本文主要是描述火災猛烈度造成建築物結構抗火失敗的機率模式。文中假設只有火勢過大(即最盛期或閃燃火災)才會威脅到建築物的結構抗火安全。在推估閃燃類型火災發生的機率時'，主要是以波松分佈配合火災統計資料中的火災發生率、區劃空間樓地板面積及火災中閃燃類型火災所佔比例來推導的。在評估建築物結構抗火時，可以用結構抗火系統的功能函數來表示，此時系統的可靠度可以定義為功能函數成功操作的機率。另外，在評估結構抗火安全景簡單的方法，宜包含火載量和抗火性能時效兩者之間的關係。其次，為了考量更多影響火災危害的因子，文中提出修正的模式，結合火災猛烈度及抗火性能時效。在修正的模式中，火災猛烈度是人載量、開口因子及材料的熱性質的函數。火災猛烈度的測量可用等價時間的觀念來表示。隨著更多的背景資料的組合，我們可預期結構抗火失敗的機率模式會有不斷的進步。

　　　　　Methods of stochastic modeling offires of sufficient severity to threaten the structural firesafety of buildings are presented. In this study, it is reasonable to assume that only large fires(i.e. fully-developed or flashover fires) can threaten the structural fire safety of buildings. Theprobability of flashover fire occurrence is estimated by employing Poisson distribution withinformation regarding the rate of fire occurrence, floor area at risk and proportion of flashoverfire. Structural fire safety is expressed as an engineering performance function for evaluatingits reliability. The reliability of a structural fire safety may be defined as the probability ofsuccessfully performing its fire resistance function. The simplest approach to assessingstructural fire safety involves the accepted relationship between fire load and fire resistanceperiod. In order to consider more factors affecting fire damage, an advanced model thatconnects fire severity and fire resistance period is proposed to modify the simplest one. In theadvanced model, fire severity is a function of fire load, opening factors and material thermalproperties. Measurement of fire severity may be expressed as time equivalent. As morebackground information is assembled and organized, we can anticipate a gradual advancementin stochastic modeling for structural fire safety.