Quantifying Risk

In the North Sea this is often done with detailed quantified risk assessments and the calculation of an overall IRR or risk of total loss of structure. Mitigation measures are incorporated until it can be shown that risk levels meet a minimum criteria and the cost of further mitigation has such high cost to benefit ratios that further mitigation is no longer practicable. ... 

The most important part of the approach adopted in this book is concerned with the analysis of dangerous reactions , in this chapter a forecast analysis of risks that can be caused by an interaction between two or several chemicals, or between chemicals and materials, is proposed. It will be a general approach, and its purpose is to develop a range of tools in order to forecast and quantify risks due to substance reactivity in deliberate or accidental contact. 

EPA research investments since 1995 in pesticide exposure and risk assessment methods have helped pioneer novel approaches to quantify risk levels. A team at the University of Washington s School of Public Health and Community Medicine found that 2-5 year olds consuming predominantly organic foods over a 3-day period had 8.5-fold lower mean levels of OP insecticide metabolites in their urine than children eating mosdy conventional (unlabeled) foods (Curl et al., 2003). The study was carefully designed to minimize potentially... 

The facility is subjected to a process hazard analysis commensurate to the level of hazard the facility represents (i.e., Checklist, PHA, HAZOP, What-If review, Event Tree, FMEA, etc.). The results of these analyses are fully understood and acknowledged by facility management. Where high risk events are identified, quantifiable risk estimation and effects of mitigation measures should be evaluated and applied if productive. 

These special analyses are prepared from the quantifiable risk analysis and a total risk scenario can be presented which depicts the estimated incident effects. An example is shown in Table 8. 

Usually the petroleum industry level of risk for a particular facility is may be based one of two parameters. The average risk to the individual (FAR or PLL) or the risk of a catastrophic event at the facility (QRA). The risk criteria can be specified in two manners. Risk per year (annual) or facility risk (lifetime). For purposes of Consistency and familiarity all quantifiable risks are normally specified as annually. Where value analysis is applied for cost comparisons of protection options, a lifetime risk figure is normally used. 

If HI is less than one, it may be inferred that even those in the human population at the high end of exposure do not incur doses in excess of the estimated threshold dose, and so are unlikely to be at risk of toxicity. For His that exceed one, it may be inferred that some fraction of the population is at risk of toxicity, and the larger the HI, the larger the (non-quantified) risk. 

Risk assessment has become a dynamic process, in the sense that what was considered safe at one time can be considered as unsafe later. When we quantify risks, we need to distinguish among parameters that represent eternal truths and other parameters that represent temporal knowledge and considerations ... 

Stratospheric ozone depletion—one relatively easily controllable class of trace gases—ozone depleting chemicals (ODCs), principally chloroflurocar-bons (CFCs)—with relatively well quantified risks... 

Criteria pollutants six common pollutants—ozone (O3), carbon monoxide (CO), sulfur dioxide (SO2), nitrogen dioxide (NO2), lead (Pb), and particulate matter less than 10 microns (10 pm) in size—regulated since 1970 in the United States and presenting relatively well quantified risks... 

Acid precipitation—two relatively easily controllable classes of trace gases— oxides of nitrogen (NOx) and oxides of sulfnr (SOx) with relatively well quantified risks... 

Risk management is especially important for the presentation of process improvement proposals to management where resources are required. The ability to quantify risk and demonstrate continuous improvement benefits is essential to project... 

Quantifying Risk for Noncarcinogenic Effects Hazard Quotient... 

The MOE does not quantify risk (the increased probability of an adverse health effect). Instead, the MOE indicates how far the dose from exposure is below the benchmark dose. If the MOE is sufficiently large, then the increased probability of an adverse health effect is either zero (because the dose is below a threshold for the adverse health effect) or de minimis (without appreciable risk or practical certainty of no harm) and, hence, acceptable or safe. 

The ratio referred to in the third step is utilized to quantify risk from noncarcinogens. As the fourth step indicates, the hazard index for individual chemicals may be summed for chemicals affecting a particular target organ or acting by a common mechanism in order to provide a final measure of noncarcinogenic toxic risk. If the sum of hazard indices is less than one, then the risk of adverse health effects is considered acceptable. 

The rate at which a contaminant is released from a somce is a critical parameter in quantifying risk at contaminated sites. Pictme two dilferent extremes of release from the somce In the first case, 1,000 kg of benzene (a confirmed human carcinogen) exists in a lined surface impoundment and is volatilizing at a rate of 0.5 kg d and is potentially inhaled by a nearby population. In the second case, the same mass of benzene is strongly sorbed to a clay soil rich in organic matter 1 m below the soil surface, from which the volatilization rate is 10 kg d. Obviously, the risk of hazardous chemicals depends on the rate of contaminant release. 

FIGURE 9.2 Toxicity endpoints and risk measures used in ecological models that have been used to assess the risk of pesticides for nontarget organisms in papers published between 2000 and May 2007. (a) Toxicity endpoints, (b) Measure used to quantify risk. Note that some publications made use of more than 1 toxicity endpoint and more than 1 measure of risk. 

Regarding the quantification of risk or, more generally, the effects of pesticides, we found only a few cases where measures were used that directly quantified risk. In most cases, possible effects on population dynamics were presented. This is helpful for the demonstration but not for the quantification of effects and, in particular, risk. Likewise, the quantification of toxicity was often only specified as a mortality rate, and in some cases it was not explained how this mortality rate was calculated. In most instances, only increased mortality was considered, for example, mortality following constant exposure, although one of the potentials of population models is to consider sublethal effects, effects of different exposure patterns, and time-dependent effects. 

When dealing with quantified risk assessment, these definitions need to be linked to some form of numerical value for a defined effect. It is also necessary to distinguish between individual risk and societal risk when drawing conclusions. 

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