Corrections for solar radiation and wind increase the accuracy of determining dangerous outdoor work environments.

NASA Dryden presents an improved and automated site-specific algorithm for heat-stress approximation using standard atmospheric measurements routinely obtained from the Edwards Air Force Base weather detachment. Heat stress, which is the net heat load a worker may be exposed to, is officially measured using a thermal-environment monitoring system to calculate the wet-bulb globe temperature (WBGT). This instrument uses three independent thermometers to measure wet-bulb, dry-bulb, and the black-globe temperatures. Two reasons for this project were limited access to the Dryden monitoring system and delays of the required manual issuances for heat-stress warnings.

ACSM Estimates of WBGT were brought closer to true WBGT values byapplying corrections for wind and solar radiation.

Dryden provided corrections to the environmental assumptions of moderate solar radiation and low wind built into the algorithm. Desert environments, such as the high Mojave in Southern California, have both high solar radiation (1,000 W/m²) and periods of significant winds during the summer afternoons in excess of 20 kn. When comparing the difference between the thermal environment monitor WBGT (actual) and the ACSM approximated WBGT against wind speed, it was found that a direct relationship existed with a positive slope (i.e., a large difference between the actual and estimated WBGT as the wind speed increases). A correction curve based on 40 days of comparisons was applied, and significant improvements to the WBGT approximations were observed. The daily difference between actual and calculated WBGT was reduced from approximately 2.0° to about 0.5° on the average.