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Old 21-03-2007, 11:14   #16
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Well you did say this -

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Originally Posted by hellosailor
they could have .............. made a controlled ascent holding their breath.
I was just pointing out that holding your breath during an ascent is not a good idea.
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Old 21-03-2007, 12:07   #17
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For non-divers .....FYI

Making an assent from 135' (4 atmo's) on just the air in your lungs would not be advisable unless one had no other choice. It's a guaranteed trip to a decompression chamber.

The highly compressed air in your body needs to extract itself as one ascends. These bubble's are what causes the bends or even death if not treated quickly. It's like taking a needle full air and injecting it into your joints.

Diving is the equivalent to going into space but the opposite. In space there is the lack of pressure.

That would be like ascending from 135' after being there for several hours. Underwater the longer you are down, at a specific depth, the more saturated the body becomes. That's why there are dive charts for different depths and times so one can decompress naturally on the way up.

Every 33 feet is equivalent to 1 atmosphere (14.7 psi) and that doubles at 66' and triples at 99' and so on. So an air bubble at 134' would expand 4 times its size back on the surface. That would rupture one's lungs if they did not exhale evenly on the assent.

Then there is the problem with nitro-mix air. Any dive below 80' for long periods, one should be using mixed air and that changes with depth. Too much oxygen can burn the lungs...................................._/)
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Old 21-03-2007, 13:14   #18
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It's unfortunate that these deaths occur when it is a diving fact that it is human error or bad judgement that causes most of them. It is still safer than automobile transportation but my life insurance company charges me alot more for coverage than non divers.

Due nto a shoulder joint problem and operation, I have been unable to dive for about 3 years and miss it especially when I go south for a vacation. Hopefully I will be able to go soon again but to be safe, I will take refresher courses and do shallow dives at first. On many dives - especially group dives, there is alot of anticipation and I have seen experienced divers miss or skip some important pre-dive checks in their hurry to get in the water. It is damn difficult for the dive master to keep tabs on 30 or so divers when they all want to get wet as soon as possible Maybe these unfortunate 3 were over excited to get into the wreck and did not follow proper safety procedures. It is unfortunate that the lessons are re-inforced after a tragedy like this and not before the dive.
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Old 21-03-2007, 21:15   #19
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Del, the difference between space and the earth's atmosphere isnt like 135 feet of water - it's only 1 atmosphere, so 33 feet. (It's a bit simpler in metric - it's near enough to 10 metres.)
Diving exposes us to pressures far in excess of what we normally have to cope with, which is why we need to follow all the precautions.
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Old 21-03-2007, 21:34   #20
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So, what happens to the human body in zero pressure?
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Old 21-03-2007, 21:43   #21
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Del-
"what happens...in zero pressure"
Well, in 1950's scifi you'd explode immediately. By the 1970's they realized this wasn't quite right, and the theory now is that you could, in fact, EXHALE to prevent your lungs from exploding and then transit a total vacuum and live to tell the tale. Not totally unharmed--but alive. It would be rapid decompression, but not necessarily explosive.

If you want odd pressure effects, there's always "tooth squeeze" when an air pocket in the root of a tooth or a cavity refuses to play nice when you are changing pressures. That can ruin a dive real fast!

"Making an assent from 135' (4 atmo's) on just the air in your lungs would not be advisable unless one had no other choice. It's a guaranteed trip to a decompression chamber. "
Uh, no. Well, yes on the first part, no on the second. Depending on how good your body sense and muscle control is, it may be no problem at all.

Now, if you HOLD YOUR BREATHE you will surely blow a lung. In point of fact a diver, even twenty feet under, can blow a lung by simply rotating from the horizontal swimming position to a vertical "standing" position, if you rotate on the ankles instead of rotating about your lungs.

It's just a 4 foot shift in the depth the lungs are at--but that's enough to cause a lung to rupture if your lungs are full and you are holding your breath.

On the other hand, divers are supposed to be taught to exhale continuously during free ascents. That doesn't mean "blow" it just means relaxing the muscles enough to let the air escape as it expands. It is a subtle amount of muscle control that "surface dwellers" never use, the same way that kids have to be taught how to hold their breath and contract muscles if they are going to swim without water going down their noses. I had problems learning that. But, I'm one of the folks who can clear their eustachion tubes with voluntary muscle control to equalize--and some folks can't do that either.

A direct ascent from 135' at the maximum suggested rate of 60fpm would imply a trip over two minutes long, so I think it would be possible--if damn uncomfortable--to do that, especially with air expanding in your lungs so you weren't "just" trying to hold your breath. Remember Johnny Weissmuller and others have done something like 8 minutes holding their breath underwater, a lot depends on the condition you are in and the willpower under crisis.

Benny-
If everyone started themselves out gently, the way you are planning, there would be fewer accidents. Our "Frogfather" was not into macho diving at all, but he trained us that we were, always, our own divemasters. Always, the only ones responsible for ourselves and always, the only ones who would be to blame if we screwed up. Divemaster? Yeah, nice, and I do appreciate an extra hand getting back on the boat or a briefing on what's below. But in terms of who plans and controls my dive?
"Hi Divemaster! Bye Divemaster!" It's not like grade school where they ask the kids to all hold hands when they are walking down the block.<G> Drop a dozen guys on a football field when the visibility is only 20', and let's face it, you're on your own. Poseidon and Darwin obviously have conspired to offer a package deal on culling. I wear a steel MedicAlert tag, knowing full well that one day it may be a body tag. If I screw up, I know what the price may be.

There was some Dive Nooze story out of Hawaii last year, about a woman who was somehow killed when her BC supposedly failed in about 35' of water so she couldn't surface during a "resort" dive or something like that. Her estate was of course suing the BC maker, the divemaster, everyone they could think of. I don't know...I was taught that I have my BC, but if I'm trimmed right I can still SWIM up, and if I don't want to swim I can ditch my gear, or ditch my weights, and if I can't ditch 'em I can cut 'em free. The fact that she was supposed to be familiar with at least three backups for getting to the surface and somehow, she didn't try any of them, somehow didn't matter to the folks doing the suing, they just want to blame everyone else. Dunno, I wasn't there, maybe it was someone else's fault. Like whoever certified her, without panic screening.
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Old 22-03-2007, 08:26   #22
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"Resort Dives" always concerned me... arrive at 8am and down to 60ft by 2pm when you supposedly will then know how to dive due to their instruction.

Let's see... fast, cheap or good... pick one of the three...
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Old 22-03-2007, 09:44   #23
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Hellosailor - I completely agree that we are our own dive masters and they don't serve much more purpose than the legal requirements for the dive charter company - I was making a point - maybe not so clearly that the scope of the ability of the 'divemaster' on a group dive is limited due to the size of the group and there are all levels of divers in that group from novice to advanced. I have spent my entire dive time on more than one occasion helping inexperienced divers just maintain buoyancy or clear their ears or numerous other things - these people are so eager to get in the water but they know little about the basics or safety - the question is - how the hell did they get certified in the first place? Unfortunately, some of them might end up being the next dive tragedy - even if they progress to advanced and penetration diving level as some lack the basic safety first and check everything at least twice credo that good divers adhere to.
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Old 22-03-2007, 11:38   #24
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Quote:
Originally Posted by delmarrey
"Making an assent from 135' (4 atmo's) on just the air in your lungs would not be advisable unless one had no other choice. It's a guaranteed trip to a decompression chamber. "
Quote:
Originally Posted by hellosailor
Uh, no. Well, yes on the first part, no on the second. Depending on how good your body sense and muscle control is, it may be no problem at all.

Now, if you HOLD YOUR BREATHE you will surely blow a lung. In point of fact a diver, even twenty feet under, can blow a lung by simply rotating from the horizontal swimming position to a vertical "standing" position, if you rotate on the ankles instead of rotating about your lungs.
Actually I was refering to the saturation of the body after a lenghtly dive and not the lungs.

I've done plenty of free dives to 30' on one breath of air, (Molokini Is. is my favorite) and one can come back up on that same breath. Although, I don't , the ascent is slower by exhaling.
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Old 22-03-2007, 11:58   #25
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Ah, saturation. That of course depends on the time spent at depth, and the profile you choose to apply. There are multiple ways to figure time versus depth or to use computers with tissue emulators in them, and none is "right or wrong" just a question that some reflect the actual effects in the body better than others, so some have no safety margin padded in.

With free diving of course there's no way to blow out your lungs since they are "dancing with what they came with" and the air can only expand them out to normal again. I wouldn't exhale then either, it would give me less bouyancy and as you note, make the ascent more work.

That's something else the "causal observer" wouldn't realize about SCUBA. You need to constantly trim your bouyancy, either with a BC or with lung capacity, in order to hold your depth or your rate of depth change. Like sailing, it looks easy from the outside.<G>
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Old 22-03-2007, 14:56   #26
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Quote:
Originally Posted by delmarrey
So, what happens to the human body in zero pressure?
I wonder about that too. I think everybody would have seen the science experiment where a flask of water is attached to a vacuum pump, and as the pressure approaches zero, the water is boiling inside the flask, and ICE is forming on the outside. (The boiling point of water gets lower as pressure does) You would imagine that at zero pressure the dissolved gases in our blood would quickly come out of solution, then the water would start to boil (since our body temp is high 30's)........ it doesn't sound too pleasant or survivable. I guess it depends on how effective our body is as a pressure vessel.
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Old 22-03-2007, 18:57   #27
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The other wreck in Subic Bay is the New York, formerly the Rochester. It was an outdated old ship sitting in Manila on Dec 7 but the guns were big and nobody wanted the Japanese to use them. The ship was towed to Subic, filled with mines and sank. The Japanese showed up around the 21st of the month I believe.

Many divers entered the wreck collecting brass artifacts. On one bad day a good friend became entangled in lines that were left behind from many many previous penetration dives. While his buddy was looking elsewhere my friend drowned. He was outside of the wreck but so entangled he couldn't get free.

There is a lot more to the story but thats the short of it.
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Old 22-03-2007, 19:47   #28
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Quote:
Originally Posted by delmarrey
So, what happens to the human body in zero pressure?
Actually, nothing very dramatic. Your body structure is strong enough to hold together, so if you do not try to hold your breath, the only problem caused by the vacuum is that you have nothing to breathe. Assuming you are otherwise well protected, the lack of oxygen is what kills you.

Your circulatory system is already a closed pressurized system. Your blood does not boil, but dissolved gasses may escape through your lungs, much like alcohol escapes and is exhaled to be detected on your breath.

So, if a crazy computer takes over your spaceship, it really does work to hyperventilate, blow the hatch on your EVA pod, jump into the open airlock, then slam the door and repressurize.

There is an interesting paper on the topic at EBULLISM AT 1 MILLION FEET that discusses explosive decompression in some detail. It describes some serious effects that I haven't seen discussed before, but it's still nothing like the "blow up like a bomb" event sometimes shown in the movies.
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Old 22-03-2007, 20:03   #29
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Breath "holding"

Actually you CAN hold your breath safely when diving. The REAL reason that divers are taught to always be either inhaling or exhaling is so that the epiglottis (I think that is the correct anatomic part) will always therefore be open. One can train oneself to always keep open the glottis just like one can train oneself to keep open the eustachian tubes from your throat to the eardrums so that one does not have to keep holding the nose and blowing into it to equalize pressure intermittently instead of continuously.

When keeping open the airway while ascending the minimum amount of air necessary to keep a constant lung volume will always escape and no more. This creates essentially a zero pressure differential between the air inside the lungs and surrounding water.

I also use this method when maintaining my depth while a surge pressure is building and dropping with waves high overhead and use my diaphragm to vary my lung volume so as to not have to continuously add to and drain air in the BC. You then "breathe" at this diaphragm "setting" that changes with the surge pressure. Does this make sense?
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Old 23-03-2007, 03:25   #30
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Actually, nothing very dramatic. Your body structure is strong enough to hold together, so if you do not try to hold your breath, the only problem caused by the vacuum is that you have nothing to breathe. Assuming you are otherwise well protected, the lack of oxygen is what kills you.

Your circulatory system is already a closed pressurized system. Your blood does not boil, but dissolved gasses may escape through your lungs, much like alcohol escapes and is exhaled to be detected on your breath.

There is an interesting paper on the topic at EBULLISM AT 1 MILLION FEET that discusses explosive decompression in some detail. It describes some serious effects that I haven't seen discussed before, but it's still nothing like the "blow up like a bomb" event sometimes shown in the movies.
Have you READ that article? It certainly seems that one would be extremely unlikely to survive an explosive decompression to ZERO pressure without some kind of pressure suit.

"Hypobaria (low pressure) has life-threatening effects primarily on 3 systems: the Lungs, the Heart and the Brain. We examine each of these in turn.
Pulmonary Damage to the lungs in rapid or explosive decompression occurs primarily due to pulmonary overpressure, the tremendous pressure differential inside versus outside the lungs. 80 mm Hg is enough to cause pulmonary tears and alveolar rupture (8); pulmonary hemorrhaging, ranging from petechiae to free blood (depending on the magnitude and rate of decompression) is also seen (9). Emphysematous changes are seen especially in the upper lungs, while atelectasis and edema predominate in the lower lungs (10). When we get to the patient, the lungs will be a bloody, ruptured mess.
Cardiovascular Myocardial damage associated with ebullism is caused by stretching of the myocardium and anoxia (11). Heart rate rises the first 20 seconds (12), then drops to 40% of baseline at sixty seconds (12). By 2 minutes the arterial pressure wave is lost (13), but the cardiac contractility is maintained at least 5-7 minutes (14). Apneic animals resumed spontaneous respirations within 30 seconds of recompression as long as the heart continued to beat, but could not be resuscitated once asystole occurred (15). If our patient has a pulse, we might get him back.
Central Nervous System In rapid or explosive decompression above 60,000 feet, CNS damage is due to decreased cerebral blood flow and global cerebral anoxia (16). Little evidence of herniation is noted (16), though some damage to cerebral white matter and myelinated spinal cord is seen (13). Cases of accidental rapid and explosive decompression to date have not shown any lasting neurological damage (17, 18), though this includes only 2 cases. Our astronaut-patient may be rehabilitatable.
Though these are the most life-threatening changes seen in ebullism, subcutaneous swelling is also seen, due to creation of water vapor under the skin (19). This can rapidly distend the body to twice its normal volume (20). Our patient will look no better than he feels, though this means little in terms of survival."
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