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Heat & Hydration: How we stay cool

Friday, 22 Jan 2016
Heat & Hydration: How we stay cool

Our engine's cooling systems

People are like cars: both have a very efficient cooling system to dissipate the heat.

As our core temperature begins to rise, our body’s hypothalamus (our ‘thermostat’), tells the heart to pump harder.

Blood vessels in our skin enlarge to allow more blood to be exposed to the (hopefully) cooler surrounding air before flowing back inside us to help lower our core temperature.

However, if the air temperature is higher, the warm blood won’t transfer heat to the surrounding air.

To cool ourselves, we begin to sweat – one of the body’s most important cooling mechanisms. As sweat evaporates it cools the skin, much like the car’s radiator.

It’s important to note that when you are working in highly physical roles your working muscles need blood flow so there is competition between blood going to muscles and blood going to skin surface.


Maintaining a fluid motion

Failing to drink enough fluid is the cause of most heat-related illnesses.

Unfortunately, our thirst mechanism doesn’t work as effectively as it sometimes should. In fact, thirst can be a poor indicator of the need to replace fluid.

⅔ of our total body weight is water. That’s:

  • 83% of your blood
  • 76% of your muscles
  • 75% of your brain
  • 25% of your bones made up of H2O.

By the time we feel thirsty we may have already lost 1-2% body water. A person can lose 2% body weight of water in an hour in hot conditions when we are working physically.

A loss as small as 2% body weight can affect our performance significantly with physical and cognitive functions affected leading to an increased risk of injury and accidents.

  • 1-2% loss body water = 6-7% reduction in physical work capacity
  • 3-4% loss body water = 22% reduction in physical work capacity
  • 4% loss body water in a hot environment = 50% reduction in physical work capacity.

When it comes to fluid replacement...

Water is the essential component. You can add low-sugar cordial or juice to water, but coffee, tea, soft drinks aren’t as effective, and alcohol only accelerates dehydration.

Drink frequently in small quantities. Pre- and post-hydration is especially important when a worker is not able to drink frequently.

Check your urine colour. If it’s dark or bright yellow drink some more water until it’s a pale yellow.

Drink water until you’re no longer thirsty... then drink a bit more. It’s a good rule of thumb.


Sources

www.thethermalenvironment.com/what-is-the-impact-of-caffeine-in-relation-to-heat-stress/

International Journal of Occupational Medicine and Environmental Health 2013;26(5):762–769 ASSESSMENT OF CONSTRUCTION WORKERS' HYDRATION STATUS USING URINE SPECIFIC GRAVITY. SAIDEH MONTAZER1, ALI ASGHAR FARSHAD1, MOHAMMAD REZA MONAZZAM2, MEYSAM EYVAZLOU1, ALI AKBAR SABOUR YARAGHI3, and ROKSANA MIRKAZEMI

www.chemistry.about.com/od/waterchemistry/f/How-Much-Of-Your-Body-Is-Water.htm

Dr Ross Di Corleto

Dr Ross Di Corleto is a noted Australian authority on the impact of heat in the workplace. He is a member of the Australian Institute of Occupational Hygienists (AIOH), he co-authored the AIOH booklet, ‘Documentation of the Heat Stress guide Developed for Use in the Australian Environment’.

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