2002 Annual

Monday, 14 January 2002
A comparison of the Stedman's Heat Index and WBGT Index
Steven D Hacker, U. S. Naval Academy, Annapolis, MD
Heat stress is a topic of interest in many different fields ranging from meteorology, sports medicine, and the U.S. Armed Forces. The standard measure of heat stress is the Stedmanís Heat Index (SHI). This index is dependent on dry-bulb temperature and relative humidity, whereas the Navy and Marine Corps use the Wet Bulb Globe Temperature Index (WBGTI). The WBGTI is measured by finding the wet bulb temperature (WB), dry bulb temperature (DB), and black globe temperature (GT). Measuring the WBGTI requires specially designed, expensive equipment. The goal of this project is to be able to relate these two heat stress indices and develop a mathematical algorithm so the use of expensive equipment is no longer required. In this study, the data were collected over approximately a one-month period at the U.S. Naval Academy, in Annapolis, MD. The equation for calculating the WBGTI is as follows: WBGTI=0.7*WB+0.2*GT+0.1*DB. The challenging factor in relating WBGTI to SHI is that the globe temperature has no obvious equivalent factor in the SHI. During preliminary analysis of one week of data the correlation coefficient between the two indices was found to be R=0.99, indicating a strong, positive linear relationship. The additional three to four weeks of data will give more definitive results and allow for more specific conclusions to be drawn. Based on the already analyzed data it is clear the two indices relate very closely to each other. It is a matter of having enough data to find a conversion factor between the two indices. Thus far, the data shows promising results and provide a basis for further research on the matter.

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