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
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Natural Resources 350.01
Introduction to Wildland Fire Management
Winter Quarter 2005
Natural Resources 350.01—Introduction to Wildland Fire Management (Lecture)
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
InstructorsDr. Roger A. Williams
Associate Professor, Forest Ecosystem Analysis and Management
320-C Kottman Hall
Administrator, Ohio Fire Protection Program
Coordinator, Rural Fire and Training
ODNR, Division of Forestry
Meeting Tuesday, 6:30pm—9:30pm; Kottman Hall 245
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%
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
Fundamentals of Wildland Fire
Combustion Process Overview
Fire requires the 3 elements displayed in the illustration to the right, often referred to as the FireTriangle.
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
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.
CO2 + H2O + solar energy (C6H10O5)n + O
(C6H10O5)n + O + ignition temperature CO2 + H20 + heat
Burning begins with endothermic reactions that absorb energy and ends with exothermic reactions that release energy.
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.
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 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 620oF for wildland fuels.
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 53,500oF. Some of the hybrid flashes about this core may be 10,340 – 21,140oF.
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.
Smoldering / Glowing Combustion
Smoldering ground fires spread slowly, about 1 in./hr.
They can raise mineral soil temperatures above 570oF for several hours with peak temperatures near 1100oF.
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.
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 600oF.
Although combustible gases are generated at temperatures above 400oF, they will not flame even when mixed with air until their temperature reaches 800 to 900oF.
The maximum temperature that can be produced by the burning of gases generated from wildland fuels is believed to be between 3500 and 4000oF.
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 1800oF.
This is still high enough to ignite gases, so once flaming starts, it continues as long as sufficient gas is produced.
Fundamentals of Wildland Fire
Intrinsic Fuel Properties
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:
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.
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/cm2 /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 600oF.
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.
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.
Fundamentals of Wildland Fire
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.
Burning Questions ?