Ground surface temperature measurements

Folks, I just wanted to share with you the nerdy experiment I conducted today. It broke 100 degrees F today in the valley so I took a walk, barefoot of course, and took with me a digital infrared surface temperature measuring device.

Here are the measurements, compared with how it felt to my feet standing still:



Old asphalt street: soles feel warm after 50 sec. Measured 141 deg F
New asphalt parking lot: soles feel hot after 20 sec. Measured 162 deg F
Steel manhole cover: soles feel very hot after 8 sec: Measured 140 deg F

Note how the manhole cover felt a lot hotter than either of the previous surfaces even though it had the lowest measured temperature! I'm pretty sure this is explained because steel is much more thermally conductive than asphalt or concrete. This is also supportive evidence that can explain why firewalking is possible because the wood ash on the surface of burning embers has very low thermal conductivity.

Next time I want to measure the spot I was standing on to see how much heat was absorbed by the soles of my feet from each of the surfaces. I'll keep y'all posted.

 

Interesting facts ! were the old asphalt and new asphalt different colors? will a blacker surface absorb more solar energy. Conductivity is also dependent on moisture levels. Do the pores in the surface of blacktop and lack of in the steel make a difference (more surface contact)
I like hot surfaces and sometimes stand still on purpose. Here in the northeast US it's rarely hot enough that I'd avoid standing around. Not everyone is as tough footed so they should be cautious.

 

Yeah, one reason I like living in this valley is because of the summer heat. I also like hot surfaces.

The old asphalt was lighter in color than the new asphalt. Also, the old asphalt seemed more rough and porous. I think the big difference with the steel is how dense the material is and how heat is transferred relatively quickly. On the asphalt, the heat from just the surface layer gets transferred to the feet then the process slows down because that layer is now suddenly cooler. With steel, the heat from the entire plate can transfer into cooler regions quickly, therefore the surface remains hot as you stand on it.

I also like standing still on purpose just to feel the heat. I find that if you periodically roll your feet from one side to another, or from ball-to-heel, heel-to-ball, that you can remain standing on a hot steel plate. But like you said, one should be cautious.

 

we got to aroung 96 yest and the asphalt was squishy in some places from the heat. The soft sponginess was enough that I could push down real hard and leave a footprint. The tar didn't stick to my soles much as my feet were dusty. I walked around the lot a few times and let the heat soak in. Never uncomfortable but certainly hot, several guys needed to run to the shady spots between cars. I was cautious but didn't feel my feet were close to burning or blistering.

 

Yeah I like leaving footprints in squishy tar as well. It's pretty neat how it feels like some kind of gel.

By the way, I recently verified my theory about surface heat absorption on asphalt. I took my infrared thermometer out with me and measured a spot on the parking lot asphalt at 158 degrees F. Then I placed the ball of my bare foot over that spot and stood for a couple of seconds then measured the spot again. It read only 136 degrees! That means if your eyes could see infrared, you would see cool footprints left on the asphalt as you walk across it.

I tried the same thing on the steel manhole cover and it only dropped about 2 or 3 degrees!

 

Cool... The high temperatures explain why I burned my right foot a bit from the hot asphalt a couple days ago

 

Did you all forget something? You could actually fry eggs on the new asphalt! Well, it might take a few minutes to get them to cook, I bet they would.

I think those temperatures would be a little too warm for my bare feet. I have trouble navigating paved roads and parking lots when it gets a little above 90 degrees (F).

 

SD: I'd like to see that picture. Are infra red thermometers a specialized piece of equipment or are they available ? I'd like to see what happens on snow also.
weez & Em: Us northerners don't see enough high temps. If you keep moving on the pavement you should be ok. Caution should be maintained, you don't want to be off your feet due to an injury.

 

Well putting the egg fluid onto the pavement would quickly cool the pavement's surface and then it would not fry. As I've discovered using my infrared thermometer, my foot also cools down the pavement just underneath where I step. However, a very small egg just might begin to fry on a thick steel plate sitting under concentrated summer sun. Perhaps I'll try that next. I found an old steel boxcar door sitting on the side of the railroad tracks that gets direct sun all day and reflected sun off a white wall. I walked over it yesterday and it was pretty hot to my feet.

Infrared surface thermometers are readily available online or at some tool and hardware stores. They cost about $25 or so.

 

If the boxcar door was hot for you I'm guessing most folks would be seeking medical help. Barefooting on railroad gravel isn't a picnic either. I'll look up some thermometers and the infrared cameras. Thanks for the info.
Am I getting nerdy as well. I don't really care, it's interesting BF stuff.

 

Thanks for the interesting and informative posts, sweet_dream! Great research!

 

Well, I could actually walk around on the boxcar door fine but it was hot standing still on it. I walk along the railroad gravel almost every day- it actually feels good to my feet- like crunchy breakfast cereal.

IR surface thermometers should be easy to find. They are commonly used to measure engine block temperatures, electronic component temps, etc. Let me know what you find about IR cameras though- the ones I've seen were like $10,000 USD.

I recall seeing one at a trade show. It was aimed at the people walking by. It was a little revealing to say the least- you could tell which people were hotter than others, and which parts of their bodies were hot or cool. I thought it'd be really cool to borrow a camera like this to make some artsy video.

 

Dude, I've seen your sole pads in pictures. They are well developed tough and strong. It's no surprise that you enjoy the big crunchy stuff too. My only issue is when the big chunks roll over and you're off balance. Then again the railroad gravel may be less shifty where you are. It is a great workout for the feet "like crunchy breakfast cereal" very good analogy.
I saw radio shack sells the thermometor but the cameras are too pricey to own. I'd rent one, be interesting to look at the heat leaks from my house in the winter. And see how much heat I can transfer while snowfooting.
Often times while at car races the track temperature is announced. It's always much higher than the air temp and I'll be walking around the course comfortably all day long. I do believe if you stay out on the pavement as the heat increases through the day it's not even noticable. But, if you take off shoes and then start walking around you will get sore. It may be related to your circulation adapting slowly to the increased temps. Vs. all at once.
Many folks strive for real black soles, not a big deal for me, do you think sole color plays a part in heat transfer? just looking for your thoughts

 

I did an "ice cube test" yesterday, where I took ice cubes of similar size and put each one down on different surfaces and measured how long it took for it to melt completely on each of the surfaces. On the steel manhole cover at 141 degrees F, it melted almost immediately, like 4 or 5 seconds. One the black asphalt at 155 degrees, it started to melt quickly then slowed down and stayed frozen for like 12-15 seconds. This is yet more evidence to suggest thermal conductivity of the surface material playing a larger role than initial temperature in perceived heat. This also supports similar theories explaining what happens during firewalking.

By the way, not to be a big advertiser or anything, but I saw infrared thermometers on sale at Harbor Freight Tools for less than $10 USD. Maybe they are still on sale, I don't know.

To answer some of the above questions- railroad gravel- yeah, the gravel gets shifty when the banks are steep. I just run over these parts and actually like the way it feels rolling under my feet. Sole color- I don't think this has anything to do with heat transfer. My soles don't often get that black, nor do I really care. However, sole moisture probably has some effect in heat transfer. The pads of my feet, although very thick, still allow sweat to permeate and they will get somewhat moist in hot weather. I think it helps to keep them from drying out and cools them after each step. Someone told me that cheetahs have moist paws to help cool them when they run 50+ miles per hour in the savannah.

 

great answers. I'll check out HF tools. I'm waiting for another heat wave to arrive here in the northeast. It's been a very comfortable summer here. None of the extended hot streaks you get. I do see other folks prancing across pavement which is not even very warm. I'll relay any new experiences of interest.

 

Really interesting. I burned my feed a couple of weeks ago on hot asphalt. I had some small blisters and a big one on my right heel. After it took 3 days to be pain free. Last time when I was barfoot the old skin came off. The new skin is quite sensitive now I have to be carefull not to get a new blister. The skin which came of was about a half millimeter think. Therefore the burning was quite deep in the skin and not on the surface.


I have to condition my feet earlier in the year

 

I can't do this for metal plates yet (if at all because behind the balls of the foot touches due to lower arches and that burns more and blisters sooner) but I can definitely do that for hot asphalt to extend my standing for several seconds (although not yet asphalt temperature over 133 degrees F).

 

Ok, this one takes the cake, carrying around a surface thermometer with you? Seriously?????

 

This Thread Was Started June 2007, I Wonder What Happened To Him

And His Trusty Thermometer.... :sunny: ..???



Cheers Glen.

 

Not anymore. There are pocket size ones about the size of a laser pointer and larger ones almost resembling a radar gun. The larger ones have more measuring options. They are also $99+ US dollars.