A field study of thermal stress and recovery using thermoregulatory behavioral and physiological indicators

Summary

A field study to optimize the work/rest regimen among foundry welders performing a light to medium work load and welding red-hot items was undertaken during the morning shift. Three work/rest regimens were tested, viz.: work(2h)/rest(1 h) with a team of three welders per shift work(1 h)/rest(1 h) with a team of four welders per shift work(2h)/rest(2h) with a team of four welders per shift.

Pulse frequency and core temperature were measured at short intervals during working periods. Thermal alliesthesial reactions (used as a thermoregulatory behavioral indicator) were quantified by the aid of a 5₈ peripheral temperature stimulus of 15, 20, 25, 30, 35 and 38°C on hand, forehead, and back of neck. For each stimulus the subject voted his pleasantness sensation on a five point scale ranging from +10 for very pleasant to -10 for very unpleasant. Temperature stimuli were applied using a Peltier thermode 5.5 x 2.7 cm² in area. The subject also voted his most pleasant temperature on back of neck by voluntary control.

The results confirmed previous studies that thermoregulatory behavioral indicators are more sensitive than physiological (e.g., core temperature) indicators in revealing the thermal comfort state of man. The results indicated that the work(2h)/rest(2h) regimen was the most satisfactory of the three regimens tested and was associated with full recovery from thermal stress after the 2 h resting break. This work(2 h)/rest(2 h) regimen was then tested during afternoon and night shifts. The results indicated that the morning shift was more advantageous than the two other shifts with respect to cardiovascular load and thermal strain during working periods, although recovery from thermal stress was achieved after the 2 h resting break in all of the three shifts. Improvement of resting place ambient thermal conditions was proposed to shorten the downtime per man per shift. Radiation shielding of resting place was viewed as economic and effective under these conditions.