Heat Stress


There is no specific standard that applies to heat stress. The only citation option is a General Duty, 5(a)(1).



Refer to the OSHA Technical Manual (OTM), Section III, Chapter 4, Sub-section IV, for heat stress sampling methods. Here are some key points:

  • The wick of the natural wet bulb thermometer should be kept wet with distilled water for at least one-half hour before the temperature reading is made. It is not enough to immerse the other end of the wick into a reservoir of distilled water and wait until the whole wick becomes wet by capillarity. The wick must be wetted by direct application of water from a syringe one-half hour before each reading.
  • The wick should always be clean, and new wicks should be washed before using.
  • The globe thermometer should be exposed at least 25 minutes before it is read.
  • A stand should be used [. . .] so that [. . .] the wet-bulb and globe thermometer are not shaded.
  • Wet Bulb Globe Temperature Indexes (WBGI): Here is some information on how the different temperature indices are calculated. This will help to understand the differences between the various readings on the heat monitor:
    • Indoor or outdoors with no solar load: WBGT = 0.7NWB + 0.3GT
    • Outdoors with solar load: WBGT = 0.7NWB + 0.2GT + 0.1DB
    • where:
      • WBGT = Wet Bulb Globe Temperature Index
      • NWB = Natural Wet-Bulb Temperature
      • DB = Dry-Bulb (air) Temperature
      • GT = Globe Thermometer Temperature

Substance Codes

[Honestly, I'm not sure which of these we need to enter on the sampling sheets. I have yet to find anything in IMIS or a CPL that indicate which IMIS codes to use. -kbh]

8320 Heat Stress - Dry

  • Do not use anything involving the Wet Bulb (WB)

8330 Heat Stress

  • The IMIS description indicates that this is for inside heat monitoring. Therefore, use the WBGTi value. [???]

8891 Humidity, Relative



QuesTemp 34 Manual