The heat exposure threshold limit values describe the temperature at which workers should be able to work without adverse health effects. Workers should not be permitted to continue to work when their deep body temperatures exceed 38 C (100.4 F).
The wet bulb globe temperature correlates with the deep body temperature of the worker, and is relatively simple to measure. Determination of the wet bulb globe temperature requires using a dry bulb thermometer, a black globe thermometer and a static wet bulb thermometer.
wet bulb globe temperature for outdoors with solar load =
= (0.7 * (static wet bulb temperature)) + (0.2 * (black globe temperature)) + (0.1 * (dry bulb temperature))
wet bulb globe temperature for indoors =
= wet bulb globe temperature for outdoors without solar load =
= (0.7 * (static wet bulb temperature)) + (0.3 * (black globe temperature))
Threshold Limits for Work and Rest Regimens
|
Work/Rest Regimen |
Light Workload |
Moderate Workload |
Heavy Workload |
|
continuous work |
30.0 C (86 °F) |
26.7 C (80 °F) |
25.0 C (77 °F) |
|
75% work, 25% rest |
30.6 C (87 °F) |
28.0 C (82 °F) |
25.9 C (78 °F) |
|
50% work, 50% rest |
31.4 C (89 °F) |
29.4 C (85 °F) |
27.9 C (82 °F) |
|
25% work, 75% rest |
32.2 C (90 °F) |
31.1 C (88 °F) |
30.0 C (86 °F) |
These limits are affected by the clothing and equipment worn by the worker.
|
Clothing |
Insulation Value of Clothing (Clo Value) |
Correction to Wet Bulb Globe Temperature |
|
summer work uniform |
0.6 |
0 degrees C (0 °F) |
|
cotton coveralls |
1.0 |
-2 degrees C (-3.6 °F) |
|
winter work uniform |
1.4 |
-4 degrees C (-7.2 °F) |
|
permeable water barrier |
1.2 |
-6 degrees C (-10.8 °F) |
For dry clothing, the correction to the wet bulb globe temperature can be estimated:
correction =
= 3 - (5 * (Clo value))
In addition, whether a worker is acclimatized or not affects the permissible threshold. If the worker is not acclimatized, the threshold limits should be reduced by 2.5 °C.
Specialty: Emergency Medicine, Critical Care
ICD-10: ,
