Validity of infrared tympanic temperature for the evaluation of heat strain while wearing impermeable protective clothing in hot environments

The purpose of this study was to investigate the validity of infrared tympanic temperature (IR T _ty) as a thermal index to evaluate the heat strain of workers in hot environments, in comparison with rectal temperatures at various depths (T _{re-4, -8, and -16} for 4, 8 and 16 cm from the anal sphincter). Eight males underwent twelve experimental conditions: two activities (rest and exercise) × three clothing levels [Control, HDPE (high-density polyethylene coverall) and PVC (polyvinyl chloride coverall) condition] × two air temperatures (25 and 32°C with 50%RH). The results showed that 1) in the conditions with most heat strain (HDPE or PVC condition at 32°C), IR T _ty was equal to or even higher than T _re; 2) during exercise, physiological strain index (PSI) using IR T _ty did not underestimate PSI-values using T _re-16, and overestimated those PSI-values from T _re-16 in HDPE and PVC conditions at 32°C; 3) during exercise, the relationships between IR T _ty and heart and total sweat rate were stronger than those between T _re-16 and heart and total sweat rate. These results indicated that IR T _ty is valid as a thermal index to evaluate the heat strain of workers wearing impermeable protective coveralls in hot environments. However, the application of IR T _ty is limited only for strenuous works wearing encapsulated personal protective clothing with a hood in heat.