[wjuniorbr (OP)]

Hello

I built an underground room measuring 2,5m x 3m x 2,3 just below the ground, the walls are about 20cm thick in solid concrete, the ceiling has iron structure and semi hollow bricks in the concrete, the whole room is revested in ceramic and porcelain tiles inside, the entrance is a 80cm x 80cm opening on the floor and itīs "sealed" with a wooden door. Its a flotation tank (among other names), its basically a concrete with ceramic tiles tub measuring 2,3m x 1,2m x 40cm. Itīs used in sessions of 1 or 2 hours (I was thinking about longer sessions) and it should be isolated from light and sound, but Im afraid of the quantity of O2 and CO2. The room is not perfectly sealed, it has 6 "pipes" in the walls that carries the electrical wires (the pipes are long and they make many curves.
I read somewhere that CO2 from breathing accumulating in the room is more urgent than the lack of oxygen itself, that CO2 is heavier than the air, so does it accumulate from the floor up? Because if it does how should I remove it if itīs already an underground room? I cant use collers because the sessions have to be made in complete silence; I thought about making 1 or 2 holes on the door with pipes making curves inside de door, will this add enought O2 to offset the breathing (by the way the person using is completely relaxed), and will it remove the CO2 since supposedly itīs on the floor because itīs heavier than the O2?
Its in Brazil so the weather is tropical most of the year. The water in the tank is 24 hours heated at about 37 celsius, it has about 700 liters of water with about 400kg of epsom salt (magnesium sulfate). Does this water affect anything in the ventilation matter?

Sorry for the long text, there is no easy way to explain without giving details. Any idea is appreciated.

[David Cooper]

The molecules of gas will be moving around at such high speed that the CO2 will always remain well mixed throughout the air in the room, so you will never have a layer of CO2 building up underneath the rest.

Judging by this info https://www.physicsforums.com/threads/how-long-can-one-live-in-a-sealed-room.685796/, there should be enough air in there to survive for a full day, so a couple of hours in there should be safe enough even if the room was fully sealed.

I can't tell you whether magnesium sulfate reacts with anything in the air, but you'd soon find out by leaving the room sealed for a few days and seeing how the air is when you finally go into it. If it hasn't sucked all the 02 out of the air by then, it's not going to do it in the space of two hours while you're in there.

[CliffordK]

Read a bit about confined space entry. 

It would not be a bad idea to get an oxygen and CO₂ sensor with alarms that can be custom configured.

Then also have somebody with you for the first few entries/extractions.  Perhaps a fan for rapid air exchange, and some kind of harness to get you out in an emergency.

[Bored chemist]

There is another potential problem. If there are micro-organisms in the water and they are digesting organic matter from the people in the water then they may well scavenge oxygen and generate CO2 and or methane.

An oxygen alarm is a good idea; so is a fan, even if you need to run the air through a long pipe with wadding to damp the sound.

[wjuniorbr (OP)]

The only device I bought so far is a O2 measuring device that measures the oxigen in the blood, but it doesnīt seem to work very well, Iīve tried to hold my breath and the o2 wonīt fall. Do you guys think some 3/4" pipes without any fan or pump will exchange the air enough to offset the breathing?
About micro organisms, I donīt think it will be a problem, they say nothing lives in the dead sea, and this tub has more salt than the dead sea.

[RD]

... About micro organisms, I donīt think it will be a problem, they say nothing lives in the dead sea, and this tub has more salt than the dead sea.

Mould is a micro-organism. Unless your 37^oC bath has a lid on it,  pure water will evaporate from it and condense on the walls of your wet-room: mould-nirvana.

[wjuniorbr (OP)]

RD - Yes there will be a lid on the tank, and I was thinking about using uv light on the bottom side of the lid so that it would eliminate other potencial problems, so it will still evaporate while the person is in session, but the room has ceramic tiles on the walls and even ceiling, making it very easy to keep clean.

[CliffordK]

A fan may be "white noise" and may not interfere with your experiment.

How are you maintaining the mouth/nose above water?

I'm not sure about waterproof medical devices.  I thought blood oxygenation varies slightly with respiration (which also allows monitoring the respiration rate). 

Anyway, I certainly would want some monitoring of the individual (pulse, respiration, perhaps video/IR), as well as monitoring the air supply. 

As far as reserve air supply.  Perhaps one could breath all day in a large room, but the reserve capacity will be greatly diminished if the room is mostly filled with water.

[wjuniorbr (OP)]

The water is so dense with salt that the person floats effortlessly, naturally the mouth and nose will stay out of water, and the ears inside.
I could try do adapt my device to use in the water, but no chance of a camera, the session is done naked.
There are still many thing to do, but here are some pictures of how it is now
newbielink:http://pt-br.tinypic.com/view.php?pic=123pbnk&s=8#.VFkCMPnF_pc [nonactive]
newbielink:http://tinypic.com/view.php?pic=scruqw&s=8#.VFkChfnF_pc [nonactive]
newbielink:http://tinypic.com/view.php?pic=34j9aut&s=8#.VFkD8fnF_pc [nonactive]
newbielink:http://tinypic.com/view.php?pic=14o1zwi&s=8#.VFkEFfnF_pc [nonactive]
newbielink:http://tinypic.com/view.php?pic=f9p089&s=8#.VFkEPvnF_pc [nonactive]

[CliffordK]

Ahh, so the tub is in the room.  That makes sense.  I was thinking the room was filled like a large tank.  So, getting out of the tub should be easy enough.  So, the issue is air flow which is probably adequate, but you may still wish to run a fan between sessions (which may keep it cleaner and smelling fresher).

If done in the dark, you would be using IR frequencies for any monitoring equipment which is less clear than visual frequencies.  If recorded (or displayed without recording) in low resolution, it wouldn't be to invasive.

How is the sound at your current amount of completion?  Tile tends to reflect sound.

[wjuniorbr (OP)]

Before and after each session I will run a big fan directly at the door, so it will renew the air.
The tiles do reflect the sound a lot, there is a great echo inside, but as it should be used in total silence, I donīt think it will be a problem. I dont know how the sound isolation is yet because Im still making the door.