The US Navy's Sea, Air and Land Special Operations Forces personnel (SEALs) perform a physically demanding job that requires them to maintain fitness levels equivalent to elite athletes. As some missions require SEALs to be deployed aboard submarines for extended periods of time, the prolonged confinement could lead to deconditioning and impaired mission-related performance. The objective of this field study was to quantify changes in aerobic performance of SEAL personnel following a 33-day submarine deployment. Two age-matched groups of SEALs, a non-deployed SEAL team (NDST, n = 9) and a deployed SEAL team (DST, n = 10), performed two 12-min runs for distance (Cooper tests) 5 days apart pre-deployment and one Cooper test post-deployment. Subjects wore a Polar Vantage NVTM heart rate (HR) monitor during the tests to record exercise and recovery HR. Variables calculated from the HR profiles included mean exercise heart rate (HRmean), maximum exercise heart rate (HRmax), the initial slope of the HR recovery curve (HRrecslope) and HR recovery time (HRrectime). The second pre-deployment test (which was used in the comparison with the post-deployment test) showed a 2% mean increase in the distance achieved compared with the first (n = 18, p < 0.05) with no difference in HRmean, HRmax, HRrecslope and HRrectime. The test-retest correlation coefficient and 95% limits of agreement for the Cooper tests were 0.79 (p < 0.001) and -68.6 +/- 267.5 m, respectively. For the NDST there were no changes in any of the HR measures or the distance run between the pre- and post-deployment tests. When individual running performances were expressed as a percentage change in the distance run between the pre- and post-deployment tests, the DST performed significantly worse than the NDST (p < 0.01). The DST showed a 7% mean decrement in the distance run following deployment (p < 0.01). The decrement in performance of the DST was not associated with any changes in HRmean or HRmax; however; there was a 17% decrease in the HRrecslope, (p < 0.05) and a 47% increase in HRrectime following the deployment (p < 0.05). In conclusion, prolonged confinement aboard a submarine compromises the aerobic performance of SEAL personnel. The resulting deconditioning could influence mission success.
This article provides a general discussion on the application of risk analysis in the development of safety codes and standards, with particular emphasis on the standards currently under development by the ASME Post-Construction Committee. It also provides an exposition of some of the implicit risk-based assumptions incorporated in the basic new construction pressure vessel code (ASME Section VIII, Div. 1). It proceeds to argue that codes and technical safety standards should be developed using explicit rather than implicit risk-based principles. The authors argue that, contrary to popular belief, pressure equipment standards have always incorporated ad hoc, anecdotal risk principles. The article elucidates this through two detailed examples dealing with provisions affecting nearly all vessels produced to Section VIII, Div. 1: i.e., joint efficiency factors and the scope of coverage of the code. The article then proceeds to a discussion of data collection and cost-benefit modeling which would support a migration to a more rigorous risk-based foundation for future code development. The authors argue that the interests of the entire community of code users—users, manufacturers, regulatory authorities, insurers, and the general public—will be better served by the rational incorporation of risk principles as a foundation for code development. Examples of the application of risk-based approaches in two of the Post-Construction Code drafts follow. [S0094-9930(00)02003-5]
The need for more efficient and cost effective design of ship board equipment has never been greater. Pressure vessels on board ships can account for significant volume and weight and thus affect the overall performance of the vessel. Classically ship board pressure vessels have been designed to ASME Section VIII, Division 1. This code requires pressure vessels that are designed using a basic design by rule approach with a 3.5 to 1 design margin on specified minimum tensile strength. In recent years the ASME Standards Committee that is responsible for Section VIII has developed two design codes, Section VIII, Division 2 Alternative Rules for Construction of Pressure Vessels and Section VIII, Division 3 Alternative Rules for Construction of High Pressure Vessels. These pressure vessel design codes offer lower design margins, an improved design by rule approach for Division 2 and allow or require design by analysis based on the vessel operating conditions and environment such as cyclic service. Use of these codes can improve ship board vessel design by lowering the weight of vessels while providing a safe reliable pressure vessel. Paper published with permission.
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