Assessment of the reliability of a correction procedure for WGT (Wet Globe Thermometer) (Botsball) measurements of heat stress

The Botsball or WGT (Wet Globe Thermometer) has been widely distributed to military users as a rugged, simple, and inexpensive alternative to WBGT (Wet Bulb-Globe Temperature) instruments. Existing hot weather guidelines for the Botsball presumed that the Botsball would always read approximately 2 F (1.6C) lower than the prevailing WBGT index. Following reports from the field of Botsball readings as much as 10F (5.6 C) lower than the prevailing WBGT index during hot, dry, and windy conditions, a wind tunnel study was conducted to assess Botsball performance characteristics over a broad range of temperatures, humidities, and wind speeds. The wind tunnel study confirmed that substantial and potentially dangerous underestimates of heat stress on the order of 11F (6.1C) may be obtained with the Botsball under very hot, dry, and windy conditions. In an effort to derive a practical correction process that would, with reasonable precision, correct the Botsball reading to parity with the prevailing WBGT index, the wind tunnel data were reexamined.