[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-112-1-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-112-1-火災學概要-025","fire-112-1-fire-science-025",112,1,25,"對可燃性氣體而言，下列那一種特性或條件所衍生的燃燒或爆炸風險相對較高？",{"A":16,"B":17,"C":18,"D":19},"較低的環境氧氣濃度","較低的環境壓力","較低的燃燒上限","較低的燃燒下限","D",null,[],false,"本題考點：可燃性氣體的燃燒界限（爆炸界限）與危險度判斷，關鍵在「燃燒下限越低越危險」。\n【正解理由】依燃燒界限的定義，可燃性氣體必須落在燃燒下限（LFL）與燃燒上限（UFL）之間才能傳播火焰，下限即「最少要洩漏到多少濃度才會形成可燃混合氣」的門檻。下限越低，代表極微量外洩即可跨過著火門檻，可燃範圍（UFL 減 LFL）同時被拉寬，形成可燃混合氣的機會與空間分布都變大；危險度指數 H＝（UFL－LFL）÷LFL 也隨下限降低而急遽放大，風險相對最高。故選 D。\n【逐項排除】\n(A) 環境氧氣濃度降低時，氧化反應的鏈鎖反應被抑制，燃燒界限上下限互相靠攏，低於最小氧濃度時甚至無法著火，風險是下降的。\n(B) 環境壓力降低會使單位體積分子數與碰撞頻率減少、散熱相對占優，燃燒上限明顯下移、範圍收窄，風險同樣下降。\n(C) 燃燒上限降低代表可燃範圍的頂端被壓低，範圍變窄，屬於風險降低的方向。\n(D) 燃燒下限降低使微量洩漏即進入可燃範圍，危險度指數同時放大，是四者中風險最高者，為正解。\n【記憶點】下限低就是「漏一點點就會炸」；上限低、壓力低、氧濃度低都只是把可燃範圍越縮越安全。","燃燒界限（爆炸界限）指可燃氣體在空氣中能夠傳播火焰的濃度範圍，以體積百分率表示。常見值可記幾組當基準：氫約 4 至 75%、乙炔約 2.5 至 100%、甲烷約 5 至 15%、丙烷約 2.1 至 9.5%、一氧化碳約 12.5 至 74%。危險度指數 H＝（UFL－LFL）÷LFL，乙炔約為 39、氫約 17.8、甲烷僅約 2，可以清楚看出「下限低且範圍寬」者指數急遽放大，這正是本題以下限高低判斷風險的量化依據。\n界限並非定值，會隨溫度、壓力與氧濃度移動。溫度升高時分子動能增加、散熱相對變小，下限略降而上限明顯上升，範圍變寬；壓力升高時上限大幅上移，壓力降低則上限下移、範圍收窄，減壓至一定程度火焰便無法傳播。以氮氣或二氧化碳稀釋時，上下限逐漸靠攏並交會於一點，該點所對應的氧濃度即最小氧濃度（MOC），是惰化與鈍化設計的理論基礎，也與二氧化碳滅火設備的鈍化濃度計算互相貫通。\n多成分混合氣體的燃燒下限以勒沙特列（Le Chatelier）公式估算：100÷L＝Σ（Vi÷Li），其中 Vi 為各可燃成分占可燃部分的體積百分率、Li 為各成分的燃燒下限。易混淆的三個名詞務必分清：燃燒界限談的是「濃度」，閃火點談的是液體表面蒸氣恰好達到下限時的「溫度」，著火溫度（自燃溫度）談的則是無外部火源即自行起燃的溫度，三者不可互換使用。本考點常延伸出危險度計算、混合氣下限計算，以及「升溫、加壓、富氧會使可燃範圍變寬」的方向判斷題。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-112-1-fire-science-024","於空氣中加入氧氣會改變空氣組成，進而影響可燃性氣體的某些燃燒特性，下列何者所受的影響較為明顯？",24,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-112-1-fire-science-026","下列何種靜電災害預防措施旨在防止靜電蓄積，而與其他旨在減少靜電產生的措施有所不同？",26,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-112-1-fire-science-023","在最小發火壓力以上，可燃性氣體的最小發火能量，會隨著下列那一種條件改變而下降？",23,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-112-1-fire-science-027","下列何種措施於室內發生火災時有助於防止或延緩閃燃的發生？",27,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-112-1-fire-science-022","兩種可燃性氣體以等比例混合，其燃燒下限分別為 1.5%、4.5%，則該混合氣體的燃燒下限約為多少%？",22,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-112-1-fire-science-028","下列那一種前期現象比較可能因後續的消防滅火或救援作為而引發複燃？",28,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-113-1-fire-science-025",113,"容器內氣體受到壓縮造成內部溫度升高，進而發火，此現象稱為？",{"webId":58,"year":59,"stem":60,"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":62,"year":63,"stem":64,"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":66,"year":67,"stem":68,"number":13},"fire-109-1-fire-science-025",109,"有關火羽流的敘述，下列何者錯誤？",{"webId":70,"year":71,"stem":72,"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℃？",1785129966563]