[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-107-1-fire-science-013":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-107-1-火災學概要-013","fire-107-1-fire-science-013",107,1,13,"假設大氣中氧氣容積為 21%，現在一密閉空間（體積為 V）內，有三分之一體積（V\u002F3）為惰性氣體時（壓力仍為一大氣壓），該空間內氧氣濃度為多少%？",{"A":16,"B":17,"C":18,"D":19},"7%","11%","14%","18%","C",null,[],false,"本題考點：惰性氣體稀釋後的氧氣容積百分比計算,依據是定溫定壓下容積比等於莫耳比。\n【正解理由】密閉空間總壓維持一大氣壓,表示多餘氣體可外洩、總體積不變。惰性氣體佔去 V\u002F3 後,原空氣只剩 2V\u002F3,而空氣中氧氣的容積比 21% 不隨稀釋改變,因此氧氣容積等於 21% 乘以殘餘空氣體積,再除以總體積 V 即得空間內的氧氣濃度為 14%,故選 C。\n【逐項排除】\n(A) 7% 等於 21% 乘以 1\u002F3,是把惰性氣體所佔的比例誤當成殘餘空氣比例,方向剛好相反。\n(B) 11% 約為 21% 的一半,對應惰性氣體佔一半體積的情形,與題給的三分之一不符。\n(C) 14% 即 21% 乘以 2\u002F3,正確反映空氣被稀釋為原來的三分之二,為正解。\n(D) 18% 僅比 21% 略低,對應的稀釋比例不到六分之一,與三分之一體積被置換的量級不符。\n【演算步驟】殘餘空氣體積 = V − V\u002F3 = 2V\u002F3;氧氣容積 = 21% × 2V\u002F3 = 0.14 V;氧氣濃度 = 0.14 V ÷ V × 100% = 14%。\n【記憶點】惰性氣體吃掉三分之一,氧氣就打三分之二折:21% × 2\u002F3 = 14%。","本題的算式其實是氣體滅火設計濃度公式的反向操作。全區放射的惰化設計常用「滅火劑設計濃度(%) =(21 − 目標氧濃度)÷ 21 × 100%」。把本題數字代進去:惰性氣體佔 1\u002F3 即 33.3%,對應目標氧濃度 = 21% ×(1 − 0.333)= 14%,兩式互為表裡。反過來,若題目要求把氧濃度壓到 15%,所需濃度 =(21 − 15)÷ 21 ≈ 28.6%。這組換算是火災學與滅火設備兩個範圍共用的高頻考點,務必雙向都會算。\n理論基礎是道爾頓分壓定律與理想氣體定律:定溫定壓下氣體的容積分率等於莫耳分率,所以注入惰性氣體只是把原有空氣按比例「擠掉」,氧氣的容積分率隨殘餘空氣比例線性下降,氧氣本身並沒有被消耗。題目特別聲明「壓力仍為一大氣壓」,意思就是多餘氣體可經開口或洩壓裝置排出,總莫耳數不變。若改成密閉不洩壓、直接加壓灌入,情況就不同了:氧氣的分壓維持不變,只有容積濃度下降,此時能否抑制燃燒要改看氧分壓,這是常見的進階變化題。\n數值記憶對照:一般可燃物的極限氧濃度約在 15% 上下,甲烷約 12%,氫氣低到約 5%,多數有機溶劑落在 11% 至 13%;人在氧濃度 15% 以下開始判斷力下降,10% 以下數分鐘即失去意識。以氮氣、氬氣等惰性氣體為滅火劑的系統之所以能兼顧人命,靠的正是「低於燃燒極限但短時間仍可耐受」的窄帶,把氧濃度控制在 12% 至 14% 附近;二氧化碳則把氧氣壓得更低,兩者的人命風險完全不同等級。\n相關考點:同一觀念會改考「注入多少體積惰性氣體才能使氧濃度降至 X%」,或給定容積求所需藥劑量。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-107-1-fire-science-012","下列何者並非容易悶燒材料之特性？",12,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-107-1-fire-science-014","我國在 106 年實施 A1、A2、A3 新式火災認定方式，下列有關 A2 火災認定之敘述，何者錯誤？",14,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-107-1-fire-science-011","在高科技無塵室作業中，下列敘述何者不是避免人員帶靜電產生危害之處理方式？",11,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-107-1-fire-science-015","有一火場之消光係數為 2 m-1，請問發光物體之能見度為多少公尺？",15,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-107-1-fire-science-010","下列有關二氧化碳滅火劑之敘述，何者錯誤？",10,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-107-1-fire-science-016","下列何者為海龍替代品滅火藥劑 FE-13 之分子式？",16,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-111-1-fire-science-013",111,"高層建築物火災特性下列何者錯誤？",{"webId":58,"year":59,"stem":60,"number":13},"fire-110-1-fire-science-013",110,"有一開口面積為 10.0 m2，開口高度為 1.44 m 之居室，當其發生火災而形成通風控制燃燒時，根據 P. H. Thomas 之研究結果，則燃燒速度為多少 kg\u002Fmin？",{"webId":62,"year":63,"stem":64,"number":13},"fire-109-1-fire-science-013",109,"下列的滅火設備，何者屬於窒息法滅火原理？",{"webId":66,"year":67,"stem":68,"number":13},"fire-108-1-fire-science-013",108,"比較室內火災閃燃（Flashover）與複燃（Backdraft），下列敘述何者正確？",{"webId":70,"year":71,"stem":72,"number":13},"fire-106-1-fire-science-013",106,"氣體本身受到壓縮，增高溫度時，亦可發火，此稱為：",1785123163584]