Safety Tidbit 5.04 - WBGT vs. Heat Index

Safety Tidbit 5.04 – WBGT vs. Heat Index

Reference:        https://www.weather.gov/ict/WBGT.

The Heat Index is a measure of how hot it feels to the human body, considering the temperature and the relative humidity. The higher either value is, the higher the heat index and the greater the stress exerted on the body. Heat Index utilizes the temperature measured in the shade, and therefore, it will be higher in the sun, where many activities take place. For temperatures taken in the full sunlight, Heat Indices can increase as much as 15°F. Humidity plays a significant effect on cooling the body. If the humidity is high, sweat on the surface of the skin does not evaporate as quickly, slowing the cooling of the body. If the humidity is low, sweat evaporates too fast, leading to dehydration.

Wet Bulb Globe Temperature (WBGT) is similar to the Heat Index in that it is an indicator of the stress on the body from the heat. While it is not as well-known as the Heat Index, it’s not a new term. WBGT was developed in the 1950s after heat-related illnesses affected the US armed services during the 1940s. After its implementation, there was a reduction in heat-related illnesses during basic training. One fundamental difference between the Heat Index and WBGT is the WBGT factors in heat loading from the sun. While Heat Index only takes temperature and Relative Humidity into account, WBGT takes several variables into account. These variables include:

• Temperature
• Humidity
• Wind Speed
• Sun Angle
• Cloud Cover
• Physical Activity

Since most outdoor work happens in the sunlight, use of the WBGT is a better tool to keep your workers safe. The Heat Index, as given by the weather forecasters and used in the NIOSH/OSHA app, are great monitoring tools. However, through good industrial hygiene by taking WBGT readings and understanding the work performed, can you adequately protect workers.

Hope this was helpful and thank you for reading my Safety Tidbits! Comments and questions are always welcome. ~ Bryan

P.S. If you have a new safety or health question, please let me know.