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• Reduce directly the thermal stress on the workplace being examined;
•
Proceed to a detailed analysis of the thermal stress.
In the following table are reported the thermal stress index WBGT limit values as provided for by
ISO 7243:
RELATIVE TO A
METABOLIC
UNIT AREA OF
RATE CLASS
THE SKIN
W/m
0
M ≤ 65
(RESTING)
1
65 < M ≤ 130
2
130 < M ≤ 200
3
200 < M ≤ 260
4
M > 260
NOTE – THESE VALUES HAVE BEEN DETERMINED BY USING A MAXIMUM REFERENCE RECTAL TEMPERATURE OF 38 °C
FOR THE PEOPLE BEING EXAMINED.
In order to calculate the WBGT index, the following probes should be connected:
• The natural ventilation wet bulb temperature probe.
• The globe thermometer probe.
• The dry bulb temperature probe, if the measurement is performed with solar
radiation.
In order to measure the WBGT index, you should refer to the following regulations:
• ISO 7726
• ISO 7243
2.1.2 Turbulence Intensity (Tu index)
Turbulence Intensity: Local turbulence intensity percentage, defined as the ratio between the local
wind speed standard deviation and the local air average speed (ISO 7726):
where:
v
= average local wind speed
a
SD = local wind speed standard deviation
From the turbulence calculation, knowing the average values of the local wind speed and
environment temperature, you can get the DR (Draught Rating), according to ISO 7730:
HD32.1
METABOLIC RATE, M
TOTAL (FOR A
SKIN SURFACE
AVERAGE AREA
2
OF 1.8 m
)
2
W
M ≤ 117
117 < M ≤ 234
234 < M ≤ 360
360 < M ≤ 468
M > 468
SD
(
) (
=
−
⋅
DR
34
t
v
a
PERSON ACQUAINTED TO THE
HEAT
°C
33
30
28
DEAD AIR
NON DEAD AIR
25
23
SD
=
×
Tu
100
v
a
(
1
n
∑
=
⋅
−
v
v
a
−
n
1
i
=
i
1
)
(
, 0
62
−
⋅
⋅
, 0
05
, 0
37
v
a
a
- 9 -
WBGT LIMIT VALUE
PERSON NOT ACQUAINTED TO
THE HEAT
DEAD AIR
26
22
25
18
)
2
a
)
⋅
+
Tu
, 3
14
°C
32
29
26
NON DEAD AIR
23
20
V2.1
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