Rebreather UBS

The right question is not "why rebreather", rather "why SCR"?

As we said before all our rebreather are SCR
The immersion with a SCR are not difficult or limited to few experts, but are only different. In other words, a specific training is necessary, exactly as for the open circuit. With SCR rebreathers it is possible diving very safely and quietly without necessarily going out of the decompression curve.

A mixture of enriched oxygen air, commonly known as NITROX, is generally used in the the following percentages:

1. 60 % O2 and 40 % N2 mix, suitable for depths up to 13 mt
1. 50 % O2 and 50 % N2 mix, suitable for depths up to 18 mt
2. 40 % O2 and 60 % N2 mix, suitable for depths up to 25 mt
3. 32 % O2 and 68 % N2 mix, suitable for depths up to 33 mt

Here the advantages of a semi-closed rebreather compared with an open circuit:

Long range: Depending on the gas mixtures, can exceed three hours.

Noiselessness: without any doubt, this is the first advantage which is noticed by the new user. In the underwater world the impact of a traditional SCUBA is aggressive, and hardly fishes and other water animals remain indifferent to this intrusion. For instance, a open circuit regulator release for a fish a noise equal to what we suffer being near a Boeing 747 with four engines working! In semi-closed circuit the breath is absolutely silent and the bubble diffusion is very limited both in amount than dimension. For these features the semi-closed circuit is very suitable for photographers and sea fauna scientists: all people that want stay under water without being noticed, ……… above all from fishes.

Buoyancy: The respiratory cycle always keeps in circle the same amount of gas, so the rebreather diver is not subject to different buoyancy from inspiration to expiration; besides, the slow and regular gas consumption only makes necessary sporadic buoyancy adjustments by the BC jacket.

Heat: After few breathing acts the heat produced by the chemical reaction in the filter makes the mixture hotter in the surrounding environment, condition which is kept for the poor dispersion. The contrary takes place in the open circuits: the mixture is initially at the ambient temperature and considerably gets cold for the expansion phenomenon.

In the open circuits the mixture is almost completely without humidity. In those closed and semi-closed rebreathers, after few breathing acts the humidity presents in the breath and the heat produced by the chemical reaction in the filter make the mixture hot and moist, condition which is kept for the poor dispersion. This allows the rebreather diver not to undergo the cooling and the liquid loss, that is dehydration. An important factor which can contribute to the pathology from MDD.

Taking care of not exceed the depth limits well definite by the used mixture, the O2 percents usually superiors to the standard atmospheric air allow considerably to use the decompression tables for air dives with superior safety margins.

At this point what are the disadvantages? Luckily very few:

• above all, before approaching to this world, it is highly recommendable to have a good underwater experience and a solid theoretical base in nitrox ambit. It is not necessary to be a supermen, but only follow carefully the recommended procedures. It is necessary to have always close at hand Nitrox recharge and soda lime.

• because the absence of Venturi effect in all rebreathers, during the first dive the breathing effort can appear bigger than in open circuit, but this sensation disappears after few dives.
• at the end of the day, a greater maintenance is necessary respect open circuit; however we consider that between two dives during the same day are not necessary recharges or other maintenances!

Attention: we confirm it, we are talking about a rebreather SCR like the UBS40, really built and thought for recreational dives in the 40 classic meters. Any diver with a good experience in the open circuit can start a rebreather training, of course after have obtained a deep and nitrox licence.

The existing risks are comparable with the standard open circuit. Here some typical troubles.

• It seems a banality, but always we must verify before and during the dive if there is gas mixture in the cylinder, and therefore if the continuous feeding flow takes place: it is one of the first rules to verify often the pressure gauge.

• If the diver abandons under water the mouthpiece, or does not adequately prepare the rebreather before the dive, it is possible a partial or total flooding of the respiratory loop (counterlungs and filter): in this case we have at disposal an emergency integrated open circuit which allows us to emerge without further problems; in other words a very simple octopus!

• The breathed gas is a Nitrox mixture: therefore, as in the open circuit, it is necessary not to exceed the limit depth of the gas mixture.

• In case of too fast descent it is possible that the continuous flow is not able to keep the volume in the breathing counterlungs which would collapse: it is a typical problem of the beginners, but it is sufficient to insert gas manually in the counterlungs by the by-pass. But really to avoid this possible event, in UBS 40 we have inserted, as optional, an automatic anti – collapse valve.

Of course these inconveniences happen very seldom, and are reduced to zero from an adequate training.

On the contrary the closed circuit always requires a high attention by the diver: for this reason the training is very hard because nothing must be left to luck or improvisation, particularly in case of the high deep that close rebreather can reach.

Now only an example about the consumptions:
Have you ever wondered how much a diver wastes with a "open circuit"? Practically almost all: we consume, on average, about only a litre of O2 in one minute.

Therefore if we breath 20 litres in one minute of air than at 30 meters of depth become 80, we throw away, to that depth, about 15 litres of oxygen and 64 of nitrogen every minute. At 30 meters a semi-closed rebreather consumes only 9,6 instead of 80! If furthermore we use Nitrox or mixtures to open circuit the inert waste of oxygen or expensive becomes huge.

For long time the rebreathers remained privilege of scuba divers used to technical dives, sometime extreme.

If we want to use rebreather for the technical dive, and we refer to the closed circuits, it is necessary to have the right mentality and obviously the right base as didactic and relative experience before approaching to this kind of dives.
But in the same time we are coming in the era in which rebreather becomes simply another way to dive, specially SCR like our UBS40. Of course in the recreative world the SCR has some limitations, but also the other systems are not ideal in all the condition of dives.