[{"data":1,"prerenderedAt":72},["ShallowReactive",2],{"q-fire-111-1-fire-science-004":3},{"subject":4,"subjectSlug":5,"subjectKicker":6,"subjectShort":7,"question":8,"related":27,"sameNumber":51,"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-111-1-火災學概要-004","fire-111-1-fire-science-004",111,1,4,"日本東京放映所及精神病診所火災起因為縱火，請問汽油在空氣中的燃燒下限為何？",{"A":16,"B":17,"C":18,"D":19},"1.4%","7.6%","1.3%","2.6%","A",null,[],false,"本題考點：可燃性蒸氣的燃燒（爆炸）界限，以及汽油燃燒下限的標準數值。\n【正解理由】燃燒界限指可燃性氣體或蒸氣與空氣混合後能夠傳播火焰的濃度範圍，以體積百分比表示；低於下限時燃料太稀、放熱不足以維持火焰傳播，高於上限時則因氧氣相對不足而無法傳播。汽油為多種碳氫化合物之混合物，教材與考題普遍採用的燃燒範圍為 1.4% 至 7.6%，其中下限為 1.4%，故選 A。\n【逐項排除】\n(A) 正確。1.4% 為汽油在空氣中的燃燒下限，也是汽油閃火點極低、常溫即具高度可燃性的量化依據。\n(B) 錯誤。7.6% 是汽油燃燒範圍的上限值，題目問的是下限，屬上下限對調的陷阱。\n(C) 錯誤。1.3% 與汽油下限僅差 0.1 個百分點，是刻意設置的近似混淆值，汽油通行採用的下限為 1.4%。\n(D) 錯誤。2.6% 屬丙酮一類溶劑的下限量級，其燃燒範圍與汽油不同，不可套用於汽油。\n【記憶點】汽油燃燒範圍 1.4%～7.6%，下限 1.4、上限 7.6，別把兩端顛倒。","燃燒界限（又稱爆炸界限）是火災學計算題與敘述題的共同基礎。下限（LEL）以下的混合氣過稀，燃燒放熱不足以把鄰接氣層加熱到著火溫度，火焰無法自持；上限（UEL）以上則燃料過濃、氧氣不足，同樣無法傳播。汽油是多成分混合燃料，能以單一組數值表示，理論依據是勒沙特列（Le Chatelier）公式：L＝100 ÷ (V1\u002FL1＋V2\u002FL2＋…)，其中 Vi 為各成分佔可燃氣的體積比、Li 為各成分自身的下限。\n危險度是常見的延伸指標：H＝(U－L)\u002FL。代入汽油得 H＝(7.6－1.4)\u002F1.4≈4.4；乙炔燃燒範圍 2.5% 至 81%，危險度高達 31.4。由此可看出燃燒範圍愈寬、下限愈低者，形成可燃混合氣的機會愈大，危險度愈高。\n燃燒界限並非固定值。溫度升高時下限略降、上限明顯上升，範圍變寬；壓力升高對上限的影響大於下限；以二氧化碳、氮氣等惰性氣體稀釋時，上限快速下降而下限變化小，兩線交會處即為最小氧濃度（MOC），這正是窒息法滅火與惰化的理論基礎。\n易混淆對照：閃火點與燃燒下限其實是同一件事的兩種表達方式——閃火點是液面上方蒸氣濃度恰好達到燃燒下限時的液溫。汽油閃火點約在攝氏零下四十度以下，代表常溫下油面上方蒸氣早已超過 1.4% 的下限並落在燃燒範圍內，因此汽油在常溫即為高危險液體，也是縱火案件常被使用的原因。相對地，柴油閃火點高於常溫，常溫下液面蒸氣濃度不足，須先加熱或以霧狀分散才易點燃，兩者的對比是本題組的固定考法。",true,[28,32,36,40,44,47],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-111-1-fire-science-003","實效濕度低於多少時，日本即發布火災警報？",3,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-111-1-fire-science-005","在苯中置入油酸鎂等金屬鹼，係採取下列何種防止靜電發生的方法？",5,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-111-1-fire-science-002","有關爆燃與爆轟，下列敘述何者錯誤？",2,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-111-1-fire-science-006","火災成長歷程中，下列何者非閃燃之現象？",6,{"webId":45,"stem":46,"number":12,"year":11,"session":12},"fire-111-1-fire-science-001","近年來已有水滅火器經型式認可，下列敘述何者正確？",{"webId":48,"stem":49,"number":50,"year":11,"session":12},"fire-111-1-fire-science-007","油類火災為何種火災？",7,[52,56,60,64,68],{"webId":53,"year":54,"stem":55,"number":13},"fire-114-1-fire-science-004",114,"下列有關隧道火災之敘述何者錯誤？",{"webId":57,"year":58,"stem":59,"number":13},"fire-112-1-fire-science-004",112,"若空氣中的氧氣體積百分比為 21%，則甲烷完全燃燒的化學理論濃度為多少%？",{"webId":61,"year":62,"stem":63,"number":13},"fire-110-1-fire-science-004",110,"在氣溫 20 ℃無風的情況下，一般木造建築物形成危險界限溫度之輻射熱通量超過多少 kcal \u002F m2 h 即有延燒之危險？",{"webId":65,"year":66,"stem":67,"number":13},"fire-109-1-fire-science-004",109,"某一火災成長至 2,000 kW 所需時間為 400 秒，請問該火災屬何種成長性火災？[Q：釋熱率（MW）； 1\u002F2 t：經過時間（sec）；k：火災成長常數（sec\u002FMW ）]",{"webId":69,"year":70,"stem":71,"number":13},"fire-108-1-fire-science-004",108,"今有 A、B 兩種可燃性氣體以 1：1 之體積混合，已知 A、B 之燃燒下限分別為 3.0%、7.0%，若兩者間互不催化亦不反應，則理論上此混合氣體之燃燒下限為若干%？",1785123161856]