Rebreather Question from a non-rebreather user

[maranda1389]

Is a rebreather safe at any depth or just deep depths? I thought I read somewhere that rebreather can be dangerous at shallow depths but my fiance said that you can use them at any depth. He said that military uses them at shallow depths and that is how he knows you can use a rebreather at shallow depths. So can you SAFELY use a rebreather at say, 40' and above or is it only for deep diving?

 

[Crush]

I am not a rebreather diver. As such, my uninformed opinion is that rebreathers are unsafe at all depths. OK, that was a joke, but there is a small element of truth in it. Rebreathers can be used in shallow or deep water, but the benefit of being able to add O2 and scrub CO2 without wasting the gas which carries it (called diluent, sometimes nitrogen is used) really begins to shine at depth. Let's assume that you are at 120 feet. Every lung full of air you breathe in is really the same amount of gas as four lung fulls of air at the surface. This means also four times the amount of oxygen in your lungs at 120 feet as you would at the surface. With regular (open-circuit) scuba gear, when you exhale you are wasting a lot of good oxygen and lots of nitrogen, all to get rid of some CO2. Rebreathers scrub out the CO2, add a shot of O2 when required, and keep the diluent (nitrogen or otherwise) circulating. It is a very efficient system. The problem is that if something fails, you are likely to get air that is too rich in CO2, or too low in O2. Since you are still breathing you might not notice this before you pass out. A failure of open-circuit scuba often means that you are getting no air, and that you will notice right away.

FWIW I'd love to learn to dive a rebreather. I am waiting for the day when rebreathers are well-designed, compact, have multiple redundancies, and are not incredibly expensive.

Edit: At surface pressure, you breathe in air at 21% oxygen and exhale it at about 16% oxygen. There is clearly good O2 in the exhaled air - if there wasn't, mouth-to-mouth emergency breathing would not work. If you descend to 30 feet, you inhale the equivalent of two lungs full of air, still with a 21% O2 content. However, you exhale the air at about 18-19% O2 content since your oxygen requirements have not increased with depth. At 30 feet you are wasting even more O2 than at the surface. This waste gets worse the deeper you go - thus, rebreathers get "better" the deeper you go.

 

[Wookie]

The simple answer to your question is that the military uses rebreathers that are designed for shallow use. They also use rebreathers designed for deep water use. They also have software and hardware to control the rebreathers that us mere mortals don't have access to. You must be very careful when going from deep to shallow on a rebreather and monitor your percentage of oxygen in the breathing loop to ensure it is sufficient to support life. IMO, rebreathers are the most dangerous when they are being used on the surface. (when the dive ends, but before you get on the boat)

Additionally, your question leads me to believe that you think diving of any kind is "safe". Diving is not safe. Some risks are worth it, some are not. For me, diving to 300 feet on open circuit scuba is worth it. Doing the same dive on a rebreather is not.

 

[*Ag*]

You can safely use a rebreather at any depth. They can be a great tool for any kind of diving, at any depth.

However, there are two schools of thought.
One says that you should use your breather on as many dives as possible, even shallow ones, in order to keep your skills up.
The other says that the extra risk associated with rebreather diving and hassle is not worth it for shallow dives and as such breathers should be used primarily for the deeper dives.

Many people enjoy diving breathers because of the lack of bubbles and use them when taking photographs etc, which often means shallow diving. Many divers use breathers exclusively for all kinds of diving... it is a personal choice. But the depth is not a factor in regards to safety.

 

[lemon]

Is a rebreather safe at any depth or just deep depths? I thought I read somewhere that rebreather can be dangerous at shallow depths but my fiance said that you can use them at any depth. He said that military uses them at shallow depths and that is how he knows you can use a rebreather at shallow depths. So can you SAFELY use a rebreather at say, 40' and above or is it only for deep diving?

yes, you can use a rebreather safely at the depths you mentioned.

 

[bletso]

A rebreather can be as unfriendly at 3 msw as at 100 msw. If you lack discipline they will kill you at any depth. For the 5 -6 years my only diving has been with my unit, no OC.

Are they safe?, Hell no, even OC is unsafe in the wrong hands. Get trained and dive.

Dale

 

[Mr.X]

duplicate post

 

[Mr.X]

Some pretty interesting commentaries. This thread won't live for too long.

X

 

[rigdiver]

Is a rebreather safe at any depth or just deep depths? I thought I read somewhere that rebreather can be dangerous at shallow depths but my fiance said that you can use them at any depth. He said that military uses them at shallow depths and that is how he knows you can use a rebreather at shallow depths. So can you SAFELY use a rebreather at say, 40' and above or is it only for deep diving?

A pure oxygen rebreather is "fairly" safe in shallow water. The big "IF" is if the CO2 scrubber is functioning properly.
Electronic CCR's maintain a certain ppO2 in the breathing loop. The sensors really don't care about %. Shallow water is not your friend with CCR's. Deeper water will cause an increased partial pressure of your breathing gas. Too many cans of worms to open here.
SCR's: Shallow water is NOT your friend.
To learn: Take the classes!!! Do the dives.

 

[Gill Envy]

you'll find many opinions on diving rebreathers, particularly with respect to safety. I think the best way to dive any rebreather at any depth is to assume you can easily kill yourself regardless of type or depth and dive accordingly with adequate precautions and training.

I recommend starting on a simple manual system to build good habits, but people seem to manage on just about every type.

Sadly, a remarkable number of people make fatal mistakes on all types of dives with rebreathers.

That said, rebreathers offer an amazing experience even for the avid recreational diver who is simply wishing to expand their NDL. I started out as a recreational rebreather diver and there are times were I think the sweet spot for rebreathers is on long recreationalish dives with a max depth of say 140ft, riding minimal to no deco gradually into the shallows on a beautiful reef... it's pure heaven to get a 2 hour+ dive in the tropics. It's not unusual for us to cover two to three OC dive sites in one dive. Avid recreational divers will find the amount of added gear needed for such dives to be tolerable but requiring steady practice. It's when you go deeper longer, that the emergency bail out and planning become dominant to the experience.

Kind Regards,
George