zx-4 - UNIT V-FUEL MOISTURE The fuel, moisture content in...

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UNIT V--FUEL MOISTURE The fuel, moisture content in natural fuels is such an important factor to fuels availability for fire ignition and combustion that we have devoted an entire unit to the subject. Most fuel complexes contain a combination of dead and live fuels; thus, a wide range of moisture contents occur within these fuels. Since all fuels may not be involved in a flaming front or be consumed, by fire, our analysis of fuel complexes must determine which fuels will be responsible for the propagation of fire. The purpose of this unit is to help you make estimations of moisture content in various dead and live fuels, to identify those fuels which can burn, and to assess the chances of ignition from firebrands landing in new fuels or of fire spreading by preheating fuels ahead of a flaming front. You will also recognize that fuel moisture content is a very important input toward making fire behavior calculations and predictions. Before starting the unit, be sure you have read the instructions to students on page 1 of your workbook. On page 2, you will find the unit objectives on which you will be tested at the end of this unit. Please study these objectives, then return to this text. The first section, starting on page 3, deals with natural fuels and their moisture contents. Fuel complexes vary greatly by areas or regions; with extremes from sparsely vegetated deserts, to rain forests with lush vegetation, to parched timber lands. If we view each as a potential fire environment, our immediate assessments must include fuel loadings and fuel moisture contents. We would expect desert fuels to be dry for extended periods, but is there enough fuel to carry fire? The rain forest has abundant fuels which are generally too wet or too green to burn, but infrequently these areas do have fires. Extended summer drought periods occasionally make our timber lands extremely dry, sometimes to the point of being "explosive", should fires occur. We can generalize at this point and say that when fuel moisture content is high, fires ignite and burn poorly, if at all; and when it is low, fires start easily, and spread and burn rapidly. These simple deductions might satisfy some fire managers, except that fuel moisture contents are frequently some place between the two extremes and fluctuate with changes in weather. During normal fire seasons, these same fire managers have experienced times when rapidly spreading fires suddenly stop, perhaps even go out, due to changes in their fuels and moisture contents. These fuels may have been on a different aspect, had a later curing date, or experienced a sudden change in relative humidity. How does one measure fuel moisture content and then anticipate what changes will take place over time and space? First of all, fire managers have agreed upon a common description and unit of measure for fuel moisture content. This is the amount of water in a fuel, expressed as a percent of the oven dry weight of that fuel. If there were no moisture at all in the fuels, as if dried
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zx-4 - UNIT V-FUEL MOISTURE The fuel, moisture content in...

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