Where do I actually stand ? Breathing Air standard

[IyaDiver]

Hi Guys,

Apology for bombing new post everyday.

I have a hypothetical question, I guess this is the correct English word for it. I hope.


Spec of Grade E breathing air for moisture.

NAUI version
•Water vapor: May vary depending on intended use


Trace Analytics brochure :

COMPRESSED GAS ASSN, CGA G-7.1–2004, Commodity Specification for Air

Gr E for SCUBA air

Note 3 states that water content of compressed air can vary with intended use.

For use with SCBA in extreme cold temperatures, dew point should not exceed -65°F
(24 ppm) or 10 degrees Fahrenheit lower than the coldest temperature expected.


English is not my first language and the meaning of "vary with intended use" is very broad. However looking at the importance of dry air in terms for freeze protection for winter use is obvious.

Where do I stand for someone based in the tropics with water temp averaging 28 degees Celcius or 82.4F or in worst coldest condition of extreem upwelling at 50 meters deep looking for Mola-Mola fish in Bali, one may get extreem cold of 16C / 60.8 F once in a blue moon and will "brag" about the upwelling...not the Mola-Mola...

So, if I use my logic and translate the definition of "vary with intended use", I shall create a user scenario which will never ever-ever-ever-ever happen in my country unless ice age comes around.

I went to dive at ambient air temperature of 30C / 86F. The sun was shining so hot and my tank was not shaded and risen to 50 C / 122F. I then jumped in the water and at 10 meters or 33 feet, a freak upwelling of 0 degrees celsius or 32F water layer waited. My hot sun baked tank internaly was still at 50 C/122F and so was the air in it. So the air exiting my 1st stage got cooled down suddenly by the surrounding water to 0C/32F but I survived regulator freezing even though Scubapro said that at the tip of the high pressure seat orifice of the regulator 1st stage during this de-pressurization 200 to 10 BAR, a -30C/-22F temperature spike can occur. However because my air water vapor was set at -10C or 14F dew point, my regulator did not freeze but I did die within two minutes. What killed me was the water temperature because I was wearing 3mm neo......RIP.

So where do I stand in this case ? Scuba dry air is a pain to breathe. I carry camel pack sometime for water bottle and drink a lot underwater.

-10 C / 14F dew point at air temperature of 50C/122F is about 2.33% RH according to my calculator. Temperature, Dewpoint, and Relative Humidity Calculator

Am I correct to say that dryness of -10C/14F is already well above my needs ?

What if you guys were me ?
I am not governed by any government regulation nor any such standard is available for Scuba air in my country. Some PADI 5 star facility I think must do air test locally but what dew point temperature of the air, I don't know.

Let's face it, none of my dive gear will break down at 2.33% RH. Its stored 99.9% of its life at 85%+ RH..... No sea or lake water in my country can freeze any regulator, even piston type reg with no enviromental sealing.

What will you guys do, aside from a hopcalite needing very dry air to work and how dry that is, I got no data sheet on it, I only got a marketing document of industrial breathing air filtration company that stated this :

Unfortunately, Hopcalite requires air void of virtually all moisture (4% relative humidity maximum) for it to operate.

Source : http://www.modsafe.com/literature/appletoapple.pdf


If the filter tower temperature during fill is 50C / 122F and RH of 2.33% in that scuba tank used in the scenario, for a 80CF tank its about 4.2 gram of water in it according to my calculator : http://www.lenntech.com/calculators/humidity/relative-humidity.htm


Steel tank is 1000 :1 or less in use here, compared to aluminum. People here doesn't like steel tank, the exterior paint can't be ignored when ruined.


So where do I stand ?

Thanks a million......

Thanks
IYA

 

[Isaac-1]

This is just based on what I have seen over the last 25 years or so, and not meant to be a guide as to what to do. I have seen an ever increasing requirement for both testing of air, and the quality this air must meet through assorted organizations standards (OSHA, PADI, CGA, etc.). It is also somewhat common for our compressors to have realtime carbon monoxide monitoring. As a result the industry seems to be overly focused on the numbers on these air sample reports, and not focused on the underlying reason for them. As I understand it the most important reason to have DRY air is to keep the water vapor from reacting with the more active chemicals in the filter stack (this is why the desiccant comes first) , as these chemicals can shed the things they have been absorbing if they become water saturated or just will plain not work when wet. Corrosion of the tanks are a distant second reason to have dry air.

 

[IyaDiver]

Thanks Isaac, indeed your statement makes a lot of sense.

Hopcalite is probably the most moisture sensitive of all the media materials for it to work well.
For activated carbon to release its bad stuff at what humidity level, I do not know. Must check.

In fact I am now looking at CO monitor and been reading real life user experience here and at Deco Stop and each brand specific requirement. The bottom line is , it must be calibrated periodically if we are looking to read 5 PPM accurately.

I must buy the calibration gas and I am having problem sourcing a local source with 10PPM. They sell 500PPM ones from CalGaz, a Liquid Air company. I hope they can custom blend for a super small buyer like me...hick hick hick. I heard in the USA if you have account with them, they can blend it. Swampdiver wrote a lot about CO monitor and its very helpful information.

Unless I can look into blending one myself to bring it down to 10PPM ( if i can ever do that accurately ), it looks like I must import from USA a 10PPM one and shipping by air is a problem for gas in a container. Shipping by sea something of less than 3 kg will still cost me 1 cubic meter or 1,000 lbs minimum charge I think. Sad fact.

Thanks again.

IYA