Instructions

HD32.3 - 7 - V1.4
The detected data must be compared with the limit values established by the regulation; if they are
over passed, it’s necessary to:
• directly decrease the thermal stress in the considered working place;
• go on with a detailed analysis of the thermal stress.
In the following table are indicated the limit values of the WBGT thermal stress index taken from
ISO 7243 regulation:
LEVEL CLASS
METABOLIC
METABOLIC LEVEL, M WBGT LIMIT VALUE
RELATIVE TO A
SINGLE SKIN
SURFACE
W/m
2
TOTAL (FOR A
MEDIUM AREA OF
1,8 m
2
SKIN SUR-
FACE)
W
ACCLIMATIZED BEING TO
HEAT
°C
NON- ACCLIMATIZED BEING TO
HEAT
°C
0
(RESTING)
M ≤ 65 M ≤ 117 33 32
1 65 < M ≤ 130 117 < M ≤ 234 30 29
2 130 < M ≤ 200 234 < M ≤ 360 28 26
3 200 < M ≤ 260 360 < M ≤ 468
STAGNANT
AIR
25
NO STAGNANT
AIR
26
STAGNANT
AIR
22
NO STAGNANT
AIR
23
4 M > 260 M > 468 23 25 18 20
NOTE: THE VALUES ARE STABILIZED, CONSIDERING A MAXIMUM RECTAL TEMPERATURE OF
38° C FOR THE CONSIDERED BEINGS.
To calculate WBGT index, it’s necessary that to the instrument are connected:
• HP3201.2, HP3201 or TP3204S wet bulb temperature probe with natural ventilation.
• TP3276.2 or TP3275 globe thermometer probe.
• TP3207.2 or TP3207 dry bulb temperature probe if the detection is made in presence
of solar irradiation.
To measure WBGT index consider the following regulations:
• ISO 7726
• ISO 7243
2.1.2 Predicted Mean Vote (PMV) and Predicted Percentage of Dissatisfied (PPD)
The thermal comfort is defined by ASHRAE (American Society of Heating, Refrigerating and Air
Conditioning Engineers INC) as a condition of psycho-physical well being of the being with refer-
ence to the environment in which he lives and works.
The evaluation of such subjective state can be objectivities and calculates using the integrated in-
dexes that consider the ambient microclimatic parameters (Ta, Tr, Va, rh), the energetic waste
(metabolic waste MET) connected with the working activity and the clothing typology (thermal in-
sulation CLO) usually used.
Between these indexes, the most precise one reflects the influence of the physical variables and
physiological ones as mentioned above about the thermal comfort: it is PMV (Predicted Mean
Vote).
Summary, it comes from the equation of thermal balance whose result is related with a psycho-
physical well being scale and expresses the medium vote (predicted medium vote) on the thermal
sensations of a sample of beings that are in the same environment.