.g., from a heated surface to the interior of the solid) is the process called conduction Convection : Convection involves the transfer of heat by a circulating fluid either a gas or a liquid. Radiation : Thermal radiation is a form of energy that travels across a space without the need for an intervening medium, such as a solid or a fluid. It travels as electromagnetic waves in straight lines, be having similarly to light, radio waves, and X-rays. Heat Transfer Mechanisms.

[Audio] 2-13 FLAME STRUCTURE The following are the two types of flame that we have to consider: 1. The premixed flame in which fuel and air are intimately mixed before ignition. 2. The diffusion flame in which fuel and air are initially separate and burn in the region in which they mix..

[Audio] 2-14 FIRE CHEMISTRY Atom - Atoms are the building blocks of chemistry. They form the basis of all matter with which we are familiar. Each atom has a dense, positively charged nucleus, or core, which contains protons (positively charged) and neutrons (no charge), and around which negatively charged electrons swarm in a regularly structured pattern. Atomic Number of an Element- The atomic number is the number of protons in the nucleus of the atom of an element. Atomic Weight of an Element- The atomic weight of an element is proportional to the weight of its atom. Isotope- Atoms that contain the same number of protons but different numbers of neutrons are called isotopes. Most elements have more than one isotope (e.g., C-12 and C-13 contain six protons, but they have six and seven neutrons, respectively). Molecule- Molecules are groups of atoms combined in fixed proportions Chemical Formula -A chemical formula represents the number of atoms of the various elements in a molecule. For example, water is H2O (two atoms of hydrogen and one of oxygen) Mole - A mole of an element or compound is the amount that corresponds to the gram molecular weight Chemical Reaction. A chemical reaction is a process by which reactants are converted into products C3H8( Propane ) + 5O2( Oxidation ) = 3CO2 + 4H2O Stoichiometric/Stoichiometry. A stoichiometric mixture of fuel and air is one in which there is an exact equivalence of fuel and oxygen (in the air) so that after combustion all fuel has been consumed and no oxygen is left. Heat of Reaction. The heat of a chemical reaction is the energy that is absorbed or released when that reaction takes place. Exothermic reactions release energy when they occur whereas energy is absorbed when an endothermic reaction takes place. Combustion reactions are exothermic.

[Audio] . [image] TABLE 2.1.3 Periodic Table Period 1 period 3 Li Be 6.94 9.01 He IIIA IVA VA VIA VII A '37.33 18044 tQ_22 tgs.og igegy 200 20138 2072 138.91 140.12 14091 144.24 (145) 150.4 151,m 157.25 15893 162. 164.93 16T26 16893 173.cg 17497.

[Audio] 2-15. [image]. 2-15. 11.

[Audio] 2-21 Physics of Fire Configuration FLAMMABLE GAS JETS AND LIQUID SPRAYS Accidental leakage of gases and liquids pressurized in pipes or hoses can lead to gas jets or atomized liquid sprays that are easily ignited to form large, turbulent flames.¹ Such an accident scenario is a serious concern in many industries and has even resulted from natural gas leaks with domestic appliances. 1. POOLS OR HORIZONTAL, UPWARD-FACING SURFACES ( 2-22) a. Flammable Liquid Fires. Liquid fuels from accidental leaks in tanks or piping generally flow to the lowest accessible surface. Such liquids are often contained by dikes, dams, or other obstructions (e.g., compartment walls) so that a pool is formed. Burning, if not already established in the liquid near the leakage origin, may then be initiated, depending on the presence of an ignition source and the flammability of the liquid. The resulting liquid pool fire has flames that pulsate by shedding roughly symmetrical ring vortices.

[Audio] 2-23 b. Fires on Solid Surfaces. Solid, upward-facing combustible surfaces, such as floors or carpeting, can produce pool fire flames similar to those from a liquid, once flaming has been established on the surface 2. WALLS OR VERTICAL SURFACES Fires established on vertical combustible surfaces are especially dangerous because of the potential for rapid upward fire spread. 3. CEILING OR HORIZONTAL, DOWNWARD-FACING SURFACES (2-24) a. Flames from Fire Plume Below Unobstructed Combustible Ceiling b. Ignition at Surface of Combustible Ceiling Ceiling or horizontal, downward-facing, surface fires are characterized by thick, moving cellular flames 2.

[Audio] 2-32 Fire Hazards of Materials & Products Smoldering is a slow, exothermic surface reaction. Smoldering is usually characterized by glowing, or incandescence, and smoke production (NFPA 921). There is no flaming. Since smoldering is a surface effect it is strongly dependent on environmental conditions in addition to the properties of the fuel and the availability of oxygen Pyrolysis is the chemical decomposition of a material into one or more other substances due to heat alone (NFPA 921) the ignition energy of a material is the quantity of heat energy per unit exposed surface area that must be absorbed by the material in order to pyrolyze, ignite, and burn(2-34) The thermal inertia of a material is the direct product of three physical properties: thermal conductivity (k), density (ρ), and heat capacity (C )- (2-34).

[Audio] 2-36 HRR( Heat Release Rate ) Heat release rate is probably the most important quantity used to characterize the flammability hazard represented by a given material. It is a measure of the rate at which a burning item releases chemical energy and is usually expressed as heat released per unit exposed surface area of a burning material or specimen (i.e., kW/m2). HRR TEST METHODS Laboratory-Scale Calorimeters 1. OSU Apparatus (2-38) 2. Fire Propagation Apparatus(2-38) 3. Cone Calorimeter(2-38) Large-Scale Calorimeters (2-40) 1. Room-Corner Fire Test for Surface Linings 2. Furniture Calorimeters 3. ICAL..

[Audio] 2-42 FLAME SPREAD TEST METHODS Tunnel Test Radiant Panel Test LIFT Apparatus Radiant Panel Flooring Test Vertical Burn Test Parallel Panel Test Large-Scale Corner, Room and Façade Tests SMOKE YIELD (2-44) Smoke has long been identified as the most significant hazard to people during fire.79 Smoke and the toxic gases contained in it are the primary cause of fatalities in fires. Smoke can also impair visibility and prevent escape from threatened areas SMOKE YIELD TEST METHODS 1. Smoke Chamber Test.

[Audio] 2-50 Introduction to Compartment Fires FIRE GROWTH The fuel available for fire growth and spread can be characterized in two ways: (1) the rate at which it burns and releases energy into the compartment environment and (2) the total energy available that could be released from the fuel CLASSIFICATIONS OF FIRE (2-51) Fires have been characterized in four general ways: (1) type of combustion process (2) growth rate (3) ventilation (4) fire stage. Classification by Type of Combustion Process (2-51) (1) precombustion (2) smoldering combustion (3) flaming combustion..

[Audio] Precombustion is the process of heating fuels to their ignition point, during which time vapors and particulates are released from the fuel. Smoldering is defined as glowing combustion on the fuel surface and may or may not be related in any way to the oxygen content in the vicinity of the smoldering process. What is implied here is that the fuel vapor production rate and temperatures involved may not be sufficient to support flaming combustion. Flaming combustion is almost self-explanatory in that the production of sufficient energy and a fuel vapor mixture with air in a flammable range is the condition that underlies and supports the presence of flame. Classification by Rate of Growth Fires may also be classified on the basis of growth rate. Fire growth can be either positive (increasing growth rate) or negative (decreasing growth rate). Classification on the Basis of Ventilation (2-52) When a fire is burning in the open, or is in the early stages of development within a compartment where there is excess air for combustion, the fire is said to be fuel-controlled. In a compartment fire with sufficient fuel available, the window or door openings may ultimately serve to control the amount of air available for combustion within the compartment. Once the fire develops to a point where it produces more fuel vapors than can be consumed in the compartment with the available air, it is considered to be a ventilation-controlled fire. 2-51.

[Audio] 2-52 Classification by Fire Stage Incipient fire refers to that stage when there is smoldering but insufficient flaming for established burning. Fire growth The fire growth stage represents increasing fire growth with respect to heat release over time. During this stage the fire would be considered fuel controlled. Steady state When the heat release rate is basically constant the fire is considered to be in the steady-state stage. Here the heat release rate may be controlled by the fuel package size and geometry (i.e., the surface area available to burn) or by the available ventilation to support combustion (i.e., a ventilation controlled fire). Fire decay the fire decay stage, the heat release rate is decreasing over time. This may be due to consumption of fuel in a fuel-controlled fire or continued oxygen depletion in a ventilation-controlled scenario.

[Audio] Fire in the Open Within the flame region, upward gas velocity on the plume centerline will increase from near zero at the base of the flames (the lowest fuel elevation actively burning) up to maximum value at about half the flame height, remaining at that value up to the flame tip, before decreasing with height in the plume, as noted. When the temperature at the plume centerline reaches the temperature of the surrounding air, the gases and smoke stop rising and begins to spread out horizontally, since there is no longer a buoyant force causing the gas to rise vertically. This situation can either represent a fire outdoors, a fire in a compartment with a high ceiling or an atrium..

[Audio] 2-53 Fire Under an Unobstructed Ceiling When a ceiling is located above a fire plume, the rising hot gases and combustion products impinge on the ceiling and begin to flow radially outward away from the plume centerline. On a smooth, flat (nonsloping) ceiling, this flow would ideally be equal in all directions. The radially outward flow due to fire plume impingement is defined as a ceiling jet.

[Audio] 2-54 Fire in a Compartment. [image]. Fire in a Compartment.

[Audio] 2-61 Basics of Fire Containment Flashover is a transition phase in the development of a compartment fire in which surfaces exposed to thermal radiation reach ignition temperature more or less simultaneously and fire spreads rapidly throughout the space, resulting in full room involvement or total involvement of the compartment or enclosed space. FIRE RESISTANCE The time, in minutes or hours, that materials or assemblies have withstood a fire exposure as determined by the tests, or methods. End-point criteria for separating non-load-bearing assemblies in fire resistance furnace tests are, therefore, based on heat transmission and integrity. Heat transmission is measured with thermocouples attached to the unexposed side of the assembly. The end-point criteria for heat transmission are exceeded when the temperature rise of the thermocouples, either on average or individually, reaches a specified limit. The integrity of an assembly is maintained as long as there is no passage of flames and gases hot enough to ignite cotton waste on the unexposed side..

[Audio] 2-76 Fundamentals of Fire Detection FIRE SIGNATURES Aerosol Signatures The process of combustion produces very large numbers of solid and liquid particles, ranging in size from 5 × 10–4 to 10 microns (μm). These particles, suspended in air, are called aerosols. Aerosols resulting from fire actually represent two different fire signatures: invisible and visible. Particles less than 0.3 μm do not scatter light efficiently and are therefore classified as invisible. The larger particles do scatter light and are classified as visible aerosols Invisible aerosols can be detected through air sampling systems such as VESDA (very early smoke detection apparatus) or incipient fire detection systems. Larger smoke aerosols can be detected by light-scattering, photoelectric or ionization detectors. Radiative Energy Release Signatures Ultraviolet (0.10–0.35 μm) Visible (0.35–0.75 μm) Infrared (0.75–22.00 μm) Convective Energy Release Signatures Convective energy from a fire rises toward the ceiling, resulting in increased air temperature at ceiling-mounted heat detectors. The response time for heat detectors depends on the heat release rate of the fire, the distance between the fire and the ceiling, and the thermal response characteristics and exact location of the detector..

[Audio] 2-80 Theory of Fire Extinguishment The term combustion usually refers to an exothermic, or heat producing, chemical reaction between some substance and oxygen. A flame is a gaseous oxidation reaction that (1) occurs in a region of space much hotter than its surroundings and (2) generally emits light Vaporization can occur with or without chemical decomposition of the molecules. If chemical decomposition occurs, the process is called pyrolysis. EXTINGUISHMENT WITH WATER (2-82) Water has a very high heat of vaporization per unit mass, at least four times higher than that of any other nonflammable liquid. In practical fire fighting, water must be applied at 10 to 100 times the rates used in the research described above because of the difficulty of delivering the water directly to the burning surface. EXTINGUISHMENT WITH AQUEOUS FOAMS (2-85) Foam breaks down and vaporizes its water content when under attack by heat and flame. Therefore, it must be applied to a burning surface in sufficient volume and rate to compensate for this loss and to provide an additional amount to guarantee a residual foam layer over the extinguished portion of the burning liquid..

[Audio] 2-85 EXTINGUISHMENT WITH WATER MIST Water Mist Effectiveness (2-86) the effectiveness of a fine mist depends on (1) The momentum and direction of the spray relative to the fire (2) droplet size (3) the compartment geometry and size and the size and location of openings Application mechanism Four mechanisms by which water mist application might extinguish a flame are as follows 1. Removal of heat by evaporation 2. Oxygen displacement by generating the steam 3. Blocking radiant heat transfer 4. overall cooling and dilution.

[Audio] 2-86 EXTINGUISHMENT WITH INERT GASES Carbon dioxide is the most commonly used inert gas. inert gases act to extinguish a fire primarily by dilution Forms of Carbon Dioxide (2-87) Carbon dioxide is the most commonly used inert gas. The solid form of carbon dioxide, commonly known as dry ice, at atmospheric pressure, exists only below –110°F (–79°C), at which temperature it undergoes sublimation directly to vapor, without melting. However, liquid carbon dioxide can exist at elevated pressures, as long as the temperature is above –71°F (–57°C) and the pressure is above 5.2 atm. This temperature and pressure condition is known as the triple point of carbon dioxide because it is the only condition at which solid, liquid, and vapor can coexist. vapor can coexist. Liquid carbon dioxide can be kept in a pressure vessel at any temperature between –71°F (–57°C) and 88°F (31°C) (the critical temperature)..

[Audio] 2-88 EXTINGUISHMENT WITH HALOCARBON AGENTS Halocarbon agent extinguishing systems are a relatively recent innovation in fire protection, but despite this, the first generation of these agents no longer can be produced as of January 1, 1994, by international agreement due to the effect of these first generation agents on depletion of the earth’s ozone layer. As a result, a new generation of halocarbon agents has been developed that not only is compatible with the ozone layer but also less likely to be involved in global warming. It can be used on electrical fires, in cases where water or dry chemicals would cause damage, or for inert gas flooding of compartments. Halogenated agents have the following two principal advantages over carbon dioxide: 1. Certain halogenated agents are effective in low volumetric concentrations such that sufficient oxygen remains in the air after compartment flooding for comfortable breathing. 2. For several halogenated agents, only partial vaporization occurs initially during flow from a nozzle, allowing the liquid to be projected farther than carbon dioxide Halon 1301 (bromotrifluoromethane) was by far the most commonly used in fire protection because it has the lowest toxicity as well as the highest effectiveness on a weight basis, including the highest volatility, which is desirable for flooding applications If a halocarbon liquid was needed for direct application to a burning surface to accomplish cooling as well as inerting of the nearby region, however, a less volatile compound, such as Halon 1211 ( bromochloro-difluoromethane) or Halon 2402 (dibromotetrafluoroethane), was the first-generation agent preferred..

[Audio] 2-90 EXTINGUISHMENT WITH DRY CHEMICAL AGENTS Monoammonium Phosphate effective against deep-seated fires because of a glassy phosphoric acid coating that forms over the combustible surface. phosphoric acid, a product of decomposed mono-ammonium phosphate, has such a strong affinity for water that an exceedingly dry atmosphere would be needed to stop corrosion. mono-ammonium phosphate is acidic and corrodes more readily than other dry chemical agents. Application of mono-ammonium phosphate can damage delicate electrical equipment. kitchen fires involving hot cooking oil, mono-ammonium phosphate is not recommended because it does not create a foam layer (saponification) on the surface of the oil. An alkaline dry chemical, such as sodium bicarbonate, is preferred..

[Audio] 2-91 SPECIAL CASES OF EXTINGUISHMENT Metal Fires Water is usually the wrong agent for fires involving metals because a number of metals can react exothermically with water to form hydrogen, which, of course, burns rapidly. Furthermore, violent steam explosions can result if water enters molten metal. certain metals react exothermically with nitrogen; therefore, the only acceptable inert gases for these metals are helium and argon. Halocarbons should not be used on metal fires..

[Audio] 2-95 Explosions Blast Waves Pressure disturbances propagating into the atmosphere away from the energy release region are called blast waves A detonation is an explosion in which the flame propagates at supersonic speeds. flames in a deflagration propagate at speeds well below the speed of sound. Combustible Dust Deflagrations(2-100) Clouds of combustible dust in an enclosure also produce deflagrations when they are ignited while the dust concentration is greater than the minimum explosive concentration (MEC) for a particular material. Chemical Reaction Explosions . Can occur in two ways, firstly , they can produce gaseous reaction products that can over pressurize vessels that are not equipped with an adequate relief vent area . Secondly exothermic reactions can generate sufficient heat to increase rapidly the pressure of the existing gases and vapors in the vessel(2-102) Steam Explosions: Melt-Water Explosive Interactions(2-103) A steam explosion is a physical explosion caused by the extremely rapid vaporization of water due to heat transfer from a second liquid that is at a temperature far in excess of the water boiling point and in direct contact with the water. As the second liquid is usually either molten metal or some other melt, a steam explosion is a violent melt-water interaction..

[Audio] Summary This section discusses on very essential topics in relation with fire system to make effective understanding on other sections. It is very important on understanding the fundamentals of chemistry and physics prior to read the content in depth. Heat is one of the main factors when fire happens, therefore section describes on temperature units, several of heat measurement technologies, heat units, heat absorption and heat of gasification etc. other important topics to discuss are heat transfer mechanism. Since fire is a product of the chemical reaction, it is very essential on understanding what happens during the reaction takes place, some of the topics are ( but not limited to ) heat of reaction, chemical reaction, stoichiometry, fire chemistry table. The section describes various terminologies such as combustion, pyrolysis, smoldering, flaming, classification of fire, classification fire stages, flashover, and different signatures of detection system and theory of different extinguishment system..

[Audio] End of the Session Practice Question. End of the Session.