Predictive safety indicators

Safety indicators, safety criteria and compliance requirements The most obvious indicators of the safety of a repository are the predicted effects on man and the environment. However, because estimation of radiation affects on man requires speculation on human behaviours, at very far-future times other safety indicators have been proposed. One example is the Scandinavian proposal for comparing radionuclide releases with the flow of natural radionuclides in the environment. Most safety assessments, however, concentrate on comparing estimated doses or risks to man out to far-future times with some acceptability criteria. On the much debated topics of dose criteria vs risk criteria, acceptable bounding levels, and timescales for the assessments there have been no single consensus decisions arrived at. Rather there has been a growing awareness that a multi-faceted approach is needed. 

The safety and the environmental effects from a repository for spent nuclear fuel should be evaluated for very long time periods, typically hundreds of thousands of years. For time periods until the next glaciation, or similar expected drastic changes of the biosphere, the individual dose received by members of a hypothetical critical group could be calculated and assessed with some confidence. For longer time periods similar predicted doserates are used as "safety indicators" together with... 

The interpretation of performance assessment results as indicators of safety reflects the uncertainties associated with predictive modelling. The IAEA-TECDOC-767 recommends different indicators for different time frames (possibly in support of a safety case based on dose or risk). Some countries have introduced a fixed time cut-off for quantitative performance assessment to account also for the uncertainties. The concept of safety indicators may Aus render a time cut-off unnecessary. Predictions beyond about a million years, however, seem to be meaningless even as an indicator of the possible fiiture bdiaviour of the repository system (i.e. safety assessment). Releases possibly occurring after these long times may indicate a well chosen and designed repository system. 

According to the Department of Energy (DOE), anecdotal evidence exists to indicate that measurement of percentage or safe behaviors is predictive. If used correctly, this means that the employee observation and feedback techniques may be used to predict safety issues that exist... 

A survey of 500 plants that have implemented predictive maintenance methods indicates substantial improvements in reliability, availability and operating costs. The successful programs included in the survey include a cross-section of industries and provide an overview of the types of improvements that can be expected. Based on the survey results, major improvements can be achieved in maintenance costs, unscheduled machine failures, repair downtime, spare parts inventory, and both direct and in-direct overtime premiums. In addition, the survey indicated a dramatic improvement in machine life, production, operator safety, product quality and overall profitability. 

As indicated earlier, non-Newtonian characteristics have a much stronger influence on flow in the streamline flow region where viscous effects dominate than in turbulent flow where inertial forces are of prime importance. Furthermore, there is substantial evidence to the effect that for shear-thinning fluids, the standard friction chart tends to over-predict pressure drop if the Metzner and Reed Reynolds number Re R is used. Furthermore, laminar flow can persist for slightly higher Reynolds numbers than for Newtonian fluids. Overall, therefore, there is a factor of safety involved in treating the fluid as Newtonian when flow is expected to be turbulent. 

Predictions of no, or low, toxicity in a general drug screening approach should be used to indicate a possible absence of toxicity in potential drug candidates. Inevitably this would require further toxicological assessment of potential drugs to ensure safety. 

This sketch briefly addresses the problem that many companies in the chemical process industry are currently dealing with regarding safety. In spite of the various kinds of safety measures and indicators used, major catastrophes still occur. In this example, all the indicators and measures implemented showed an excellent safety performance compared to other companies. So why did this accident still occur in spite of all the outstanding indicators Were there no signs indicating that an accident was on its way What was wrong with the safety measures and indicators that they didn t predict the accident ... 

Although the literature indicates that seizures and arrhythmias are associated with TCA plasma levels greater than 1,000 ng/mL, the QRS duration might be a better early predictor than plasma levels in overdose cases. For example, in a series of 49 TCA overdoses, seizures occurred only in cases with a QRS duration above 0.10 second, and ventricular arrhythmia was seen with a QRS greater than 0.16 second (430). Thus, for acute overdose, the ECG may provide a reliable and quick measure of risk with TCA drugs however, how well a QRS of less than 0.10 second predicts ultimate safety or how long after ingestion the ECG must be followed, is uncertain (431). 

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