Quantitative risk assessment uncertainties

Felter, S.P., et al., An evaluation of the scientific basis for default uncertainty factors for use in quantitative risk assessment of the induction of allergic contact dermatitis, Contact Derm. Al, 257-266, 2002. 

In this paper I have tried to show that measurement of health benefits attributable to TSCA is not feasible. I hope that in doing so I have not belabored the obvious. For new chemicals and for most existing chemicals, prospective evaluation of health benefits to be achieved by various exposure controls will have to be based on extrapolation from microbial and animal data. However, while such extrapolation may be useful in a qualitative sense, quantitative risk assessment techniques involve considerable uncertainty, and in any case have not been developed for chronic effects other than cancer. 

For food allergens, validated animal models for dose-response assessment are not available and human studies (double-blind placebo-controlled food challenges [DBPCFCs]) are the standard way to establish thresholds. It is practically impossible to establish the real population thresholds this way. Such population threshold can be estimated, but this is associated with major statistical and other uncertainties of low dose-extrapolation and patient recruitment and selection. As a matter of fact, uncertainties are of such order of magnitude that a reliable estimate of population thresholds is currently not possible. The result of the dose-response assessment can also be described as a threshold distribution rather than a single population threshold. Such distribution can effectively be used in probabilistic modeling as a tool in quantitative risk assessment (see Section 15.2.5)... 

Because the literature describes several limitations in the use of NOAELs (Gaylor 1983 Crump 1984 Kimmel and Gaylor 1988), the evaluative process considers other methods for expressing quantitative dose-response evaluations. In particular, the BMD approach originally proposed by Crump (1984) is used to model data in the observed range. That approach was recently endorsed for use in quantitative risk assessment for developmental toxicity and other noncancer health effects (Barnes et al. 1995). The BMD can be useful for interpreting dose-response relationships because it accounts for all the data and, unlike the determination of the NOAEL or LOAEL, is not limited to the doses used in the experiment. The BMD approach is especially helpful when a NOAEL is not available because it makes the use of a default uncertainty factor for LOAEL to NOAEL extrapolation unnecessary. 

Quality assurance and quality control (QA/QC) A system of procedures, checks, and audits to judge and control the quality of measurements and reduce the uncertainty of data. Some quality control procedures include having more than one person review the findings and analyzing a sample at different times or using different laboratories to see if the findings are similar Quantitative risk assessment (QRA) A process that relies on mathematical modeling and estimations usually derived from animal test results and the probability of risk for a chemical substance at the low dose to which the human population is normally exposed Radionuclide A nuclide with radioactive properties... 

The traditional scientific and political response to these data gaps has been to collect more information and use a technique called quantitative risk assessment to calculate the probability of harm given particular exposures, applying numerous assumptions in the process. While this process has been termed the sound science approach, it is often far from that. Quantitative risk assessments often narrow the types of information that go into decision-making and hide uncertainties. They are time-consuming and costly to complete and while debates over details of these assessments occur, the default policy option is that no policy action is necessary. 

A quantitative risk assessment (QRA) is an integrated, quantitative analysis (including uncertainty) of accident scenarios, their likelihood, and possible consequences. Current QRAs examine human actions as well as systems failures, external events as well as internal failures, and worker risk as well as public risk. A salient feature of a QRA is that it is integrated, in that it ... 

My thesis in this paper is that in order to be "good", a quantitative risk assessment must characterize and deal with the major uncertainties associated with the problem. But before I can address this issue I must first concern myself with what I mean by"good." Good against what criteria Good given what objectives ... 

Carol N. Scott. Executive Director of the Committee to Coordinate Environmental Health and Related Programs, U.S. Department of Health and Human Services, speaking from the perspective of the public policy analyst, noted that in an ideal political and social climate a risk assessment should, in advance of a crisis, present to knowledgeable risk managers a quantitative risk assessment which expresses all of the uncertainties incorporated in the assumptions. However, too often the crisis occurs first, and the public-press-politician synergistic relationship takes over, as in the case of the ethylene dibromide situation, or someone leaks misinformation to the press, as in the case of Alar, or politics takes over, as in the case of the controversy over the appropriate ways to use and regulate biotechnology. 

Aven, T. and Renn, O. 2009b. The Role of Quantitative Risk Assessments for Characterizing Risk and Uncertainty and Delineating Appropriate Risk Management Options, with... 

Exploring uncertainty in quantitative risk assessment used for decision support in electricity distribution system asset management... 

We use a case to illustrate the use of methods to explore uncertainty in QRA as input in electricity distribution decision making. The case is based on a quantitative risk assessment model estabhshed in (Nordgard Solum 2009), being further elaborated for the purpose of this paper. It is emphasised that the case is for illustrative purposes only and that it does not represent the decision basis for a real decision. 

Cox (2006) argues for the need for simplifying the traditional quantitative risk assessments, primarily because of the uncertainty, complexity and dynamic nature of what is being analysed. 

Methods for toxicological safety assessments are multiple and varied - some are more reliable than others, some more radical than others, but all are important. Their nature greatly depends on their endpoints, namely, the degree of practical safety they attempt to attain. Unfortunately, the true validity of these methods can only be assessed retrospectively, that is to say, by the record of cases of health impairment they were able to prevent over a reasonable period of time. Because of this and the uncertainty inherent in any extrapolation technique, the final products expressed in numerical form can only be considered as opinions. Some important toxicological opinions presented in numerical form are the LD50 the quantitative risk assessments, the threshold limit values (TLV), and the acceptable daily intakes (ADIs). 

Consultations with other appropriate bodies Review and summary of previous reports, with report references Outline conceptual model with nature and location of gas sources, migration pathways and receptors clearly identified Description of possible pollutant linkages for ground gas Identification of potentially unacceptable risks posed by ground gas, including criteria used to identify those risks Discussion of uncertainties and gaps in information Description and justification of next steps proposed at the site, e.g. carry out site investigation and quantitative risk assessment Yes D/No Yes D/No Yes D/No Yes D/No Yes n/No Yes D/No Yes D/No ... 

A Quantitative Risk Assessment (QRA) is always performed on one or more models of a real world, a system or an event. The model never contains all information on modeled system and this state of deficiency of information related to understanding or knowledge of a system or an event is called uncertainty. The necessity of identifying and expressing the uncertainty is widely recognized (Helton Burmaster, 1996) and this need is even more important when there is an intention to use the QRA as a tool in more cases. As the outputs of the QRA methodology for gas pipelines (CGA, 2013 a) are currently used in valid codes of practice of Czech gas industry (CGA, 2013b), the need of uncertainty evaluation is clear. 

The insufficiency of quantitative risk assessment in the maritime-related literature together with the vision to establish a secure and resilient SCMI system has resulted in a need for an integrated risk assessment methodology capable of tackling the uncertainties associated with a system s operation (John, 2013). 

Aven, T., 2003. Foundations of risk analysis a knowledge and decision-oriented perspective. Chichester Wiley. Aven, T., 2011. Quantitative risk assessment the scientific platform. Cambridge Cambridge University Press. Aven, T., 2013. Probabilities and background knowledge as a tool to reflect uncertainties in relation to intentional acts. Reliability Engineering System Safety, 119(0), 229-234. doi http //dx.doi.0rg/lO.lOl6/j. ress.2013.06.044. 

Discussing the uncertainties involved in risk calculations is an important aspect of risk characterization. Quantitative risk assessments are fraught with uncertainty. Estimates of exposure (chronic daily intake) are probably accurate to roughly a factor of 10. Toxicity values—the reference dose for noncancer health effects and the slope factor for cancer risk—are also essentially order-of-magnitude estimates. As a result of these uncertainties, quantitative risk assessment gives a number that could be... 

---