What should your SAC be?

[serambin]

Using the formula given by Charlie99 in another thread, I figured my SAC for a recent dive trip.

Average .46

Lowest .31

highest .74 on a dive where I was actively catching Lobster.

Most dives were in the mid .30's to the low .40's. Are those reasonable rates? Can your SAC rate be too low?

Thanks,

Stan

 

[jhelmuth]

You've already discovered that it varies with workload, experience and comfort in the water. Don't get hung up on it.


btw... your SAC rate is good for most men - FYI.

 

[Diver0001]

Using the formula given by Charlie99 in another thread, I figured my SAC for a recent dive trip.

Average .46

Lowest .31

highest .74 on a dive where I was actively catching Lobster.

Most dives were in the mid .30's to the low .40's. Are those reasonable rates? Can your SAC rate be too low?

Thanks,

Stan

Your SAC should be what ever it is.

To borrow a line from a movie.... "you're not here to make the [SAC], you're here to understand it".

R..

 

[The Kraken]

Yes, your SAC rate can be too low. It's called "dead".

the K

 

[PavoDive]

Yes, your SAC rate can be too low. It's called "dead".

the K

:rofl: :rofl:

I used to train to improve my SAC... now I think I'd better stop doing that

 

[DA Aquamaster]

I agree with all of the above. In my younger and more competetive days I used to focus a lot more on SAC rate and trying to lower it.

The problem is that trying to slow your respiration to reduce your SAC can lead to hypercapnia (elevated CO2 levels) which is associated with an increased risk of oxygen toxicity and nitrogrn narcosis.

For example the US Navy studied enriched air in the 1950's and found that the potential for an O2 hit was too unpredictable. This was due in part to the harder breathing regulators of the day but also due to their use of some divers with extensive helmet diving experince and a consequently high tolerance for elevated CO2 levels due to the generally poor ventilation in an old diving helmet. The result of this combination was a number of divers in the experimental group with very low SAC rates and high CO2 retention which increased oxtox incidents.

Personally, when Nitrox first became popular locally I cringed when several divers told me how much their SAC rate had improved on Nitrox. They were getting much better mileage from a tank of Nitrox than air, but were doing it by slowing their breathing rate to more efficiently consume the higher percentage of O2 in their lungs. What they did not realize that they were retaining more CO2 and placing themselves at elevated risk of an O2 hit if diving at the high a PPO2 and increased risk of nitrogen narcosis on deeper nitrox dives in the 100-130 ft range. At the time, the recommended maximum PPO2 during the working portion of the dive was 1.6. Currently the more conservative view is that a PPO2 of 1.6 is reserved for deco or non working portions of a dive with 1.4 being the max for the working portion of the dive.

Personally, if air consumption is a concern and you have already done the normal development and skill improvement things like eliminating extraneous movement underwater, improved your trim and bouyancy control, etc. and you still need more gas, get a larger tank or a set of doubles.

At this point, I measure my SAC now and then for planning purposes. I will swim at a constant cruise speed at a constant depth like 66 ft for 10 minutes to measure the SAC, which is normally around .6. However I do not try to reduce it, and I evaluate the gas remaining at the end of most dives to ensure my consumption was about what was expected.

 

[serambin]

I agree with all of the above. In my younger and more competetive days I used to focus a lot more on SAC rate and trying to lower it.

The problem is that trying to slow your respiration to reduce your SAC can lead to hypercapnia (elevated CO2 levels) which is associated with an increased risk of oxygen toxicity and nitrogrn narcosis.

For example the US Navy studied enriched air in the 1950's and found that the potential for an O2 hit was too unpredictable. This was due in part to the harder breathing regulators of the day but also due to their use of some divers with extensive helmet diving experince and a consequently high tolerance for elevated CO2 levels due to the generally poor ventilation in an old diving helmet. The result of this combination was a number of divers in the experimental group with very low SAC rates and high CO2 retention which increased oxtox incidents.

Personally, when Nitrox first became popular locally I cringed when several divers told me how much their SAC rate had improved on Nitrox. They were getting much better mileage from a tank of Nitrox than air, but were doing it by slowing their breathing rate to more efficiently consume the higher percentage of O2 in their lungs. What they did not realize that they were retaining more CO2 and placing themselves at elevated risk of an O2 hit if diving at the high a PPO2 and increased risk of nitrogen narcosis on deeper nitrox dives in the 100-130 ft range. At the time, the recommended maximum PPO2 during the working portion of the dive was 1.6. Currently the more conservative view is that a PPO2 of 1.6 is reserved for deco or non working portions of a dive with 1.4 being the max for the working portion of the dive.

Personally, if air consumption is a concern and you have already done the normal development and skill improvement things like eliminating extraneous movement underwater, improved your trim and bouyancy control, etc. and you still need more gas, get a larger tank or a set of doubles.

At this point, I measure my SAC now and then for planning purposes. I will swim at a constant cruise speed at a constant depth like 66 ft for 10 minutes to measure the SAC, which is normally around .6. However I do not try to reduce it, and I evaluate the gas remaining at the end of most dives to ensure my consumption was about what was expected.

I completely understand what you're saying, but in the years of free diving the one thing you had to do was to ignore the co2 warning. In fact, the co2 warning came at about 1/2 the time you could say down if you waited on the o2 warning.

Stan

 

[pdoege]

I agree. But free and scuba are different.

When I free dive I am under for at most 2 minutes. Then I spend at least 2 minutes on the surface.

When I scuba I am under for 45-120 minutes.

Cranking up the CO2 on a long, deep (120 minutes at 100 feet or so) can really open a diver up to a CO2 hit or 02 tox.

I chase the the CO2 warning all the time when I free dive. If I catch myself doing it while I am scuba diving I think that I am doing something wrong.

I normally force myself to breathe at a rate that does not involve the CO2 warning kicking in. I do try to come close, of course....

To answer the original question, I get around a .41 on a cave dive in decent flow. I imagine that is .6 going in and .2 coming out or thereabouts. So you are definitely in the expected SAC range.

Regards,
Peter

I completely understand what you're saying, but in the years of free diving the one thing you had to do was to ignore the co2 warning. In fact, the co2 warning came at about 1/2 the time you could say down if you waited on the o2 warning.

Stan