Subjective risk ratings

The Canadian approach to Road Safety Audits includes the traditional aspects of identifying the safety issues and also includes a subjective risk rating as well as a few suggested solutions. The subjective risk rating was requested by the recipients of the Road Safety Audits so that they could apply a priority hierarchy in addressing the issues. The inclusion of a few potential solutions was to fully utilise the expertise of the auditors who have a professional engineer on the team with expertise in road safety. 

Kniesner and Leeth (1991), who indeed included these rates as independent variables, noted that wage allowances for hazardous jobs may be formalised as a result of government or union action. Such action clearly causes wage differentials, but the problem ofworkers actual perception of job risks remains. This latter problem is related directly to the general issue of objective versus subjective risks, an issue which is not discussed further here. 

In connection with road traffic, with its special condition of self-determination of the rate of work, studies by Taylor [6-40] and Wilde [6-41] have indicated that there is an adequate awareness of the risk content in particular situations. Both authors carried out field experiments which showed that drivers regulate their behavior within the MME-system so that the risk they experience fluctuates only between narrow limits. Thus Taylor reported that drivers tend to increase the speed of the vehicle in situations in which low risk is perceived, and to reduce speed if the perceived risk increases again. The perceived risk was determined in these experiments using the psycho-physiological measure of the galvanic skin response. In a similar experiment Galton and Wilde [6-42] showed that the subjective risk was determined on the basis of a verbally formulated risk scale. The test route consisted of 11 sections with heterogeneous traffic... 

The following parameters represent the subjective facility risk rating values obtained from the DMs using a numerical scale (1-5), where higher numbers represent higher risk as presented in Table 3.1. The risk values are... 

Where a number of residual hazards remain there may be a need to determine priorities for dealing with them. This can be done either subjectively based on the assessor s knowledge of the processes or by evolving, for each residual hazard, a numeric value or risk rating based on a number of factors ... 

The example just shown assumed one discount rate and one oil price. Since the oil price is notoriously unpredictable, and the discount rate is subjective, it is useful to calculate the NPV at a range of oil prices and discount rates. One presentation of this data would be in the form of a matrix. The appropriate discount rates would be 0% (undiscounted),.say 10% (the cost of capital), and say 20% (the cost of capital plus an allowance for risk). The range of oil prices is again a subjective judgement. 

Before a decision is made, all three items, ie, investment, return, and rate of return, would be examined, as would the current cash position, perceived risk, other venture opportunities, and a variety of subjective criteria. Eor this elementary situation, economists would also employ an incremental approach analogous to the above, based on the tenet that each increment of investment should itself make an adequate return. Rarely is there a unique correct decision. Only future events determine the wisdom of the selection even then, the results that another decision would have produced are rarely known. This is the essence of profitabiHty analysis. 

Risk and Uncertainty Discounted-cash-flow rates of return (DCFRR) and net present values (NPV) for future projects can never be predicted absolutely because the cash-flow data for such projects are subject to uncertainty. Therefore, when stating predicted values of (DCFRR) and (NPV) for projects, it is also desirable to give a measure of confidence in the predictions. 

It is obvious that such an approach would be lengthy and would require many pages of documentation that would be difficult to check. It is also obvious that such an approach is still subjective in that the evaluator must make decisions as to the consequences of each failure, the expected failure rate, and the acceptable level of risk for the supposed failure. 

In this study detailed fault trees with probability and failure rate calculations were generated for the events (1) Fatality due to Explosion, Fire, Toxic Release or Asphyxiation at the Process Development Unit (PDU) Coal Gasification Process and (2) Loss of Availability of the PDU. The fault trees for the PDU were synthesized by Design Sciences, Inc., and then subjected to multiple reviews by Combustion Engineering. The steps involved in hazard identification and evaluation, fault tree generation, probability assessment, and design alteration are presented in the main body of this report. The fault trees, cut sets, failure rate data and unavailability calculations are included as attachments to this report. Although both safety and reliability trees have been constructed for the PDU, the verification and analysis of these trees were not completed as a result of the curtailment of the demonstration plant project. Certain items not completed for the PDU risk and reliability assessment are listed. 

Nitrite-based programs require a relatively high application rate to ensure that all anodic areas within the system are fully protected from the risk of pitting corrosion. Undertreatment exposes anodic areas, which are subject to localized pitting as a result of the concentrating power from surrounding cathodic sites. 

The Combined Lysis of Thrombus in Brain Ischemia Using Transcranial Ultrasound and Systemic rt-PA (CLOTBUST) study was a phase II randomized trial which compared continuous transcranial Doppler ultrasound insonation, in subjects with ultrasound evidence of MCA occlusion being given IV rt-PA, to sham insona-tion. ° There was an increased rate of arterial recanalization with the continuous insonation (49% vs. 30%, p = 0.03) and no increased risk of sICH. 

Safety and risk factors evaluate approximately the speed at which a toxic substance reaches a toxic vapour concentration in air. An accurate way to do this would be to know the vapourisation speed for this substance and the air renewal rate of the room in which it is handled. This is why regulations recommend measurement of the vapourisation speed for a particular substance and include it in safety sheets. One can hardly use this figure since it is rarely mentioned. The only substances which were subjected to such measurements are the most commonly used although these figures only are remotely linked to the real conditions. So it was decided to suggest a method derived from the vapour pressure of the substance, which is a factor the vapourisation speed depends on precisely. 

The clinical scenario and the severity of the volume abnormality dictate monitoring parameters during fluid replacement therapy. These may include a subjective sense of thirst, mental status, skin turgor, orthostatic vital signs, pulse rate, weight changes, blood chemistries, fluid input and output, central venous pressure, pulmonary capillary wedge pressure, and cardiac output. Fluid replacement requires particular caution in patient populations at risk of fluid overload, such as those with renal failure, cardiac failure, hepatic failure, or the elderly. Other complications of IV fluid therapy include infiltration, infection, phlebitis, thrombophlebitis, and extravasation. 

Antioxidants and antimicrobial preservatives are the subject of a further specific guideline (CPMP/CVMP/QWP/115/95, adopted July 1997). These materials are designed to be aggressive, and there are certain risks associated with their use. They are used, respectively, to (a) reduce the rate or extent of oxidation of active ingredients or other ingredients or... 

Risk Estimation. As mentioned above, chronic risk is expressed as a probability of occurrence per year or per lifetime of some adverse consequence caused by exposure to the pollutant. Statutory mandates have focused on human health effects as the primary expression of chronic risks. The basis of the risk calculation is the dose/response curve that relates the adverse effect to the amount or rate of a chemical taken in to the subject. Because of regulatory emphasis of cancer, most of the work devoted to the deviation of dose/response curves has been concerned with the probability of appearance of a tumor as the adverse effect. 

The radiofrequency pulses involved in MRI cause thermal heating of the tissues, and are thus subject to FDA limits on the amount of RF power that is transmitted to a subject during a medical scan. The RF power unit is specified as the specific absorption rate (SAR) and is measured in watts per kilogram of body tissue (W/kg tissue). Powers that exceed this level put the subject at risk of tissue damage incurred as a result of the tissue s inability to remove the heat through blood flow. 

The Log-Rank Test provides a method for comparing risk-adjusted event rates, useful when test subjects in a study are subject to varying degrees of opportunity to experience the event. Such situations arise frequently in toxicology studies due to the finite duration of the study, early termination of the animal or interruption of treatment before the event occurs. 

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