Table 5. 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
		−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