Above which level of heat stress index it is not possible to work comfoably -
0 No thermal stress 10-30 Moderate to mild heat strain 40-60 severe heat strain 70-90 very severe heat strain 100 upper limit of heat tolerance Park's Textbook of Preventive and Social Medicine, 25th edition, Page No. 807
20 - 40
40 - 60
60 - 80
80 - 100
Environment and health