[{"data":1,"prerenderedAt":72},["ShallowReactive",2],{"q-fire-108-1-fire-science-031":3},{"subject":4,"subjectSlug":5,"subjectKicker":6,"subjectShort":7,"question":8,"related":26,"sameNumber":51,"hasEssay":25},"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":19,"answerNote":20,"images":21,"imagesPending":22,"lawTimestamp":11,"explanation":23,"explanationDeep":24,"freq":12,"indexable":25},"fire-108-1-火災學概要-031","fire-108-1-fire-science-031",108,1,31,"假設建築物外部風速為 V 時，其迎風面的風壓為 P，當風速提高為 2V 時，建築物所受風壓變為：",{"A":16,"B":17,"C":16,"D":18},"2P","4P","1\u002F2 P","B",null,[],false,"本題考點：風壓與風速的關係——迎風面風壓來自動壓，與風速的平方成正比。\n【正解理由】依柏努利方程式，氣流的動壓（速度壓）為 q＝½ρV²，建築物迎風面所受風壓 P＝C·½ρV²（C 為風壓係數、ρ 為空氣密度）。在空氣密度與風壓係數不變的前提下 P∝V²，風速由 V 提高為 2V 時，代入得 (2V)²＝4V²，風壓成為原來的 4 倍，故選 B。\n【逐項排除】\n(A) 2P：把風壓誤當成與風速成正比；風速加倍時的增幅是平方而非線性，2 倍為明顯低估。\n(B) 4P：符合 P∝V²，風速 2 倍代入平方後得 4 倍風壓，與柏努利方程式導出的動壓式一致，為正解。\n(C) 2P：與 (A) 同屬線性關係的誤判（原卷其中一項為 √2 P，根號於文字擷取時遺漏）；若風壓僅為 √2 倍，對應的風速只提高約 1.19 倍。\n(D) 1\u002F2 P：關係方向完全相反，風速提高不可能使迎風面的風壓下降。\n【記憶點】風壓吃風速的平方：風速加倍，風壓四倍。","建築物迎風面所受的風壓，是氣流被建物阻擋後動能轉為壓力的結果，由柏努利方程式導出速度壓 q＝½ρV²，再乘上依建物形狀與部位而定的風壓係數 C，得 P＝C·½ρV²。空氣密度取 1.2 kg\u002Fm³ 時，風速 10 m\u002Fs 的速度壓約 60 Pa，風速加倍到 20 m\u002Fs 即約 240 Pa，四倍關係一算便明。風壓係數的典型值為迎風面約 ＋0.8、背風面約 −0.4～−0.5，側面與屋頂多為負值（吸力）；同一陣風會在建物迎風側形成正壓、背風側形成負壓，兩者的壓差才是驅動室內外空氣交換的實際動力。\n這個平方關係在火災上的意義：颱風或強風天發生火災時，風速加倍代表作用於外牆與開口的壓力變成四倍，室內外壓差大幅提高，火勢沿風向水平延燒的速度顯著加快；外部風壓也可能壓過機械排煙或加壓防煙所設定的壓差而使其失效，這正是煙控設計須把外部風壓與煙囪效應一併納入評估的原因。\n對照記憶：風壓與風速平方成正比、輻射熱與絕對溫度四次方成正比、孔口流量與壓差平方根成正比，這三組比例關係是火災學計算題的常客，遇到「變成幾倍」的題目先辨識屬於哪一組。另煙囪效應造成的壓差可用 ΔP＝3460·h·(1\u002FTo−1\u002FTi) 估算（壓差單位 Pa、h 為與中性帶的高度差、溫度以 K 代入），與風壓合成後決定高層建築中性帶的位置與煙的流動方向，是與本題同源的延伸考點。\n還有一個容易被忽略的細節：風速本身隨高度增加而變大，工程上多以指數（冪次）律描述，都市區地表粗糙度大、風速隨高度上升較緩，開闊地則上升較快。因此同一棟建築物高樓層所受的風壓遠大於低樓層，高層火災的風助延燒與煙控失效風險也集中在上部樓層。",true,[27,31,35,39,43,47],{"webId":28,"stem":29,"number":30,"year":11,"session":12},"fire-108-1-fire-science-030","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？",30,{"webId":32,"stem":33,"number":34,"year":11,"session":12},"fire-108-1-fire-science-032","下列有關防止靜電災害的方法中，何者錯誤？",32,{"webId":36,"stem":37,"number":38,"year":11,"session":12},"fire-108-1-fire-science-029","煙霧的流動為由高壓處往低壓處流，因此加壓造成壓力差可以有效控制煙霧流動。若於一安全梯間流入體積流率為 Q(m3\u002Fs)的空氣，形成 P 的壓力差，現欲將壓力差提高到 2P，則流入的空氣體積流率應為多少？",29,{"webId":40,"stem":41,"number":42,"year":11,"session":12},"fire-108-1-fire-science-033","電氣火災中，下列何者為積污導電現象？",33,{"webId":44,"stem":45,"number":46,"year":11,"session":12},"fire-108-1-fire-science-028","火場中煙霧的成分複雜且多具毒性，火災時若吸入下列何種氣體，會妨礙細胞中氧化酵素之活性，造成細胞呼吸停止？",28,{"webId":48,"stem":49,"number":50,"year":11,"session":12},"fire-108-1-fire-science-034","化學物質災害搶救程序 H.A.Z.M.A.T.中有關區域管制事項，下列敘述何者正確？",34,[52,56,60,64,68],{"webId":53,"year":54,"stem":55,"number":13},"fire-111-1-fire-science-031",111,"常見消防機關宣導，使用延長線勿將其綑綁，以免引發火災，究其原因為何？",{"webId":57,"year":58,"stem":59,"number":13},"fire-110-1-fire-science-031",110,"有關影響粉塵爆炸的因素，下列何者錯誤？",{"webId":61,"year":62,"stem":63,"number":13},"fire-109-1-fire-science-031",109,"建築物火災在閃燃發生後之全盛期火災的特性，不包括下列何者？",{"webId":65,"year":66,"stem":67,"number":13},"fire-107-1-fire-science-031",107,"下列何者並非造成電氣火災的原因？",{"webId":69,"year":70,"stem":71,"number":13},"fire-106-1-fire-science-031",106,"建築物火災時要防止火勢由外牆的窗戶向上延燒，下列改善措施何者錯誤？",1785123163349]