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Simplifying Heat Stress Prevention

  • Published
  • 23 June 2021
  • Category
  • General

By John Longphre, M.D., M.P.H.

As the temperature rises in the summertime, so do employer concerns about heat stress prevention.

I was recently asked to review an overly complex heat-stress plan that a client was trying to implement. It had all sorts of data, urinalysis charts, instructions for co-worker hydration teams, and so on. It did NOT include anything about the heat-battery effect or the need for salt replacement, which are fundamental considerations.

I recommend taking a simple, three-pronged approach, which I call Heat Stress Prevention for Regular People.

Dehydration (water loss)

People tend to focus on hydration at the expense of other important factors. This is what you need to know:

  • Urine volume: In an intensive care setting, the fluid status of a patient is checked to measure hydration. The average adult male should make about 100cc (or mL) of urine per hour, and an average female slightly less.  A beer can contains just over 300cc of fluid. A hydrated man should be able to fill a beer can with urine every three hours.
  • Being thirsty: Thirst is a lagging indicator. If an employee feels thirsty, he or she is already a quart (or so) too low. Employees should continuously top off their tanks with fluid to replenish the supply they are losing throughout the workday.

Heat-Battery Effect

Imagine a 10-pound steel cannonball heated to 150°F. Now imagine 10 pounds of thin sheet steel, also heated to 150°F.  They weigh the same. Which one will retain heat the longest? Correct! The fat little cannonball will have a harder time expelling heat. (Technically, the “surface-area-to-volume ratio” is smaller for the cannonball.) The thin sheet steel has a larger surface area from which to radiate heat. Similarly, people who are overweight or obese have a harder time getting rid of excess heat than do thinner people.

In extremely hot and humid environments, I advise employees to occasionally immerse both their arms (or legs, or even their whole body) in chilled water to cool their blood. When cooled blood circulates, it helps lower body temperature. Think of an air-cooled engine versus a liquid-cooled engine. We instinctively know it takes a lot longer for a box fan blowing air to cool someone off than it does to simply jump into a swimming hole. Employees can be given circulating-liquid-based cooling (arm) sleeves to wear if providing cold buckets of water onsite is not a practical solution.

Salt Loss

The amount of salt lost when people sweat is often underestimated. Sweating helps cool the body. Fluids and electrolytes (including sodium, potassium and magnesium) lost from sweating must be replaced to prevent chemical imbalances that can diminish physical and mental performance. The body uses sodium to regulate fluids and support the heart, liver and kidneys. Potassium and magnesium help prevent cramps.

In addition to drinking water, many people rely on beverages advertised as sports drinks to replace fluids and electrolytes. Most of these beverages are high in sodium and sugar (primarily for taste) and low in potassium, although a few products are high in potassium, low in sodium and generally have little to no sugar. Check the labels on various products for contents and calories. I recommend alternating between high-sodium and high-potassium drinks. In large quantities, high-potassium drinks can be harmful, but alternating them with high-sodium drinks is healthy and safe.

It’s easy to make a salt-replacement drink that is zero-carb (i.e., no sugar) by adding 1-2 salt tablets or dissolving one-eighth to one-fourth teaspoon of table salt in 300-500 mL of a preferred beverage. Water mixed with fruit juice or frozen fruit slices is a popular option.

Bouillon broth and salty snacks are also handy to have on hand when doing physically demanding jobs in hot environments. It’s also important to note that while bananas contain potassium, they are high in sugar, so they are not the ideal food for potassium replacement in high-heat situations.

In review, although we tend to focus on dehydration, please don’t neglect the heat-battery effect and salt replacement.

Dr. John Longphre is Senior Vice President, Incident Intervention, at WorkCare.