While nearly all individuals understand the importance of measures of air temperature, heat index, humidity and dewpoint, there is an additional factor known as wet bulb globe temperature (WBGT). Looking specifically at the stress caused by the heat of direct sunlight, WBGT is a measure of perceived temperature. Construction workers and others completing job tasks in the sun should be aware of WBGT and the dire consequences that follow a high rating.
Wet bulb globe temperature uses numerous factors in its calculation and encourages workers or those exercising in the direct sunlight to take precautions. At various measures, experts encourage individuals to take breaks, such as:
- WBGT below 80: No dangerous effects.
- WBGT between 80 and 85: After 45 minutes of work in the direct sunlight, the body will begin to feel stress and individuals should take at least 15 minutes of breaks every hour.
- WBGT between 85 and 88: After 30 minutes of work in the direct sunlight, the body will begin to feel stress. Experts suggest at least 30 minutes of breaks every hour.
- WBGT between 88 and 90: After 20 minutes of work in the direct sunlight, the body will begin to feel stress. At this stage, workers should take 40 minutes of breaks each hour.
- WBGT over 90: Working in the direct sunlight for only 15 minutes will stress the body. This is the most dangerous WBGT stage. Those in direct sunlight should take 45 minutes of breaks each hour.
While the heat index (“feels like”) is the calculated relationship between air temperature and humidity, WBGT factors in the cooling effect of water evaporation. Evaporation of sweat from the surface of the skin cools the body. When environmental conditions slow or prevent this evaporation, the body cannot regulate its own temperature.
Those working in the direct sunlight can suffer devastating heat illnesses including heat stroke, heat exhaustion, rhabdomyolysis and heat syncope. Construction workers must take steps to protect themselves from dangerous exposure on nearly every jobsite.