No Sunshine on this Road Grit

One habit we’re always taught is the hand washing habit.  “Wash those mud claws before you sit down for dinner, Ralphy!” – sounds like a voice that could be a memory from my childhood, but isn’t.  That’s mainly because my name isn’t Ralphy.

Hopefully, I’m not incriminating myself, but I did play in the dirt pretty often, and I wasn’t pretty before, during or after I did that. In the summertime, my brother and I sometimes made use of those brown snowballs that weren’t really snowballs. I guess they could have been called summer snowballs, but it seems they could hurt almost as much as the icy ones.  We were very creative and energetic, and had the bruises that went with the latter.

The admonition that for most of us has been built into a habit is the one that tells us to wash our hands frequently.  Hands are important, but there are other things that count pretty mightily. To help me explain what those things are, let me segue from the topic slightly, and over to the subject of grit. Anyone who’s taken a cross country motorcycle trip knows what road grit is, and people who drove cars prior to air conditioning know it pretty well too.  If you could see me now, you’d notice the head shaking and hand waving.  I’ve had my share of grit, and owned cars before air conditioning and seat belts. My first car (an old Chevy) didn’t need a key to start it.

Nowadays, when you get home from a long trip, you’ve collected tar film on your hands and your face – mainly because the filter inside the cowling of most cars and trucks is not sufficient to trap all the particles.  A dirt and tar plume can extend a hundred feet above a busy highway, and every car stays immersed in it for as long as it takes to get to the place to which they’re traveling.

Dirt plumes are not just on the highway.  Kids running up and down the hallway carpet can make their own kind of plume, with all sorts of chemicals from cleanings long forgotten, and pets long remembered.   Grit and dirt forms most readily and thickly on our faces, hands, and hair, because all those areas are exposed.  But, there’s something about dirt and dust plumes that makes a hands-only cleaning insufficient. You see, the vast majority of dust is in the sub-micron arena, in terms of size.  There are millions of particles whose size is five hundred nano-meters or even one or two or ten microns. As the size of a particle increases, there is less likelihood it’s going to stay in the plume, because it’s heavier and falls out more quickly.  Additionally, based on random internet readings (disclaimer: I’m not an expert in any health discipline) there are just fewer of the larger particles to start with.

An inch is about 25 millimeters, which is 25,000 microns. So, a one micron particle is 25,000 times smaller than an inch.  It’s 2,500 times smaller than a tenth of an inch, and 250 times smaller than a hundredth of an inch. Let’s say (I don’t know really) – that the fabric of your underwear has threads spaced at about 1/100 of an inch.  Just looking at my own pair of shorts, such a number seems to me to be reasonable.

So, let’s put this into perspective – sorry for all the math.  Consider that the space between the threads is a window.  There are horizontal and vertical threads, so this a good mental picture.  Now, for visualization lets consider that the “window” between the threads is about 250 millimeters (about ten inches).  It’s easier to think about things in inches, in our brains, rather than microns.  We will keep the relative size relationships the same, so the visual aid will represent the real situation.  The micron particle would then be correctly scaled and represented by a size of .04 inches inside of the ~10 inch window.  The particle would have a tiny size (about 1/25 of an inch, or a little more than half the size of a grain of sand) relative to the 10 inch “window” that we visualize as being between the threads of the fabric.

Envision that grain of sand flying through the 10 inch window opening, which is the real situation relative to micron sized particles entering your clothing from a plume.  In terms of only the opening, there’s literally nothing to stop them.  It seems they will deposit on your skin as if you were stark naked!  You would still get some deposits even if you wore leather underwear.  Leather has a porosity with gaps of about 1.5 microns, so micron sized particles might bang their way through with a pretty high success rate – I’d guess.  There are other factors.  There’s the moisture and the oil that clings to the fabric, and that might block the way for some particles, and there could be electrostatic forces that would dissuade other particles from depositing themselves onto your clothed skin. But, IMO – some of the particles from the road trip would get through even leather underwear. With lightweight shirts, the deposit rate could be quite high.  I’m no expert – just a guy with the time to consider his own questions – til now unasked, and my thoughts are that we should wash all the other stuff after a road trip.

Now, here’s the thing:  different skin areas absorb pollutants at different rates than other skin areas. According to random internet sources of unknown accuracy, the skin on your head absorbs about 40 percent of the absorb-able stuff that lands on it, your hands absorb about 15 percent, and your legs around 15 percent.  The same source implies that your genitalia absorb almost 100 percent! One hundred percent?! Wow – I’m thinking I don’t want any pollution attaching itself to those parts of me!  Based on my musings here, carried on for nine paragraphs that you may or may not believe, it seems you should probably be washing those “other things” as well as your hands!

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