First dive at 40 meters - Newbies recreational

[David Novo]

18 m/ min is not no gas planning. This is a freaking emergency.
I meant 50l/ min per person as I divided 150 bars by 2.
This spreadsheet helps.

If you have an adequate amount of gas, you do not need to ascend at 18m/min in an emergency.

For a dive to 40m and following PADI's ascent profile, I would calculate my gas reserve as follows:

Average pressure = (5+1) / 2 = 3 bar
Ascent time = 40m / 9m/min + 3 min (safety stop) + 1 min to solve issues at bottom = round to 8 min
Combined SAC = 30 l/min x 2 = 60 l/min
Reserve gas = 3 bar x 60 l/min x 8 min = 1440 litres = 120 bar (assuming a 12L steel tank - aluminium "12L" tanks just have 11.1L)
Usable gas (assuming 200 bar in the beginning) = 200 bar - 120 bar = 80 bar

This assumes direct ascent from the bottom.
If you still need to return to where you started (desirable but not mandatory as in an overhead environment), your usable gas is 40 bar each way. This means that you should turn back and start ascending at 160 bar.

P.S.: Were you taught to plan gas as shown in the spreadsheet? A 50 bar reserve is not appropriate for dives to any depth.

 

[Edward3c]

@Dody We are not trying to be better than you. We don't want to read about you or your wife in the Incidents reports.

Would you allow a new engineer straight out of training to take on one of your complex projects, or would you want to coach them so when they do the complex project they are better prepared than just having the theory? That’s what we’re attempting to do here.

 

[Raphus]

@Dody We are not trying to be better than you. We don't want to read about you or your wife in the Incidents reports.

Would you allow a new engineer straight out of training to take on one of your complex projects, or would you want to coach them so when they do the complex project they are better prepared than just having the theory? That’s what we’re attempting to do here.

To be honest you are far better then an average diver, because you are interested. And you try to learn.

I would take david novos advice.
Some In SB have so many dives and experienced so many issues underwater, that a new diver can not think about.

 

[Dody]

If you have an adequate amount of gas, you do not need to ascend at 18m/min in an emergency.

For a dive to 40m and following PADI's ascent profile, I would calculate my gas reserve as follows:

Average pressure = (5+1) / 2 = 3 bar
Ascent time = 40m / 9m/min + 3 min (safety stop) + 1 min to solve issues at bottom = round to 8 min
Combined SAC = 30 l/min x 2 = 60 l/min
Reserve gas = 3 bar x 60 l/min x 8 min = 1440 litres = 120 bar (assuming a 12L steel tank - aluminium "12L" tanks just have 11.1L)
Usable gas (assuming 200 bar in the beginning) = 200 bar - 120 bar = 80 bar

This assumes direct ascent from the bottom.
If you still need to return to where you started (desirable but not mandatory as in an overhead environment), your usable gas is 40 bar each way. This means that you should turn back and start ascending at 160 bar.

P.S.: Were you taught to plan gas as shown in the spreadsheet? A 50 bar reserve is not appropriate for dives to any depth.

In all SSI materials, we are taught to plan the dives so that we surface with at least 50 bars. Now, I have read SB where divers mentioned 500 psi which considerably less. I have also read that cave divers use the rule of 3. 200/ 3 = 66,67 bars. That's why I quickly created this spreadsheet to learn some values by heart. In fact, I always plan and think as if I only had 50 bars less than what I really have but I don't use this spreadsheet for gas planning. I would say that this is useful for dynamic thinking. I love playing with numbers. Practical example. I have 100 bars. I know that it gives me 10 minutes at 30 meters with a 15 SAC (when really it 20 minutes). From this, I can calculated instantly my available air for any combo (SAC/ depth) with a pre included safety of 50 bars. Sometimes, I realize that my dive plan was too conservative when I am at safety stop with 85 bars while my plan indicated 60. In this case, I know that I can safely give me 10 minutes playing between 5 meters and surface.

 

[Celt]

Can you please create a thread or send direct info about how to deal with OOA alone at 40 m? Knowledge does not kill. I do not plan to dive solo ever but it might be useful someday

It’s BS there is no way to make a safe assent from 40m if out of air. I made an emergency assent from 43m it’s very hard to exhale enough and go fast enough to make it. Think of OOA at depth as certain death and bring enough reserves.

 

[Mike1967]

I made an emergency assent from 43m it’s very hard to exhale enough and go fast enough to make it.

Why did you need to do that?

 

[Edward3c]

In all SSI materials, we are taught to plan the dives so that we surface with at least 50 bars. Now, I have read SB where divers mentioned 500 psi which considerably less. I have also read that cave divers use the rule of 3. 200/ 3 = 66,67 bars. That's why I quickly created this spreadsheet to learn some values by heart. In fact, I always plan and think as if I only had 50 bars less than what I really have but I don't use this spreadsheet for gas planning. I would say that this is useful for dynamic thinking. I love playing with numbers. Practical example. I have 100 bars. I know that it gives me 10 minutes at 30 meters with a 15 SAC (when really it 20 minutes). From this, I can calculated instantly my available air for any combo (SAC/ depth) with a pre included safety of 50 bars. Sometimes, I realize that my dive plan was too conservative when I am at safety stop with 85 bars while my plan indicated 60. In this case, I know that I can safely give me 10 minutes playing between 5 meters and surface.

Yes, different training bodies use different values. BSAC once used 30bar to start the ascent, then 30bar on surface, later it moved to 50bar, now its 70bar on the surface with new divers planning their dives on thirds.

Some research for you: You have a 300bar 12Lt cylinder how much usable gas have you got? Its not a trick question because those of us who have 300bar cylinders must know the answer.

 

[David Novo]

In all SSI materials, we are taught to plan the dives so that we surface with at least 50 bars. Now, I have read SB where divers mentioned 500 psi which considerably less. I have also read that cave divers use the rule of 3. 200/ 3 = 66,67 bars. That's why I quickly created this spreadsheet to learn some values by heart. In fact, I always plan and think as if I only had 50 bars less than what I really have but I don't use this spreadsheet for gas planning. I would say that this is useful for dynamic thinking. I love playing with numbers. Practical example. I have 100 bars. I know that it gives me 10 minutes at 30 meters with a 15 SAC (when really it 20 minutes). From this, I can calculated instantly my available air for any combo (SAC/ depth) with a pre included safety of 50 bars. Sometimes, I realize that my dive plan was too conservative when I am at safety stop with 85 bars while my plan indicated 60. In this case, I know that I can safely give me 10 minutes playing between 5 meters and surface.

That is not how the rule of thirds works. In my post above, I used the rule of halves (80/2 = 40 bar) which applies if it is desirable but not mandatory (as in an overhead environment) to return to where you started.

In a cave (overhead environment), it is mandatory to return to where you started so divers used the rule of thirds (80/3 = c. 27, resulting in a turning pressure of 173 bar in the 200 bar tank & 120 bar reserve case) or an even more conservative approach.

Rule of halves, thirds, etc is not related to the reserve but to the turning pressure.

P.S.: You can't conclude that your dive plan was too conservative in the case you described as you did not have to donate gas. Furthermore, if you wanted to surface with 50 bar, the answer to the question if 150 bar was enough is definitely no.

 

[Celt]

Why did you need to do that?

A diver came to me completely OOA on a wreck in 43m and when I donated my reg I couldn’t get it back and had to make an emergency assent with him.

 

[Mike1967]

A diver came to me completely OOA on a wreck in 43m and when I donated my reg I couldn’t get it back and had to make an emergency assent with him.

Oh ok, you didn't have another one?