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

Thermal perception	PET (°C)	UTCI (°C)	Grade of physiological stress
Very cold	4>	> −40	Extreme cold stress
		−40 ~ −27	Very strong cold stress
Cold	4 ~ 8	−27 ~ −13	Strong cold stress
Cool	8 ~ 13	−13 ~ 0	Moderate heat stress
Slightly cool	13 ~ 18	0 ~ 9	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