Assessing risk for heat-related illnesses means looking beyond the thermometer to other indicators that add to the potential for illness or injury. The “heat index” is defined by the Occupational Safety and Health Administration (OSHA) as a single value that takes both temperature and humidity into account. Put simply, it can feel much warmer when the heat index value is factored in because it combines air temperatures and humidity to describe perceived outdoor temperature.
The key thing to know is the higher the heat index, the hotter the weather feels given that sweat does not readily evaporate and cool the skin. According to OSHA, the heat index is a better measure than air temperature alone for assessing the risk to workers from environmental heat sources.*
Take care to protect your employees in these conditions. Provide water. Offer regular breaks in the shade. If air-conditioning is unavailable or impractical, consider creating a cooling station where a portable evaporative cooler can be placed to help lower temperatures by as much as 30°F. Precaution and prevention are the keys to keeping employees safe when the mercury AND heat index rise.
*Source: https://www.osha.gov/SLTC/heatillness/heat_index/index.html; wording taken verbatim from Introduction to OSHA’s “Using the Heat Index: A Guide for Employers”