Regular scuba diving, which is also known as open circuit diving (OC), is where the diver exhales into the water column.

With rebreather diving, when the diver exhales the gas is recycled. Instead of blowing bubbles in the water, the gas flows through the loop where the carbon dioxide is scrubbed out of the breathing gas and oxygen and a diluent gas are added as required. The gas is then re-breathed and the cycle starts again.

Rebreather diving can be either semi closed (SCR) or closed circuit (CCR). With most SCR, there is a constant flow of air/gas/bubbles into the water column. This is due to the high constant flow of gas into the breathing loop. With a CCR, only the required amount of gas/air is entering the loop so there is no need for constant venting. Therefore, while at a constant depth, there will be no bubbles released into the water. When the diver ascends, there will be bubbles as the air in the loop expands and is released. This is the same principle as with a BCD/drysuit.
When comparing diving a CCR to diving open circuit, a rebreather is definitely more gear intensive. However, a KISS rebreather is by far the least gear intensive rebreather on the market, when compared to both SCR and CCR. When comparing the Sport and the Classic, the Sport is the simpler of the two units.
Price: When comparing the purchase of a KISS rebreather to the purchase of a good set of open circuit gear which allows for the same type of diving, the cost is comparable. The Sport KISS is not much more expensive than a good set of open circuit gear and has many more benefits.
Complexity, recreational diving: Prior to taking a KISS class, an advanced nitrox class must be taken. It is important to understand the gas laws and the properties of oxygen.
Complexity, technical diving: For technical diving, much more than just the basics need to be understood as the diver will need to be able to problem solve underwater. For those divers who are already open circuit technical divers, new skills will need to be learned and old skills, re-learned.
Bailout cylinders: Jetsam highly recommends the use of bailout cylinders on all dives. Any problem that occurs underwater should be as simple to solve as switching to a bailout regulator.
If you would like more information about rebreathers and what they are, then go to our links page and spend some time reading. In particular, pay attention to the hazards of rebreather diving as mentioned in these write-ups. Rebreathers have claimed the lives of brilliant Nobel Prize winners, experienced scientific divers and rebreather instructors. No one is immune to the risk. You can live for a few weeks without food, a few days without water, but only a few minutes without oxygen. A rebreather can kill you in a matter of minutes and only you can prevent it from happening!! Only you, the diver can make your rebreather safe. You will do this through training and properly learning how your unit works and also by slowly gaining experience. This applies to any rebreather, not just the KISS rebreathers.
Warm & moist air: This is due to the chemical reaction of the carbon dioxide being scrubbed out of the gas in the loop by the scrubber material. The by-product of this action is heat and moisture. This helps the diver to stay warmer and hydrated longer. The gas a diver breathes from an open circuit tank is “refrigerated” and will drop the diver’s core body temperature quickly.
Time: 2 to 3 hours of gas. With open circuit, the diver inhales the breathing gas and exhales what they do not use into the water column. With a CCR, the diver inhales the breathing gas and exhales what they do not metabolize. Then the gas that is not metabolized is recycled. As every lung full of gas goes much further, small cylinders can be used.
Silence: Dives are quiet and peaceful as there is no noise from regulators and bubbles. This allows the diver to get much closer to the wildlife and have a more relaxing experience.
Size of equipment: both the Sport & the Classic are smaller than regular open circuit gear, with the Sport also being lighter. The Classic is about the same weight as a fully rigged aluminum 80 cuft tank.
Best mix: The diver is always breathing the “best mix” at every depth. When diving open circuit nitrox, the diver is breathing the best mix when at the deepest part of the dive. With a CCR, the diver is breathing the best mix at all times, as he is controlling the amount of oxygen that goes into the breathing loop.
Trimix: Both units are trimix compatible. It is also affordable as only small cylinders need to be filled. This gives the diver an option to dive trimix on every dive, even on recreational dives.
Maintenance: Both units are user maintainable. The maintenance is no more intensive than caring for open circuit gear, just different.