January 2002 Safety Thoughts

Anti-Fogging Strategies

by Dave Hansen, Safety Officer

One of the most dangerous situations a road rider can find themselves in is to be stuck in traffic with a fogged up face shield, goggles or glasses, essentially leaving the rider blinded. How can this be prevented?

Well, the first step is to understand what's happening & why, then try to eliminate some of the causes. The idea being that if we can eliminate or minimize the causes, then we may be able to treat a minimal amount of fogging enough that it doesn't become a blinding hazard.

The fogging occurs because the water vapor in the air comes in contact with a surface that is cooler than the dew-point and remains in contact with this cooler surface long enough to lose enough heat to allow the water vapor to condense, accumulating as water droplets on the cool surface. The dew point temperature is strictly dependent upon the amount of moisture content in the air which we commonly know as humidity.

To eliminate the fogging phenomenon, we can try to prevent the cooling & condensing of the water vapor. On the outside of our shield, goggles or glasses, the air is usually moving fast enough, even when we\rquote re stopped, to prevent the cooling & condensing to occur. The air movement inside our shield, goggles or glasses is usually more restricted, particuarly when we're sitting stopped in traffic. The fogging is compounded by the fact that our own body is continually giving up moisture through evaporization, raising the humidity (and the dew point) of this trapped air.

Methods to eliminate the cooling/condensing include:

  1. Keep the air moving fast enough to prevent cooling. The Smith Aero goggles has addressed this by adding a battery powered fan & vents to this line of goggles.
  2. Using a double thickness of material in the shield or goggles to help keep the inner surface temperature higher than the dew-point temperature.

Once we've done what we can to address the actual fogging phenomenon, we will still be left with some occurance of fogging. The next line of defense becomes minimizing the optical interference caused by the water vapor consensation. This is done through surface treatment with either chemical applications or with special polymer films bonded directly to the optical surface. In either case, the goal is to prevent individual droplet formation, instead creating an even film of moisture that remains optically clear.

Some commercially successful anti-fog coatings have been developed & marketed by Cannon for their EOS cameras, but I haven't researched enough to know who has a similar coating on motorcycle shields or goggles.

This leaves us with the final area of discussion; the chemicals. Anti-fog agents are surfactants. They lower the optical material's surface tension to prevent moisture beading, spreading the moisture in a flat film across the optical material's surface. This also allows the moisture to re-evaporate more quickly because the moisture layer is thinner & accepts heat quicker. These anti-fog agents are varied and include both commercial products as well as home remedies.

Among the commercial products, Rain-X has developed an anti-fog spray. I mention this because their Rain-X glass treatment product works exactly opposite of how anti-fog agents work, increasing sur face tension, causing water droplets to form & run off the surface.

Home remedies are varied & include dish soap, baby shampoo, spit, and home-made mixtures comprised of ethylene glycol, water & a commercial wetting agent. I use a product I bought several years ago at a bike show that looks like a stick of pink wax. I don't know what's in it, but it seems to work & until it's used up, will remain my solution for anti-fogging.


Words of Safety