[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-107-1-fire-science-030":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-030","fire-107-1-fire-science-030",107,1,30,"固體燃料火焰延燒最快的方式為下列何者？",{"A":16,"B":17,"C":18,"D":19},"向上","向下","水平","與延燒方向無關","A",null,[],false,"本題考點：固體可燃物的火焰延燒方向性,考的是火焰傳播方向與預熱區的相對關係。\n【正解理由】火焰是高溫低密度氣體,浮力使火焰與熱煙持續往上竄,上方尚未燃燒的材料同時承受火羽流的對流加熱與火焰的輻射加熱,預熱最充分、表面最早裂解出可燃氣體並達到燃燒下限,因此火焰陣面沿表面向上推進最快,屬於同向流火焰傳播;向下與水平則為逆向流傳播,火焰被浮力帶離未燃面,只剩有限的輻射與固體傳導可供預熱,速度低上一至數個數量級,故選 A。\n【逐項排除】\n(A) 正確:向上延燒兼具對流與輻射預熱,又有煙囪效應助長,是最快的方向,理由如上。\n(B) 錯誤:向下延燒時火焰往上離開未燃區,預熱最弱,是三個方向中最慢者,實驗上常僅為每分鐘公釐等級。\n(C) 錯誤:水平延燒時火焰僅部分貼附材料表面,預熱效果介於向上與向下之間,並非最快。\n(D) 錯誤:延燒速度受浮力與預熱條件支配,方向性極為明顯,不可能與方向無關。\n【記憶點】火往上跑最快——上竄有對流加輻射,向下只剩輻射,快慢差好幾個數量級。","火焰傳播依火焰流動方向與傳播方向的相對關係分為兩型:同向流傳播(火焰與傳播方向一致,如向上延燒)與逆向流傳播(火焰逆著傳播方向,如向下與水平延燒)。決定速度的關鍵是預熱區長度——火焰把未燃表面加熱到熱分解溫度所影響的距離。向上延燒時,火羽流貼著壁面上竄,預熱區可長達數十公分甚至數公尺,且隨火焰變高而加速,呈現自我加速的正回饋;向下延燒的預熱區只有數公釐,幾乎完全靠輻射與固體內部傳導,速度因此穩定而緩慢。實驗上厚質壓克力板向下延燒約每分鐘公釐等級,垂直向上延燒卻可達每秒數公分以上,差距輕易超過兩個數量級。\n把材料傾斜也會改變速度:傾角愈接近垂直向上,火焰愈貼附表面,延燒愈快;向下傾斜則火焰離開表面,速度下降。這解釋了幾個經典火場現象——建築外牆保溫材與帷幕牆的立面延燒為何一發不可收拾、垂直電纜束為何比水平電纜架延燒更快、窗口噴出火焰為何會沿外牆向上層竄燒形成上下層延燒。\n對照記憶:向上延燒受對流主導,向下與水平延燒受輻射主導;通風、材料厚度、熱慣性(密度乘比熱乘熱傳導係數)則共同影響絕對速度,薄材料因熱慣性小而比厚材料更快被點燃。\n幾何配置也會放大方向效應:兩片可燃面相互平行且間距狹窄時,彼此的輻射會互相回饋,使夾縫內的溫度遠高於單面燃燒,堆疊紙箱、貨架走道與書櫃間隙的火勢因而特別猛烈;若這個狹縫又是垂直的,便同時具備輻射回饋與煙囪效應,延燒速度可再往上跳一級。\n延伸考點:同一組概念會以「火焰傳播速度的影響因素」「外牆立面火災」「電纜火災」「森林火災上坡延燒為何較快」等形式出題,上坡延燒之所以快,原理與向上延燒完全相同,都是火焰貼近未燃燃料造成的預熱強化。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-107-1-fire-science-029","下列何者並非學校實驗室火災之特性？",29,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-107-1-fire-science-031","下列何者並非造成電氣火災的原因？",31,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-107-1-fire-science-028","下列何者並非古蹟火災防護之特性？",28,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-107-1-fire-science-032","下列何者並非防火區劃構件構造之性質？",32,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-107-1-fire-science-027","下列何者並非高科技廠房火災之特性？",27,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-107-1-fire-science-033","燃燒時若生成的熱與散失的熱保持平衡，燃燒溫度保持均勻之燃燒為下列何者？",33,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-111-1-fire-science-030",111,"下列對高樓逃生通道設計原則的描述，何者錯誤？",{"webId":58,"year":59,"stem":60,"number":13},"fire-110-1-fire-science-030",110,"某建築物火場產生大量煙霧，正向煙囪效應在中性帶以上 10 公尺處的壓力差為 12 Pa，若建築物內、外的溫度差不變，請問中性帶以上 20 公尺處的壓力差為何？",{"webId":62,"year":63,"stem":64,"number":13},"fire-109-1-fire-science-030",109,"海龍替代滅火藥劑中，下列何者在大氣之滯留時間最久？",{"webId":66,"year":67,"stem":68,"number":13},"fire-108-1-fire-science-030",108,"下列何種措施，可以防止由大樓窗口噴出的火焰向上層延燒？",{"webId":70,"year":71,"stem":72,"number":13},"fire-106-1-fire-science-030",106,"依照 McCaffrey 火羽流理論，下列何者正確？",1785123163777]