Risk Assessment and Management at Deseret Chemical Depot and the Tooele Chemical Agent Disposal Facility (1997) / Chapter Skim
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APPENDIX A
APPENDIX A
Pages 57-74
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From page 59... ...
Examples are air pollutants emanating from a chemical manufacturing facility or from automobiles on a busy highway and radon seeping into basements from underlying bedrock. RISK ASSESSMENT AN ILLUSTRATIVE EXAM PLE Risk Consider a concrete sidewalk with a large, vertically displaced crack in it.
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From page 60... ...
The example of a cracked sidewalk illustrates the risk assessment process: Hazard identification is a straightforward process that involves the simple visual observation of the fact RISK ASSESSMENT AND MANAGEMENT AT DCD AND THE TOCDF that a tripping hazard exists because of the large, vertically displaced crack in the sidewalk. Consequence evaluation is somewhat more involved because it requires that consideration be given to all possible outcomes of a person actually tripping over the crack.
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From page 61... ...
To summarize, hazard identification, consequence evaluation, and exposure assessment have established the following: A hazard exists for users of the cracked sidewalk. Ten thousand people are potentially exposed to the hazard at some time (e.g., over a period of a year or two)
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From page 62... ...
RISK ASSESSMENT FOR A COMPLEX FACILITY This simple example helps to put the basic ideas of risk assessment in focus. However, it can be deceptive because, in the real world, especially in complex situations where quantitative risk assessments are used, neither the risks nor the useful models of risks nor the presentation of results is this simple.
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From page 63... ...
The aleatory uncertainty captures variability that is observed but is beyond the explanation of the physical models used in the analysis. The epistemic uncertainty allows for our lack of knowledge (i.e., lack of observation)
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From page 64... ...
Figure A-2a is a representation of pure epistemic uncertainty. Here some event will either surely happen (p = 1 )
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From page 65... ...
Chemical agents may be stored in sturdy steel ton containers, making exposure to workers or the public quite unlikely. A large pro pane tank, potentially subject to destructive earthquakes, can be maintained with a limited volume of propane to minimize the tank's structural response to the earthquake, thereby reducing the chance of rupture and subsequent explosion.
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From page 66... ...
, and emergency planners. Historically, the first risk measure proposed for risk studies was the "expected consequences." This widely used measure is the basis (limit or requirement)
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From page 67... ...
For fatalities, the risk profile dis- and the risk is plays the probability of an accident involving "x or more" fatalities as a function of x, the number of fatali ties. The three risk profiles for the three simple results above are all shown on Figure A-3.
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From page 68... ...
An easy way to understand the presentation of results, called a risk curve or a risk profile, is to think of the list of scenarios above, R = { |
From page 69... ...
(Sometimes the QRA, like the DCD/TOCDF QRA, also evaluates the impact on workers.) Both are used to manage risk by changing facility design or operation and by managing emergency response practices.
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From page 70... ...
The same can be said of the world of practice. The three traditions have progressed rather independently of each other but have converged in the Army's Chemical Stockpile Disposal Program.
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From page 71... ...
· suggesting alternative ways to reduce risk · evaluating risk reduction alternatives selecting preferred alternatives (including implementing decisions) Step 1: Understanding the Risk Understanding the results of risk assessment implies more than knowing the summary numerical results of the QRA and HRA.
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From page 72... ...
Changes to Emergency Response Capabilities Plans, preparations, and mitigation activities by the Chemical Stockpile Emergency Preparedness Program and other emergency response organizations can be revised or restructured to deal more effectively with the major identified contributors to risk. The relative risks associated with alternative responses can also be assessed.
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From page 73... ...
Step 3: Evaluating Risk Reduction Alternatives For every proposed change (in design, equipment, or procedures) , it is necessary to assess the impact of the change on safety, ease of operation, environmental performance, public and worker health, short-term and long-term economic costs and benefits, schedules, regulatory compliance, political and public acceptability, and flexibility to respond to future mandated or voluntary changes (OTA, 1995~.
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From page 74... ...
1996. Report of the Risk Assessment Expert Panel on the Tooele Chemical Agent Disposal Facility Quantitative Risk Assessment.
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