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Wind Chill (°C)
> -28
-28 to -39
-40 to -44
Alarm level
-44 to -47
-48 and colder
(*): With v
higher than 50 km/h the frostbite process can be faster.
a
In order to calculate the WCI index, the following probes should be connected:
• The dry bulb temperature probe for air temperature measurement t
• The hot-wire probe for wind speed measurement.
In order to measure the WCI index, refer to the following:
•
ISO 7726
•
NOAA Specifications, National Weather Service.
2.1.4 Average Radiation Temperature t
The average radiation temperature is defined as the temperature of a thermally uniform simulated
environment that would exchange with a man the same thermal radiation power exchanged in the
real environment.
In order to evaluate the average radiation temperature you have to measure: The globe
thermometer temperature, the air temperature and the wind speed measured near the globe
thermometer. The average radiation temperature calculation formula is the following:
• In case of natural convection:
• In case of forced convection:
where:
D = globe thermometer diameter
ε
= 0.95 assumed emissivity of the globe thermometer
g
t
= globe thermometer temperature
g
t
= air temperature.
a
v
= wind speed
a
The average radiation temperature does not correspond to air temperature: If within a room very
high temperature surfaces are present (for example, a fireplace), these hot areas remarkably
influence the average radiation temperature.
The average radiation temperature is detected with the globe thermometer. A temperature probe
formed by a 150 mm copper ball, painted black matt, with emissivity equal to ε
HD32.1
Low
Medium: The exposed body parts can freeze within 10 to 30 minutes
High: The exposed body parts can freeze within 5 to 10 minutes (*)
High: The exposed body parts can freeze within 2 to 5 minutes (*)
High: The exposed body parts can freeze in less than 2 minutes (*)
⎡
(
)
. 0
25
⎢
4
=
+
+
t
t
273
⎢
r
g
⎣
⎡
(
)
4
=
+
t
t
273
⎢
r
g
⎢
⎣
Frostbite risk
r
1
4 /
⎛
⎞
−
t
t
×
8
10
⎜
⎟
g
a
⎜
⎟
ε
D
⎝
⎠
g
×
×
8
0
6 .
(
1
1 .
10
v
+
−
a
t
ε
×
g
0
4 .
D
g
- 11 -
.
a
1
4 /
⎤
(
)
⎥
×
−
−
t
t
273
⎥
g
a
⎦
1
4 /
⎤
)
−
t
273
⎥
a
⎥
⎦
g
= 0.95 (according
V2.1
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