an estimate of the likelihood and consequences of these scenarios, an evaluation of the risk based on equation (2) and finally a comparison of the calculated risks to the acceptable risks to find out whether the evaluation criteria are satisfied。 Currently, probabilistic methods are not often used, however, they will increase in popularity once acceptable risk values are established and risk assessment tools become readily available。 Therefore, one of the major issues that must be addressed prior to carrying out a risk assessment analysis is the establishment of acceptable risk criteria。 Acceptable risk levels depend on the risk assessment objectives to be satisfied and any defined risk level is debatable。
Unfortunately risk levels found in the literature are at moment only suitable in building。
In contrast to deterministic calculations, probabilistic methods may be able to consider more elements not element-by-element evaluation and to provide risk estimates。
Presently, the probabilistic approach cannot use because of the lack of appropriate risk assessment tools and the unavailability of specified risk levels acceptable。 However, with the introduction of performance-based codes, the availability of risk assessment models and the establishment of risk levels acceptable, the probabilistic approach will be the preferred method in performance-
based design as it quantifies the risk levels and allows the identification of designs that will have acceptable risk levels at minimum cost。
The CFAST Model and the Fire Phenomenon Effect on Persons
The phenomenon of the fire analysed to mathematics base has the purpose of representing a complex reality。 Consequently it is inevitable to introduce simplification elements that will be more or less prominent。
In the first a model is based on an assembly of initial hypotheses that outline, further that its reference "scenario", the possible evolution。
Such hypotheses, clearly, are able to cover only a part of the event active that will be possible to happen。
The efficaciousness and the correspondence of the models depend, then, mainly from the knowledge of the operation mechanisms, characteristic of the various " phenomenona” present, and of existing interaction。
In the case of fire models, the first studies have regarded points on the single phenomenon: the combustion, the fire plume, smokes development etc。 Only later the single formulation has been aggregate, valuing the interrelations and determining the appearance of the first procedure as "simulated" or models of fire。
The path is still uncompleted, but numerous are the inpidualized phenomenona and scanned in specific details。
In particular result of interest with the zone models can be obtained by CFAST (see Peacok, 2000)。
The "phenomenona" inpidualized in CFAST includes:
-the fire;
-the fire plume;
-the ceiling and wall jets;
-layers;
-the vents flows;
-the vent fires;
-the heat transfer;
possible result only profits as comparison parameters, in the project operations, with the caution necessary。
Two source of heat are utilized when a person is exposed to fire:
-the gas product from the combustion;
-the irradiation from the fire and from all the parts which have elevated temperature。
The effects that are possible are the "heat stroke" or hyperthermia, or the damages to the respiratory tract。
In the experimentations using pigs there has been not damages, for exposures of 2 minutes to temperature of l20°C or 5 minutes to l00°C or, still, l0 minutes to 90°C。 Other tests with person have shown the possibility of standing, for covered inpidual protection, for about 30 minutes to a temperature of 100°c and 60 minutes in the case of 75°C。 船舶设计中的消防安全性能分析英文文献和中文翻译(6):http://www.youerw.com/fanyi/lunwen_94979.html