Lizardland
28-06-06, 00:24
I've just survived my first year of diving a KISS rebreather and thought I'd do a quick write up on it.
The KISS is a simple closed circuit rebreather (KISS stands for Keep It Simple, Stupid) made by Jetsam in Canada www.jetsam.ca (it's inventor, Gordon Smith, sadly died earlier this year). Unlike most rebreathers which have a computer controlling it, the KISS relies on the diver to make all the decisions.
A rebreather works by filtering the carbon dioxide by a lime based chemical from a diver's breath and replacing the oxygen used then recirculating this for the diver to breathe again. A pony sized bottle of oxygen is enough to drive a rebreather for 9-10 hours. The KISS contains 2.7kg of lime, rated for three hours of diving but will last much longer, probably five, maybe even six hours in an emergency (I plan for 4hrs).
Most people think that rebreathers are complicated to dive, the KISS couldn't be simpler. The only electronics on it are three oxygen monitors which track what the partial pressure of O2 that the diver is breathing. Oxygen is added by a special valve which bleeds oxygen into the loop at around 1litre per min, the same rate (roughly) your body uses it at. The rest of the gas mix is made up of diluent which is added automatically as you descend or take a big breath. During the dive, the diver simply keeps a check on the oxygen displays. If the readings fall below a certain level (I use 1.2 normally) then you add a squirt of O2 to boost it. If the reading rises above then you add diluent to dilute the mix to a safe level. Things happen slow on a RB so you only really need to check the displays once every minute or two or any time you change depth. If you have the oxygen valve set up right then you very rarely need to make any adjustments. And that pretty much is all there is to diving it.
So what advantages are there? First, it's very light, only 17kg empty so lighter than most twinsets. You always get the best mix for whatever depth you are at, like diving the ideal nitrox all the time. Unlike normal scuba, your gas consumption is independent of whatever depth you are at. A couple of pony bottles has enough gas for at least 4hrs whether that's at 10m, 40m or 100m. It is completely silent, no bubbles except when you ascend. Your buoyancy doesn't change when you breathe in and out, you can hover with no effort an inch above the bottom without moving. Once it is set up then that is it - if I rig it on Friday then I can dive all weekend without having to worry about fills, changing tanks between dives, etc. You also breathe warm gas on every dive, this makes a massive difference. I've done 3-4hrs in the water without feeling the cold at all.
For me the big advantage is cost. On dives less than 20m then normal scuba is probably cheaper per dive so I don't bother with the RB. On 20-30m it's roughly equal to nitrox diving. Beyond 30m it starts to become cheaper than open circuit to dive. The rebreather costs about £4 per hour to run, compare that to nitrox fills for deeper dives (especially if doing deco diving) and you start to see a saving. For trimix it is massive - recently I spent a week doing trimix diving, everyone else spent about £300 on gas but it cost me about £30 to do the same diving. In fact, it makes trimix so cheap that I use it on pretty much all my dives regardless of depth - it's great having no narcosis on Clyde wrecks.
Maintenance is very easy. The KISS is designed to be serviced by the user rather than a technician in a shop and most spare parts can be bought in either B&Q or Maplin. It is supplied with three tools which is enough to strip it down completely in about 10min. The only maintenance you need to do regularly is greasing the o-rings every now and again and rinsing the whole unit with virkon (a disinfectant). After every dive you need to empty out the liquid from your lungs which condenses in it (yeugh). The oxygen sensors need replacing every 12-18months (about £150 for all three) but you try to stagger the intervals so they don't all need done at once, batteries every 6-12months (depending on use) and lime every 4hrs of dive time (or if it's been 50m+ then I chuck it every dive).
Disadvantages... well it isn't all rosy. You cannot afford to get distracted during a dive. You control the rebreather, not a computer so you need to be aware of everything that happens. On an Inspiration, if you do nothing then it will add oxygen and keep you alive. The KISS may not, it adds some oxygen but it might not be enough without you doing something. You need to remember to check the handsets every time. This might seem a design fault but more people have died using very sophisticated rebreathers, in fact the KISS is probably the only rebreather with a 100% safety record. The KISS also has a lot of plastic, if you're hevy handed in your assembly/disassembly then it is easy to damage threads or seals.
So what can go wrong? If you keep checking your displays then you should never have a problem. If a display fails then you can dive safely on two. If two fail then you can still dive with one if you are very careful. If your oxygen fails then you have about 3-4min to do something before you can't breathe so plenty of thinking time. If you're diluent fails then it isn't a problem, you can continue to dive without it as long as you do not descend any deeper (I've done dives with bot diluent and oxygen switched off completely). To be honest, after a while most rebreather divers really only worry about one thing, the scrubber failing. If this fails then CO2 is no longer removed, you pass out and you die. There is no rebreather on the market which can warn you about this happening but luckily it is a very, very rare event and there are warning signs. You can also flood the unit with water if you let the mouthpiece fall out while in the water without closing it. I've had this happen, you need to be very unlucky to completely flood it, it should keep working. When I did it, it still worked for 90min of deco and I poured about a litre of water out it afterwards. Because of its simplicity, the KISS is very easy to control when things go wrong.
There are around 300 KISS units in service (mine is No.59). It is ordered direct from Jetsam in Canada and is supplied completely disassembled. The diver is responsible for building the unit. The oxygen valves are only sent to instructors so you cannot use the unit until you have done the training course. This is a fairly recent development, when I bought mine you did not need to be trained. I'd a couple of years experience on similar rebreathers so I didn't bother with training.
I'd have to check the website but I think the cost of one new is around £3000 but you can get stung for import tax and shipping costs. On top of that you need to add a couple of small tanks (most people use 3l ponies but some use 5's or 7's). The rebreather comes with everything else you need and it attaches on to a standard backplate and wing set up. I'm sure you could probably rig it on a stab jacket but I've never seen it done. If you don't need the depth rating of the KISS (it is rated to 100m) then there is a smaller, cheaper version available called the Sport KISS (rated only to 50m and something like 2hrs on the scrubber). Personally, I don't think it is as well made or as reliable as the Classic KISS (it was designed for travel and diving on holiday) and anyone would be better off buying a Classic.
BTW, are there any other rebreather divers on the forum? If so, you've been very quiet :D
Cheers,
Stuart
The KISS is a simple closed circuit rebreather (KISS stands for Keep It Simple, Stupid) made by Jetsam in Canada www.jetsam.ca (it's inventor, Gordon Smith, sadly died earlier this year). Unlike most rebreathers which have a computer controlling it, the KISS relies on the diver to make all the decisions.
A rebreather works by filtering the carbon dioxide by a lime based chemical from a diver's breath and replacing the oxygen used then recirculating this for the diver to breathe again. A pony sized bottle of oxygen is enough to drive a rebreather for 9-10 hours. The KISS contains 2.7kg of lime, rated for three hours of diving but will last much longer, probably five, maybe even six hours in an emergency (I plan for 4hrs).
Most people think that rebreathers are complicated to dive, the KISS couldn't be simpler. The only electronics on it are three oxygen monitors which track what the partial pressure of O2 that the diver is breathing. Oxygen is added by a special valve which bleeds oxygen into the loop at around 1litre per min, the same rate (roughly) your body uses it at. The rest of the gas mix is made up of diluent which is added automatically as you descend or take a big breath. During the dive, the diver simply keeps a check on the oxygen displays. If the readings fall below a certain level (I use 1.2 normally) then you add a squirt of O2 to boost it. If the reading rises above then you add diluent to dilute the mix to a safe level. Things happen slow on a RB so you only really need to check the displays once every minute or two or any time you change depth. If you have the oxygen valve set up right then you very rarely need to make any adjustments. And that pretty much is all there is to diving it.
So what advantages are there? First, it's very light, only 17kg empty so lighter than most twinsets. You always get the best mix for whatever depth you are at, like diving the ideal nitrox all the time. Unlike normal scuba, your gas consumption is independent of whatever depth you are at. A couple of pony bottles has enough gas for at least 4hrs whether that's at 10m, 40m or 100m. It is completely silent, no bubbles except when you ascend. Your buoyancy doesn't change when you breathe in and out, you can hover with no effort an inch above the bottom without moving. Once it is set up then that is it - if I rig it on Friday then I can dive all weekend without having to worry about fills, changing tanks between dives, etc. You also breathe warm gas on every dive, this makes a massive difference. I've done 3-4hrs in the water without feeling the cold at all.
For me the big advantage is cost. On dives less than 20m then normal scuba is probably cheaper per dive so I don't bother with the RB. On 20-30m it's roughly equal to nitrox diving. Beyond 30m it starts to become cheaper than open circuit to dive. The rebreather costs about £4 per hour to run, compare that to nitrox fills for deeper dives (especially if doing deco diving) and you start to see a saving. For trimix it is massive - recently I spent a week doing trimix diving, everyone else spent about £300 on gas but it cost me about £30 to do the same diving. In fact, it makes trimix so cheap that I use it on pretty much all my dives regardless of depth - it's great having no narcosis on Clyde wrecks.
Maintenance is very easy. The KISS is designed to be serviced by the user rather than a technician in a shop and most spare parts can be bought in either B&Q or Maplin. It is supplied with three tools which is enough to strip it down completely in about 10min. The only maintenance you need to do regularly is greasing the o-rings every now and again and rinsing the whole unit with virkon (a disinfectant). After every dive you need to empty out the liquid from your lungs which condenses in it (yeugh). The oxygen sensors need replacing every 12-18months (about £150 for all three) but you try to stagger the intervals so they don't all need done at once, batteries every 6-12months (depending on use) and lime every 4hrs of dive time (or if it's been 50m+ then I chuck it every dive).
Disadvantages... well it isn't all rosy. You cannot afford to get distracted during a dive. You control the rebreather, not a computer so you need to be aware of everything that happens. On an Inspiration, if you do nothing then it will add oxygen and keep you alive. The KISS may not, it adds some oxygen but it might not be enough without you doing something. You need to remember to check the handsets every time. This might seem a design fault but more people have died using very sophisticated rebreathers, in fact the KISS is probably the only rebreather with a 100% safety record. The KISS also has a lot of plastic, if you're hevy handed in your assembly/disassembly then it is easy to damage threads or seals.
So what can go wrong? If you keep checking your displays then you should never have a problem. If a display fails then you can dive safely on two. If two fail then you can still dive with one if you are very careful. If your oxygen fails then you have about 3-4min to do something before you can't breathe so plenty of thinking time. If you're diluent fails then it isn't a problem, you can continue to dive without it as long as you do not descend any deeper (I've done dives with bot diluent and oxygen switched off completely). To be honest, after a while most rebreather divers really only worry about one thing, the scrubber failing. If this fails then CO2 is no longer removed, you pass out and you die. There is no rebreather on the market which can warn you about this happening but luckily it is a very, very rare event and there are warning signs. You can also flood the unit with water if you let the mouthpiece fall out while in the water without closing it. I've had this happen, you need to be very unlucky to completely flood it, it should keep working. When I did it, it still worked for 90min of deco and I poured about a litre of water out it afterwards. Because of its simplicity, the KISS is very easy to control when things go wrong.
There are around 300 KISS units in service (mine is No.59). It is ordered direct from Jetsam in Canada and is supplied completely disassembled. The diver is responsible for building the unit. The oxygen valves are only sent to instructors so you cannot use the unit until you have done the training course. This is a fairly recent development, when I bought mine you did not need to be trained. I'd a couple of years experience on similar rebreathers so I didn't bother with training.
I'd have to check the website but I think the cost of one new is around £3000 but you can get stung for import tax and shipping costs. On top of that you need to add a couple of small tanks (most people use 3l ponies but some use 5's or 7's). The rebreather comes with everything else you need and it attaches on to a standard backplate and wing set up. I'm sure you could probably rig it on a stab jacket but I've never seen it done. If you don't need the depth rating of the KISS (it is rated to 100m) then there is a smaller, cheaper version available called the Sport KISS (rated only to 50m and something like 2hrs on the scrubber). Personally, I don't think it is as well made or as reliable as the Classic KISS (it was designed for travel and diving on holiday) and anyone would be better off buying a Classic.
BTW, are there any other rebreather divers on the forum? If so, you've been very quiet :D
Cheers,
Stuart