Compliance · ACGIH / NIOSH
ACGIH Heat-Stress TLV (WBGT)
Occupational: heat stress
The ACGIH heat-stress Threshold Limit Value is a screening guideline for protecting workers against heat illness, using the Wet Bulb Globe Temperature (WBGT) as its index. WBGT is a single figure that combines air temperature, humidity, radiant heat, and air movement (the four factors that together determine the heat load on the body), measured with a natural wet-bulb thermometer, a black globe thermometer, and a dry-bulb thermometer. The guideline compares the measured WBGT against screening thresholds that vary by workload (light, moderate, heavy, or very heavy metabolic rate) and by whether workers are acclimatized to the heat.
The standard
What the ACGIH Heat-stress TLV Is
Published by the American Conference of Governmental Industrial Hygienists, the TLV is a health-based recommendation rather than a regulation. Where the measured WBGT approaches or exceeds the screening threshold, it prescribes work-rest regimes (structured cycles of work and recovery) and further controls. The threshold values by workload and acclimatization are given in the limit table on this page.
Limit values
ACGIH WBGT Limit Values
Every value ACGIH and NIOSH publish for the parameter below, with its averaging period, as the standard states it.
Who it applies to
Who Uses It
Employers and safety professionals in any hot working environment use the WBGT TLV to manage heat risk: foundries, glass and steel works, bakeries, laundries, and other hot indoor industries, as well as outdoor construction, agriculture, roofing, utilities, and emergency response during hot weather. Industrial hygienists use it to set work-rest schedules, hydration and acclimatization plans, and to decide when conditions demand that work pause. Because heat stress can be fatal and is aggravated by clothing, exertion, and lack of acclimatization, the guideline is widely adopted as the practical basis for heat-illness prevention programs.
Monitoring
How Monitoring Demonstrates Compliance
Heat-stress screening rests on measuring WBGT at or near the work location, distinguishing the indoor index (without solar load) from the outdoor index (which adds the sun's radiant heat). A WBGT meter integrates the wet-bulb, globe, and dry-bulb readings into the single index that is compared against the screening threshold for the relevant workload and acclimatization state in the limit table on this page. Because the threshold depends on how hard the work is, an accurate estimate of metabolic rate accompanies the measurement. Fixed or portable WBGT monitors log the index continuously so that work-rest cycles can be adjusted as conditions change through the day.
Recommended
best match-
Thiamis connects 1 instrument
A gateway that connects the third-party instruments you choose to the Aethair Platform.
Also measures 4 more
Heat IndexRelative HumidityAir TemperatureWet Bulb Temperature -
Who measures each parameter
| Parameter |  Aethair PRO |  Aethair IAQ | External |
|---|---|---|---|
| WBGT (Heat Stress) | — | — | 1 instrument via Thiamis |
Devices
Devices That Cover ACGIH WBGT
How much of this standard one Aethair monitor covers, followed by the third-party instruments in the sensor catalog that measure its parameters. Each connects to Environet through a Thiamis gateway, which adds whatever the monitor leaves out.
Covers it on its own
Solutions
Solutions Judged Against ACGIH WBGT
Heat Stress & Outdoor Work
WBGT for worksites, athletics, and events
Occupational Safety & Industrial Hygiene
Worker exposure, confined space, and heat stress
Questions
ACGIH WBGT FAQ
What is WBGT and why not just use air temperature?
Wet Bulb Globe Temperature combines air temperature, humidity, radiant heat, and air movement into one index, because the body's ability to shed heat depends on all four, not on temperature alone. High humidity or strong radiant heat can make a modest air temperature dangerous, something a plain thermometer would miss.
Why do the thresholds depend on workload and acclimatization?
The heat a body must lose rises with physical effort, so a harder task is safe only at a lower WBGT: the screening thresholds fall as metabolic rate increases. Acclimatized workers, whose bodies have adapted over days of exposure, tolerate more heat than unacclimatized ones and so are given higher thresholds.
What is the difference between the indoor and outdoor WBGT?
The indoor (or shaded) index omits solar radiation and uses the natural wet-bulb, globe, and dry-bulb readings, whereas the outdoor index in sunlight adds the radiant load from the sun and sky. The correct formula must be used for the setting, since the same conditions give different values.
How do I monitor heat stress on site?
Use a WBGT meter with wet-bulb, globe, and dry-bulb sensors positioned at the work location, logging the index through the shift. Use the configurator to build a heat-stress station and fold it into a wider meteorology configuration where you also track ambient conditions.
Monitor Against ACGIH WBGT
Schedule a callBuild a Configuration All standards
A 30-minute call: you tell us about your application, then we demo the solution for it.