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zx-8 - UNIT IX-EXTREME FIRE BEHAVIOR This unit is on...

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UNIT IX--EXTREME FIRE BEHAVIOR This unit is on erratic or extreme fire behavior. After you have read the instructions to students on page 1 of your workbook, carefully read the unit objectives on page 2. When you have finished, return to this text. We will start out this unit by reviewing some terminology relating to what is frequently called "extreme" fire behavior. On page 3, a definition is given: "It implies a level of wildfire behavior that ordinarily precludes methods of direct attack. Predictability is difficult because such fires often exercise some degree of influence on their environment, behaving erratically, sometimes dangerously." The terms erratic or severe fire behavior might be preferred by some to describe the levels of fire activity that will be discussed in this unit. To others, the terms are somewhat interchangeable. In any case, we are concerned with levels of fire activity that present serious control problems and can threaten lives and property. Such levels of fire activity usually have one or more of the following involved: very high to extreme rates of spread; prolific crowning and/or spotting; presence of fire whirls; and a tall, well-developed convection column. The most extreme fire situations are usually described as being one of the following: Under item A, first note blowup. This is defined as a sudden increase in fire intensity or rate of spread sufficient to preclude direct control or to upset existing control plans. It's often accompanied by violent convection and many other characteristics of a fire storm. The second term is fire storm. This is violent convection caused by a large, continuous area of intense heat. It is often characterized by destructive, violent surface indrafts near and beyond the perimeter and sometimes by tornado-like whirls. The third is conflagration. It is a large, raging, destructive fire, and the term is often used to denote such a fire with a moving front as distinguished from a fire storm. The term blowup is most used by firefighters to describe extreme fire conditions on any size wildfire. Even relatively small fires can reach the blowup stage when they suddenly reach intensity levels that defy all control actions and pose a threat to life and property. Fire storms and conflagration fires are usually associated with mass fire, which connotes both large size and high rates of energy release. Fire storms have occurred during wartime when many ignitions over a wide area quickly coalesce into a single fire. Fire storms can develop under light wind conditions but produce strong indrafts as the many fires burn together. Conflagration fires have definite moving "heads" or fronts. They are strongly affected by wind and topography; thus the depth of the intense burning area is usually relatively narrow.
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