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Common Scuba Questions: Defogging a Mask
Common Scuba Questions: Defogging a Mask
Limited-visibility diving can be safe and enjoyable if you plan accordingly, knowing in advance that your ability to see will be restricted. But when you enter the water thinking you’ll be able to see clearly and discover that everything is hazy, it can definitely put a damper on your dive — especially if the reason for the blur is the fog inside your mask.
If you find yourself underwater with the fog closing in, there are ways to remedy the situation. However, the best solution is to take steps before entering the water to prevent a fogged mask from becoming a nuisance during the dive.
 Preparing Your Mask

It is important to read the manufacturer’s instructions. A newly purchased mask usually needs attention before it is ready for diving. During the manufacturing process, most masks are coated with a protective chemical. Unless this film is removed, it’s practically impossible to keep the mask from fogging underwater.

Before its first use, you must scrub the mask window(s) with a mild abrasive such as nongel toothpaste or a gritty cleanser that won’t scratch the lens. Apply it with your fingers or a cloth and rub thoroughly. It might take more than one treatment to completely remove the film.

Unless you’ve invested in a nonfogging mask, an antifogging solution should be applied to the inside of the mask window before diving. Fog is actually made up of thousands of tiny water droplets that form on the internal surface of the glass. A “no-fog” or “defog” solution reduces the surface tension so that droplets can’t form on the glass and helps remove microscopic particles that give the droplets additional surface on which to adhere.

Most divers rely on a commercial no-fog solution. There are several on the market and not all work the same way. Some require reapplication before each dive; others are intended to last the entire day. All work most effectively when applied according to the manufacturer’s recommendations.

Following the instructions on the container, apply one or more drops to the inside of the mask window and spread evenly. The appropriate time to apply is generally just before donning your mask to enter the water. Read the directions carefully — the solution you’ve chosen may require rinsing the mask with water before donning. Failure to do so could result in eye irritation.

Individuals with a sensitivity to commercial no-fog preparations have found that baby shampoo rubbed on the inside of the glass and then rinsed off can also help prevent fogging during a dive. You’ve probably also noticed a hard-core group of divers who swear by the superior fog-preventing powers of their own saliva.

 

Preventing Fog

No matter how well you prepare your mask, it will fog up before you even get into the water if you handle it inappropriately. Once you remove the mask from your gear bag, keep it out of direct sunlight. If you are not going to don your equipment immediately after assembling it, tuck the mask inside the buoyancy compensator (BC) or put it somewhere out of the sun where it won’t get damaged.

When it’s time to gear up, do not place the mask on your head — front or back. That is the surest way to cause it to fog up immediately. Fog is caused by condensation of water vapor due to a difference in temperature between the inside and outside of the mask window glass. Your forehead and hair can radiate enough heat to create instant fog. Once a mask has fogged above water, it becomes more difficult to keep it from fogging up again during the dive.

Instead, clip the mask onto your BC, carry it over your elbow or hang it around your neck until you are ready to don it for entry. Avoid exhaling through your nose into the mask — hot breath also encourages fog formation.

 

Defogging Underwater

Despite all the right preventive measures, masks still sometimes fog up during a dive (photo 3). On a number of occasions I’ve seen divers suffer through their entire bottom time peering through the blur rather than execute the simple steps necessary to clear the fog out of their mask.

Step 1. Introduce a small amount of water into the mask. Place a thumb on each lower outside corner of the mask frame and your forefingers on the top corners (photo 4). Carefully pull the top of the mask away from your face just enough to break the seal, allowing sufficient water into the mask to form a small pool in the bottom of the air pocket, but not enough to reach eye level. Let go and reseal the mask to your face.

Alternatively, some divers prefer to introduce water by sticking a finger under the mask seal on one side. Others lift the bottom of the mask off their face with their thumbs. It doesn’t matter how water gets into the mask, as long as you control the amount. You may even flood your mask completely if you like. However, a sudden rush of cold water onto your face can trigger a gasp response that adds to the discomfort and disorientation caused by the fogged mask.

Step 2. Bend your head forward so the mask window is horizontal and the water runs over the inside of it. Move your head to swish the water around and ensure that it covers the entire glass surface (photo 5). Lift your head to verify that the fog has been rinsed off — if not, try swishing again.

Step 3. Clear the water out of your mask. Exhale through your nose while tilting your head backward and pushing inward on the top of the mask frame — or for a mask with a purge valve, tilt your head forward and exhale. (For more information about mask clearing, see “Final Check,” Dive Training, February 2003.)

Once your mask has been cleared of water, return to exhaling through your mouth instead of your nose — or you’re likely to cause the mask to fog up again.

Defogging your mask underwater is effective, but unfortunately the relief may be only temporary. If the fog returns, try removing your mask and cleaning the inside of the glass with your fingers. You can also minimize the annoyance of persistent fogging during a dive by leaving a small amount of water in the bottom of your mask. Then you simply swish as needed.

 

Mask Maintenance

Over time, your mask may begin to fog regularly despite your best preventive efforts. Periodic scrubbing with a mild abrasive removes the invisible film that builds up from mineral-laden rinse water and chemical leaching. (Check the manufacturer’s recommendations first.)

After each dive outing, rinse your mask thoroughly in fresh water and wipe the glass with a clean soft cloth or chamois, or place the mask in a well-ventilated, shaded area to dry. Store it in a box or bag to separate it from the rest of your scuba equipment.

Use the proper preventive measures and maintain your mask with care, and you may never have to worry about diving in a fog.

 - Dive Training Magazine