Recovering from an Enclosure Fog Up

[vinsanity]

I have an Olympus Tough TG-4 with enclosure. This weekend in Cabo I had the front of my enclosure fog up. It was about 75* out, with water temp of 70* at 70 ft.

I assembled it the night before in an AC hotel and put 2 reusable desiccant packs in it. I noticed after my first dive, that fog developed inside the front of the enclosure. Having no better option, I opened it up, and wiped it off with a dry towel, and found that it just refogged in about 20 mins of sitting on the boat in the shade.

Once you are out on the boat, what can you do to recover from enclosure fogging?

 

[Chris Ross]

Sounds like your desiccant was saturated. You need to store them in a 100% sealed container after regeneration as they will happily suck up water from the air till they are saturated. How do you store them to transport to site? I would suggest something like double zip locks. Does your desiccant have indicator?

If your desiccant is fresh/non saturated then wiping out and adding a desiccant pack on the boat should absorb the moisture.

 

[outofofficebrb]

If you’re on a day boat with no AC, the only thing I can think of is to utilize the driest source of air you have...compressed air for your tank. Make it a habit of carrying an inexpensive air nozzle. They’re less than $15. You can blow gently as you wipe up the fog and then give it as much dry air as possible. If you have more fresh dessicants then you can stick one in there right after.

The air nozzle is also great for blowing salt water or water away from the openings and seals and off the camera entirely when you use it with strong blasts. It is perfect for right before you open your housing since it eliminates as much water as possible from also getting into your housing. It eliminates you having to dry it with a towel and introducing lint close to the o rings and is super convenient. I carry them in case the boat doesn’t have camera facilities (most LOBs do); dayboats usually don’t. It hooks up to the LP hose and it’s super easy to use.

Sometimes really cold AC does more harm than good. Also, keep your housing in the shade and keep it covered. Avoid letting it heat up. Dunk tank is a good place to do that but then comes the risk of damage or flood in there when people are moving things around and banging it unless there’s a lot of space. For that reason, I carry a personal cooler from AO that is my personal dunk and rinse tank and it also keeps it “cool”. If you are ever in a market for a new housing, know that aluminum housings are usually more resistant to to fogging.

 

[Chris Ross]

Interesting suggestions, however understanding the basis for condensation helps and contradicts some of these ideas. Flushing with dry tank air is a good idea but just blowing it out you need to race to get the housing closed before the humid air floods back in. If we assume the housing is 100% water and air tight, the only water vapour in there is what was in there when the housing was open. Condensation occurs when the temperature of the housing reduces to below the dew point of the air. The dew point temperature is a function of the relative humidity of the trapped air. This chart shows how the moisture content in air varies with temperature. http://www.gasparetto.it/wp-content/uploads/2014/09/psychrometric-chart.png

If you close the housing in 25°C and 75% humidity, it will fog if you jump into 20°C water; follow the line up from 25°C to the curve for 75% humidity and you see it has 15g H2O/gmol of dry air. follow the 15 line across to 100% humidity and drop down to the temperature axis again and it is right around 20°C.

Silica gel helps by absorbing water but it must be fresh are there are some catches. It takes a few hours to reach equilibrium and if the temperature gets above 25°C then it will release some of the water. It also needs to have plenty of capacity. So letting the housing get hot may release some water which takes time to re-absorb. Air conditioning reduces humidity but it takes time to reach a new low equilibrium temperature. So if you leave the AC off during the day it make take a few hours to pull the humidity down and the air may be more humid than you think. AC is also less efficient if it is oversized and runs for a few minutes making really cold air then stops for a long period. It gets cold but humidity does not fall as low as it should. Ambient relative humidity also goes up at night. Cold air in general can hold less water so closing the housing when it is cold should help as long as the humidity is not high.

Silica gel has bulk density of around 0.8 g/cc. If we assume a 1 litre housing and that the silica gel can achieve 10% humidity this means the gel has absorbed 0.5g of water. Silica gel can absorb 40% of it weight in water, requiring 1.3g of gel which is about 1.6 cc. allowing for the fact that you need to transport the gel I would want about 4x that amount allowing for the fact it may not be fully regenerated and some moisture absorption outside of the housing and a safety factor, that's a little over a standard teaspoon.

One thing the charts don't have is effect of pressure. Pulling a vacuum reduces pressure which reduces dewpoint making fogging less likely. Silica gel is also more effective in a vacuum.

 

[outofofficebrb]

I have a vacuum on my housing and it is also aluminum so that probably helps a lot. I don’t ever use silica gel packets and don’t always open the housing in an AC environment. In fact, on my last trip, I did it on the dive deck many times and followed my recommendations on keeping it cool, dunked in a tank, covered, etc. I had access to an air nozzle and compressed air and used that for drying the exterior before opening. This was in Indonesia so it was quite humid. Short of getting into extremely technical data, it worked for me. Either ideal environmental conditions and/or my habits or a combination of both made it possible. With limited to no resources for the OP once it is fogged, that is the best suggestion I have.

 

[Chris Ross]

I went through the technical explanation to get my head around why a polycarbonate housing would be more likely to fog than an aluminium one. In theory the aluminium one is just as if not more likely to fog than a polycarbonate housing as the metal is a better conductor of heat and will cool off quicker. It certainly seems to be the small compact housings that are most prone to fogging. Blowing out with tank air as you are closing the housing should help. It's moisture in the enclosed air that causes the fogging and the drier the air the more likely you are to be successful.

What you don't want to do is take a tough compact that has been used without a housing and place it in one. trapped water in and around all the buttons and seals takes forever to dry out.

 

[tursiops]

What you don't want to do is take a tough compact that has been used without a housing and place it in one. trapped water in and around all the buttons and seals takes forever to dry out.

^^This^^
So use that air nozzle to really dry off the TG-4 before you put it in the housing.
In addition, the Olympus housing has a rubber rectangle on the back door that presses against the camera to hold it fixed when closed. That rubber can absorb water, and takes forever to dry.
So, if your housing floods, the tough ol' TG-4 might survive just fine, but relentless fogging might be the issue after you "dried" everything off. I found I had to leave my Olympus housing open in AC for 3 days to get that rubber to dry off.

 

[outofofficebrb]

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[tursiops]

Hi!

I'm back to link you to what I'm talking about so you can visualize and know what you are trying to buy if you are interested. I'm including a few different places/options/versions so you can decide who you want to buy from and which one. The swing vote might be which website you already want to buy something with so you can get free shipping or if it's Amazon Prime.

https://www.amazon.com/Scuba-Choice...=1517272486&sr=8-1&keywords=air+nozzle+diving

XS Scuba Combo Filler

Innovative Rubber Air Nozzle

XS Scuba Combo Tire Filler / Air Nozzle

I hope this helps!

Also BC Air Nozzle

 

[vinsanity]

Thanks guys. That's some great info that I'll keep in mind.