Heat Injuries and Expeditions

The normal range for core temperature is 36.5°C-37.5°C but in reality we can exceed these temperatures. An extreme but survivable core temperature would be about 41°C, beyond which you’d expect to see organ and brain damage as the body effectively cooks itself very gradually. Scans of people’s brains after suffering heat injuries demonstrate that tissue is damaged as if it’s been cooked! If our core temperature exceeds our safe limit then we may collapse from heat exhaustion. The more exposure we have to heat injuries; the more susceptible we become to them, so it’s best to take some precautions.

Avoiding the heat is the obvious starting point. Planning your activity so that it falls early or late in the day, or even at night to avoid the sun. Drinking plenty of water and minimising your activity, trying not to exert yourself too much are all sensible starting points. But this isn’t always possible.

We’re going to focus on the times when these options aren’t always available to us. Working in remote areas when we don’t get to choose when we’re active means that we must have a more thorough understanding of heat injuries so that we can recognise them and do something about it.

First let’s look at what causes us to overheat and then at what mechanisms we have to cool us down. There are a few different factors, and it’s worth bearing this mind because it’ll help you work out how to adjust what you do.

Heat Generation

S = Heat storage in the body (if positive, body temperature rises)

• M = Metabolic heat production

  This refers to the biochemical processes which give our muscles the energy to contract.

  
  

• W = External work performed

  This refers to the contraction of muscles and the heat that is given off as a byproduct. Due to the inherent inefficiency of biological systems, only a fraction (typically around 20-25%) of the metabolic energy (M) is converted into this external work. The byproduct is heat.

Heat Release

• R = Radiative heat exchange (heat lost or gained via infrared radiation)

  
  

• C = Convective heat exchange (influenced by air temperature and air speed)

  
  

• K = Conductive heat exchange (contact with surfaces, usually minimal)

  
  

• E = Evaporative heat loss (sweating)

Environment

• High humidity reduces the effectiveness of evaporation.

• High air temperature can reduce convective and radiative heat loss.

• Increased air speed enhances convective and evaporative cooling.

So that’s all of the factors which contribute to your heat retention and heat loss. Some are more relevant to different environments. For example, we will encounter dry, still air in the desert but we will get humid hot air in a jungle. This means that the most effective mechanism for cooling will change slightly. Sweating doesn’t work as well in humid areas as in dry ones.

We are trying to reduce the heat that’s stored in the body (S). We have all these tools we can use so we don’t just have to rely on our body doing its thing, we can help it along. If we understand that sweat is really just the process of convective heat loss (C) then you can use moisture you find to help cool you down.

The other major factor in convective heat loss is air speed. I’ll often choose to train on a bike where I travel faster than running if it’s really hot because the added air speed on a bike helps keep you cooler, which lets you train better.

So when we don’t have the luxury of choosing when or what we’re doing we just need some practical ways to keep cool. One thing about conductive heat loss that I notice is that once you’ve sweated enough that you have a sweat all over your body, you tend to stay cooler for longer (which is stating the obvious). The subtlety is that we don’t always manage to get to this stage, as you’ll notice if you’re particularly red and your skin feels dry. The redness is caused by capillaries bringing blood closer to the surface to aid with heat loss. But something that is very simple and effective is just very lightly wetting your skin using as little water as possible (this isn’t to be done instead of drinking).

Let’s say we end up getting too hot. What does this feel like? Well from my experience you’ll begin to feel all the hallmarks of fatigue – difficulty in thinking clearly and struggling with tasks that are normally second nature are my first indicators that I’m getting close to having an issue.

After these you may notice your eyesight is changing, either blurring, or maybe seeing spots/stars. Eventually muscle cramps will become more and more noticeable along with muscle fatigue. Beyond this there is also a neurological function built in to all of us which will be screaming at you to stop working. This is called the “central governor of fatigue” and I’ll talk about it more in another article. In short you’ll know when you’re on the way out so it’s time to have a strong word with yourself. I know that my decision making is compromised and that I am no longer as proficient at technical skills.

There are different consequences to this depending on what you’re doing. Navigating in the desert is critical but doesn’t cause instant death. Being on vertical ground in 45°C and transferring between rope systems is critical. When I’m feeling drained from the heat I’ll often have to double check things or even just have a pause before committing to the next system so that I can collect my thoughts. I try to avoid adding “extra” safety mechanisms because these often cause confusion and mess up your working area with additional clutter, increasing the chances of a mistake.

In summary

Avoiding heat injuries on expeditions means you must understand what your body is trying to do to lose heat and think about ways you can help it. This changes depending on the environment you’re in and some specific conditions around you like humidity and air movement. Use tactics beyond just drinking and staying in the shade. 

Be aware of what you’ll feel as you begin to fatigue so that you can increase your safety margins when in life threatening positions. Don’t come up with complex strategies to minimise risk, you need simplicity and practicality that is easy to check.

Chris Andrews on the way back from climbing in Wadi Rum, Jordan.

I don't use AI. I write each post in one go, and I don't proof read what I've written. Hopefully the repetition, spelling mistakes and mental unload will make this obvious to you. (In this one I did have a pause to get the numbers and formulas together)