worker who has collapsed because of heat stress

What is heat stress?

Heat stress is a type of thermal stress that results in a buildup of body heat generated from a combination of factors. These can include the physical effort exerted while working, environmental factors like temperature, humidity, air movement, or radiant heat from the sun or hot equipment and the clothing you wear.

It’s important for employers and employees to understand the risks associated with working in hot environments and develop practices that reduce these risks. Some suggestions include:

  • flexible work schedules
  • hydration and cool down time, and
  • appropriate clothing and PPE.

What is a heat stress monitor?

Heat stress monitors can provide individual measurements for air temperature, relative humidity, airflow, globe temperature based on the effects of radiant heat and wet bulb temperature that takes the effects of humidity and the body’s ability to cool itself into account.

These values are then used by the instrument to calculate humidex (heat index), and WBGT (wet bulb globe temperature) which can be used with published work/rest guideless.


Work/rest guidelines:

The American Conference of Governmental Industrial Hygienists (ACGIH) published this recommended screening criteria for heat stress exposure for workers in 2017. ACGIH states that this table is more protective than the TLV® or Action Limit. Because the values are more protective, they are not intended to prescribe work and recovery periods.

Work allowanceTLV®   Action Limit   
LightModerateHeavyVery HeavyLightModerateHeavyVery Heavy
75-100%31.028.0----28.025.0----
50-75%31.029.027.5--28.526.024--
25-50%3230292829.52725.524.5
0-25%32.531.530.53030292827

The table assumes people are working an 8-hour workday in a 5-day work week with conventional breaks.

Example of workloads:

  • Rest: Sitting
  • Light work: Sitting or standing to control machines, performing light hand or arm work (e.g., using a table saw, occasional walking, or driving.
  • Moderate work: Sustained moderate hand and arm work, light pushing or pulling, walking at a moderate pace, or moderate arm, leg and trunk work.
  • Heavy work: Sustained moderate work, pick and shovel work, carrying, pushing/pulling heavy loads, walking at a fast pace.
  • Very heavy work: Very intense activity at a fast to maximum pace.

Our heat stress monitor offering:

Levitt-Safety carries a wide range of heat stress monitors from leading manufacturers like LSI, Sper Scientific, Equivital and TSI. We can answer any questions you may have about which product is best for your application and provide quotes and equipment training. Fill out the form on this page and a member of our team will contact you.


Sensidyne Heat Sheild heat stress monitor

LSI HeatShield Heat Stress Monitor

  • Measures wet bulb, dry bulb, globe temperatures and relative humidity
  • Calculates WBGT index
  • Multiple language options, internal memory and 400-hour life rechargeable battery

Shop now

The HeatShield monitor is also available with wireless satellite modules to measure environmental conditions at three levels and calculate head-torso-ankle weighted average WBGT.

Accessories for HeatShield heat stress monitor:

  • Hot wire anemometer to measure air velocity.
  • Tripod to mount HeatShield
  • Tripod support for HeatShield and anenometer

Shop all accessories


product image of the Sper Scientific WBGT heat stress monitor with SD card

Sper Scientific WBGT Heat Stress Monitor

  • Provides readings for relative humidity, temperature, dew point and WBGT temperature
  • Data logging with the use of removable SD card
  • Features WBGT audible alarm, min/max reading, auto power off and low battery indicator
  • Includes soft carrying case, batteries, manual, SD card

Shop now


Product image of equivital EQ02 heat stress monitor

Equivital EQ02 Life Monitor

  • Monitor heart rate, breathing rate, skin temperature and motion with a combined wearable ECG and respiratory monitor
  • Medical-grade thermometer and tri-axis accelerometer
  • Hot swap ancillary power packs ensure continuous vital sign monitoring
  • 8 GB memory facilitates 50 days of continuous logging rich physiological data

Accessories for Equivital EQ02 Life Monitor:

  • Chest belt in various sizes
  • Docking station

Fill out the form to learn more.


TSI Quest QUESTemp Area Heat Stress Monitor

Product image TSI Questemp area heat stress monitorThe QUESTemp° 32/34/36 area heat stress monitors are designed for quick and accurate evaluation of potential heat stress environments.

These instruments deliver high-performance monitoring through Wet Bulb Globe Temperature (WBGT) sensing technology and the calculation of a WBGT index value.

Measurement parametersQT 32QT 34QT 36
Dry bulb, wet bulb and globe temperatures
Air velocityOptional
WBGT (indoor index)
WBGT (outdoor index)
Heat index/ Humidex
Temperature reading: Celsius or Fahrenheit
Data logging intervals: 1, 2, 5, 10, 15, 30 or 60 minutes
Time and date stamp with clock and calendar
Displayed stay times: ACGIH TLV, U.S. Navy PHEL charts
Head-torso-ankle weighted average WBGT (optional with tri-sensors)OptionalOptionalOptional

TSI Quest QUESTemp Waterless Wet Bulb Heat Stress Monitors

TSI Quest QUESTemp 44-46-48N Area Waterless Wet Bulb Heat Stress MonitorsThe QUESTemp 44-46 uses a waterless wet bulb sensor designed for working environments where daily instrument upkeep is difficult.

These instruments deliver high-quality humidity sensors and a proprietary algorithm to perform the calculation of the WBGT values, eliminating the hassle of daily wet-bulb maintenance.

Measurement parametersQT 44QT 46
Dry bulb, wet bulb and globe temperatures
Air velocityOptional
WBGT (indoor index)
WBGT (outdoor index)
Heat index/ Humidex
Temperature reading: Celsius or Fahrenheit
Time and date stamp with clock and calendar
Displayed stay times: ACGIH TLV, U.S. Navy PHEL charts
Head-torso-ankle weighted average WBGT (optional with tri-sensors)OptionalOptional

Contact us

Our team of instrument specialists is here to answer any questions you may have about heat stress monitors. Fill out the form on this page and a member of our team will contact you

Start Shopping Online Now!
  Subscribe
  What can we help you with?
  Send Us Feedback