Table 2. The levels of physiological equivalent temperature(PET) and universal thermal climate index(UTCI) (Jo, 2017)

Thermal perception PET (°C) UTCI (°C) Grade of physiological stress
Very cold <4 <—40 Extreme cold stress
—27∼—40 Very strong cold stress
Cold 4∼8 —13∼—27 Strong cold stress
Cool 8∼13 0∼—13 Moderate cold stress
Slightly cool 13∼18 9∼0 Slight cold stress
Neutral 18∼23 9∼26 No thermal stress
Slightly warm 23∼29   Slight heat stress
Warm 29∼35 26∼32 Moderate heat stress
Hot 35∼41 32∼38 Strong heat stress
Very hot >41 38∼46 Very strong heat stress
>46 Extreme heat stress