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NRM 415 Exam Two
| Question | Answer |
|---|---|
| what are factors that influence fire behavior? | air temperature, relative humidity, precipitation, atmospheric stability, wind, topography, and other interactions between the site and weather elements |
| what is the difference between the impact of weather versus climate on fire? | climate impacts fire in the ecosystem and seasonality. weather can be short term impacts (daily) |
| relative humidity | the amount of moisture in a given volume of air, relative to what that air can hold when it is saturated at the same temperature (vapor pressure deficit) |
| what air temperature holds the most moisture | hotter air holds more than cold air |
| factors influencing precipitation | duration, amount, fuel type, fuel size |
| atmospheric stability | the degree to which vertical motion in the atmosphere is enhanced or suppressed |
| stable atmosphere | vertical motion suppressed (less vertical mixing) |
| inversion | layer of warm air saturated between cold air (caps vertical movement) |
| unstable atmosphere | vertical motion is enhanced (greater vertical mixing, smoke diluted in atmosphere) |
| are stable or unstable conditions more likely to be suitable for conducting a prescribed burn? | unstable preferred because 1) supports fire activity and 2) safety |
| how does wind influence fire? | supplies oxygen, spread, drying, spotting, and residence time decreases with increased this |
| wind relative to terrain features | slope/valley, land and sea breeze, foehn winds |
| slope/valley | slopes heat faster than bottom in morning, mid day bottom catches up (air rising) effects spread. at night, opposite |
| land and sea breeze | impact due to difference in temperature between aquatic and land. direction of air between land and water |
| foehn winds | warm, dry wind moving downhill on leeward side. cool wind comes on the warm side the mountain, the cool air condenses into water molecules as it gets higher up the mountain and drops rain, then continues to the other side of the mountain as dry wind |
| topography | influences the type and nature of physical features of the landscape (configuration) |
| topographic features | elevation (higher, lower fuel availability),; features like canyons, saddles, chutes (chimney effect); slope; aspect |
| topographic effects via slope | speed differences uphill vs. downhill (faster uphill) due to slope elongation, direction of fuels to flame front, and elevated heat transfer |
| influence of aspect | warmest on the south and west sides in the northern hemisphere |
| fuel size in relation to surface area and volume | the smaller the fuel is, the greater the surface area and the smaller the volume |
| fuel bed | the average height of surface fuel that is contained in combined zone of spread and fire front orientation (horizontal/vertical that carries the fire) |
| fuel orientation | can have vertical and horizontal components. vertical is usually more compact than horizontal. snow can make things like grasses horizontal, so season and timing impact fuel arrangement |
| what orientation are ladder fuels | vertical in terms of tree orientation and direction of spread |
| what are the seven fuel characteristics | fuel loading, size and shape, compactness, horizontal continuity, vertical arrangement, moisture content, and chemical content |
| what fuel characteristic(s) influences ignition, spread, and intensity | compactness and chemical content |
| what fuel characteristic(s) influences ignition, spread, intensity, and torching | loading |
| what fuel characteristic(s) influences spread, spotting, and crowning | horizontal continuity |
| what fuel characteristic(s) influences spotting, torching, and crowning | vertical arrangement |
| what fuel characteristic(s) influences ignition, spread, intensity, and spotting | size and shape |
| what fuel characteristic(s) influences ignition, spread, intensity, spotting, torching, and crowning | moisture content |
| reburn potential | occurs when a fire moves quickly through an area and fails to consume all fuels or when the fire "creates" future fuels that become available at a later time. there must be intermediate time between fires for this to be |
| fuel loading | the amount of fuel present expressed quantitatively in terms of weight of fuel per unit area |
| how do loosely compacted fuels influence fire behavior | normally react faster to moisture changes, have more oxygen available for combustion, and rate of spread and intensity are usually greater |
| how to closely compacted fuels influence fire behavior | less surface area exposed, oxygen restricted, inhibit convective and radiant heat transfer, in most cases a tightly will burn with a low spread rate and low intensity because of the supply of air |
| two categories of fire effects | directness of impact (order) and manifestation of the effects (temporal) |
| 1st order effects | happen during or immediately after the fire |
| 2nd order effects | associated with fire, but occur as a consequence of first order effects. delayed spatially or temporally |
| which of the seven principle fuel characteristics pertain to physical characteristics | size and shape, loading (fuel quantity), compactness, horizontal continuity, and vertical arrangement |
| which of the seven principle fuel characteristics pertain to fuel chemistry | chemistry and moisture content |
| fuel chemistry at a basic level | fuel is composed of chains of monomers linked by energy bonds (called polymers). during combustion, the fuel is broken into monomers and energy is released from the energy, which is let off as heat |
| macromolecules | large molecules formed by joining small organic molecules |
| polymers | molecules made from repeating units of identical or nearly identical compounds linked together by a series of covalent bonds |
| what is a unit of vegetation biomass made of | cellulose, hemicellulose, and lignin |
| cellulose | organic compound made up of only carbon, hydrogen, and oxygen |
| lignin | complex organic tissue that is primarily made of dead tissues |
| extractives | compounds found within the porous parts of the plant structure in some plants |
| what do extractives provide | they are the major contributor of combustible volatile compounds |
| high heat of combustion | when they burn, they generate a lot of heat |
| high volatility (evaporability) | volatilize very easily, evaporating from the plant structure, to be available to interact with heat and oxygen, facilitating flaming combustion |
| low limits of flammability | burst into flames at relatively low heat temperatures compared to other compounds in the plant |
| lipids | organic compounds found in the structural makeup of cell membranes |
| how does fuel chemistry effect a fire | chemicals in biomass determine fire type and behavior by influencing volatility and intensity, if there are more combustible chemicals = more explosive/intense, also impacts ignition, intensity, and spread |
| fuel age in relative in chemistry | younger = more extractives and less lignin (opposite in older) |
| fuel moisture impact of ignition and rate of spread | because water has a high specific heat capacity, it takes longer for it to heat up enough to evaporate out of the biomass |
| how is moisture content calculated | based on weight of wet fuel and then weight when dried ((wet weight - dry weight)/ dry weight) * 100 = % |
| vapor pressure deficit | how long it takes a given unit of fuel to lose or gain moisture (time lag). moisture moves to wherever there is less moisture (atmosphere or fuel) |
| equilibrium moisture content (EMC) | when the moisture content of fuel and air are close to being equal such that there is no movement of moisture between them |
| time lag | the time it takes a fuel particle to gain or lose about 63% of the difference between its initial/current moisture content and its equilibrium moisture content |
| duration | gain or loss of moisture doesn't happen at the same rate throughout the duration of loss/gain |
| fuel size | smaller and thinner (more slender) the fuel is, the quicker it is to gain/lose moisture |
| fuel time lag categories | 1 hour, 19 hour, 100 hour, and 1000 hour time lag fuels |
| 1 hour time lag fuels | diameter < 0.25 in, shortest time to reach EMC, respond to moisture changes fast, most concern to management, great use in predicting fire behavior |
| 10 hour time lag fuels | diameter 0.25-1 in, some use in predicting fire behavior |
| 100 hour time lag fuels | diameter 1-3 in, very little use in predicting fire behavior |
| 1000 hour time lag fuels | diameter >3 in, slowest to gain/lose moisture, can gain moisture from soil after long rains, not typically used in predicting fire behavior, can show seasonal trends in moisture and fire seasonality predictions |
| burn plan | basically a prescriptive plan that lays out what the person conducting the burn considered as the optimal conditions under which a burn can be conducted |
| three things a burn plan needs | to be made prior to prescribed burn day (safety), to have knowledge backing in and weather considered, and to be stuck to (follow the plan and cancel if necessary) |
Created by:
ethompson238
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