Maximum number of dives a day - DCS

[Brandon]

I have found my limit to be about 4 hours of diving in one day. I'm generally too tired to do more than that. Four one hour dives is easy to do with Nitrox 32, and you are unlikely to come anywhere near your CNS limits.

I was looking at my log, and the only dives where CNS limits were a concern with 32 within NDLs, are dives with an average depth deeper than ~70ft. I have very few of those, and they are all dives with a max depth between 100 and 130ft and for 30-40 mins. I generally have the energy for one dive like that per day.

My mean average depth is somewhere around 35ft, with the majority having an average depth between 29 and 45 feet. That would give an average PPo2 somewhere around 0.7, which should allow for 7.5 hours of diving over one day. An average depth of 70ft (ppo2=1.0) should still allow for 4 hours of diving. Both of those assuming 80% of the NOAA daily limit.

Alex is spot on here - run the math on a series of 5 dives with average depths ranging from 29-45', bottom times of an hour, a 1 hour SI and diving 32%, and you'll find that your available bottom time generally exceeds the gas you'd have available in a single cylinder. You'll also find that most recreational dive boats brief dives that will put you right around this average depth, and it's pretty hard to get bottom times of greater than an hour, or a surface interval of less than an hour. These dives are in the "sweet spot" for the recreational limits.

That said, the best answer given so far in this thread is "it depends".

Alex's example is one very specific (though common) scenario; your mileage will vary if you change any of the variables. As an illustration, if you did the same set of dives on air, you'll probably get bent after the second or third dive. You really need to do the math yourself and understand the limitations.

You were given a variety of tools in your OW and nitrox classes to learn how to plan a dive. Use them. Bring in additional resources if you want - your dive computer's plan/simulate mode, computer software (DivePAL, vPlanner, DecoPlanner, etc), or mobile apps (iDeco, Baltic Deco Planner, etc). Any of these methods can provide you with a reliable answer specific to the dives you plan on doing.

 

[tursiops]

It is nearly impossible to max out your CNS clock on 32%.
Some on the groups I take to Bonaire will routinely do 6-7 dives a day, starting before breakfast.
The reason is that the nitrogen limits keep you from accumulating too much O2....follow your computer on the nitrogen, and the O2 will stay within its limits.
Liveaboards may have a dive schedule like 0700, 0900, 1100, 1400, 1600, and a night dive at 2000.
For recreational diving, the issue is nitrogen limits, not oxygen limits (except depth, of course).

 

[hroark2112]

I would recommend you take a better course on nitrox...find a great TDI instructor and take TDI nitrox, or better yet Advanced Nitrox.

 

[Akimbo]

I would recommend you take a better course on nitrox...find a great TDI instructor and take TDI nitrox, or better yet Advanced Nitrox.

On the other hand you could just follow your computer like the vast majority of recreational divers… and make sure your DAN insurance is current.

 

[Brandon]

I would recommend you take a better course on nitrox...find a great TDI instructor and take TDI nitrox, or better yet Advanced Nitrox.

Yeah... sure do seem to be a lot of these "how many dives can I do in a day" type of questions popping up recently from supposedly certified divers...

 

[scubadada]

I'm travelling to a location which offers unlimited diving.
I'm just wondering how many dives a day can one do safely.
I've often done 4 dives in a day, and 5 once without incident.

However I'd like to know what is a safe way to do this.
I've read many cases of divers getting bends while still staying within the limits of their computers.

I've seen the CNS charts which seems to suggest that 4 dives a day will max out your CNS clock.

Suggestions anyone?

It is nearly impossible to max out your CNS clock on 32%.
Some on the groups I take to Bonaire will routinely do 6-7 dives a day, starting before breakfast.
The reason is that the nitrogen limits keep you from accumulating too much O2....follow your computer on the nitrogen, and the O2 will stay within its limits.
Liveaboards may have a dive schedule like 0700, 0900, 1100, 1400, 1600, and a night dive at 2000.
For recreational diving, the issue is nitrogen limits, not oxygen limits (except depth, of course).

Hi WhiteSands,

This is not a trivial question and one that I have been interested in for some time. It is quite easy to control one's nitrogen exposure by paying atttention to your dive computer. This should not limit the number of dives per day but may limit the duration of your dives should you want to remain out of decompression. On the other hand, oxygen exposure is often neglected. According to the NOAA tables, one is allowed 5 hours of exposure per 24 hours (note, not per day) at a pO2 of 1.0. This would translate into 5 hours at and average depth of 70 feet using nitrox 32. It is not difficult to exceed this limit doing 4, 5 or 6 dives per day, more in a 24 hour period. Dive computers fall into 2 catergories, those that track O2 exposure per 24 hours like my Oceanic computers, and those that allow for an O2 elimination half life (most commonly 90 minutes), like the Scubapro computers. I do not know which technique is correct, but, intuitively, an O2 half life of elimination, as is the case with nitrogen, seems correct.

I, not infrequently, exceed my NOAA 24 hr O2 exposures and have gotten away with it to date. That does not imply that I do not think about it. My most frequent dives are drifts in Boynton Beach, Florida at an average depth of about 55 feet. Four dives often make up 5+ hours. I have switched from EAN 36 to 32 to limit my oxygen exposure. We often do a wreck dive to a considerably deeper depth to make this profile even more at possible risk.

I'm glad to see that you are concerned and interested in this topic, the choice is yours

Best, Craig

 

[tursiops]

According to the NOAA tables, one is allowed 5 hours of exposure per 24 hours (note, not per day) at a pO2 of 1.0. This would translate into 5 hours at and average depth of 70 feet using nitrox 32. It is not difficult to exceed this limit doing 4, 5 or 6 dives per day, more in a 24 hour period.

You are absolutely correct, except that it is worse than that: the usual recommendation is not to exceed 80% of the limit.....kind of like using PPO2=1.4 instead of 1.6, to get a safety margin. So not 5h at an average depth of 70 feet with 32%, but only 4h! But you say this is not difficult. I think it would be very unusual to do that kind of diving....but I am thinking of reefs, not deep drift dives. Your move from 36% to 32% was smart in your conditions! And dropping the average depth from 70 feet to even just 60 feet will give about a 20% increase in BT before you hit the NOAA clock limits. The point is to be aware of this stuff, and watch the computer!

 

[John C. Ratliff]

I have found my limit to be about 4 hours of diving in one day. I'm generally too tired to do more than that. Four one hour dives is easy to do with Nitrox 32, and you are unlikely to come anywhere near your CNS limits.

I was looking at my log, and the only dives where CNS limits were a concern with 32 within NDLs, are dives with an average depth deeper than ~70ft. I have very few of those, and they are all dives with a max depth between 100 and 130ft and for 30-40 mins. I generally have the energy for one dive like that per day.

My mean average depth is somewhere around 35ft, with the majority having an average depth between 29 and 45 feet. That would give an average PPo2 somewhere around 0.7, which should allow for 7.5 hours of diving over one day. An average depth of 70ft (ppo2=1.0) should still allow for 4 hours of diving. Both of those assuming 80% of the NOAA daily limit.

All of that bing said, if you're using a computer, and following the computer's rules, and understand what it is telling you, you can safely do 4-5 dives in a day using nitrox.

Be aware that the U.S. Navy has a 100 foot limit on 32% nitrox. Look it up in the U.S. Navy Diving Manual. (Table 10-1 if my memory is correct.)

SeaRat

 

[sharkbaitDAN]

The Navy table is pretty much identical to every EAD table I've ever seen, with a working PPo2 of 1.4 and a max of 1.6. The dives I happened to be talking about were using mixes between 28 and 34, with maximum depths between 100 and 130. May max ppo2 was 1.47 for any of those, and that was for less than one minute, I think I wanted to get a photo of the bow of a wreck looking up.