Heat/Humidity in the field

[SCBrian]

I recently had to pull from a backpacking trip due to record high temps.  97* and 90+ humidity as I was in the valleys.  Legit hard to breath, and I work in a kitchen .  I was showing the signs of moderate heat exhaustion (Diarrhea, nausea, vomiting, cold clammy skin, etc, etc) and being able to see the temps continuing at those levels for the next 2 days, I made the decision that I'd rather "Walk out myself while I could, rather than risk others due to my stubbornness".  The annoying part was the 'easy' part of the trip would have only been 1 day away(ish). 
Intake of H20 was probably just shy of 2l/hour, urine production (at the end) was (I kid you not) ~4oz orange, smelly, foamy every other hour or so...
What are the tricks and tips you have for overcoming this type of situation in the field?
Would a zero day (even in the heat/humidity) have improved things?
Night movement would have been questionable due to the terrain (mountainous) sometimes the path was only 12" wide with steep drop offs...

[Raptor]

I deal with heat and humidity a lot. It will kill you...literally...if you are not careful.

What I found that works is to do what you did. Recognize the limit and act accordingly. Take a break in the shade during the heat of the day.

I try to limit any outside work to the early AM and stop at 11am regardless. I avoid direct sunlight and hydrate continuously. I do not resume any work until 7pm and quit at dark. You were very wise to monitor both intake and waste expulsion. Urine output is a critical thing to monitor. If you consuming fluids and not having to urinate you are not consuming enough fluids.

I wear a long sleeve white cotton shirt to both provide sun protection and absorb the sweat. I also wear a wide brimmed hat. Unfortunately this does can add to the heat load, especially the hat.

I have at times placed a cool wet towel over my head and neck. That does provide some relief but it is not a panacea. 

There is however one "trick" that I do use. That is to put some lemon juice and a small pinch of salt in the water I am consuming to provide a bit of magnesium, calcium & potassium (electrolytes) into the water. I seem to absorb the water better that way than with the sugary gatorade/power aide type drinks. Obviously YMMV.

Keep in mind the heat can be "no shit taken" deadly:
https://www.nbcnews.com/news/us-news/body-man-found-death-valley-national-park-car-runs-gas-officials-say-rcna33861

If I were in a position where I had to walk/hike in a difficult area. I would start at dawn and stop by 10am and not resume until 7pm and walk until I could not see. Not a good answer.

 

[MacWa77ace]

So I'm not sure if this relates. But this is what I've been doing for years living here in SE Florida doing 3-4 hours of hard outdoors work on the weekends, in the middle of summer, in 97 degree/ 50-70 % humidity. That's not a whole day of hiking though.

Also I used to do 3 hours of body building 5 days a week [back in the day].


Pre hydrate. Make sure you're drinking plenty of water hours if not a day before you start. And keep up your regular amounts during the exertion. If you  only drink when you're get thirsty its to late, you're dehydrated.

Carb up before starting your exertions.

Actaully I was 'carbing up' about 1/2 hour before starting at the gym, where i ate a cooked baked potato with mustard and milk on it, 1/2 cup cooked oatmeal in milk with a banana, an orange or grapefruit, coffee and an aspirin.

Use those 'air conditioning' cloths that you dampen and put over your neck or head to reduce your skin temps. Keep your ears cool and the sun off your head.

Make sure your clothing is correct for the environment. Make sure you're not getting sunburned so cover your skin or wear sunscreen. Not sure how great sunscreen is when your sweating or want to sweat to keep cool.

Know your environment. In my AO on a clear sunny day in summer it will be 80-90% humidity first thing in the morning, but the temp may be 80-86, so that is still too hot to work. But the humidity will drop as long as it stays clear and be at about 50-60 % by 10am. temp at 86 - 90. That's better, so I usually start at about 10. That still puts me working in the sun at 1pm @ 97 but the humidity is now 40-50%. Plus I'm trying to stay climatized to the heat here by working hard and sweating mid day.

86 degrees at 90% humidity feels like 105 degrees. First thing in the Morning.
86 degrees at 56% humidity feels like 89 degrees. 10:30 am coolest part of the day in my AO.
97 degrees at 40% humidity feels like 102 degrees. 1 pm

Humidity is what get's to me if its hot. And my shirt gets totally drenched. I can take heat index of 102 at 40%. But not Heat Index of 105 at 90% humidity. YMMV

I usually urinate right before starting because I've been pre-hydrating all morning, and then I'll start feeling the urge again before I'm done. And while I haven't measured it, its a normal amount. And I've probably sweated a liter or more, so i've hydrated in the morning and usually finish about 32oz x 2 of ice water mixed with Gatorade in the 3-4 hours.

[SCBrian]

Oh, dont get me wrong, I'm in Charleston, and I work in Kitchens, I'm *USED* to the humidity. But normally at the end of the shift/day, I can de-ass the area and get into some agreeable climate.  I think what got me was the multiple days of it building on each other. 

[Lambykins]

We have a scanner at work. Monitors fire department and rescue squad (ambulance).
In the last four days there have been many calls for heat prostration, passing out from heat, a couple of legit heat stroke victims, etc.
You don't want to mess around when it gets this hot...

[tirls]

I try to keep in the shade, keep my pulse points cool, take breaks if I feel my pulse getting too high. If you have the option cool yourself down with water (not ice cold). I´ve started carrying an umbrella with UV protection for summer hikes to protect myself from the sun and give myself a shady spot. Having a healthy cardiovascular system helps, but I´ve found that as soon as it´s a steep incline I just have to take breaks and give myself time to cool down somewhat. Weather appropriate clothing is another thing. I hike with a long-sleeved linen shirt, loose trousers and sandals in the summer, look at what people living in these kinds of climates wear traditionally. Try to carry as little weight as possible.

Most importantly listen to your body. If you have constant high racing pulse, you need to take a break and not power through until you have no other option than to stop. There´s something called the wet-bulb-temperature, at which point evaporative cooling through sweat stops working. For humans the critical wet bulb temperature is around 30-35°C (it´s dependend on air humidity, so not the temperature you measure). At these temperatures even sitting in the shade can become deadly. There are calculators online for it.

Being able to acclimate definitely helps with heat for me. Humidity still is unpleasant, but if I´m used to the temperature I can bear it as long as I have enough water and shade. I have one of these clip-on ventilators for hats and a cheap collapsible fan like the ones you get in Italy. Looks silly, but if its over 100 I don´t care.
 
Another thing to be careful of is consuming too much water. It is staggeringly painful, I had horrible muscle spasm in my entire body. I couldn´t walk anymore or breathe properly to the point that my lips turned blue. If you need to drink a lot, try to take electrolytes and snack on something salty. You can have the same symptoms as for heat exhaustion in the beginning, but drinking only makes it worse.

[MacWa77ace]

That's interesting. I'm not experienced with the wet bulb indicator and its use. I read the article there and will further research it. I can relate to the heat index calculation which is what I use to know why I feel fine or to hot and if I'm going to sweat or be in danger.

My heat index examples above, and from experience comparing how i felt against the index, I know what is going to make me sweat and what is going to be OK.

If that site had a 'danger' or 'uncomfortable' wet bulb graph i could compare it to my known 'heat index' and use it effectively.

But if I do a 'wet bulb' calculation using the same numbers it doesn't tell me I'll feel hot or OK by the numbers, only by the calculator's 'advise' statements.

for example use these numbers 97 degrees and 40% humidity

The heat index say's it 'feels like' 105 degrees F and I know that is hot and I know it feels hot to me.
But the wet bulb says it's 82 F degrees. In my mind 82 degrees is not hot.

Sort of like I can judge distances in yards or miles, and speeds in MPH, and be really close without using any instruments. But if I have to convert that to Meters, Kilometers etc. Samsonite, I'm way off.

Adding in the wetbulb to my heat index numbers for my referece.

86 degrees at 90% humidity feels like 105 degrees. First thing in the Morning. Wetbulb = 83 degrees
86 degrees at 56% humidity feels like 89 degrees. 10:30 am coolest part of the day in my AO. Wetbulb = 74 degrees
97 degrees at 40% humidity feels like 102 degrees. 1 pm  Wetbulb = 77 degrees

And just for giggles, 74 degrees at 40% humidity [indoor A/C setting at work] is 59 degrees wetbulb and me being from Florida climatization, when I see 59 degrees on anything I'm really cold. LOL.

I'm also noticing that the wet bulb calculator's warning messages are saying its safe at temp and humidity ranges that are going to be iffy for me personally doing hard outdoor work and overheating myself.

At 95 degrees and 70% humidity I know I've got a limited work window before i wear out. and if i continue I'll really start to stress and could be in danger. And I have to shorten work windows to increase 'rests' periods.

But at those temp/humidity the wet bulb calculator says "The wet-bulb temperature is within a safe range." So you'd have to relate it to your personal experience.


AH! Found one. https://arielschecklist.com/wbgt-chart/  Chart B is what we need. the only thing is I'll have to convert all these numbers FROM wetbulb TO heat index and memorize them until they're ingrained, because I have a weather station that shows temp/humity and i can look at it and know the 'feels like' heat index from those just two numbers and act/prep accordingly. 

[MacWa77ace]

Holy Cow! 

So I just ran my numbers for my work schedule and in SE Florida in the summertime I start in the RED and end in the BLACK according to CHART B, the entire work period.

And I'm NOT following the Chart B's work/rest interval advise.

BUT, I AM working within MY physical limits.

I go for the first 1.5-2 hours with no rest period. I have pre-hydrated all morning, and drink about 32oz during the first work period.

Then may rest about 10-15 minutes and start on the second work period. The second work period is the most strenuous task. During this second period the sun is directly overhead, and I can go about 20-30 minutes and rest about 10. And I do that until I'm done which is about an 1-1.5 hrs worth of work. The work interval durations go down depeding on the 'heat index' and the rest intervals go up as needed. But I'm trying to finish as fast as possible so I don't like to rest long.

I don't do the most strenuous first because I don't think I could do the easier part after the hard part. I want to quit.

[Raptor]

Excellent post! Excellent data! Thank you!

Holy Cow! 

So I just ran my numbers for my work schedule and in SE Florida in the summertime I start in the RED and end in the BLACK according to CHART B, the entire work period.

And I'm NOT following the Chart B's work/rest interval advise.

BUT, I AM working within MY physical limits.

This chart is excellent data but like most data and recommendations there is a lot of individual variation possible.

For instance an older person (70+) or very young person (new born to 13) likely have very different heat tolerances. So YMMV.Also people who have become acclimated to the heat and are otherwise  healthy may be able to stretch the boundaries of the this chart.
That said it does not mean that even acclimated people should ignore the advice.  The data is clear. 

This past weekend the temps in my AO were unusually high 99F+. At 11 pm last nightI checked the temps outside and it was still 89F. The good news is that the heat wave is due to some dry air coming so humidity is down to around 60% to 70% vs the usual 90%.
I did do some light work (weeding and trimming branches, cleaning the pool filters, using the blower, etc.) out side and started at 7am Saturday and quit by 10am. When I came in my face was beet red and despite staying constantly hydrated through out (& jumping in the pool twice for a break) I was clearly on the verge of heat exhaustion when I called it quits. I did not realize this until I saw my face. I immediately took a luke warm shower then hydrated and sat under a fan to rest. The ambient air temp was well above 93F when I called it quits. I should know better. Heat issues like cold issues (hyperthermia) can easily sneak up on people who are not paying attention. I was clearly not paying attention.   

[tirls]

The wet bulb temperature doesn´t always seem to work, I did realize that as well. It gives me 70°F for 122°F at 5% humidity. My feeble European heart is not doing 122°F no matter what humidity it is, whilst I shouldn´t be working at all on some summer days according to the table.

[MacWa77ace]

The wet bulb temperature doesn´t always seem to work, I did realize that as well. It gives me 70°F for 122°F at 5% humidity. My feeble European heart is not doing 122°F no matter what humidity it is, whilst I shouldn´t be working at all on some summer days according to the table.

Do you really get that low of humidity in the summer over there?

That's weird, look at the first chart I posted, it gives 94.2 WB for those numbers. In the Black danger zone.

I've been in high heat and low humidity environments before, but not 'working'. And IIRC it was about 110 at 5% [in the Red Zone] with light breeze, in the direct sun, and it felt cool to my Florida boy climatization.

Possibly because if I was sweating it was evaporating as fast as it was coming out. Unlike high humidity environs where the sweat piles up in your clothing until its saturated.

That combination of high temp and extremely low humidity could get really dangerous as far as dehydration. If you don't think your sweating but you really are losing water. Even if you don't feel hot or your clothes aren't wet with sweat you could read your body wrong and keel over.

[MacWa77ace]

For instance an older person (70+) or very young person (new born to 13) likely have very different heat tolerances. So YMMV.Also people who have become acclimated to the heat and are otherwise  healthy may be able to stretch the boundaries of the this chart.
That said it does not mean that even acclimated people should ignore the advice.  The data is clear. 

As I get older I can't tolerate what I used to. But I'm working hard mid day in the summer to try to keep my heat/humidity tolerances and endurances up. 

This past weekend the temps in my AO were unusually high 99F+. At 11 pm last night I checked the temps outside and it was still 89F. The good news is that the heat wave is due to some dry air coming so humidity is down to around 60% to 70% vs the usual 90%.
I did do some light work (weeding and trimming branches, cleaning the pool filters, using the blower, etc.) out side and started at 7am Saturday and quit by 10am. When I came in my face was beet red and despite staying constantly hydrated through out (& jumping in the pool twice for a break) I was clearly on the verge of heat exhaustion when I called it quits. I did not realize this until I saw my face. I immediately took a luke warm shower then hydrated and sat under a fan to rest. The ambient air temp was well above 93F when I called it quits. I should know better. Heat issues like cold issues (hyperthermia) can easily sneak up on people who are not paying attention. I was clearly not paying attention. 

Your humidity is lowest at 7am in your AO? Mine is high most early mornings, 80+ %. Then drops continuously if it is clear, as the temp rises. If I didn't WANT to work hard during mid day I could start at about 4pm and comfortably work in the evening where it'd be an average 90 and 40% humidity. That's about in the Yellow Zone per the above chart.

My pool in August, if we don't have to much rain, will hit 95 degrees, and a few years ago during the drought we had down here it hit 97. My pool water temp! Not the air temp. Let me tell you, jumping in that after doing my heat/stress work is not comfortable at all and not really worth it.  My pool was 90 two weekends ago and 88 last weekend. 88 feels so much better than 90, that must be the sweet spot cutoff for me, LOL.

[tirls]

Do you really get that low of humidity in the summer over there?

No, I was just playing around. We don´t get those temperatures either. The highest officially measured temperature is 106F here. I´ve definitely measured higher ones, but those aren´t official and don´t count.

Thankfully once it gets really hot it´s due to air straight from Africa and Spain, so mostly quite dry. The times it does get unbearable is if you´re in between the weather fronts and a thunderstorm comes, then we sometimes have 100F with a humidity of 90% and up. But nothing as bad as Florida.