99
Table 4.2 UTCI equivalent temperature categorized in terms of thermal stress
UTCI (°C)
range
Stress category
Physiological responses
above +46
extreme heat stress
Increase in Tretime gradient
Steep decrease in total net heat loss
Averaged sweat rate >650 g/h, steep increase
+38 to +46
very strong heat
stress
Core to skin temperature gradient < 1 K (at 30 min)
Increase in Tre at 30 min
+32 to +38
strong heat stress
Dynamic Thermal Sensation (DTS) at 120 min > +2
Averaged sweat rate > 200 g/h
Increase in Tre at 120 min
Latent heat loss >40 W at 30 min
Instantaneous change in skin temperature > 0 K/min
+26 to +32
moderate heat stress Change of slopes in sweat rate, Tre and skin
temperature: mean (Tskm), face (Tskfc), hand (Tskhn)
Occurrence of sweating at 30 min
Steep increase in skin wetness
+9 to +26
no thermal stress
Averaged sweat rate > 100 g/h
DTS at 120 min < 1
DTS between −0.5 and +0.5 (averaged value)
Latent heat loss >40 W, averaged over time
Plateau in Tre time gradient
+9 to 0
slight cold stress
DTS at 120 min < −1
Local minimum of Tskhn (use gloves)
0 to −13
moderate cold
stress
DTS at 120 min < −2
Skin blood flow at 120 min lower than at 30 min
(vasoconstriction)
Averaged Tskfc < 15 °C (pain)
Decrease in Tskhn
Tre time gradient < 0 K/h
30 min face skin temperature < 15 °C (pain)
Tmsk time gradient < −1 K/h (for reference)
−13 to −27
strong cold stress
Averaged Tskfc < 7 °C (numbness)
Tre time gradient < −0.1 K/h
Tre decreases from 30 to 120 min
Increase in core to skin temperature gradient
−27 to −40
very strong cold
stress
120 min Tskfc < 0 °C (frostbite)
Steeper decrease in Tre
30 min Tskfc < 7 °C (numbness)
Occurrence of shivering
Tre time gradient < −0.2 K/h
Averaged Tskfc < 0 °C (frostbite)
120 min Tskfc < −5 °C (high risk of frostbite)
below −40
extreme cold stress
Tre time gradient < −0.3 K/h
30 min Tskfc < 0 °C (frostbite)
(Blazejczyk et al. 2010)
4 Relevance of Thermal Indices for the Assessment of the Urban Heat Island
Table 4.2 UTCI equivalent temperature categorized in terms of thermal stress
UTCI (°C)
range
Stress category
Physiological responses
above +46
extreme heat stress
Increase in Tretime gradient
Steep decrease in total net heat loss
Averaged sweat rate >650 g/h, steep increase
+38 to +46
very strong heat
stress
Core to skin temperature gradient < 1 K (at 30 min)
Increase in Tre at 30 min
+32 to +38
strong heat stress
Dynamic Thermal Sensation (DTS) at 120 min > +2
Averaged sweat rate > 200 g/h
Increase in Tre at 120 min
Latent heat loss >40 W at 30 min
Instantaneous change in skin temperature > 0 K/min
+26 to +32
moderate heat stress Change of slopes in sweat rate, Tre and skin
temperature: mean (Tskm), face (Tskfc), hand (Tskhn)
Occurrence of sweating at 30 min
Steep increase in skin wetness
+9 to +26
no thermal stress
Averaged sweat rate > 100 g/h
DTS at 120 min < 1
DTS between −0.5 and +0.5 (averaged value)
Latent heat loss >40 W, averaged over time
Plateau in Tre time gradient
+9 to 0
slight cold stress
DTS at 120 min < −1
Local minimum of Tskhn (use gloves)
0 to −13
moderate cold
stress
DTS at 120 min < −2
Skin blood flow at 120 min lower than at 30 min
(vasoconstriction)
Averaged Tskfc < 15 °C (pain)
Decrease in Tskhn
Tre time gradient < 0 K/h
30 min face skin temperature < 15 °C (pain)
Tmsk time gradient < −1 K/h (for reference)
−13 to −27
strong cold stress
Averaged Tskfc < 7 °C (numbness)
Tre time gradient < −0.1 K/h
Tre decreases from 30 to 120 min
Increase in core to skin temperature gradient
−27 to −40
very strong cold
stress
120 min Tskfc < 0 °C (frostbite)
Steeper decrease in Tre
30 min Tskfc < 7 °C (numbness)
Occurrence of shivering
Tre time gradient < −0.2 K/h
Averaged Tskfc < 0 °C (frostbite)
120 min Tskfc < −5 °C (high risk of frostbite)
below −40
extreme cold stress
Tre time gradient < −0.3 K/h
30 min Tskfc < 0 °C (frostbite)
(Blazejczyk et al. 2010)
4 Relevance of Thermal Indices for the Assessment of the Urban Heat Island