Heat Index vs. Web Bulb Globe Temperature
Wet Bulb Globe Temperature (WBGT) is a more accurate, though more complex, way to measure heat stress than the heat index. In addition to combining temperature and humidity, WGBT takes into account radiant heat, wind velocity, the angle of the sun, cloud cover and other factors. Because it’s more difficult to measure, WGBT isn’t used as often as the heat index. However, if you have an industrial hygienist or other safety professional familiar with WBGT on your site, you can get a more accurate idea of the risks faced by workers.
In June’s issue of Lifelines, we covered the critical importance of acclimatization in helping Laborers avoid life-threatening heat illnesses like heat exhaustion and heatstroke on the job. This month, we discuss how the most effective way to prevent heat stress is to pair acclimatization with the lifesaving trio of water, rest and shade.
It’s no secret that water, rest and shade help keep workers going when temperatures rise. But how hot does it need to be before heat becomes a real hazard? And how can employers balance the need for worker safety while still getting the job done? Understanding and using the heat index is the key to answering these questions.
The National Oceanic and Atmospheric Administration’s (NOAA) heat index chart measures the combined effect of temperature and humidity on the body. OSHA has simplified this chart into four risk categories, each with recommended measures employers can take to protect workers.
When the temperature outside calls for protective measures, the first step employers should take is to make sure they’re providing adequate water, rest and shade to workers. Here are several recommendations to maximize their effectiveness on your jobsite:
- Provide water, rest and shade together. A short, planned rest break that gives workers a chance to cool off in the shade and drink some water is very effective at decreasing body temperature. Heat stress occurs when the body can’t cool off fast enough.
- Create shade for workers. If there’s no natural shade on site from trees, buildings or other structures, consider creating artificial shade by bringing in overhead tents or canopies. If workers are performing a stationary task, setting up shade overhead can help keep workers cool while they work.
- Take breaks before the effects of heat stress set in. Research shows that once fatigue sets in, productivity decreases and the risk for injury increases. This is due to the effect fatigue has on the body – decision-making abilities decrease, along with reaction time and hand-eye coordination. Allowing for short rest breaks not only keeps workers from becoming dehydrated, but it also helps prevent fatigue. For this reason, planned rest breaks can actually increase productivity on site and lower the risk for injury.
- Watch for the signs of heat stress. Train supervisors and all workers on site to recognize the signs of heat stress. Muscle cramps, nausea, headaches and dizziness are all signs of dehydration and heat exhaustion. If workers complain of these symptoms or notice them in coworkers, they should alert a supervisor immediately. Left untreated, heat stress can progress to heat exhaustion or even a fatal case of heatstroke.
California is the only state in the U.S. that has a specific heat illness regulation, which requires employers to acclimatize workers to the heat and then provide water, rest and shade once they’re on the job. Although it’s not a specific regulation under federal regulations, OSHA’s general duty clause requires employers to provide a workplace “free from recognizable hazards … likely to cause death or serious harm.” The LHSFNA recommends all employers treat heat as a hazard and take steps to protect workers.
The LHSFNA’s Preventing Heat Stress in Construction pamphlet provides more detailed information about heat illness on the job. The Fund’s two-sided Heat Equation card provides a printed copy of the heat index along with additional recommendations for understanding and preventing heat stress. These and other publications can be ordered through the Fund’s online Publications Catalogue.