OP
The whole cave diving is based on risk mitigation and risk assessment. Or better the whole diving industry is based on that. Also your whole life. Nobody things about refusing breaks of a car, but it is possible.
In cave diving, you must find a way between 'safe' and doable. That is the risk assessment. Diving on 1/4 or 1/6 is safer than 1/3, everybody can calculate. But if the risk that something happens is only 0.01%, do you always want to be extremely safe with 1/6 and never go further? Every diver will answer no. The real risk I don't know, the 0.01% is just a number I mentioned. But if the risk is 1%, a lot of divers will not go to the 1/3 from 1/6, but then to 1/5 or 1/4. Doing it always safe is impossible. Always there will be planes falling out of the sky, alsways there will be divers without gas. But it is how much risk are you willing to take.
The 1/3 works in a lot of situations and in a lot of situations not.
So let's say you are in no flow cave in a team of 3. Then you can normally without major restrictions dive 'safe' according to standards on 1/3 if the divers are experienced enough. We don't discuss now what is experienced enough, but go further. They do dives on 1/3, all succesfull, never had a big problem, only somewhere a freeflow, never runned out of gas, and now they want to do longere penetrations.
Then you add a stage cylinder. Make the calculation easy, all cylinders have the same volume, all are filled with 210 bar. You say ok, 210 bar in the stage half use is 100 bar, that means 50 bars in the twinset. So 210-50 is 160 bars. From that 160 you can use 1/3 on way in, so that is 50 bars (always round to the safe side), that means 50 bars can be used from the twinset where also already 50 bars reserve are calculated for the stage. Hoppa 210-50=160 bars, that will be the new turn pressure.
They swim in with the stage, 210 bar at beginning, drop it after using 100 bars, so 110 bars left, they drop it. Then swim further till they reach 160 bar in twinset and go back. Pickup the stage, come out of the cave with 10 bars in the stage, 110 in the backgas. So all is done safe.
If someome forgot to close the valve in the stage and all that gas is gone, they still have enough in their backgas to finish the dive. Even no gas sharing is needed. Only the dive is ended with only 60 bars left in the backgas.
On a next dive, at the turnpressure in the backgas a non resolvable freeflow starts. This means 1 backgas is not usable. They swim back to the stage and also here 60 bars are left in the backgas that is shared till the stage is found again. The stage is working, so the diver without backgas can swim out on itself. (or of course can also share again, but there is only 50 bars needed from a twinset by 1 diver to get out. The whole team has plenty of gas left.
On the 3rd dive, the backgasproblem is there again and the stage on the way back is drained. This means more gas must be shared because 1 diver has no backgas and not stage left to get out. But still the team is not empty when exit the cave.
If there is no backgasproblem and 2 or all 3 stages of the team are drained, they still can exit safe.
If there are 2 twinset having the same problem on the same place, there is a bigger problem. Theoretically there is still enough gas in a twinset left for 3 divers, but only 2 divers can use it. The answer about this theoretically problem will be: what is the chance that this happens? if this happens the team is stupid because they started with bad equipment.
So the team did risk assessment. And accepted this risk.
So then you want to make the dive more complex and add more stages. Normally you use the same amount of backgas and use the same reserves of 1 stage lost. So the turnpressure is again 160 bar and the drop of every stage is again 110 bar. But with more cylinders, there is a higher risk of losing somewhere gas. But again the question is: how big is the chance that you loose and 2 stages and 1 backgas? And the risk is accepted most times.
This means the only way of having no problems with gas is stay at surface and don't dive. Every dive has a risk. And the more complex you make a dive, the higher the risk, but there are still accepted risks.
With ccr diving the same. A team must have enough bailout for 1.5 diver to reach the exit. So why not for everydiver enough bailout?
Doing exploration dives is more risky than doing a normal complex dive in a cave where more divers have been already. When changes exploration into daredevil diving? Humans also tend to talk more positive about more 'famous' people who do extreme things than about unknown people.
But one of the most important things is to think about reserves of gas. And the 1/3rd on every cylinder is for sure not the best way.
The half +14 bars is normally only used in open water recreational diving.
In cave diving, you must find a way between 'safe' and doable. That is the risk assessment. Diving on 1/4 or 1/6 is safer than 1/3, everybody can calculate. But if the risk that something happens is only 0.01%, do you always want to be extremely safe with 1/6 and never go further? Every diver will answer no. The real risk I don't know, the 0.01% is just a number I mentioned. But if the risk is 1%, a lot of divers will not go to the 1/3 from 1/6, but then to 1/5 or 1/4. Doing it always safe is impossible. Always there will be planes falling out of the sky, alsways there will be divers without gas. But it is how much risk are you willing to take.
The 1/3 works in a lot of situations and in a lot of situations not.
So let's say you are in no flow cave in a team of 3. Then you can normally without major restrictions dive 'safe' according to standards on 1/3 if the divers are experienced enough. We don't discuss now what is experienced enough, but go further. They do dives on 1/3, all succesfull, never had a big problem, only somewhere a freeflow, never runned out of gas, and now they want to do longere penetrations.
Then you add a stage cylinder. Make the calculation easy, all cylinders have the same volume, all are filled with 210 bar. You say ok, 210 bar in the stage half use is 100 bar, that means 50 bars in the twinset. So 210-50 is 160 bars. From that 160 you can use 1/3 on way in, so that is 50 bars (always round to the safe side), that means 50 bars can be used from the twinset where also already 50 bars reserve are calculated for the stage. Hoppa 210-50=160 bars, that will be the new turn pressure.
They swim in with the stage, 210 bar at beginning, drop it after using 100 bars, so 110 bars left, they drop it. Then swim further till they reach 160 bar in twinset and go back. Pickup the stage, come out of the cave with 10 bars in the stage, 110 in the backgas. So all is done safe.
If someome forgot to close the valve in the stage and all that gas is gone, they still have enough in their backgas to finish the dive. Even no gas sharing is needed. Only the dive is ended with only 60 bars left in the backgas.
On a next dive, at the turnpressure in the backgas a non resolvable freeflow starts. This means 1 backgas is not usable. They swim back to the stage and also here 60 bars are left in the backgas that is shared till the stage is found again. The stage is working, so the diver without backgas can swim out on itself. (or of course can also share again, but there is only 50 bars needed from a twinset by 1 diver to get out. The whole team has plenty of gas left.
On the 3rd dive, the backgasproblem is there again and the stage on the way back is drained. This means more gas must be shared because 1 diver has no backgas and not stage left to get out. But still the team is not empty when exit the cave.
If there is no backgasproblem and 2 or all 3 stages of the team are drained, they still can exit safe.
If there are 2 twinset having the same problem on the same place, there is a bigger problem. Theoretically there is still enough gas in a twinset left for 3 divers, but only 2 divers can use it. The answer about this theoretically problem will be: what is the chance that this happens? if this happens the team is stupid because they started with bad equipment.
So the team did risk assessment. And accepted this risk.
So then you want to make the dive more complex and add more stages. Normally you use the same amount of backgas and use the same reserves of 1 stage lost. So the turnpressure is again 160 bar and the drop of every stage is again 110 bar. But with more cylinders, there is a higher risk of losing somewhere gas. But again the question is: how big is the chance that you loose and 2 stages and 1 backgas? And the risk is accepted most times.
This means the only way of having no problems with gas is stay at surface and don't dive. Every dive has a risk. And the more complex you make a dive, the higher the risk, but there are still accepted risks.
With ccr diving the same. A team must have enough bailout for 1.5 diver to reach the exit. So why not for everydiver enough bailout?
Doing exploration dives is more risky than doing a normal complex dive in a cave where more divers have been already. When changes exploration into daredevil diving? Humans also tend to talk more positive about more 'famous' people who do extreme things than about unknown people.
But one of the most important things is to think about reserves of gas. And the 1/3rd on every cylinder is for sure not the best way.
The half +14 bars is normally only used in open water recreational diving.
