Presentation on theme: "Natural Resources 350.01 Introduction to Wildland Fire Management Winter Quarter 2005."— Presentation transcript:
Natural Resources 350.01 Introduction to Wildland Fire Management Winter Quarter 2005
Natural Resources 350.01—Introduction to Wildland Fire Management (Lecture) Course Syllabus Course ObjectivesThe student will gain an understanding of fire behavior, the factors affecting this behavior, fire safety, effective control of wildland fires, and how to use prescribed fire in wildfire management and other ecosystem objectives. This course will meet the requirements and standards prescribed for courses developed under the interagency curriculum established and coordinated by the National Wildfire Coordinating Group, specifically courses designated as S-100 (Fire Management) and S-190 (Wildland Fire Behavior). Credit Hours3 U Pre-requisites:None InstructorsDr. Roger A. Williams Associate Professor, Forest Ecosystem Analysis and Management 320-C Kottman Hall Phone: 614-688-4061 Email: firstname.lastname@example.org Mike Bowden Administrator, Ohio Fire Protection Program Coordinator, Rural Fire and Training ODNR, Division of Forestry Phone: 614-265-1088 Email: Michael.Bowden@dnr.state.oh.us Meeting Tuesday, 6:30pm—9:30pm; Kottman Hall 245 Time/Place TextbooksCourse material will be provided by instructors at a minimal cost. Reading assignments may be given during the course
Course Quizzes— 40% EvaluationExam 1— 30% And GradingExam 2— 30% Total—100% Grading Scale: NumericalLetterNumericLetter Grade GradeGradeGrade 100- 93A79 - 77C + 92 - 90A -76 - 73C 89 - 87B +72 - 70C - 86 - 83B69 - 67D + 82 - 80B -66 - 60D 59 - 0E A quiz will be given at the beginning of each lecture period that covers material presented during the previous class. Two exams will be administered in the course, with the first exam covering topics covered during the first half of the course, and the second exam covering topics covered during the second half of the course. AcademicThe following offenses will result in charges of academic misconduct with the appropriate action taken in Misconductresponse: 1. The submission of plagiarized work to meet academic requirements including the representation of another's works or ideas as one's own; the unacknowledged work for use and/or the paraphrasing of another's work; the inappropriate unacknowledged use of another person's ideas; or the falsification, fabrication, or dishonesty in reporting results of any research or findings. 2. Any form of cheating on exams or other class work. Disabilities Statement: Any student who feels s/he may need an accommodation based on the impact of a disability should contact me privately to discuss your specific needs so that necessary arrangements can be made. This syllabus and course materials are available in alternative formats upon request. Also, you may contact the Office for Disability Services at 614-292-3307 in room 150 Pomerene Hall to coordinate reasonable accommodations. The website for the Office for Disability Services is- http://www.ods.ohio-state.edu
Course Outline—Natural Resources 350.01 (Lecture) January 4: 1.Introduction 2.Fundamentals of Wildland Fire a.Combustion Process Overview b.Intrinsic Fuel Properties c.Heat and Heat Transfer d.Four Phases of Combustion e.Fuel Consumption f.Products of Combustion January 11: 1.Fire Behavior a.The Fire Environment b.Fire Growth c.Fire Spread and Intensity d.Extreme Fire Behavior e.Predicting Fire Behavior January 18: 1.Wildland Fuels a.Fuel Change over Time b.Fuel Description and Properties c.Fuel Classification d.Fuel Moisture January 25: 1.Fire Weather a.Basic Weather Concepts and Processes b.Atmospheric Stability c.Winds- General, Local, and Topographic Effects d.Fire Climate and Fire Season February 1: 1.Exam 1 2.Fire Ecology a.Fire History and Fire Regimes b.Adaptations of Plants to Fire c.Effects of Fire on Vegetation, Wildlife, Soil, and Water Resources d.Fire and Ecosystems- Dynamics, Landscape Scales and Patterns, Biodiversity February 8: 1.Fire and Culture a.Fire History- Practices, Management, Conservation b.Creating a National System of Fire Management- Frontier, Backcountry, Mass, Wilderness, and Intermix Fires 2.Administration of Fire Regimes a.Purpose of Fire Management- Strategic, Historical, Political, Administrative Political, Economic, Legal, and Cultural Considerations b.Structure of Fire Management in the U.S.
February 15: 1.Programs for Fire Management a.Fire Prevention b.Fire Detection c.Fire Information and Communication Systems d.Fuel Management e.Fire Economics f.Fire Research g.Planning for Fire Management February 22: 1.Fire Suppression a.Suppression Strategies b.Suppression Resources c.Organizing for Fire Suppression d.Suppression Tactics e.Postfire Activities f.Fireline Safety March 1: 1.Prescribed Fire a.Why Prescribed Fire- Evaluating Forest Conditions and Objectives b.Prescribed Fire in the Context of Natural Fire Regimes c.Prescribed Fire Planning d.Prescribed Fire Weather e.Prescribed Fire Operations- Preburn Preparations, Personnel, Firing Operations and Methods, Methods of Control, Monitoring and Evaluating f.Smoke Management March 8: 1.Course Summary 2.Exam 2
Fundamentals of Wildland Fire Combustion Process Overview
When there is not enough heat generated to sustain the process, when the fuel is exhausted, removed, or isolated, or when the oxygen supply is limited, then a side of the triangle is broken and the fire is suppressed. The Fire Triangle Fire requires the 3 elements displayed in the illustration to the right, often referred to as the Fire Triangle. The underlying theme is that wildland fire personnel seek to manage one or more of the three elements in order to suppress an unwanted fire or guide a prescribed fire.
Plant material burned in a wildland fire is produced by the process of photosynthesis: CO 2 + H 2 O + solar energy (C 6 H 10 O 5 ) n + O Both decay and fire reverse this process. Decay is a slow process with a barely noticeable release of heat over a long period of time. Fire, on the other hand, is a rapid release of the heat energy stored by photosynthesis. When vegetation is burned, the chemical energy is transformed to thermal energy, radiant energy, and the kinetic energy in the rising air in the convection column over the fire. This reversal process is known as combustion: (C 6 H 10 O 5 ) n + O + ignition temperature CO 2 + H 2 0 + heat
Burning begins with endothermic reactions that absorb energy and ends with exothermic reactions that release energy. Endothermic reactions are known as preignition. Exothermic reactions are known as combustion. The point of transition is known as ignition
During the preignition phase, the fuel is brought to ignition temperature. Usually there is a pilot source of ignition, but spontaneous ignition is also possible. Initial effect of increasing temperature on fuel is a dehydration process– free and absorbed water in the fuel is driven off. This heat also causes volatilization of waxes, oils and other compounds. At higher temperatures pyrolysis (thermal degradation of the fuel) occurs– long polymeric molecules are broken down to lower molecular weight gases and semi-volatile tar and solid char. The volatile products are involved in flaming combustion, while char may oxidize (burn) by glowing combustion. Preignition
As the temperature rises during the preignition phase, free water evaporates and the volatiles are released. This dehydration process removes volatiles by the distillation of water and extractives. Preheating first acts on low- temperature volatiles. Even a warm day is enough to evaporate some extractives, thus the characteristic smell of a forest. Continued preheating works on absorbed water within the fuel particles– its fuel moisture. Absorbed moisture must be driven off before the heating of the fuel itself can begin. More water per unit mass of dry matter requires more heat to vaporize it before the fuel can be ignited. If this process requires too much energy (hence very wet fuels) than what is supplied, ignition does not take place. Preignition
The heated vegetation produces combustible gases as products of pyrolysis and by volatilization of waxes, oils, and other compounds in the vegetation. Pyrolysis is the degradation of cellulose molecules and polymers prior to combustion. Pyrolysis itself means “heat divided”, and dependent upon the ultimate amount of heat applied and the fuel material, a particular pathway of cellulose degradation will occur. Preignition
Preignition (summary) In order for a fire to start energy must first be added in order to bring the fuel up to combustion temperature. Surface water and water within the fuel itself must be driven off before pyrolysis can occur. Pyrolysis is the breakdown of substances in the fuel by heat to release flammable gasses. In plant material, cellulose begins to breakdown at around 250 °C. The initial reaction is endothermic (i.e. it requires an external source of heat) and will merely char the fuel, but once temperatures reach a critical point and the flammable by-products of pyrolysis ignite the heat released will drive a runaway exothermic reaction.
Ignition Ignition is the transition between preignition and combustion, the temperature at which a pilot source of heat is no longer required. Once ignited, the heat generated by combustion brings other fuels to ignition, continuing the cycle.
Ignition Ignition is the transition from preignition to combustion. In all types of combustion, fuel ignition requires that the fuel temperature be raised to some minimum level by the application of heat. If the time the heat is applied is too short, the necessary quantity of heat cannot be supplied, and the fuel will not ignite regardless of the temperature of the heat source.
Ignition Ignition temperature depends upon the stage of pyrolysis at which the fuel is considered to be actually ignited. Charring can begin at relatively low fuel temperatures, and once started can continue by glowing combustion if there is little heat loss. (This is most likely to occur in deep layers of compact, fine dead fuel). The attachment of a flame to a solid particle occurs when the rate of combustible gas generation by the particle is sufficient to maintain a flame. The temperature for flame attachment, or piloted ignition, is around 620 o F for wildland fuels.
Ignition Spreading fire can therefore be considered a series of ignitions: 1.Heat is supplied from the fire to the potential fuel. 2.The surface becomes dehydrated. 3.Further heating raises the surface temperature until the fuel begins to pyrolyse and release combustible gases. 4.When the gas evolution rate from the potential fuel is sufficient to support combustion, the gas is ignited by the flame and the fire advances to a new position. There are obviously many factors that affect this process, in terms of what we refer to as the rate of fire spread, and this will be discussed later in this course.
Ignition by Lightning Whether or not a lightning strike results in ignition depends on the character of the bolt and the character of the material it strikes. During the first few microseconds of a return stroke, the core of the bolt ( 1-inch diameter) is heated to a maximum of about 53,500 o F. Some of the hybrid flashes about this core may be 10,340 – 21,140 o F. The air and subsequent gases are superheated in this column. The woody fuels at the surface are exposed to this column of hot gases for the duration of the flash. Accordingly, the degree of heating of the fuel is a function of the flash duration and independent of the magnitude.
Depending upon duration and characterization of the fuels involved, lightning strikes may produce smoldering combustion or may quickly heat and ignite volatiles to produce flames in a short period of time.
Combustion May or may not involve a flame. Volatiles produced during the preignition phase ignite to form a visible flame. After flaming combustion has burned most of the volatiles, the remaining carbon may burn as a solid by surface oxidation called smoldering or glowing combustion. Flaming Combustion Smoldering / Glowing Combustion
Smoldering ground fires spread slowly, about 1 in./hr. They can raise mineral soil temperatures above 570 o F for several hours with peak temperatures near 1100 o F. Even though these are lower temperatures than what is experienced in flaming combustion, they can still cause death of soil organisms and decompose organic material as a result of the duration of the heat.
Combustion Combustion efficiency varies, and depends upon fuel type, fuel conditions, heat source, temperatures, etc. If combustions is not complete, some of the volatile products will remain suspended as very small droplets of liquid. These, plus residual carbonized particles that float in the air, are smoke. Water vapor from dehydration and combustion may also condense giving smoke its whitish appearance.
Flaming Combustion The size and shape of a flame can be used in describing characteristics of a fire, and useful in predicting its behavior. The severity of a surface fire in terms of its resistance to control can be keyed to flame length, and flame height can be related to the height of the lethal scorching of tree foliage, as well as other potentially predictive behaviors.
If pyrolysis is slow, not much gas is generated and the flames are short and intermittent.
But when large amounts of fuel are burning rapidly, the volume of gas is large and some of that gas must move a considerable distance from the fuel before enough oxygen is available and the mixture becomes flammable. Long and massive flames are produced in this process.
As the temperature of the fuel continues to rise, combustible gases are produced more rapidly and the chemical reactions become more strongly exothermic, reaching a peak of about 600 o F. Although combustible gases are generated at temperatures above 400 o F, they will not flame even when mixed with air until their temperature reaches 800 to 900 o F.
The maximum temperature that can be produced by the burning of gases generated from wildland fuels is believed to be between 3500 and 4000 o F. But this is in the most ideal situations, and it is much more common to find maximum temperature ranges in wildland fuels to be 1300 to 1800 o F. This is still high enough to ignite gases, so once flaming starts, it continues as long as sufficient gas is produced.
Intrinsic Fuel Properties Fundamentals of Wildland Fire
Intrinsic fuel properties are those that delineate the plant parts, including fuel chemistry, density, and heat content. We will examine the physical and chemical properties that are important in a study of the combustion process and of emissions, the products of combustion.
Wildland Fuel Consists of: 1.The cell wall polysaccharides, i. e., cellulose and hemicelluloses, which are readily pyrolized. 2.Lignin, which mainly forms char. 3.Extractives, particularly the terpenoid hydrocarbons. 4.Lipids, which provide a ready source of combustible volatiles. 5.Ash content, which exerts a suppressing effect. 6.Other properties that are intrinsic to the fuel are density, heat content or heat of combustion, and thermal conductivity.
Most plant material consists of polymeric organic compounds. Plant tissue is approximately, by weight: carbon – 50% oxygen – 44% hydrogen – 5% The content of most wood: cellulose: 41– 53% hemicellulose: 15 – 25% lignin: 16 – 33% Lignin content is much higher (up to 65%) in decaying (punky) wood, in which the cell wall polysaccharides are partially removed by biological degradation.
Woody fuels are high in cellulose and lignin, but low in extractives. Green vegetation has a higher extractive content. The chemical diversity found in plant material affects the rate of burning and the amount and type of emissions produced. Cellulose: Principle constituent of all higher plants. Is a condensation polymer of the hexose sugar D-glucose (adopts a linear structure). Provides the structural strength and rigidity of the cell wall Cellulosic materials are a major contributor of combustible volatiles. Hemicelluloses: Carbohydrate polysaccharides with shorter chain lengths than cellulose.
Lignin: The material that gives wood its stiffness. Is an aromatic polymer of wood, consisting of 4 or more phenylpropane monomers per molecule. Since cellulose is degraded more easily than lignin, dead fuels have progressively higher lignin content as they age. If lignin heated to 750-850 o F, only about 50% volatilizes; the balance remains as char residue. Lignin is more stable than the cellulosic or extractive components when heated and produces considerable carbaceous char Char formation is required for glowing combustion.
Extractives: Class of compounds consisting of: Aliphatic and aromatic hydrocarbons Alcohols Aldehydes Gums Sugars Complex mixtures of terpenes, fats, waxes, oils. Although extractives constitute a smaller fraction in fuels than cellulose and lignin, the have special properties. Their high heat of combustion, volatility, and lower limits of flammability in air influence the way fuel burns.
Ether, benzene-ethanol, and oil extracts of some species, such as gallberry, saw palmetto, and wax myrtle, can make very explosive situations in terms of combustion. These extracts have low ignition temperatures and are very volatile. These species, mixed with slash pine (as seen in this wildfire photo in Florida) makes for very dicey conditions. Note the black smoke rising from the burning of these extracts.
Fundamentals of Wildland Fire Heat and Heat Transfer
The temperature of a substance is a function of the kinetic energy of the motion of its molecules, measured in degrees. Although the temperature of a fire is one of its noticeable features (i.e., fire is hot), a temperature value alone does little to characterize the fire. More valuable is quantification of time-temperature relationships or heat flux. Basically, heat flux is the amount of heat flowing through a given area in a given time, usually expressed as calories/cm 2 /second. We will first go over some basic heat and heat transfer definitions.
Heat and Heat Transfer Definitions Heat– a form of energy, often referred to as thermal energy. When heat is applied to a substance, the molecular activity increases and the temperature therefore rises. Heat is the energy of molecular motion, is one of the elements in the fire triangle, and is one of the ingredients necessary for a wildland fire to start and continue to burn. Heat of preignition– the total heat required to raise the temperature of a unit of mass to the ignition temperature, usually taken to be 600 o F. Heat of combustion– the energy that maintains the chain reaction of combustion, and is sometimes known as heat value or heat content. It is the total amount of heat released when a unit quantity of fuel is oxidized completely. An average value of 18,620 KJ/kg (8000 Btu/lb) is used for forest fuels. Heat flux (heat release rate or intensity)– the amount of heat produced per unit of fuel consumed per unit of time, or energy per unit area. It is not a property of the fuel but rather of the energy transfer process.
Heat can be supplied to the combustion process in several different ways. Heat sources include lightning, improperly managed campfires and carelessly discarded cigarettes and matches. What keeps the combustion process going? Heat must be transferred from a burning fuel to fuels not yet involved. There are three methods of heat transfer: radiant, convection, and conduction.
Heat transfer is the process or mechanism by which energy is moved from one source to another. Heat transfer occurs whenever there is a temperature difference in a medium or between media (fuels). It is one of the factors to be considered in determining movement of fire across a landscape. Conduction occurs when heat is transferred from a warmer object to a cooler one. Conduction can be observed when a vehicle equipped with a catalytic converter comes in contact with tall, dry grass. Grass can ignite from the hot metal on a catalytic converter.
Thermal conductivity expresses the quantity of heat transferred per unit of area per unit time per degree of temperature gradient. The thermal conductivity of wildland fuels becomes greater as the density of the fuel increases. Because heat capacity of the fuels also increases with density, high density fuels usually require more heat for ignition than do low-density fuels.
Heat can be conducted more rapidly into deeper layers of the high-density fuels, thus slowing the temperature rise at the surface so that more heat is required to raise the surface temperature to the ignition point. More heat is also required to raise the temperature of the surrounding surface layer because the dense fuel has greater heat capacity. This difference in heat requirements for ignition is one of the reasons that fuel like decayed wood can often by ignited with a spark, but solid and dense wood requires a larger firebrand.
Convection is the transfer of heat by the movement of a gas or liquid. For example, heat is transferred from a hot-air furnace into the interior of a house by convection. Currents of hot air tend to move vertically upward unless a wind or slope causes some degree of lateral movement. Convection currents are primarily responsible for the preheating of the higher shrub layers and crown canopy. Convection is also of vital importance to people working near a wildland fire.
Radiation is a form of energy called radiant energy, existing as electromagnetic waves that travel at the speed of light. Radiant energy travels outward in all directions. A good example of radiant heat is the sun. Waves of heat from the sun radiate through space until they are absorbed by an opaque object. Because it travels on a straight line, radiant heat can be reduced by natural or artificial barriers such as brick walls or rock outcroppings.
There is no need for direct contact between a source of radiation and a body it may affect. Radiation accounts for most of the preheating of fuels ahead of a fire front. Radiant heat can preheat fuels and cause them to ignite and burn.
Radiation is proportional to the absolute temperature of the emitting body raised to the fourth power. -- For example, a change in the source temperature from 800 to 1000 K will result in a doubling of radiant energy emitted. For a point source of radiation, the radiation intensity decreases inversely as the square of the distance. -- This means that the radiation intensity 10 m from the source is only one-fourth that at 5 m.
As the distance from the source increases, the same total amount of radiation is spread over a greater area, hence the amount received per unit area is less. Since waves move along straight paths, the intensity of the radiation received depends on the angle of the incoming radiation and the distance from the source. Radiation perpendicular to the receiving surface is the most intense. However, wildland fire is not a point source… flames usually have considerable surface area; therefore, because so many points are producing radiant energy, the decrease in intensity with distance from a flame source is much less than a point source.
Fine fuels, such as dead grass, needles, foliage, small twigs, and most branches from 0.25 – 3.0 inch in diameter are mostly consumed in the fire front. Other components of the fuel complex burn after the front has passed, some flaming and some smoldering or glowing. The consumption of downed woody fuels affects the amount of duff consumed and the amount of mineral soil exposed. Other things being equal, the more fuel consumed the greater the impact on the site.
Forest floor material, such as litter and duff on top of the mineral soil, and organic soils may be ignited during fire events. These may develop into smoldering fires that can burn for days or even months. Large woody fuels (greater than 3-inches diameter) can sustain fires of relatively high intensity for a prolonged period of time, defying direct suppression efforts.