How to Decide to Fight a forest fire or Let it Burn
November 2018
by Melissae Fellet, ASME.org How do forest managers and firefighters decide to fight a wildfire or let it burn? At a time when wild fires have run wild across western North America,The question seems almost irrelevant.In 2018, the carrfire in northern Califonia engulfed more than 1000 homes and killed three firefighters,while a complex of three fires around Mendocino burned even larger.Together,those two fires consumed almost as much land as the entire state of Rhode Island-and there were many more fires in Idaho,Oregon,Montana, and Washington. The devastation and destruction may not end soon.Fire season is getting longer and neighborhoods increasingly strech into wild land.Yet fire is not inherently bad.Fire are nature's way of disposing of dead and rotting trees and clearing brush so that new trees can take root.Paradoxically,suppressing fires makes the next fire even worse,since it leaves all that fuel on the ground where it can feed a more powerful conflagration. Since 1960,researchers and engineers at the U.S. Forest Service Fire Sciences Laboratory in Missoula,Mont.,have used experiments and computer models to learn how fuel,weather,and terrain influence the spread of wildfire.Now that same fundamental science can guide controlled burns of dense forests,leaving flame-resilient ecosystems behind. 護林員和消防員是怎樣做出選擇是去撲滅大火還是任其燃燒的呢？ 有一次，野火經過美國的西北野外，好像和問題沒啥關系。在2018年，加利福利亞北部的大火“卡爾”吞沒了1000座房屋，燒死了三個消防員,然而門多西諾的三場大火燒得更大。總之，兩次大火肆虐了羅德島州上的盡可能多的地方，愛達荷州，俄勒岡州，蒙大拿州和華盛頓州的火情更多。毀壞沒有很快結束。火季正在變長，社區日益深入荒蕪之地。但是大火本質上不壞。大火是大自然處理死樹腐樹并將它們清理到荒蕪之地的一種方式。因此新樹得以扎根。自相矛盾的是，撲滅大火會讓下次火情更糟糕，因為它把所有的燃料留在了地上，可以提供更強大的大火。
Listen to ASME TechCast:How Engineers Close Communication Gaps with Non-engineers Bret Butler, a research mechanical engineer at fire lab,remembers the summer of 2017,when smoke clogged the skies around Missoula for several months."It was so smoky for so long, it was clear the fires exceeded our technical capabilities[to fight them,]"he says."We're not going to fight our way out of the fire conundrum.We have to reduce the fuel load." Wildfires,started naturally or intentionally,are trickly to predict and control.Each plants provides a unique type of fuel,local variations in wind speed and humidity influence fire spread,and terrain provides a few natural boundries to limit flames. The Missoula fire lab is uniquely equipped to study how those factors combines to change the way flames spread.The most unique part of the lab is a long wind tunnel and a system that alters the temperature and relative humidity of the air in the tunnel. Fans on the lab's roof draw outside air though heating and cooling coils to adjust it temperature.The air also passes through misters to adjust the humidity.Interior fans reciculate the air until it reaches the desired conditions,and then directed it into the wind tunnel.A bed of fuel,typically shredded aspen,rests on a table tilted to recreate sloped terrain.Temperature,humidity,and wind speed sensors record the conditions of the fuel as it burns in real time. | 
發表于 2018-12-6 22:16:31
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