The heat index is based on the relative humidity. When this relative humidity is HIGH, it significantly reduces the ability of our sweat to evaporate off our skin. This sweating and evaporation process is how our bodies are cooled.
Our Heat-Related Illness Prevention Plan’s “action temperature(s)” MUST be based on the HEAT INDEX – not the standard temperature.
We MUST also factor in PPE usage as much of the “chemical PPE” does NOT breathe, and this will seriously compound a worker’s ability to cool themselves via sweating and evaporation. This means, REGARDLESS of the heat index, workers wearing this type of PPE can suffer heat-related illnesses even in lower temps and drier air. Anyone who has worn A, B, or C ensembles will attest to this fact.
Lastly, too many people do not recognize how humidity impacts our ability to cool. When we visit the mountains, what do they always tell us? Drink plenty of water. Now why do they have to say this repeatedly? Because there is usually less humidity in higher elevations, so when we do sweat (and trust me, we sweat when hiking), the sweat evaporates almost instantaneously due to the low humidity level. So we are not wiping our brows, our clothes are not damp from sweating, etc. These have become reminders to drink more due to our workload. But when we do not have these reminders, many people forget to hydrate, even in 70-80F temps can suffer from heat exhaustion.
Our blood is our body’s coolant, but the sweat and evaporation of that liquid sweat actually cools us. We have to HYDRATE BEFORE our body sees the demand for sweat production. So if your pee is not clear in the morning before work, start DRINKING water or some sports drink to HYDRATE even before you begin work. Those whose job requires them to sweat heavily over 8-12 hr shift need to hydrate heavily when they get home and in the morning before they return to work. Trying to play catch up while already sweating heavily is a LOSING GAME.
STAY AWAY from caffeine drinks or diet aids when sweating heavily. As our bodies heat up, our heart rate will increase to pump our “coolant” (i.e., blood) faster to aid in our cooling. This increased heart rate also spurs more sweating, as does our increase in core temp. Add caffeine’s effect, and we can have a serious cardiac event, regardless of age and other life impacts.
PLEASE download the OSHA/NIOSH Heat App and utilize it in the planning and execution of our Heat-Related Illness Prevention Plans. It is an excellent tool that makes managing these hazards MUCH easier, especially for field and frontline supervisors who may not be as well versed in the science behind Heat-Related hazards. Just know that the frequencies of breaks and the fluid intake can change day to day depending on conditions and workloads, as well as NOT everyone on the job will be at the same risks based on their work loads.