The phenomenon of Fog.

So I was riding home last night at 2330 hours as I often do from my range OIC duty and I experienced a safety issue I've never seen before or read about here or elsewhere. Basically my face shield on my schuberth C3 fogged up thick and opaque instantly, and not on the inside, on the outside. There had been controlled burning on the range so quite a bit of smoke in places, fog was beginning to build in the low stream beds, temp on the MFD was 54' Fahrenheit. The bike had set outside for 6 hours and was soaked with dew, I had to wipe the seat and optics down a bit when I mounted the bike for the ride home.
I've experienced fogging on my glasses and slightly on the inside of the shield (the fog shield/pin-lock does a good job of controlling that) but I've never experienced that rapid and complete fogging of a face shield before. I was going about 45mph and the vents were open. I lifted the shield full up to defog what I thought was on the inside with ventilation, no luck.... Finally I realized it was on the outside and used my left glove to wipe away the fog to see a bit.
I guess the take away is it was sudden, blinding, and rapidly disorienting. My only option was fully opening the visor.
FYI

Happened to me too with the windscreen

Not sure about the science behind this phenomenon, but it has happened to me but with my windscreen. My route to work takes me through several low lying areas adjacent to streams and wetlands. With the right combination of temp, dew point and speed, the windscreen (faceshield in your case) will get chilled sufficiently to allow the moisture to condense on the windscreen. When this happened, I was able to adjust the angle of the windscreen to allow for a faster airflow and let the moisture bead up and flow off.

I have had that before. Just use the hand as a wiper. Or open the visor. I suppose it's all temperature, atmospheric pressure, altitude and other related.
I have also had ice build up, freezing rain build up on the outside of the visor. Again, the hand becomes the wiper, or open the visor to see under it (cold, cold air comes in).
dc

Knowing what the dew point (that temp where water vapor freely leaves the air to form fog, moisture on surface objects, or clouds at greater altitude) was at that exact time would be helpful information.

When the difference between the dew point and the air temp is < 4 degrees F, we get surface moisture/fogging.

The heat from your head, trapped inside a helmet, may have instantly tipped the scales in that direction - has happened to me, and temps/dew points were later found to be 'in alignment.'

Crack your shield and soldier on until riding for a while cools your helmet interior a bit.

Used to have that happen often in the winter in the Fairbanks area. The temperature could vary by 25-30 degrees as you drove up and down on the mountain roads north of town. I was in a truck so it was not quite as disconcerting.

I had this happen to me while climbing up to the summit on Beartooth - the weather changed rapidly from sun to drizzle, then sleet and snow. My shield fogged rapidly on the outside causing the disorientation mentioned by the OP. I flipped it up, and in an instant my prescription glasses fogged. My next helmet/shield will include a Pinlock visor option since I routinely ride in cold/chinook type weather areas where I live. The OP also mentions smoke. This is an extremely dangerous mix - no amount of wiping the shield will rid the smoke from the air so the addition of fogging is real safely problem which I have thankfully not experienced on a bike but have in a cage (still no fun at all).

David13 said:

I have had that before. Just use the hand as a wiper. Or open the visor.

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If you wear glasses like I do your glasses will also fog when you lift the shield. When this happens my wife takes the lead and I follow her taillight.

Thanks for all the input. Dang Greeneald your smart. I had all the conditions for fog, I just didn't list them all as I thought no one wants to hear all that helicopter instructor pilot gobbledygook, but I have underestimated your encyclopedic knowledge and I am impressed yet again.
I have experienced fogging of the visor and glasses and visor in the past but nothing this rapid and overwhelming. To put the situation in more context, I was 45mph on a dark unlit, unmarked road with twisties, on high beam in a turn when this occurred. I literally became instantly blind, could not see through any portion of the visor at all of course I came off the throttle slowed and lifted visor but was still somewhat blind by the high beam so had to go to low beam. It's so dark back there that I keep the high beams on as much as possible and go low beams in the fog banks. Safety is my hobby, always excited about discussing that topic.

Well, there's fog on the visor and then there's fog everywhere.

On way to latest Missoula National, we spent the night in what must have been Walden, CO.

Next morning was pretty foggy, but not too bad in town, so we headed out. It quickly became clear there really wasn't visibility enough to support more than maybe 20 mph and you'd worry about getting rear ended if nothing else. Animals in front of course.

Just turned around and went back to town for an hour or so until it lifted.

agree 100%

I have found that when it's the ground type fog, that turning on my aux lights with yellow lens makes a huge difference.

If it's my shield and or glasses, as stated earlier; there isn't much that you can do other than to crack open the helmet shield and soldier on. Certainly not fun, but its the price that you pay for admission I guess.

sdc

lkchris said:

Well, there's fog on the visor and then there's fog everywhere.

On way to latest Missoula National, we spent the night in what must have been Walden, CO.

Next morning was pretty foggy, but not too bad in town, so we headed out. It quickly became clear there really wasn't visibility enough to support more than maybe 20 mph and you'd worry about getting rear ended if nothing else. Animals in front of course.

Just turned around and went back to town for an hour or so until it lifted.

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