在傳統火災和煙霧控制系統中，係利用在小的開口和縫隙處的壓力差形成物理性質障礙物去限制煙霧從一個地方傳播至另一個地方然後利用灑水系統除去火和煙霧。美國防火標準大都採用國家火災保護協會（NFPA）使用手冊為準則。在此一原則下可利用簡單區域模式針對每一個區域採用控制體積法去解出質量和能量守恆方程式去求解。簡單區域模式的缺點是動量守恆僅由開口的效能決定。其優點是，不同模式經由電腦的計算與模擬將可以快速地比較他們之間差異的性質。故應用此一區域性近似模式在大空間跨距之建築物包括：大型購物中心、航空大廈、運動場所和倉庫，並不適當。CFD在火災模擬時稱之實場場模式"Field-modeling"，主要是為了要和簡單區域模式"Zone- modeling"作區別；當能限制衝量守恆的參數，CFD將有無比的能力去做火災結果的工程評估並且有更佳的空間性和火災在不同時間下所模擬出來的物理現象。為了增加CFD能合乎實際的需求，程式中提供戶外建築物的設定和火、煙霧開始發生初始值的設定。本篇將討論建築物分別在區域（ASMET）和實場（FLUENT AND FDS）模式下模擬結果的差異。 Conventional fire and smoke control systems use pressure differences across small openings and cracks in physical barriers as a means to restrict smoke propagation from one space to another and water- spray curtains to diminish or eliminate fire and smoke. Most fire codes of United State of American depend upon the National Fire Protection Association (NFPA), guidebooks. In turn these propose the use of simple zone models that solve conservation of mass and energy in a control-volume sense for each zone. One weakness of zone modeling is that momentum conservation is only captured through use of loss coefficient at openings. The strength of zone models is that they are very fast compared with computational fluid mechanics (CFD) based models. Atria, covered shopping malls, convention centers, airport terminals, sport arenas, and warehouses are examples of large spaces for which these conventional zone-model approaches are not always effective. CFD , sometimes called "field- modeling" in the fire community to distinguish it zone-modeling, has an unparalleled potential as an engineering estimator of fire consequence in atria since it permits specification of momentum conservation as well as much finer spatial and temporal resolution of the fire physics. In addition CFD approaches provide a link between outside building weather conditions and fire and smoke development. This paper will discuss the results of calculations for an example building atrium based on zone (ASMET) and field (FLUENT and FDS CFD)-based models.