Do you walk in a heatwave?

[David M]

I was wandering if anyone walks in heatwaves as most of Australia is experiencing now or would you cancel the walk?

[Moondog55]

I would cancel.
Once it gets over 38C the risks increase too much.
Not much you can do if the walk has already started and the heat wave wasn't predicted but I would not go walking this week-end for instance, risk of bushfires more than the risk of heat related illness although that is on my mind lately

[gayet]

No.

I did pull the pin part way yesterday - but that was hardly heatwave, more gross lack of fitness and difficulty handling the higher than expected (at that time of day) temperature. I'll take necessary steps to increase fitness!

If its known that temperatures are expected to be high, then the walking is unlikely to be pleasant and the risks are higher than the benefit. Stay put, start earlier if movement is essential, postpone the walk till better conditions are likely.

[Bubbalouie]

Can't say I do, I am happy to walk in upto 33C after that it gets too uncomfortable to be enjoyable any more. When it's no longer enjoyable there isn't much point . That said, I'm not so good with heat, i really enjoy cooler (cold?) weather though.

[davidm]

I was stuck out in the blue mountains on that day last january when it hit 46. Not a pleasant experience!

[whynotwalk]

I have done ... but only when caught out towards the end of a multi-day trip. I would rather not, as heat exhaustion is as dangerous as hypothermia.

In yesterday's weather (40+ degrees in parts of central and southwest Tassie) a colleague had to deliver a resupply to Junction Creek (Arthur Plains). It was well over 40, and he said he (a) walked for 10 minutes, then rested and drank lots of water, and (b) walked slowly, averaging only about 1km per hour. The keys to survival are cooling down as often as possible and keeping your fluids up ... Of course the safest is not to go in the first place

cheers

Peter

[michael_p]

I was wandering if anyone walks in heatwaves as most of Australia is experiencing now or would you cancel the walk?

A few years back I cancelled a walk due to the heat. It was only a short walk to a local swimming hole but it was forecast to be 40C and with a very high fire danger so I decided to cancel. It's far safer to do so.

Cheers,
Michael.

[GPSGuided]

Comes back to why you are walking. I walk for enjoyment and health, hence there's no need to subject oneself to major health risks.

[wayno]

if i was caught in a heatwave on a trip, i'd cut it short and switch to walking in the early morning... and stop before the heat of the day

[nq111]

It can be really dangerous.

Like high altitude mountaineering there is specialised gear, different procedures, a new set of skills to learn and a need for experience to understand your limits.

Also, the most important thing you can do for those conditions (more important than the list above) is heat acclimate - i.e. accustom your body to exercising in the heat for 3 or more weeks earlier. That is pretty tough to achieve for the occasional heatwave down south. But it is amazing how well the human body can adapt to activity in hot conditions given the chance. We are tropical animals after all.

[pazzar]

I was caught out on Mt Manfred when it hit 42 last January. I never want to be in that situation again. I went over 3 hours without water, and I wasn't sure how I was going to get out. I had seriously considered using my PLB if the situation had worsened. Having said that, I've walked comfortably in temperatures in the high 30's and been fine. I think it all comes down to water availability for me.

[corvus]

Walked out from Pelion via Arm River track a few years ago after doing a food drop and we encountered 38 in the full sun(horrendous for us in Tassie with ultra strong UV) fortunately there are plenty of creeks/streams on or near this track so dehydration was not a problem.
Hottest conditions I have ever waked in and would not like to do it ever again .
corvus

[Zone-5]

Never do it, I'm serious!

I've done it in spite of +48°C in daylight but only because of a breakdown in a remote location which needed a trek out to get help.

We walked out at nights only. It was the desert north of Broken Hill in early Jan a few years ago.

I had seriously considered using my PLB if the situation had worsened.

If I had had a PLB, I would have used it.

I now pack for worst case scenario on every trip!

[goanna]

I think it really depends on many factors especially how hot is your heat wave? How fit and experienced the party?

See this link for a report of a nice day out in fairly hot weather.

http://www.johnevans.id.au/Pages/Walk%20Descriptions/2014_01_14.html

[wayno]

acclimatisation to the heat is very important, acclimatised people can sweat more and will drink more than non acclimatised people.
the british army did a field test in the middle east with acclimatised vs non acclimatised soldiers working in the heat...
thre was a noticeable difference in water consumption and how many soldiers were overcome by heat stress between the groups
also keep your head wet, keep your hair short and have a hat thats well ventilated, your brain can only cope with a five degree temp increase over normal body heat, your body heat can cope with ten degree rise,,, when you're hot blood passes from your scalp through special holes in the skull straight into the brain to cool it down, having water evaporating from your scull and having a ventilated hat help cool the blood down before it passes to the brain....

[wayno]

i usually shave my head and keep it close to a crew cut over summer to improve heat loss from my head when exercising....

[GPSGuided]

... keep your head wet, keep your hair short and have a hat thats well ventilated, your brain can only cope with a five degree temp increase over normal body heat, your body heat can cope with ten degree rise,,, when you're hot blood passes from your scalp through special holes in the skull straight into the brain to cool it down....

Good practices but some factual corrections needed here.
1. Protein starts to denature around 41 deg C. A rise of 5, let alone 10 would be death defying.
2. There are no special hole in the skull that permits blood from the scalp area to enter the brain. The brain is supplied by four major arteries that enters from the base of the skull.

[wayno]

incorrect gpsguided
please view this documentary which outlines the physical mechanism whereby blood does floow directly from the scalp to the brain when the body is hot.. it gets into the detail in the later half

[calliejane24]

I am heading out to western Queensland for field work next week.....where the maximum temperature is forecast to be mid-40s. It is truly unpleasant working under those temperatures and when you're on a tight work schedule, it's always go, go, go. How I wish I could pull the pin!

[GPSGuided]

incorrect gpsguided
please view this documentary which outlines the physical mechanism whereby blood does floow directly from the scalp to the brain when the body is hot..

Do you prefer to believe in a documentary than established anatomy and personal knowledge?

Edit: Ok, I've watched the video and you have partly misunderstood on a technical point. The documentary talks about the vascular circulation of the scalp having connections with the interosseous vessels of the cranium ie. Vessels within and between the two bony plates of the skull bone, also known as the marrow space. That is NOT the "brain". The bony skull is not the brain and the brain resides within the bony cranium and has a separate blood supply.

As for heat loss from the head, that's because of the very high blood flow through the region. The interosseous blood flow is but a tiny portion of that main flow. As a fact, cutting through the scalp will induce a profuse bleed but scalping the full layer off the bony skull is largely bloodless.

Last edited by GPSGuided on Thu 16 Jan, 2014 5:53 pm, edited 2 times in total.

[Pteropus]

I am heading out to western Queensland for field work next week.....where the maximum temperature is forecast to be mid-40s. It is truly unpleasant working under those temperatures and when you're on a tight work schedule, it's always go, go, go. How I wish I could pull the pin!

I know the feeling. Several years ago I was in the mulga conducting surveys, and there was a week of temps in the mid-to-high 40°C range. I was carrying 10 litres of water. One day my 3 litre Camel Back bladder burst in my pack. I had 20 litres in the vehicle at all times too. At lunch time I would look for a wilga tree and have a camp for half an hour or so. I once attempted a bush poem on the back of a data sheet too:

An ode to the shady wilga! (A. Smith)

Temps had been in the high 40s for six days in a row,
All the animals were hiding and I just wanted to go.
I was running out of water, and running out of food,
It was so *&%$#! hot at night I had to lay on my camp cot in the nude!
I would wake at half past four to go out to find the bear,
But I tell you what, it was so *&%$#! hot that I honestly couldn’t care!
The wind was scorching from the west, like a big blast furnace,
And the water in my bottle was hotter than if it were from a thermos!
By midday I was looking to have a camp, somewhere in the shade,
I really needed a dark cool place to hide, preferably a cave!
The vegetation was sparse though, box and sandlewood,
For all the shade they provide life was not so good...
Then there is iron bark, rosewood and sparse crowned mulga,
BUT as all the hot animals know what shade is best for them, Thank Christ for the shady wilga!!
I fell asleep under a big shady wilga tree,
It was nice and cool as can be!

303 shady wilga.JPG (332.3 KiB) Viewed 11447 times

[Giddy_up]

This shows how the brain cools, pretty amazing…...




http://www.upright-health.com/brain-cooling.html

[David M]

More on cooling of the human brain (abstracts only).

Brain cooling in humans--anatomical considerations
http://www.ncbi.nlm.nih.gov/m/pubmed/8838492/

Brain temperature and limits on transcranial cooling in humans: quantitative modeling results.
http://www.ncbi.nlm.nih.gov/m/pubmed/97 ... 92/related

Selective brain cooling seems to be a mechanism leading to human craniofacial diversity observed in different geographical regions.
http://www.ncbi.nlm.nih.gov/m/pubmed/15 ... 76/related

Human paranasal sinuses and selective brain cooling: a ventilation system activated by yawning?
http://www.ncbi.nlm.nih.gov/m/pubmed/21 ... 92/related

[Drifting]

I tried to take the family to Mt Buffalo during a heatwave in '02. That morning a dry thunderstorm rolled through, lit the mountain on fire (about 4 km from our house actually), and then whole *&%$#! mountain and the rest of NE Victoria burned down, not to mention a sizable chunk of Canberra.

When it gets that hot, go to the beach.

[madmacca]

The risk of heat illness is something that can be managed (note 'managed', not ignored) through carrying (and drinking) plenty of water, starting early and having an extended midday stop (preferrably by a water source), replacing electrolytes, dousing your clothes in water when you have the opportunity, etc.

The threat of bushfire in a heatwave is more concerning, although this is really a matter of heat and wind, rather than heat alone. In making a walk/no walk decision, I am looking really at the fire risk rating that day. Heat will affect where and how far I walk.

[GoForFun]

It also depends where the walk will take place. Along a river and with some shade it may be ok, but keep in mind that at the end of the day the walk may not be very enjoying and more a kind of a struggle.
Anyway, if you decide to go, have fun, drink a lot of water and rest several times!
Greetings

[GPSGuided]

Note however, the longer the duration of an activity that requires a high volume of hydration, the harder it is to maintain electrolyte balance. So, maintaining electrolyte balance becomes quite difficult on these extreme weather days. It ain't easy and will expose many risks even for the best equipped.

[wayno]

salt lick....

[GPSGuided]

salt lick....

How many licks?

[Watertank]

Given the risks involved and the fact that if I get into trouble I may take emergency services away from other critical activities I consider that it is not only my wishes but the possible needs of others that mean I stay away from the bush during high risk days.