Air management question

[jumppilot]

Hello all,

After a 10 year break I'm getting back into diving. I have my advanced and used to be a tech at a dive shop but it's been years since I thought of any of this.

Concerning air management, how does everyone plan a dive to ensure you have a safety margin upon surfacing. What is a good safety margin?

Really, it's just been so long I don't remember if 1,000psi at 100 feet is critical or just a "time to ascend" point.

Thank you everyone. Looking forward to joining the forum family!

 

[TMHeimer]

I learned to begin the ascent have 100 PSI for every 10 feet of depth, so your 1,000 PSI for 100' fits. I generally use the rule of thirds. Also, at certain max depths I have a general idea such as at 80' (30 min. NDL on Air): 10 mins. out, 10 back, 5 messing around near the anchor and 5 mins. to spare.

 

[jumppilot]

I learned to begin the ascent have 100 PSI for every 10 feet of depth, so your 1,000 PSI for 100' fits. I generally use the rule of thirds. Also, at certain max depths I have a general idea such as at 80' (30 min. NDL on Air): 10 mins. out, 10 back, 5 messing around near the anchor and 5 mins. to spare.

Thank you. That's a great rule of thumb and easy to remember.

 

[KellyAsh]

We always tell students and divers that 700 PSI is the point at which you signal your DM to let them know you are low on air and time to ascend to your 3 minute safety stop. No need for math while trying to maintain buoyancy at the end of a tiring dive after so long out of the water.

To extend the time that 700 psi will last, as well as the rest of your tank, work on inhaling slowly over the span of 5 seconds then slowly exhale over the span of 10 seconds. You might not be able to do this at first but a 3 second inhale and 5 second exhale is still MUCH better than uncounted breathing. This 5 and 10 second breathing pattern lowers your breathes per minute to 4 from an average of 20-30 for normal breathing on the surface.

It's definitely a skill that needs to be developed but you can progress very quickly if you focus on it over a few dives.

 

[00wabbit]

Read about rock bottom gas management. This will equip you with the information needed to know exactly how much air you need to reserve.

 

[rongoodman]

Talking about psi without specifying tank size is meaningless, so I'll assume you mean Al80s. 1000 psi would be too low for me at 100'--1300 psi is about right. Remember, you have to have enough gas to get you and your buddy, both presumably stressed, to the surface, taking into account any required deco, and you also need to allow a little time to sort things out before you start up. There have been lots of discussions here over the years about Rock Bottom/Minimum Gas. Here is one and here is another.

 

[LeadTurn_SD]

We always tell students and divers that 700 PSI is the point at which you signal your DM to let them know you are low on air and time to ascend to your 3 minute safety stop. No need for math while trying to maintain buoyancy at the end of a tiring dive after so long out of the water.

To extend the time that 700 psi will last, as well as the rest of your tank, work on inhaling slowly over the span of 5 seconds then slowly exhale over the span of 10 seconds. You might not be able to do this at first but a 3 second inhale and 5 second exhale is still MUCH better than uncounted breathing. This 5 and 10 second breathing pattern lowers your breathes per minute to 4 from an average of 20-30 for normal breathing on the surface.

It's definitely a skill that needs to be developed but you can progress very quickly if you focus on it over a few dives.

Hmmm.

Not even sure where to start with that statement...

At what depth are they when they hit 700 psi?

What size tanks?

It could certainly be enough from the shallows for a single diver, but is it enough from deep water; is that really enough gas (assuming an Al 80, approx. 77.4 cu feet @ 3,000 psi = approx. 18 cu feet at 700 psi) to get two divers to the surface from depth??

I think looking into air consumption and adequate reserves is a very worthwhile math exercise for all divers, and need not be done during the dive... you need to do it beforehand.

Best wishes.

 

[ajduplessis]

You cant really make any knowledgable calculations until you know what your gas consumption rate is. The rest are just numbers until you know your SAC.

 

[Oldbear]

Hello all,

After a 10 year break I'm getting back into diving. I have my advanced and used to be a tech at a dive shop but it's been years since I thought of any of this.

Concerning air management, how does everyone plan a dive to ensure you have a safety margin upon surfacing. What is a good safety margin?

Really, it's just been so long I don't remember if 1,000psi at 100 feet is critical or just a "time to ascend" point.

Thank you everyone. Looking forward to joining the forum family!

JumpPilot...welcome to Scuba Board and welcome back t diving.

SBers have presented you with a few good ideas. I like the Rule of Thirds and use it personally quite often. When I teach a Open Water course here is the formula we use.

Finding Turn Pressure
Starting Pressure: e.g. 3000 psi
minus
Reserve (500 psi) , ascent & safety stop (300 psi): 800 psi
leaves
Remaining pressure:3000 - 800 = 2200 psi

Start Pressure: 3000 psi
minus
Half remaining pressure:2200 / 2 = 1100 psi
leaves
Turn pressure: 3000 - 1100 = 1900 psi

This formula works pretty well for simple dives that a new OW diver might plan. Also with experience comes personal adjustments to meet your needs, e.g. the Rule of Thirds.

What ever formula you decide to try, plan you dive and dive your plan...then make adjustments and do it all over again...many time.

Happy Bubbles,

~Oldbear~

 

[Imla]

To extend the time that 700 psi will last, as well as the rest of your tank, work on inhaling slowly over the span of 5 seconds then slowly exhale over the span of 10 seconds. You might not be able to do this at first but a 3 second inhale and 5 second exhale is still MUCH better than uncounted breathing. This 5 and 10 second breathing pattern lowers your breathes per minute to 4 from an average of 20-30 for normal breathing on the surface.

It's definitely a skill that needs to be developed but you can progress very quickly if you focus on it over a few dives.

I really don't now if Hondurans have a completely different physiology than Norwegians, but if you had a respiratory rate of 30 at the surface (Not exercising) I would probably be inclined to dispatch an ambulanse in your direction.
The normal RR is 12 + or - a little. What he needs in the start is to make a dive plan, which includes max depths, rock bottoms, and get a conscious attitude towards gas management, and when the dive comes, to breath what his body needs. I would not reccommend a RR of 4 to anyone!