UNCERTAINTY OF PROBABILITY COMPONENT OF ACCIDENTAL RISK

Concept of accidental risk is intended to be an objective measure for assessing the risk of accidents in the technosphere. Metric of risk should combine estimation both probability (possibility) of the accident and the damage it caused. For various reasons, any parameter of risk has uncertainty. The problem of uncertainty quantifying arose very early in the study of accidental risk. Often used in practice dotted (scalar) estimation of probabilistic component of risk metric are in most cases inadequate since embody great internal uncertainty In order to provide maximum objectivity by the hazards of various kinds evaluating in the area of technological safety was proposed and received wide use such a measure as a risk. Despite the wide diversity of opinions of experts concerning the determination of the term "risk", apparently, most of them would agree with the interpretation of risk as "a combination of event probability and its consequences". Thus, from a mathematical point of view, the accidental risk of any emergency events (or objects, or technologies) can be specified by a vector quantity having two components: PCR and DCR: - PCR (a component of risk associated with the possibility of an accident) - a quantity, that is quantified the magnitude of subjective probability (possibility) to implement accident. For quantitative estimates the PCR can be axiomatically defined as the quantitative value having the dimension year -1 , taking any value in the range 0 . 1; - DCR (risk component characterizing damage from an accident) - a quantity, which express the total negative consequences of the accident in terms of money. Quantitative assessment of the emergency danger in the methodology of risk associated with both performing calculations on mathematical models, and using the methods of expert estimations. Due to various circumstances, which will be discussed below, are obtained result - the value of risk - has uncertainty, which must also be quantified. The problem of uncertainty existence and uncertainty quantification is inherent in any parameter accidental risk, it is a key problem of risk-methodology on the whole. This problem was first recognized and placed on the agenda at an early stage of technical risk research, when group of prof. Norman Rasmussen prepared report "WASH-1400" on safety of commercial nuclear reactors (US NRC, 1975), and, a little later - when US NRC (special committees of National academy of sciences) published his first report (US National Research Council, 1983). However, twenty five years after these events the same committee stated (US National Research Council, 2009), that the problem of analysis and quantification of uncertainty in risk-methodology is still far from being resolved. In a quantitative sense, the uncertainty presence means, that instead of the scalar (dotted) values the model parameters of dangerous accidents should be characterized by interval (the range of values), which is a segment of the real number axis. Finally, the result of calculation of risk - risk-metric - will also be an interval. In the quantitative assessment of uncertainty theory by the parameters of accidental risk uncertainty quantification, several alternative approaches have been developed, that were designed: a) for the expression of uncertainty parameter;