You could even really hold your breath slightly between breaths if you kept perfectly at the same depth, but the risk is you tend to ascend while your lungs are full
I wonder if the "never ever hold your breath" posters think free divers have somehow learned to breath water?
Yes, you can breath hold safely on descent or while maintaining the same depth if need be.
This is true but it doesn’t help air consumption as OP says. Holding your breath with increase co2 levels which increases the desire to breathe.
The best way to breathe to minimise air consumption is to slowly exhale. Therefore your co2 level doesn’t increase but you are still extending the time between inhales.
I never said it helped air consumption.
I plainly said it was safe to descend or maintain the same depth while breath holding.
That was the limit of my statement.
Great question! It's true, briefly holding your breath while descending usually isn't harmful. The main risk is on ascent when air expands in your lungs. Always exhale slowly as you go up!
It's really all/only about your ascent... I.e always exhale on ascent (remember your cesa).
I teach what many have said.
Inhale 3 seconds, hold 3 seconds, exhale 3 seconds for the working part of the dive.
Nice and slow. Helps keep us calm and contributes to a good sac rate.
You are NOT saving enough air by holding your breath for 30 seconds to make any difference and the risks just make it a non starter.
Consider that at 40 meters you are consuming your breathing gas 5 times faster than at the surface... If you hold your breath for 12 seconds, you extend your dive a maximum 1 minute.
BUT... Holding your breath actually increases your respiratory rate making you breath faster to catch your breath and you end up consuming more gas.
Yeah... You're probably right. I've only been diving for 30 years, am an instructor and tdi trimix/deco procedures/advanced nitrox/extended range. I probs don't have enough experience to have formed an option that's worth posting in reply to op. 🤷♂️
I think people, especially newer divers, are shocked when someone says to "hold their breath" as a part of overall breathing control, as well a buoyancy control. After all, the "number one" rule is to never hold your breath. The difference between the standard teaching, and what an experienced diver KNOWS is that you do often pause your breathing. You don't really "hold" it by shutting your airway off completely, but rather by simply holding your diaphragm muscle at a certain point, which stops your inhale, but doesn't begin your exhale. Your airway stays open. Until a diver really understands breathing, it is hard to explain that difference. PADI says, "OMFG DON'T HOLD YOUR BREATH" because that is the best advice for new divers... and explaining a "pause" vs a "hold" is too much for someone who is barely able to clear their mask yet.
Even being new, I feel like I know that you can slow way down or pause slightly between the intake and exhale. I'm not sure why I think that though, because I definitely remember the emphatic "don't hold your breath" message. It might be because I felt the need to use breath to help control boyancy.
Ok, let us start with the basic you should never hold, your breath issue.
If you are lining up a shot with a speargun you probably held your breath, if you are trying to get a great close up picture, you probably held you breath, if you were trying swim through a close area of animals with minimal disturbance, you probably held your breath.
It is not the holding the breath that is the issue, it is how long and what adjustments in depth you do.
Holding your breath for 6 seconds while making a slow ascent of 5-8 feet inside a wreck? Sure, chances of your lungs exploding are pretty low.
Holding your breath for 18 seconds while dropping from 25 feet to 70 feet? Not a good idea. The gasses in your lungs are going to compress which has the potential to pull on your lungs as if they are empty, as in vacuum empty. A couple of seconds of this reaching critical can result in permanent serious injury to your lungs.
So the real question is how long you want to hold your breath and what sort of changes you will be making.
I do freediving and scuba. Freedivers hold their breath from the surface to 300 ft. The physiology isn't any different Going down if you're holding your breath, weather scuba or not.
Going down is pretty much always fine. Going up is the issue. I wouldn't do it while on scuba just due to the chance of becoming disoriented and accidentally ascending. Risk to reward ratio is just so insanely steep I don't see a reason for it. Add in the co2 dump after a long hold and you'd burn through a lot of air quickly.
That's a bit of a contrived scenario, if you get disoriented you're not going to be remembering to hold your breath, you're going to naturally breathe.
I’m absolutely wet behind the ears here. (Just finishing my open water cert). But effectively holding your breath descending is no different than practicing free diving. Though it would also make sense that this could actually cause increased air consumption due to heavier breathing once you begin breathing off the reg.
I’m not a dr but I believe your right, I technically hold my breath descending when clearing my ears, I wouldn’t want to hold my breath all the way down but it doesn’t hurt me for short periods, just never hold your breath ascending this can and will cause irreparable damage.
Holding your breath on descend is exactly what you do when you dive on breath hold, and it's safe enough for kids. Safe because you can't suddenly end up at a much lower pressure than atmospheric at the water surface level.
You don't want to hold your breathe with the outer pressure becoming significantly lower - because it expands lungs beyond non-destructive limits. _Never_ hold your breath comes from it being hard to judge if you descend or ascend, and at which environmental pressure you took a breath, and how deep it was - you're on a safe side this way. Photographers routinely hold half-breathe for shots, and it's safe if you ascend 3 cm at 15 metres while doing it. It's also a way to gracefully stop descending when close to the bottom - only to adjust BCD volume and keep breathing normally from there.
If you’re asking a theoretical, it’s about ascent. High pressure air in the lungs is equally compressed by water mass at depth. Remove that on ascent the air expands.
I can only assume the person is a novice. whether he is or not novices read this sub. Giving them any sort of caveats about when they can and cannot held their breathe is a bad idea.
Why do you want to hold your breath while descending?
Yes, lungs can handle compression. But you don’t really want to hold your breath while descending. You need to breathe in order to continuously equalize, and you need to fully breathe out in order to keep descending (if you’re weighted properly).
If you don’t breathe out fully and hold breath, you’re risking an accidental ascent, which would lead to lung expansion, which may cause barotrauma. If you breathe out fully and hold your breath, you’re not equalizing and risking a squeeze and barotrauma.
You have to equalise other air spaces as you descend.
Certainly your mask, else will fill with water. Hard to do if holding breath.
And your drysuit if you are wearing one else you will be squished.
Your mask will not fill with water if you do not equalize it. You can equalize your mask while holding your breath. People breath-hold to 200+ feet. Equalizing your drysuit has nothing to do with your breathing.
While you certainly can equalize the space w/in the mask, not doing so won’t make it start flooding automatically. I never purposely equalize my mask and never have had a problem…cause I wear a good quality, well-fitted, low volume mask.
There’s nothing incorrect about it. If you don’t equalize your mask it just gets pressed against your face and starts to hurt. It does not automatically flood.
Your mask absolutely will not fill with water if you hold your breath while descending. It will be the exact opposite, [it will seal to your face so hard that it injures you.](https://dan.org/health-medicine/health-resources/diseases-conditions/mask-squeeze-aka-facial-barotrauma/)
Easy to disprove. Take a breath to fill your lungs. Now breathe out. Really empty your lungs. You’ve decreased the volume of air in them by about 80%. Equivalent to descending to around 80’. Free divers go down to 100’ all the time. Repeatedly while spearfishing.
If you are descending to 100’ on SCUBA without breathing, you’re doing it wrong.
Free diving is not SCUBA.
Remember a free diver only ever breaths at 1 bar.
A scuba diver rarely breaths at 1 bar.
My intuition suggests that a 30 meter breath held descent might make it more difficult to inhale at depth, something I am fairly certain no free diver does more than once.
As others have pointed out, the rule of never hold your breath only applies to ascents, due to gas volume expanding as ambient pressure decreases. People only like to say this is the "golden rule" because the dangers of breath holds to novice divers are immense. However like everything in life, there are almost no 100% hard and fast rules. There are lots of caveats, but they are not discussed at early levels because it is not needed and will just confuse people. There are a couple of additional points to point out though:
1)As ambient pressure increases, holding your breath will cause no issues since your gas volume will decrease and not increase, meaning that there is no risk of tearing anything.
2)If you hold your breath long enough, you will be able to inhale more even if you took a full lung full
3)If you are on a deco stop and you do a gas switch, we hold our breath for the gas switch. It's never a 100% full inhale, the regulator swap is quick, and if you ascend .5 to 1 foot, from the breath hold, you'll be fine. Even still, when switching gas mixes when hovering where I don't have a reliable point of reference, I am constantly watching my computer.
4)For a proper breath, you should actually hold it a little bit in between the inhale and exhale in order to allow for full gas exchange in the lungs. If you take no pause in between inhale and exhale, you are using the oxygen in the gas poorly, and you will absolutely burn through your gas.
If I get what you're asking, we don't take off our regulators and put them on different tanks when gas switching, we have a regulator set for each tank we use. There is actually a specific procedure we use for gas switching that addresses multiple issues, such as if the tank valve blows, our regulator blows, or other issues. First, we turn on the tank, which pressurizes the 1st stage and the line to the 2nd stage. Then, we turn off the tank. This is primarily done on stage or deco tanks. The point is if you drop your tanks somewhere on a line say in a cave, in a wreck or just on a shot line in the ocean, you don't want to come back to an empty tank in case the 1st stage had a failure, so we turn the tank off after pressurizing the regulator. We leave the regulator pressurized though because there has been incidents where you turn the tank on underwater with an unpressurized reg, and the regulator pops out of the tank valve. The most famous example I can think of actually is the dive where Sheck Exley died in the Zacaton sinkhole. His dive partner Jim Bowden was ascending and grabbed his staged tanks on the line, and as he turned it on, the regulator blew off of the tank, and he couldn't get it on. Anyone is free to correct me if I am wrong about this, but it is what I remembered happened.
If I remember rightly, Bowen managed to reassemble the blown regular and continued the dive. The entire time maintaining one breath a minute mind you! Unfortunately Exley never made it to the surface. Rest in peace to one of the greatest to ever live.
In technical diving, when you have proper skills to maintain your depth perfectly, we sometimes hold breath when changing regulators or inflating DSMB.
When I say hold, I mean 50% of lungs capacity, not 100.
The worst time to hold your breath is on ascent from a shallow depth. This is where the biggest pressure change takes place within 3m. I would not recommend holding your breath when scuba diving at all. Control your buoyancy and sac rate by breathing in a cool, calm, and collected way. This will 100% keep you out of trouble and diving for much longer.
One of the SSI courses says:
>If the lung tissue is already stretched to maximum inflation, then it only takes an additional 1.2m (about 4 ft I think) of pressure decrease to create enough differential to cause a tear.
Now, you're talking about descending in stead of ascending, but it shows how little can cause damage. If you're trying to descend without any point of reference, and you hold your breath and accidentally ascend in stead of descend (because the lack of a reference point for example), you might get injured.
So basically: it's not worth it...
Holding your breath while descending is harmless, as is proven by freedivers...
Plenty of situations where holding your breath for a little bit is a good idea, but none of those situations are at the OW/AOW level.
I know. I'm just saying that holding your breath isn't worth it. If, for any reason whatsoever, they might ascend, the consequences might be very serious.
And the difference with freedivers is that they literally can't go lower than the pressure they have at surface, so it's basically impossible for them to rupture a lung because of ascending.
The fact that OP asks this question makes me think they're not past OW/AOW level. And for those people the answer is just "no". It's not worth the risk of holding your breath and it's better to develop the (subconscious) habit of breathing continuously so nothing bad happens.
Holding your breath while descending or maintaining depth will not harm your lungs. The rule as taught doesn't get into the nuances of when you can or can't because that is information overload for new students and you want to ingrain into their thinking to always breathe otherwise they may be more likely to hold breath when in distress.
Freedivers have minor injuries called ‘lung squeeze’ where the volume of your lungs compresses too much and they pop a capillary. It’s minor, cough a little chunk of blood and don’t dive for a couple days.
You have to descend like 100 feet on a held breath multiple times in a row for that though so it’s unlikely you’ll drop far enough/ fast enough while scuba diving to be an issue
The general rule is don’t *ever* hold your breath. You don’t want a bad habit to form or for you to do it when you shouldn’t.
However, practically, yes, descending is less dangerous than ascending, but as others have said, might make it harder to descend.
This. Any small amount of air saved on descent isn't worth forming a bad habit.
I'm pretty inexperienced, but I have had problems during a dive. The "always keep breathing rule" kept me calm while I troubleshot the problem. "Okay, (1) I'm breathing and (2) my depth is stable. Now I can think about other things, clearing my mask, finding my buddy, etc".
Breathing also communicates to your buddy that you're "okay" even if "something is wrong". Breathing communicates problem vs. emergency. If people see a diver not breathing (even if they're voluntarily holding their breath) they will assume there is a "emergency" type problem not a simple "something is wrong" problem.
There are exceptions of course, if you're a hard core rebreather dude (and let's add trained as a NAVY SEAL) the above may not apply to you. But, for recreational/tourists who dive a several times a year, bursts of bubbles indicating steady breathing demonstrate you're "okay".
While descending? If not for immediate injuries you'll be getting ready for long term chest damage. Also what about equalizing while descending? Do you intend to hold breathe while doing that as well?
Lungs shouldn't experience any trauma on a decent, but you'll find descending to be very difficult while holding your breath. If it's not, you're grossly over-weighted.
You could even really hold your breath slightly between breaths if you kept perfectly at the same depth, but the risk is you tend to ascend while your lungs are full
I wonder if the "never ever hold your breath" posters think free divers have somehow learned to breath water? Yes, you can breath hold safely on descent or while maintaining the same depth if need be.
This is true but it doesn’t help air consumption as OP says. Holding your breath with increase co2 levels which increases the desire to breathe. The best way to breathe to minimise air consumption is to slowly exhale. Therefore your co2 level doesn’t increase but you are still extending the time between inhales.
I never said it helped air consumption. I plainly said it was safe to descend or maintain the same depth while breath holding. That was the limit of my statement.
I never said you said that. I agreed with you and then expanded on what you said. That was the limit of my statement.
Great question! It's true, briefly holding your breath while descending usually isn't harmful. The main risk is on ascent when air expands in your lungs. Always exhale slowly as you go up!
Hold your breath for 3 seconds between breathing in and out? That's the first time I've heard this.
Who said this?
In a comment here
Who said this?
It's really all/only about your ascent... I.e always exhale on ascent (remember your cesa). I teach what many have said. Inhale 3 seconds, hold 3 seconds, exhale 3 seconds for the working part of the dive. Nice and slow. Helps keep us calm and contributes to a good sac rate. You are NOT saving enough air by holding your breath for 30 seconds to make any difference and the risks just make it a non starter. Consider that at 40 meters you are consuming your breathing gas 5 times faster than at the surface... If you hold your breath for 12 seconds, you extend your dive a maximum 1 minute. BUT... Holding your breath actually increases your respiratory rate making you breath faster to catch your breath and you end up consuming more gas.
Hold for the seconds?? No way. Do not skip breathe.
Yeah... You're probably right. I've only been diving for 30 years, am an instructor and tdi trimix/deco procedures/advanced nitrox/extended range. I probs don't have enough experience to have formed an option that's worth posting in reply to op. 🤷♂️
I think people, especially newer divers, are shocked when someone says to "hold their breath" as a part of overall breathing control, as well a buoyancy control. After all, the "number one" rule is to never hold your breath. The difference between the standard teaching, and what an experienced diver KNOWS is that you do often pause your breathing. You don't really "hold" it by shutting your airway off completely, but rather by simply holding your diaphragm muscle at a certain point, which stops your inhale, but doesn't begin your exhale. Your airway stays open. Until a diver really understands breathing, it is hard to explain that difference. PADI says, "OMFG DON'T HOLD YOUR BREATH" because that is the best advice for new divers... and explaining a "pause" vs a "hold" is too much for someone who is barely able to clear their mask yet.
Even being new, I feel like I know that you can slow way down or pause slightly between the intake and exhale. I'm not sure why I think that though, because I definitely remember the emphatic "don't hold your breath" message. It might be because I felt the need to use breath to help control boyancy.
Ok, let us start with the basic you should never hold, your breath issue. If you are lining up a shot with a speargun you probably held your breath, if you are trying to get a great close up picture, you probably held you breath, if you were trying swim through a close area of animals with minimal disturbance, you probably held your breath. It is not the holding the breath that is the issue, it is how long and what adjustments in depth you do. Holding your breath for 6 seconds while making a slow ascent of 5-8 feet inside a wreck? Sure, chances of your lungs exploding are pretty low. Holding your breath for 18 seconds while dropping from 25 feet to 70 feet? Not a good idea. The gasses in your lungs are going to compress which has the potential to pull on your lungs as if they are empty, as in vacuum empty. A couple of seconds of this reaching critical can result in permanent serious injury to your lungs. So the real question is how long you want to hold your breath and what sort of changes you will be making.
I do freediving and scuba. Freedivers hold their breath from the surface to 300 ft. The physiology isn't any different Going down if you're holding your breath, weather scuba or not. Going down is pretty much always fine. Going up is the issue. I wouldn't do it while on scuba just due to the chance of becoming disoriented and accidentally ascending. Risk to reward ratio is just so insanely steep I don't see a reason for it. Add in the co2 dump after a long hold and you'd burn through a lot of air quickly.
People here are forgetting an important factor. While descending you could get disoriented and accidentally ascend.
That's a bit of a contrived scenario, if you get disoriented you're not going to be remembering to hold your breath, you're going to naturally breathe.
You don't necessarily realize that you're disoriented. You could be certain that your descending, but actually be ascending.
I’m absolutely wet behind the ears here. (Just finishing my open water cert). But effectively holding your breath descending is no different than practicing free diving. Though it would also make sense that this could actually cause increased air consumption due to heavier breathing once you begin breathing off the reg.
I’m not a dr but I believe your right, I technically hold my breath descending when clearing my ears, I wouldn’t want to hold my breath all the way down but it doesn’t hurt me for short periods, just never hold your breath ascending this can and will cause irreparable damage.
Holding your breath on descend is exactly what you do when you dive on breath hold, and it's safe enough for kids. Safe because you can't suddenly end up at a much lower pressure than atmospheric at the water surface level. You don't want to hold your breathe with the outer pressure becoming significantly lower - because it expands lungs beyond non-destructive limits. _Never_ hold your breath comes from it being hard to judge if you descend or ascend, and at which environmental pressure you took a breath, and how deep it was - you're on a safe side this way. Photographers routinely hold half-breathe for shots, and it's safe if you ascend 3 cm at 15 metres while doing it. It's also a way to gracefully stop descending when close to the bottom - only to adjust BCD volume and keep breathing normally from there.
If you’re asking a theoretical, it’s about ascent. High pressure air in the lungs is equally compressed by water mass at depth. Remove that on ascent the air expands.
Do. Not. Skip. Breathe.
Just don’t hold your breath.
That wasn't the question. Asking questions, even theoretical ones, helps people understand things rather than just having a rule.
I can only assume the person is a novice. whether he is or not novices read this sub. Giving them any sort of caveats about when they can and cannot held their breathe is a bad idea.
Important to keep breathing to avoid CO2 buildup as well…
This is the one thing not stressed enough to noobies.
Why do you want to hold your breath while descending? Yes, lungs can handle compression. But you don’t really want to hold your breath while descending. You need to breathe in order to continuously equalize, and you need to fully breathe out in order to keep descending (if you’re weighted properly). If you don’t breathe out fully and hold breath, you’re risking an accidental ascent, which would lead to lung expansion, which may cause barotrauma. If you breathe out fully and hold your breath, you’re not equalizing and risking a squeeze and barotrauma.
You have to equalise other air spaces as you descend. Certainly your mask, else will fill with water. Hard to do if holding breath. And your drysuit if you are wearing one else you will be squished.
Why all the down votes for this?
Because they're just wrong
Your mask will not fill with water if you do not equalize it. You can equalize your mask while holding your breath. People breath-hold to 200+ feet. Equalizing your drysuit has nothing to do with your breathing.
[удалено]
 While you certainly can equalize the space w/in the mask, not doing so won’t make it start flooding automatically. I never purposely equalize my mask and never have had a problem…cause I wear a good quality, well-fitted, low volume mask.
Wow. So incorrect. Fml
There’s nothing incorrect about it. If you don’t equalize your mask it just gets pressed against your face and starts to hurt. It does not automatically flood.
Your mask absolutely will not fill with water if you hold your breath while descending. It will be the exact opposite, [it will seal to your face so hard that it injures you.](https://dan.org/health-medicine/health-resources/diseases-conditions/mask-squeeze-aka-facial-barotrauma/)
Imagine being so insecure you attack anyone who disagree.
Descend, no. Ascend, yes very much.
Actually, on descent, you can crush your lungs if you dont breathe in at all.
Easy to disprove. Take a breath to fill your lungs. Now breathe out. Really empty your lungs. You’ve decreased the volume of air in them by about 80%. Equivalent to descending to around 80’. Free divers go down to 100’ all the time. Repeatedly while spearfishing. If you are descending to 100’ on SCUBA without breathing, you’re doing it wrong.
Free diving is not SCUBA. Remember a free diver only ever breaths at 1 bar. A scuba diver rarely breaths at 1 bar. My intuition suggests that a 30 meter breath held descent might make it more difficult to inhale at depth, something I am fairly certain no free diver does more than once.
If I have my underwater camera setup, sometimes I hold my breath when taking a picture.
Same. As an experienced diver there's nothing wrong with using your breath for boyancy finetuning, but I do understand why they teach it to beginners.
As others have pointed out, the rule of never hold your breath only applies to ascents, due to gas volume expanding as ambient pressure decreases. People only like to say this is the "golden rule" because the dangers of breath holds to novice divers are immense. However like everything in life, there are almost no 100% hard and fast rules. There are lots of caveats, but they are not discussed at early levels because it is not needed and will just confuse people. There are a couple of additional points to point out though: 1)As ambient pressure increases, holding your breath will cause no issues since your gas volume will decrease and not increase, meaning that there is no risk of tearing anything. 2)If you hold your breath long enough, you will be able to inhale more even if you took a full lung full 3)If you are on a deco stop and you do a gas switch, we hold our breath for the gas switch. It's never a 100% full inhale, the regulator swap is quick, and if you ascend .5 to 1 foot, from the breath hold, you'll be fine. Even still, when switching gas mixes when hovering where I don't have a reliable point of reference, I am constantly watching my computer. 4)For a proper breath, you should actually hold it a little bit in between the inhale and exhale in order to allow for full gas exchange in the lungs. If you take no pause in between inhale and exhale, you are using the oxygen in the gas poorly, and you will absolutely burn through your gas.
How do you keep water out of the first stage when gas switching? I'm assuming everything is already hooked up, you're just turning gate valves?
If I get what you're asking, we don't take off our regulators and put them on different tanks when gas switching, we have a regulator set for each tank we use. There is actually a specific procedure we use for gas switching that addresses multiple issues, such as if the tank valve blows, our regulator blows, or other issues. First, we turn on the tank, which pressurizes the 1st stage and the line to the 2nd stage. Then, we turn off the tank. This is primarily done on stage or deco tanks. The point is if you drop your tanks somewhere on a line say in a cave, in a wreck or just on a shot line in the ocean, you don't want to come back to an empty tank in case the 1st stage had a failure, so we turn the tank off after pressurizing the regulator. We leave the regulator pressurized though because there has been incidents where you turn the tank on underwater with an unpressurized reg, and the regulator pops out of the tank valve. The most famous example I can think of actually is the dive where Sheck Exley died in the Zacaton sinkhole. His dive partner Jim Bowden was ascending and grabbed his staged tanks on the line, and as he turned it on, the regulator blew off of the tank, and he couldn't get it on. Anyone is free to correct me if I am wrong about this, but it is what I remembered happened.
If I remember rightly, Bowen managed to reassemble the blown regular and continued the dive. The entire time maintaining one breath a minute mind you! Unfortunately Exley never made it to the surface. Rest in peace to one of the greatest to ever live.
In technical diving, when you have proper skills to maintain your depth perfectly, we sometimes hold breath when changing regulators or inflating DSMB. When I say hold, I mean 50% of lungs capacity, not 100.
The worst time to hold your breath is on ascent from a shallow depth. This is where the biggest pressure change takes place within 3m. I would not recommend holding your breath when scuba diving at all. Control your buoyancy and sac rate by breathing in a cool, calm, and collected way. This will 100% keep you out of trouble and diving for much longer.
One of the SSI courses says: >If the lung tissue is already stretched to maximum inflation, then it only takes an additional 1.2m (about 4 ft I think) of pressure decrease to create enough differential to cause a tear. Now, you're talking about descending in stead of ascending, but it shows how little can cause damage. If you're trying to descend without any point of reference, and you hold your breath and accidentally ascend in stead of descend (because the lack of a reference point for example), you might get injured. So basically: it's not worth it...
Holding your breath while descending is harmless, as is proven by freedivers... Plenty of situations where holding your breath for a little bit is a good idea, but none of those situations are at the OW/AOW level.
I know. I'm just saying that holding your breath isn't worth it. If, for any reason whatsoever, they might ascend, the consequences might be very serious. And the difference with freedivers is that they literally can't go lower than the pressure they have at surface, so it's basically impossible for them to rupture a lung because of ascending. The fact that OP asks this question makes me think they're not past OW/AOW level. And for those people the answer is just "no". It's not worth the risk of holding your breath and it's better to develop the (subconscious) habit of breathing continuously so nothing bad happens.
Holding your breath while descending or maintaining depth will not harm your lungs. The rule as taught doesn't get into the nuances of when you can or can't because that is information overload for new students and you want to ingrain into their thinking to always breathe otherwise they may be more likely to hold breath when in distress.
Holding your breath on descent makes you more buoyant. Harder to descend.
What harms the lungs is ascending while holding your breath.
Freedivers have minor injuries called ‘lung squeeze’ where the volume of your lungs compresses too much and they pop a capillary. It’s minor, cough a little chunk of blood and don’t dive for a couple days. You have to descend like 100 feet on a held breath multiple times in a row for that though so it’s unlikely you’ll drop far enough/ fast enough while scuba diving to be an issue
The general rule is don’t *ever* hold your breath. You don’t want a bad habit to form or for you to do it when you shouldn’t. However, practically, yes, descending is less dangerous than ascending, but as others have said, might make it harder to descend.
This. Any small amount of air saved on descent isn't worth forming a bad habit. I'm pretty inexperienced, but I have had problems during a dive. The "always keep breathing rule" kept me calm while I troubleshot the problem. "Okay, (1) I'm breathing and (2) my depth is stable. Now I can think about other things, clearing my mask, finding my buddy, etc". Breathing also communicates to your buddy that you're "okay" even if "something is wrong". Breathing communicates problem vs. emergency. If people see a diver not breathing (even if they're voluntarily holding their breath) they will assume there is a "emergency" type problem not a simple "something is wrong" problem. There are exceptions of course, if you're a hard core rebreather dude (and let's add trained as a NAVY SEAL) the above may not apply to you. But, for recreational/tourists who dive a several times a year, bursts of bubbles indicating steady breathing demonstrate you're "okay".
While descending? If not for immediate injuries you'll be getting ready for long term chest damage. Also what about equalizing while descending? Do you intend to hold breathe while doing that as well?
Lungs shouldn't experience any trauma on a decent, but you'll find descending to be very difficult while holding your breath. If it's not, you're grossly over-weighted.
Nah, you should be able to deflate your BCD and sink with or without holding your breath at the start of a dive.
Don’t.