Empirical approach to outdoor WBGT from meteorological data and performance of two different instrument designs.

The wet bulb globe temperature index (WBGT) is a common method to assess the environmental contribution to heat stress as part of an occupational exposure assessment. The two purposes of this study were (1) to compare empirical relationships of some meteorological conditions to WBGT, and (2) to evaluate a smaller globe and alternative method to assess natural wet bulb using a relative humidity sensor. Data were collected in six West-central Florida locations over multiple days for a total of 14 measurement days. Multiple linear regression was used to explore relationships relevant to the two purposes. It was clear that estimating WBGT directly from meteorological data or through estimates of the components of WBGT can be accomplished with a 95% confidence of ± 2°C-WBGT. The 50 mm globe size is a reasonable approximation of the standard size (150 mm). The relative humidity method of the waterless natural wet bulb provides a very good estimation of natural wet bulb temperature. The determination of WBGT from the electronic instruments (small globe with or without the relative humidity method) provided a good estimate of the WBGT.