Holding a safety stop - the effect of breathing/weighting

[ross9]

In recent dives I've been trying to cut down my weight. I feel like I'm making good progress as I'm a lot more comfortable generally through the dive and I'm putting a lot less air in my BCD. But it's not right yet.

The one area where I still struggle a little is at the safety stop, particularly when it comes to the effect of my breathing on my buoyancy. I've been told that it's important to take deep breaths during the safety stop to aid in eliminating CO2 and offgassing. However I find deep breathing at the safety stop has a huge effect on my buoyancy - it results in me moving between 4 and 6 metres or even as wide as 3 and 7.

My most recent dive where this was an issue I was in a 3mm shorty, 4kg (9lbs) weight on a belt, jacket style BCD and a 12L/200 bar steel tank.

I have ambitions of moving into deco diving in future but wouldn't be comfortable going down that path until I'm better able to hold a stop in shallow depths.

What can I do to help hold the safety stop?

 

[NothingClever]

You’re smart. Keep diving. You’ll get it.

 

[PfcAJ]

Just breath normally.

deep breaths don’t do anything to help offgassing.

 

[Colliam7]

The one area where I still struggle a little is at the safety stop, particularly when it comes to the effect of my breathing on my buoyancy. I've been told that it's important to take deep breaths during the safety stop to aid in eliminating CO2 and offgassing. However I find deep breathing at the safety stop has a huge effect on my buoyancy - it results in me moving between 4 and 6 metres or even as wide as 3 and 7

Based on your description, it may well be that your breathing is 'too' deep at your safety stop. Normal breathing is a better approach as others have said.

Several questions do come to mind, that potentially affect suggestions.

At your safety stop:
1. What is your ‘orientation’? Are you horizontal? Are you vertical? Somewhere in between?

2. Are you ‘free hovering’, or are you holding a descent / anchor line?

3. What happens if you stop breathing for, say, 20 seconds? If you take and hold a normal – not excessively deep – breath, do you descend, do you ascend, do you stay at approximately the same depth?

 

[Zef]

I would recommend avoiding the deep breaths and just breath normally. The CO2 should not be a problem as you are naturally expelling that as you exhale throughout the dive....unless you are holding your breath you should not have an excessive buildup of CO2 in your system.

The more important culprit is N2...the safety stop provides a brief period for N2 to migrate out of fast compartment type tissues and be off-gassed in one's exhalate at a depth where one is not absorbing a significant amount of N2 in slower compartment tissue types. N2 off-gassing then continues during the surface interval.

I would think that a greater rate of breathing, within reason, would have a larger affect on N2 off-gassing than larger volume breaths. The issue one faces when taking large breaths during the safety stop is that the expansion of air in ones lungs and BC is exponential as one rises in the water column, the largest changes as you know are between 10 meters and the surface with the amount of expansion increasing the high one moves...so a large breath causing one to rise upwards makes it more likely that one will lose control and cork to the surface. Sinking due to the large exhale means that one is potentially moving lower than the ideal depth for off-gassing to occur. My computer indicates a typical decompression/safety stop zone as between 3 meters and 6 meters.

I caveat everything above with the fact that I am not expert, and hope that someone with more expertise will come along and either correct what I have stated or corroborate it.

-Z

 

[Jack Hammer]

Breath normally and relax. Try to keep your lungs tidal volume in the middle. That means when neutral you are mid breath.

 

[ross9]

Thanks all - perhaps I'm reading too much into the 'deep' breathing. I shall try to relax a little more at the safety stop and breath normally. It's partly still that irrational fear you have as a beginner of 'corking' to the surface from taking too deep a breath which results in over compensating when breathing. I.e. you take a deep breath, start ascending beyond the stop, so quickly breath out deeply but then descend too far - cycle repeats.

What is considered an acceptable fluctuation from a stop depth due to breathing? 0.5m either side? Can you ultimately get to a point where you don't move at all?

At your safety stop:
1. What is your ‘orientation’? Are you horizontal? Are you vertical? Somewhere in between?

2. Are you ‘free hovering’, or are you holding a descent / anchor line?

3. What happens if you stop breathing for, say, 20 seconds? If you take and hold a normal – not excessively deep – breath, do you descend, do you ascend, do you stay at approximately the same depth?

1. Horizontal - not perfectly but definitely closer to horizontal than the midpoint
2. The example I gave above in the 3mm shorty was free hovering. If I have an anchor line at hand then if I hold at a fixed point it helps to limit the deviation from the stop depth - but that's not a long term solution
3. Good question and something I will test when I'm next in the water. I presume if I have an almost empty tank and I ascend or descend while holding a normal breath, that suggests more fine tuning of my weighting?

 

[OTF]

As others have said there is no need to take huge breaths on a safety stop, chill and breath normally. If you want to make your stop extra safe, stay an extra couple minutes.

Free hovering a stop without a visual reference is HARD in the beginning. It's a very good skill to practice. Look at particles in the water to tell if you're moving, don't hyperfocus on your depth gauge or computer. Practice holding position, then practice doing tasks (like a mask flood or DSMB deploy) while holding position and it's amazing how much your buoyancy will improve. Dive a lot! Yes you will get to a point where you don't move at all, even while preforming tasks.

At the end of any given dive you will always be more buoyant than the beginning because you used up a few pounds of compressed air that was weighing you down at the beginning. This is especially noticeable with aluminum tanks. Wetsuits are also more buoyant at shallow depths when they aren't being crushed by the pressure.

Do a weight check. Get in shallow water after a dive with ~500psi left in your tank and few extra weights. Add/subtract weight until you're controlled and neutral with minimal air in the bcd. This will mean you're a little heavy at the beginning of the dive, but that's what the BC is for.

You mentioned deco diving in your first post. It's an excellent goal, you'll get there, but don't rush into it. Just dive a lot and try to improve your skills on every dive. There is PLENTY to see and do at recreational depths, and you'll be a better deco diver if you build up experience and skill before starting a deco class.

 

[lowwall]

In recent dives I've been trying to cut down my weight. I feel like I'm making good progress as I'm a lot more comfortable generally through the dive and I'm putting a lot less air in my BCD. But it's not right yet.

The one area where I still struggle a little is at the safety stop, particularly when it comes to the effect of my breathing on my buoyancy. I've been told that it's important to take deep breaths during the safety stop to aid in eliminating CO2 and offgassing. However I find deep breathing at the safety stop has a huge effect on my buoyancy - it results in me moving between 4 and 6 metres or even as wide as 3 and 7.

My most recent dive where this was an issue I was in a 3mm shorty, 4kg (9lbs) weight on a belt, jacket style BCD and a 12L/200 bar steel tank.

I have ambitions of moving into deco diving in future but wouldn't be comfortable going down that path until I'm better able to hold a stop in shallow depths.

What can I do to help hold the safety stop?

Is your BCD completely empty of air at your safety stop? If so, then being able to ascend and descend just by inhaling and exhaling means your weighting is correct.

If you still have air in your BCD then you are overweight. That air is going to make it more difficult to hold a set depth as the bubble expands and contracts quickly due to the steep pressure gradient at shallow levels.

That aside, just breathe normally at your safety stop. Depth changes aren't instantaneous as the air moves into and out of your lungs, breathing at a normal rate allows the movements to pretty much cancel each other out.

 

[Doc Harry]

Keep working on reducing the amount of weight that you carry. With a 3 ml shorty, you should not have any air in your BC during the last 15-20 minutes of your dive, and you should be running on breath control only. Breathe normally at the safety stop. If you need air in your BC at the safety stop, then you are still over-weighted.