Table 4.

Assessment scales of thermal indices suitable for ORM applications based on criteria C1 to C11. For index abbreviations see Table 1. Physiological stress categories refer to PT_J, PET, and UTCI but not to PST

Thermal sensation	PST [°C]	PTJ [°C]	PET[°C]	UTCI[°C]	Physiological Stress
+ 5 sweltering	≥ 54
+ 4 very hot	44 to 54	≥ 38	≥ 41	> 46	Extreme heat stress
				38 to 46	Very strong heat stress
+ 3 hot	34 to 44	32 to 38	35 to 41	32 to 38	Strong heat stress
+ 2 warm	24 to 34	26 to 32	29 to 35	26 to 32	Moderate heat stress
+ 1 slightly warm		20 to 26	23 to 29		Slight heat stress
0 neutral (comfortable)	14 to 24	0 to 20	18 to 23	9 to 26	No thermal stress
− 1 slightly cool		− 13 to 0	13 to 18	0 to 9	Slight cold stress
− 2 cool	4 to 14	− 26 to − 13	8 to 13	− 13 to 0	Moderate cold stress
− 3 cold	− 16 to 4	− 39 to − 26	4 to 8	− 27 to − 13	Strong cold stress
− 4 very cold	− 36 to − 16	≤− 39	≤ 4	− 40 to − 27	Very strong cold stress
− 5 frosty	≤− 3			<− 40	Extreme cold stress