[{"data":1,"prerenderedAt":73},["ShallowReactive",2],{"q-fire-108-1-fire-science-012":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-108-1-火災學概要-012","fire-108-1-fire-science-012",108,1,12,"建築物之中性帶高度受室內溫度、室外溫度及上下開口的影響，下列敘述何者錯誤？",{"A":16,"B":17,"C":18,"D":19},"室內溫度上升，中性帶會向下偏移","上半部開口越大，中性帶會向上偏移","位於中性帶上，室內室外壓差為零","迎風面中性帶會下降，而背風面中性帶會上升","D",null,[],false,"本題考點：中性帶的定義，以及室內外溫差、上下開口大小與外部風壓如何改變其高度。\n【正解理由】中性帶是建築物內外靜壓相等的高度，位置由室內外空氣密度差與上下開口面積比共同決定；有風時迎風面外側疊加正的動壓，使外壓大於內壓的範圍向上延伸，壓力相等處被往上推，背風面則因外側呈負壓而使中性帶下降。選項所述方向與此恰好相反，故選 D。\n【逐項排除】\n(A) 敘述正確。室內溫度上升使室內空氣密度變小、浮力效應增強，下方開口的進氣壓差加大，平衡點靠向下開口，中性帶向下偏移。\n(B) 敘述正確。上半部開口加大時排氣阻力下降，質量平衡要求進氣側分擔更大壓差，平衡位置往上移，中性帶向上偏移。\n(C) 敘述正確。中性帶依定義即為室內壓力等於室外壓力的高度，壓差為零；其上為正壓向外流出，其下為負壓向內流入。\n(D) 敘述錯誤，為本題應選者。迎風面外側受正風壓，中性帶應上升；背風面外側為負壓，中性帶應下降，方向與選項所述相反。\n【記憶點】室溫高、下開口大則中性帶降；上開口大、迎風面則中性帶升。","中性帶位置可由開口流量平衡推得。設下開口面積 A1、上開口面積 A2,中性帶距下開口 h1、距上開口 h2,進氣質量流率等於排氣質量流率時可得 A1²×ρo×h1 = A2²×ρi×h2,亦即 h1\u002Fh2 =(A2\u002FA1)²×(ρi\u002Fρo)。室內溫度上升時室內密度 ρi 變小,h1\u002Fh2 隨之變小，中性帶靠向下開口而下降；上開口加大使 A2 變大,h1\u002Fh2 變大，中性帶上升。選項 A 與 B 都能由這一條式子直接讀出，不需要死背方向。\n壓差大小則用煙囪效應公式 Δp = 3460×(1\u002FTo − 1\u002FTi)×h(單位 Pa,溫度取絕對溫標 K,h 為距中性帶的高度)。此式透露兩件事：一是壓差與距中性帶的距離成正比、在中性帶恰為零；二是室內外溫差越大，單位高度的壓差越大，這正是高層建築火災中煙流快速上竄的驅動力。\n外部風的影響常被忽略。風吹向建築物時外牆承受的風壓為 Δpw = ½×ρ×V²×Cp,風壓係數 Cp 在迎風面為正、背風面與側面為負。此壓力疊加於原有的靜壓分布上：迎風面外壓被抬高，原本內壓大於外壓的區段被壓縮，中性帶因而上升；背風面外壓被拉低，中性帶下降。因此同一棟建築物的不同立面，中性帶高度並不相同，這也是排煙口配置需一併考量風向的緣由。\n易混淆對照：中性帶是壓力平衡面，煙層界面是溫度與能見度的分界，兩者並非同一條線；火災成長時室溫升高，中性帶下降、煙層界面也下降，方向相同但成因不同。延伸考點是逆煙囪效應——夏季空調使室內溫度低於室外時，浮力方向反轉，氣流由上層流入、下層流出，中性帶的上下正負壓關係整個顛倒。",true,[28,32,36,40,44,48],{"webId":29,"stem":30,"number":31,"year":11,"session":12},"fire-108-1-fire-science-011","室內火災所產生的熱煙層由天花板向下沉降的時間直接影響逃生；以此觀點而論，下列何者較不利於逃生？",11,{"webId":33,"stem":34,"number":35,"year":11,"session":12},"fire-108-1-fire-science-013","比較室內火災閃燃（Flashover）與複燃（Backdraft），下列敘述何者正確？",13,{"webId":37,"stem":38,"number":39,"year":11,"session":12},"fire-108-1-fire-science-010","安裝爆炸氣道（或洩爆孔、氣孔）可適度降低侷限空間中粉塵爆炸的危害，則下列敘述何者錯誤？",10,{"webId":41,"stem":42,"number":43,"year":11,"session":12},"fire-108-1-fire-science-014","依 Thomas 閃燃公式（Thomas Flashover Correlation），有關室內火災發生閃燃所需最小釋熱率，下列敘述何者錯誤？",14,{"webId":45,"stem":46,"number":47,"year":11,"session":12},"fire-108-1-fire-science-009","就同一種可燃性粉塵而言，下列何種措施有助於降低發生粉塵爆炸的危險性？",9,{"webId":49,"stem":50,"number":51,"year":11,"session":12},"fire-108-1-fire-science-015","下列何種現象對於局部電阻所產生的效應恰與其他三者相反？",15,[53,57,61,65,69],{"webId":54,"year":55,"stem":56,"number":13},"fire-113-1-fire-science-012",113,"直徑一公尺的柴油儲罐因火災受熱溫度達到 727 度，其柴油輻射率為 0.99，波茲曼常數為 5.67×10 -11 (kW\u002Fm 2 K4 )，請問會產生多少的輻射熱（kW\u002Fm 2 ）？",{"webId":58,"year":59,"stem":60,"number":13},"fire-112-1-fire-science-012",112,"下列何種化合物不是可燃性物質？",{"webId":62,"year":63,"stem":64,"number":13},"fire-111-1-fire-science-012",111,"密閉空間燃燒中天花板會向地面放射大量輻射熱促進地面可燃物燃燒速度，此現象為何？",{"webId":66,"year":67,"stem":68,"number":13},"fire-110-1-fire-science-012",110,"根據 NFPA265 對閃燃現象（flashover）之定義，下列敘述何者錯誤？",{"webId":70,"year":71,"stem":72,"number":13},"fire-109-1-fire-science-012",109,"下列常見之乾粉滅火藥劑敘述何者正確？",1785129967516]