[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-109-1-fire-science-025":3},{"subject":4,"subjectSlug":5,"subjectKicker":6,"subjectShort":7,"question":8,"related":27,"sameNumber":52,"hasEssay":26},"火災學概要","fire-science","火災學 · Fire Science","火災學",{"id":9,"webId":10,"year":11,"session":12,"subject":4,"number":13,"stem":14,"options":15,"answer":20,"answerNote":21,"images":22,"imagesPending":23,"lawTimestamp":11,"explanation":24,"explanationDeep":25,"freq":12,"indexable":26},"fire-109-1-火災學概要-025","fire-109-1-fire-science-025",109,1,25,"有關火羽流的敘述，下列何者錯誤？",{"A":16,"B":17,"C":18,"D":19},"火羽流的溫度與速度隨著天花板高度呈現垂直下降","火羽流在燃料上方形成，周遭冷空氣捲入至火羽流下方，形成空間對流","不同生成氣體隨火羽流上升累積在天花板形成負壓區，火羽流底部則形成正壓區","火羽流分為連續火焰區、閃耀火勢區與熱煙氣區","C",null,[],false,"本題考點：火羽流(fire plume)的分區、空氣捲吸機制與火場正負壓分布。\n【正解理由】火羽流是燃燒生成的高溫氣體受浮力驅動向上流動所形成的柱狀流場。熱煙氣上升後蓄積於天花板下方，該處因熱氣堆積、密度小而形成相對高壓的正壓區；火羽流底部近地板側則因熱氣不斷被抽離、周界冷空氣被捲吸補入，形成相對低壓的負壓區。本項把正、負壓區的位置完全對調，與浮力驅動下「上正下負、中間為中性帶」的壓力場不符，故選 C。\n【逐項排除】\n(A) 正確。火羽流向上發展時持續捲吸周遭冷空氣稀釋，質量流率增加而熱量被攤薄，溫度與速度隨高度增加而遞減，愈接近天花板衰減愈明顯。\n(B) 正確。火羽流在燃料上方生成，其下部因抽引作用使周遭冷空氣自側向捲入(entrainment)，形成火場的空間對流循環。\n(C) 錯誤，為本題應選者。天花板下方蓄熱區為正壓、火羽流底部為負壓，本項恰好顛倒。\n(D) 正確。依 McCaffrey 的火羽流分區，自下而上依序為連續火焰區、閃耀(間歇)火勢區與熱煙氣(浮力煙流)區。\n【記憶點】熱氣往上跑，壓力就往上堆：天花板正壓、地板側負壓，中間是中性帶。","火羽流是火災學的核心模型，命題方向大致固定在三個層次。其一是分區：McCaffrey 依無因次高度 z\u002FQ^(2\u002F5) 把火羽流切成三段——連續火焰區內流速隨高度增加而上升、溫度接近定值；閃耀火勢區(間歇火焰區)火舌時有時無，流速大致持平；熱煙氣區(浮力煙流區)已無火焰，僅剩浮力驅動的高溫氣流，溫度與速度都隨高度呈冪次衰減。考生常誤以為「愈高愈快」，實際上只有連續火焰區內速度隨高度上升，越過火焰尖端之後便一路衰減。\n\n其二是捲吸。火羽流上升時因剪應力與壓差把周遭空氣吸入，捲吸的空氣量遠大於燃料本身理論需氧量，這是煙量遠大於燃燒生成氣體量的原因，也是估算排煙量時必須以火羽流質量流率而非燃燒產物量為準的理由。捲吸同時稀釋煙氣、降低溫度，因此火羽流的溫升與離火源高度呈反比趨勢。若火源緊靠牆面或角隅，單側或雙側捲吸被阻斷，同樣熱釋放率下火焰高度會明顯拉長，這也是常見的延伸考法。\n\n其三是壓力場與中性帶。室內火災因熱氣密度小而上浮，上層蓄熱使壓力高於室外，下層則低於室外，兩者相等的高度即中性帶。開口位於中性帶以上者噴出火焰與濃煙，位於以下者吸入空氣，這正是「開口部噴出火焰向上層延燒」與「冷空氣自下方捲入」兩個現象的共同解釋。把正負壓區顛倒，等於把整個浮力驅動的流場倒過來看。\n\n易混淆對照：火羽流是垂直向上的柱狀流，天花板噴流則是火羽流撞擊天花板後轉為水平放射的薄層流，兩者接續但不同；探測器與撒水頭的作動時間計算用的是天花板噴流的溫度與速度，不是火羽流軸心值。相關考點還包括火羽流虛點源修正、軸心溫度與高度的關係式，以及煙層下降時間與火羽流質量流率的連動。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-109-1-fire-science-024","在古蹟及歷史建築物火災風險評估指標中，有關防火因應措施安全評估項目中，不包括下列何項？",24,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-109-1-fire-science-026","閃燃發生時間之影響因素中，通風為其中之一項，請問：A0(H0)1\u002F2 的通風因子公式中，A0 與 H0 各代表何意？",26,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-109-1-fire-science-023","若要看清某一物體，該物體與其背景間有一定之對比度。對比度之計算：C=(B\u002FB0)-1，有關對比度下列何者正確？",23,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-109-1-fire-science-027","下列有關泡沫滅火劑，何者敘述正確？",27,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-109-1-fire-science-022","預防過氧化丁酮之火災爆炸時，下列何種原則正確？",22,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-109-1-fire-science-028","森林火災的種類與敘述，下列何者正確？",28,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-111-1-fire-science-025",111,"近來消防機關大力推行安裝住宅用火災警報器，其安裝位置在天花板或牆壁上緣，主要考量因素為何？",{"webId":58,"year":59,"stem":60,"number":13},"fire-110-1-fire-science-025",110,"請依據可燃性氣體完全燃燒時的化學理論濃度，計算丙烷的燃燒下限？",{"webId":62,"year":63,"stem":64,"number":13},"fire-108-1-fire-science-025",108,"木材受熱分解進而燃燒的過程中，當加熱到引火溫度時，可燃性氣體釋出量迅速增加，試問木材的引火溫度約為多少℃？",{"webId":66,"year":67,"stem":68,"number":13},"fire-107-1-fire-science-025",107,"下列何者並非複燃（backdraft）發生之原因？",{"webId":70,"year":71,"stem":72,"number":13},"fire-106-1-fire-science-025",106,"依據實驗，人穿著普通作業服時，其受熱之界限值約為多少？",1785123162884]