How low is "low Air"

[Fatboy]

Hi guys.
Total Newbie Question
(I just became OW)
On a recent dive, my gauge went to 500 and I was quite concerned, (but remembered to stay calm, plus I was only at about 30 feet). I signaled my buddy and we made our way to the surfacing area. I surfaced at 350 and am wondering if I was too worried. . . I like a margine of safety and believe that red mark on the gauge is there to tell me something. . .
Any comments?

 

[DORSETBOY]

I like to finish my dives with 50-70 bar left "spare", this is primarily for safety but also cos it's best not too run tanks too dry.
A general guide I use is to have a greater safety margin for deeper dives and / or in poorer conditions.

 

[rmediver2002]

Hi guys.
Total Newbie Question
(I just became OW)
On a recent dive, my gauge went to 500 and I was quite concerned, (but remembered to stay calm, plus I was only at about 30 feet). I signaled my buddy and we made our way to the surfacing area. I surfaced at 350 and am wondering if I was too worried. . . I like a margine of safety and believe that red mark on the gauge is there to tell me something. . .
Any comments?

Your response was absolutely correct when you noticed the gauge was at 500 psi.

During your future dives track your gauge periodically during the dive, most paople do glance at the gauge and make sure it is not in the red but I am talking about really tracking it.

See how much air your using at a paticular depth for a given time, you may find this is a bit different than you surface air consumption rate depending on how you arrived at your initial figure. Adjust from there and begin using it as a tool when planning your future dives, then begin "testing" yourself and estimating your pressure before each check, make it something of a game to increase your skills at gas management.

Keep Diving!!

Jeff Lane

 

[Scubaroo]

Learn about gas management! Something never covered in my OW class (or most I'll bet), is how to manage your air supply. There won't always be a DM or instructor saying when to turn the dive.

Search and read up on the following two terms for starters - "SAC" and "rock bottom".

You need to learn what your equivalent surface consumption is while diving, and use this along with the planned dive profile, to calculate if it is a safe dive profile for the size of the single tank you're most likely diving. You could find that you're doing a 60' dive, and while your buddy can last 40 minutes at that depth, you can only last 30 minutes on a single tank. So planning a 40 minute dive is a receipe for trouble. You also need to learn how to plan for an emergency, like your buddies second stage having an uncontrollable freeflow at depth, and losing all of his/her air - do you have enough in your tank still to BOTH surface safely?

Noticing that you've got 500psi left is *not* when you surface. You begin your surface at an agreed-upon pressure that you work out prior to the dive commencing, or an agreed-upon time limit has been reached. 500psi is an arbitrary figure anyway, and won't apply to all dives - say you're shore diving, and you find yourself at 500psi - and you've been heading away from shore the entire dive...

Keep learning!

 

[MikeFerrara]

If you do a search you'll find lots of stuff here about gas management. The short answer is that you need to end the dive with enough gas to get you and your buddy back to the surface. If you must get back to the entry point you must turn the dive with enough gas to get you both back.

If you're at 30 ft and only have to go to the surface 500 psi in an al80 (13 cu ft) should be plenty.

I would also encourage you do go back and discuss this with your instructor. They should be teaching this stuff.

 

[Diver0001]

Hi guys.
Total Newbie Question
(I just became OW)
On a recent dive, my gauge went to 500 and I was quite concerned, (but remembered to stay calm, plus I was only at about 30 feet). I signaled my buddy and we made our way to the surfacing area. I surfaced at 350 and am wondering if I was too worried. . . I like a margine of safety and believe that red mark on the gauge is there to tell me something. . .
Any comments?

First of all, your response to end the dive in a controlled manner when you reached 500psi was good.

What I would suggest is to *reach* your safety stop depth with at least 500 psi.

The main problem faced by beginners seems to be when to "turn" the dive in order to ensure that you get back to your safety stop depth with the 500 psi you wanted. So...when to turn the dive: The easiest way to get used to this is to go out and come back along more or less the same line (direction, depth and tempo) in fairly shallow water (45-55ft).

In that case, assuming you start with 3000 psi and you want 500 in reserve then you really have 2500 psi to work with during the dive. That means you need to turn the dive at about 1250+500 (1/2 of 2500 plus your 500 reserve) or 1750 if you're just going back the same way you came. If you do this two things will happen; first, you'll reach 500psi as you ascend to your safety-stop depth and second, when you reach 500psi you should be more or less back to where you started.....

What I would suggest is to go out and try this a few times in a location where you're reasonably sure you can find the same line out and back again, like along a straight bit of shoreline..... That'll give you some basic starting point to work on finding a comfortable even tempo and for learning how to control your pressure when you reach safety stop depth..... and you will have also learned a basic navigation trick as a bonus.

R..

 

[MikeS]

On a recent dive, my gauge went to 500 and I was quite concerned, (but remembered to stay calm, plus I was only at about 30 feet). Any comments?

It looks like you've figured out it depends on depth. It also depends on how fast you are consuming air. Ironically, the more concerned you are, the less time the gas will last since your breathing rate will increase. But with 500 psi in an Aluminum 80 tank you were in no immediate danger. At a surface air consumption rate of 1 cubic foot a minute you could have stayed there for six minutes without running out of gas. And you still had other options, your buddy’s alternate air source, and a controlled swimming ascent is not difficult from 30 feet. The most important thing is to stay calm, breath, think, breath, think and make a good decision which is what you did.

I like to finish my dives with 50-70 bar left "spare", this is primarily for safety but also cos it's best not too run tanks too dry.

This is my biggest complaint with PADI dive planning, it suggests finishing the dive with 500 psi but offers no clues let alone a methodology for getting there.

II would also encourage you do go back and discuss this with your instructor. They should be teaching this stuff.

I’m a PADI Dive Master and I’m still waiting for the class that teaches gas management. In fact it’s hard to find an Instructor that even understands it. While you could make the argument that there are millions of divers diving safely without this knowledge so it’s not important, I want to know. So where can you find the information?

A good place to start is The U.S. Navy Diving Manual. It’s free, you can get it online at,
Navy Diving Manual but you have to weed through a lot of extraneous navy stuff to get to actual diving information. A good place to start is Chapter 3 on Underwater Physiology and then Chapter 7 on Scuba Air Operations. Between the two you should be able to calculate how long the gas would have lasted based on your activity level, depth, and tank.

Here are some clues:
* Figure out how fast you’d be consuming air on the surface based on the activity level in cubic feet per minute.
.
* Based on that, figure out the rate for a given depth in cubic feet per minute.

* Figure out how many psi of tank pressure equates to a cubic foot of gas.

* Calculate the reduction in psi of tank pressure per minute for a given activity level at a given depth.

* Than put it all together and figure out how long you could have stayed at 30 feet before 500 psi of air ran out.

It’s not easy and may take a bit of work which is probably why PADI doesn’t teach it.

Hope this helps,

Mike

 

[diverlady]

Now I mostly do wreck dives in the Great Lakes so here's what my Club encourages. At 1500psi you start heading back to the mooring line. At 1000psi you should be at the line ready to begin your ascent. You should be back ON the boat with no less than 500psi. Remember, your buddy may need YOUR octo so you need to have enough gas to support the possibility.

You didn't mention your buddy's gas levels. Were you aware of them? I tell my buddy regularly what my gas level is and usually get his/her gas level reported to me or I'll ask for them (or just look at his/her gauges). Now with someone who I've dived a lot with, I won't do it so often but I try to make a point of doing so with newer divers to get them in the habit early.

Diverlady

 

[MikeFerrara]

Now I mostly do wreck dives in the Great Lakes so here's what my Club encourages. At 1500psi you start heading back to the mooring line. At 1000psi you should be at the line ready to begin your ascent. You should be back ON the boat with no less than 500psi. Remember, your buddy may need YOUR octo so you need to have enough gas to support the possibility.


Diverlady

What if 500 psi isn't enough to get you (or you and buddy) back to the line?

What if 1000 psi isn't enough to get both of you up or it's a shallower dive and 1000 psi is way more than you need in reserve?

What good does that 500 psi do you on the boat?

The point I'm trying to make is that these numbers need to be adjusted for the depth, size of the tanks being used and the conditions/dive plan. If yoou use 1500 traveling away from the line, 500 won't get you back to it.

 

[MikeFerrara]

It’s not easy and may take a bit of work which is probably why PADI doesn’t teach it.


Mike

Actually it is easy if you let it be.