Heat Stroke

When we got back from Disneyland I felt quite strange - disoriented, unusually exhausted, and a little nauseous.   And not just from the bill! (HKD 3,000+ for taxis, admission, Elsa dress, food and ice-creams).

I eventually concluded that I had mild heat-stroke.  Which was an unexpected first for me, since I'm normally immune from these sort of 'girlie' problems.   I realized that I'd started the day quite dehydrated from weekend exercise, and although we'd drunk lots of liquid it was water not sports drink, so I'd failed to replace the missing salts.   Although it was 'only' about 32 degrees, it was sunny and rather humid at about 70% humidity, which made the 'effective temperature' much higher - equivalent to a dry 39 degrees in the shade (102F).

From my background in southern New Zealand I know quite a lot about hypothermia., but nothing about heat-stroke.   It was obviously time to get educated, and once my head cleared I did some research.

One key point which I'd not fully appreciated is how the combination of heat and high humidity can overwhelm the bodies ability to cool itself.   High humidity reduces the effectiveness of sweating, which dramatically increases the 'effective temperature' - 30 degrees at 80% humidity is like a dry 38 degrees.  On top of this bright sunlight can add a further 8-10 degrees.

From these levels, one can enter the danger-zone in much sooner than I'd realized.  At 80% humidity, raising the temperature just 3 degrees to 33 increases the effective temperature by 10 degrees to 48!   Raising the humidity from 80% to 100% (at 30 degrees) increases the effective temperature by 6 degrees to 44!  All this before any additional heat from sunshine.   Attempting strenuous activity in these conditions can quite quickly dangerously overheat the body.

Warning signs at the start of a hiking trail

With that in mind I reassessed our plan for Tuesday's public holiday.   Hannah had wanted to go hiking  to ride in the Deuter.   I'd hoped to do a 5 hour track up Tates Cairn (538m) and on to Lions Rock,  using the approach route up near Buffalo Hill that I'd done on my own when it was 33 degrees and 60% humidity (effective temperature 40 C degrees).

But the forecast was for temperatures 29-33 C with humidity 80%-100% and broken cloud.  So effective temperatures 35+ to 57+ degrees!   Plus no shade for most of the route along the ridge (+8-10), and carrying Hannah for most of the way up.

So what might have been doable at 60% humidity looked dangerous at 80+ humidity.    Instead I chose a more shaded and less strenuous hike, and took care to rehydrate overnight, and pack lots of sports-drink and some frozen water-bottles for emergency relief.

A Recipie for Heat-stroke

1 dehydrated Daddy
33 C degrees temperature
80-100% relative humidity
30kg load to carry
4 hours hike up 1 rocky hill

Mix together well and roast for 1-2 hours, or until moist and flaky.