would be a 70% probability that FMDv release would cause an infection resulting in an outbreak during the 50-year life span of the NBAF in Manhattan, Kansas. In contrast, the uSSRA concludes that the cumulative probability for 142 risk events (including catastrophic events such as tornadoes and earthquakes) leading to an accidental release of FMDv over 50 years is about 0.11% (or 1 in 46,000 per year), which is orders of magnitude lower than the first estimate. Improvements in the 65% design phase documents for the facility compared with the earlier and less complete design documents on which the 2010 SSRA was based may explain some of the risk reduction. However, the committee believes that questionable and inappropriate assumptions were used in the uSSRA that led to artificially lower estimates of the probabilities and amounts of pathogen released.

In contrast with the 2010 SSRA, which cited fomites and lack of respiratory protection as the most likely pathways of accidental FMDv release, the uSSRA concludes that the most likely release mechanisms are those associated with natural hazards, specifically earthquakes and tornadoes. The uSSRA concludes that these are about 20 times more likely than operational pathways.

Despite improvements, the committee finds that the uSSRA underestimates the risks of pathogen release and infection and inadequately characterizes the uncertainties in those risks. The committee finds that the extremely low probabilities of release are based on overly optimistic and unsupported estimates of human error rates, underestimates of infectious material available for release, and inappropriate treatment of dependencies, uncertainties, and sensitivities in calculating release probabilities.

The committee is concerned that the vanishingly small estimates of risk found throughout the uSSRA are inconsistent with most modern, complex industrial systems. In many instances, the committee could not verify uSSRA results, because methods and data were unevenly or poorly presented. The uSSRA also contains inconsistent information, which made it difficult to interpret data or to reconstruct risk scenarios and thereby made it difficult to determine the degree to which risks were underestimated.

The committee recognizes that significant complexities accompany a risk assessment of this nature, yet the practice of risk analysis is sufficiently mature to be able to treat such complexities (Kumamoto and Henley, 1996; NASA, 2011) and therefore the committee’s expectations for such a risk assessment are customary and attainable. The number of facilities comparable with the NBAF is small, so there is little empirical validation of the risk estimates. However, because a pathogen release from the NBAF could have devastating widespread agricultural, economic, and public health consequences, a risk assessment that reaches inappropriate conclusions could have substantial repercussions.

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