Heat Strain Assessment for Workers Using an Encapsulating Garment and a Self-Contained Breathing Apparatus

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Abstract
This study evaluated the physiological response of subjects wearing a Tyvek[rgrave]-Saranex[rgrave] totally encapsulating suit and a self-contained breathing apparatus (SCBA) while working under four environmental conditions. The work was performed on an ergometer connected to a measuring unit that maintained the work load at 255 W (220 kcal/h). Five young male cyclists (mean age = 28.7 years), familiar with the use of a SCBA and an encapsulating suit, were scheduled to perform this work under all four environmental conditions in a randomized series. A control session without the SCBA and the suit was performed at the end of the experiment in a cool environment. Each session was conducted in an environmental chamber and was scheduled to last 90 minutes, that is, three periods composed of 25 minutes of work each, followed by a 5-minute rest period. Physiological measurements included heart rate, six-point skin temperature (arm, chest, back, neck, lateral thigh, and medial thigh), and rectal temperature. Dry bulb temperature (Tdb) was varied from 30.5° to 32.5°C and globe temperature (Tg) from 30.5° to 40°C. Air velocity was constant at 1 m/s and relative humidity was kept between 35 and 45 percent. Measurement of all parameters was obtained every 2 minutes. The average rectal temperature increase varied from 0.28°C (when Tdb = 30.5°C and Tg = 30.5°C) to 1.30°C (when Tdb = 32.5°C and Tg = 40°C). The results showed that heart rate and skin temperature are well correlated with the rise in rectal temperature. A regression analysis showed that dry bulb temperature, globe temperature, and their two-way interaction, along with time, are good predictors of the rise in rectal temperature [coefficient of correlation (R2) = 0.77]. The successive addition to the model of heart rate (R2 = 0.82) and skin temperature at the chest (R2 = 0.85) improved an already good model fit. Dessurealt, P.C.; Konzen, R.B.; Elus, N.C.; Imbeau, D.: Heat Strain Assessment for Workers Using an Encapsulating Garment and a Self-Contained Breathing Apparatus. Appl. Occup. Environ. Hyg. 10(3):200–208; 1995.