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