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mack_turtle

rank trails in order of heat stroke danger

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3 hours ago, bear said:

I actually just put a mandatory 4-5 clise-out meeting Fridays for all my direct reports.

Then I skyped then to tell them I'd never be there unless there's and ongoing Incident.

Considering repeating for M-Th

you rock!  Personally, I just decline most meetings that have no good reason or agenda, e.g. "let's meet to discuss"., meetings after 4 on Friday or at lunch any day of the week, or after 6pm unless the people are 11.5 or 12 hours away...

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I am on vacation this week and one of my customers has 2 calls with their client that they need me on. I provide no value on the calls. But they are going to pay me my consulting fee to be on the calls and they happen early enough in the morning that it won't interfere with my plans. That buys a lot of IPA. 

But the afternoon calls are a hard no. Back in my corporate life I had meetings from 8 to 5 plus evening calls with Asia. Even an occasional 6AM call with Europe. I don't miss those days.

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I’ve been riding in the mornings since the heat intensified, and was curious to try a late afternoon ride to see how that felt.  It was 99 in the shade at Pedernales Falls State Park when I started about 7:00 pm.  I was able to keep moving and though the air was really hot I wasn’t too uncomfortable unless I was in full sun for too long.  Finished just before sunset and did not feel too overheated, and definitely less sweaty than my morning rides.

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58 minutes ago, Bart said:

if you stop on that hot limestone, it felt like an oven. 

The surface temps the last couple of weeks has been brutal. Been working on concrete and it's like being in a tanning bed 5-6hrs a day.

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Yesterday I left around 11 a.m., (seemed like the perfect time when the humidity wears off and the heat has not hit full strength yet) I rode from my door out through Sunset Valley to the VCT entrance on Ben White, down the switchbacks to ride Sweet 16 to the Travis Country pumptrack. by the time I got there, I didn't even have the energy to do a lap around the pump track, I just limped home.

I was hoping that riding under the BCGB canopy would make things less awful. Everything down there smells like the ashe junipers are about to burst into flame. good riddance! I'm trying to figure out if the heat got to me, or it was a combo of the heat + riding some of the most challenging, technical trail segments I know. total ride was barely 11 miles. that's my shortest BCGB ride yet.

I'll experiment with some r**d riding today to see if that's somehow better. less shade but more movement and less effort spent wrangling the bike over ledges and stuff.

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It was probably really humid in the green belt, even if you didn't think so. I have been limiting my riding to places like Suburban Ninja and Brushy, and hillsides along the 360 and 620 corridors - a little bit of a breeze and some elevation really seem to make a difference. Still try and hit SATN once a week, too.

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12 hours ago, mack_turtle said:

in case it was not plain enough to me that heat + humidity was a bad combination: https://www.psu.edu/news/research/story/humans-cant-endure-temperatures-and-humidities-high-previously-thought/

it gets worse with age.

There's no link to the actual paper, and what is written there has so many holes.  A couple of questions:

1) How many watts cycling or walking?  That matters.  (one reason I don't go to the BCGB or Thumper this time of year).

2) Airflow.  Was there any?

They could have made it educational by comparing heat of vaporization (540 cal / g at 98°F) vs convection.  Even at 100% humidity with no sweat evaporating, you will get some convection cooling (probably an order of magnitude lower than vaporization).

In the end, I'm not even sure why they performed this experiment.  You can calculate this easily.  With no evaporation, this boils down to what thermal engineers do all day long every work day of the week.

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FWIW, this matches a study I read ten or more years ago regarding the relationship of high ambient temp and core temp. It was part of an article to warn motorcyclists of the dangers of overheating in the Summer. Back then the point two university studies had determined was 93F, a few degrees higher than what this study determined.

It went on to say how once air temperature reaches a certain point the heat becomes less effectively removed from the body even if the sweat is evaporating. The greater the air temp is higher than the skin temp, the more heat will transfer from the air to the body instead of cooling it. This results in heat building up in the core over time (and exertion) and increases risks for a number of health issues.

Essentially, the convection is occurring, only it is in the other direction, heating the cooler surface, the skin/body.

I think this is also how an Air Fryer works. 😁

Edited by Ridenfool
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Heat input + Heat generated = Heat output (evaporation + conduction/convection) to maintain temperature.

Neglecting heat input and conduction/convection....

If you're doing nothing, just sitting around and are an average male, you'll be burning 2000-2500kcal a day.  Assuming the latter, that means 104kcal per hour.  At 540cal/g, you'd need to vaporize 192g of water (192mL) to maintain temp.  If you are riding tempo, you're likely going to be burning 600-800kcal/hr.  Assuming the latter, that means you need to evaporate 1.48 liters of water per hour to not overheat.  If the humidity doesn't allow you to evaporate that much water, you will either overheat or (more likely) your body will force you to slow down.

I need to research convection cooling.  I am assuming it's very small compared to evap, but I'd like to find out for sure.

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The "Heat Index" provided by weather sources is based upon calculating for evaporation based upon current temp and humidity. This is what it feels like outside to one of us hairless monkeys.

Currently I see 87F air temp, 95F heat index, and 60% humidity. Normal skin temp range is 91 to 98 degrees. If the heat index (sweat effectiveness) is higher than current skin temp the heat will move from the air to the skin and increase core temperature. Add to this the heat the body is producing and is unable to shed and the rate of core temp increase steepens.

This will be true with heat transfer via conduction, convection, and radiation. So, sweat evaporating from the skin is a convection path, the sweat-soaked shirt unable to evaporate fast enough and holding heat (water is efficient at holding heat) is a conduction path, and the sun shining on bare skin is a radiation path for heat.

Let's say skin temp is 95F and the heat index is 97F. A 2 degree spread probably isn't enough to remove all the heat being produced by a rider. Add to this heat gain from sunshine, and the stored heat in soaked clothing and it is unlikely there is any other outcome than for the core to increase in temperature.

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Thanks.  I was familiar with wet bulb temp and heat index as the "feels like", but I was definitely not as familiar with what it means as far as evaporation.  I had to read up on the details, and found this excellent summary which includes solar irradiation estimate.

https://www.weather.gov/ama/heatindex

BTW, increased convection helps with evaporation, but evaporation is different from pure convection.

I would still like to see a separate chart that takes airflow into account.  All the heat index stuff basically assumes you're in the shade and not moving.  Looking at this from the engineering side, we always have to take into account:  airflow, ambient temp, humidity, and altitude.   All those affect conduction, convection, and evaporation.  For sure when I ride in the heat, I hate going up a slow hill which usually also means head wind is getting blocked by the hill, or I have a tail wind (the worst).  This is why I stick to the flatlands.  It feels way different even in high heat index conditions.

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This just reminded me of one of my hottest/awful feeling rides ever.  It was RHR 24 hour race, usually around Halloween (one week before or after, same as the EB).  It was crazy hot at hour 6 (6pm).  It was also fairly dry and the single bottle of hydration mix + extra water bottle per lap (~50-70min laps) was not enough.  I went into debt.  I decided to do a long stop around 6pm, rehydrate, cool down, and avoid the hottest part of the day (a section in the first part of the course...the long winding climb was the worst!) Even though I lost a lap to some people, it was the best strategy.  I was able to finish the race while others just went too deep and dropped out. 

I wasn't scared that time...but I was at the BCGB one time.  Ran out of water, couldn't find my way to the tennis courts, not feeling great.  I thought of Bear Gryll's advice (head downhill toward the water) and sat in a nasty pool of green water which cooled me down significantly and I was able to ride the main trail to Zylker and water.

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3 hours ago, Ridenfool said:

I think this is also how an Air Fryer works. 😁

now the question is: what trail should we just nickname "Air Fryer" now?

 

I don't think I am capable of creating enough "air flow" to make a different. maybe that's why road rides feel slightly less horrible, especially if you avoid the hilly routes that involve slowly grinding up the climbs.

Edited by mack_turtle
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1 hour ago, mack_turtle said:

I don't think I am capable of creating enough "air flow" to make a different. maybe that's why road rides feel slightly less horrible, especially if you avoid the hilly routes that involve slowly grinding up the climbs.

Yep, it's all about the airflow.  When you stop for a light, it feels horrible, and the sweat starts accumulating, but the payoff is when you start moving again.  It feels like AC.  On days when evap is not great, I also take an insulated water bottle with lots of ice and splash a little bit in the crooks of my arms and on my head if I hit a red light.

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Thumper is hands down the hottest trail in Austin during the brutal heat, IMO. I brought some race fit buddies back there yrs ago in August and we seriously couldnt get out fast enough. It's like a sauna down in that valley with the humidity and zero air flow. We made it to Bull Creek and had to cool off in the skank water before climbing out.  We all rated that as, 'the bad decision dirt ride"

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