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4 Evaluation of Accident Event Modeling
Pages 37-48

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From page 37...
... OVERVIEW OF METHODS FOR ACCIDENT EVENT MODELING Section 4 of the uSSRA begins with a description and analysis of the pathways that could lead to pathogen release from each of three originating locations within containment and from non-containment areas outside the laboratories. The uSSRA created conceptual models of release pathways and provided estimates of the total amount of material available for release (MAR)
From page 38...
... . This is accompanied by a table that provides the following for each node of the event tree: failure probabilities and "reduction factors" that are to be applied to the MAR, one reduction factor that is assigned when the mitigation system at each event tree node fails, and another when it is fully functional.
From page 39...
... DEVELOPMENT OF FAILURE PROBABILITIES AND REDUCTION FACTORS It is impossible in the time provided for this evaluation to review every event tree and accompanying table in Section 4 and to comment on the adequacy of the data and assumptions that are used to support all of the large number of estimates of probabilities and reduction factors associated with each of the many nodes of each event tree. Even with a sound method, the reliability of the assessment remains completely dependent on the scientific reliability of each of the hundreds of inputs used.
From page 40...
... . For determining amounts of FMDv, the uSSRA states that it chose to use only references that involved primary bovine thyroid cells for input data "because the bovine thyroid cell assay is the most sensitive for determining the concentration of FMDv" (p.
From page 41...
... Because factors in the model multiply to yield risks, an order-ofmagnitude underestimation in each of several multiplied factors quickly reduces the final risk. Low, Median, and High MAR Values Accounting for variability in MAR is a valid objective, as is the use of Monte Carlo simulations.
From page 42...
... . Inasmuch as animal caretakers routinely go from infected to uninfected rooms the next day, using routine shower and decontamination practices without respirators and without transmitting FMDv to control animals, readers familiar with FMDv would question why N95 respirators would be required and what base of institutional knowledge the uSSRA chose to build from.
From page 43...
... Therefore, the committee views the use of a 2.5% failure rate in a real-life setting as an under-representation of reality. Factors Related to Respiratory Transference With respect to transference to the respiratory tract, the uSSRA assumes that failure rates due to poor fit of N95 masks would be only onetenth the rate identified in a published study, in which failure rates of about 25% were found when the mask fit was poor.
From page 44...
... , using the leveraging method developed by the Pacific Northwest National Laboratory, including provision for the facility size and considering spatial variation of wind speed along the damage path of a tornado. A site-specific tornado risk model that relates tornadic wind speed with the annual probability of occurrence (or the mean recurrence interval, commonly referred to as the mean return period)
From page 45...
... In light of the risks provided in the uSSRA, it is unlikely that any further refinement in analysis would yield changes that would affect the final cumulative risk across events. Tornado Design Aspects The uSSRA suggests that the current NBAF 65% designs provide a tornado-hardened zone to ensure protection against loss of containment in the event of a tornado and protection against envelope penetration and development of cracks up to wind speeds of 228 mph.
From page 46...
... EARTHQUAKES Seismic Risk Assessment The uSSRA assesses the risk of earthquakes at the site by using U.S. Geological Survey spectral acceleration data to determine a 2% POE over 50 years at the NBAF site.
From page 47...
... To a large extent, this is a design issue and such lab appurtenances should be well secured and detuned from the main structure. Assessment of Methods and Assumptions The seismic risk analysis in the uSSRA fails to address fundamental issues in the selection of appropriate design spectral acceleration and the attendant performance of the containment system under design earthquake conditions.
From page 48...
... 2010. Short-lived carriage of foot-and mouth disease virus in human nasal cavities after exposure to infected animals.


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