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Old 19-09-2010, 22:12   #46
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Originally Posted by troymclure View Post
Note: I am not an experienced freediver/snorkeller but i've been doing alot of reading up on it lately as i'm just getting into it all.

Seen a few people recommended purging the snorkel when you surface. Just thought i'd point out that this is only reccommended after taking breathes of air on the surface without the snorkel first.

SWB (shallow water blackout) is the cause of many snorkelling (and specifically freediving) deaths every year. I've read a post suggesting that purging a snorkel when surfacing increases risk of SWB.
What you have read may or may not be correct. It sounds more to me like basic drowning? Most experts will argue the primary cause of what is technically known as “shallow water black-out” is a rush of oxygen to the brain nearing the surface due the effects of Boyle’s law? This will occur just before the victim reaches the surface and has no relation to them attempting to take a breath at the surface.

Free-diving/spear fishing I use a very basic snorkel without a purging valve and actually let it fill with water as I dive. A compellingly proven fact is that bubbles scare fish!

For the average recreational snorkeler who is going to spend most of their time swimming along the surface admiring the bottom the reputable brand valved models are perfectly safe and extremely convenient. U S Diver’s are a well-known quality brand.
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Old 19-09-2010, 23:23   #47
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Howdy surfer shane, actually kinda interested in finding out why it's not reccommended (apparently) too purge snorkels upon surfacing, will see if i can find the post again but in meantime, what do you think of the theory that it simply adds to physical exertion upon surfacing?

ie found this site Freediving safety

Which says that a divers lowest amount of O2 level is 20 seconds after surfacing.

A deep and foreceful exhallation that is done when purging a snorkel may use up a possibly critical amount of oxygen? It would also remove a large amountof air from the lungs which means less oxygen to go back into blood, ie might be better better to have some air in lungs for first 20 seconds after surfacing. Or at least thats what i'm theoriziing, again it's not something which is probably likely too affect someone if they're just snorkelling diving a few metres (ie me at the moment) but then again may as well do everything we can too minimize risks etc.
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Old 20-09-2010, 00:01   #48
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OK update my bad, got SWB and DWB (deep water blackout mixed up).

Think what i'm talking about is DWB not SWB, which is more related to diving 10m and lower. Though there seems to be a bit of crossover between the two and alot of safety stuff applies to both.
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Old 20-09-2010, 01:01   #49
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I have never regretted the investment I made in my mask. excellent fit and split lenses to accommodate my prescription. Made a HUGE difference the first time I used them. You go to a lot of time trouble and expense to actually get to the water. It is way worth it to be able to see everything once you get there!
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Old 20-09-2010, 01:14   #50
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Originally Posted by troymclure View Post
OK update my bad, got SWB and DWB (deep water blackout mixed up).

Think what i'm talking about is DWB not SWB, which is more related to diving 10m and lower. Though there seems to be a bit of crossover between the two and alot of safety stuff applies to both.
I suppose the DWB thing is more about knowing your limits? The snorkel is not going to make a lot of difference as I have discovered in these sorts of situations you often just ditch it and breathe directly from the mouth once clear of the surface. Often this situation is induced by sheer panic and the whole underlying idea of free-diving should be to avoid this by remaining calm and relaxed.

Anxiety and doing other stuff like hyperventilating before a dive, kicking like a maniac to reach the depth or using too heavy a weight belt are sure ways of heading for drowning. Feel free to relax and glide to the bottom enjoying the experience; it is amazing how long you can be down there when you are not really trying. If you are really interested in this stuff look up people like Terry Maas’s books and articles on Amazon and the web.

As far as the snorkel goes, the good thing about the valved ones is that you are much less likely to take water into your lungs due the chop on the surface or from simply not having purged it thoroughly. They are generally also much easier to purge. For the average snorkeller this can make the experience much more enjoyable.

Reminds me too I have been slack on the diving of late and need to get the flippers and mask back on; maybe I have been too busy enjoying sailing?
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Old 20-09-2010, 01:39   #51
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I have never regretted the investment I made in my mask. excellent fit and split lenses to accommodate my prescription. Made a HUGE difference the first time I used them. You go to a lot of time trouble and expense to actually get to the water. It is way worth it to be able to see everything once you get there!
Agree and also wondering how long I have before I need those prescription lenses!

The biggest “secret” I have found is to find a mask that will naturally stick to your face when you lightly press it on WITHOUT either inhaling or using the head strap. This pretty much guarantees the shape of the mask naturally fits your face and it won’t leak like a sieve once you are in the water. I could keep raving on about stuff like how I actually prefer my single lens black silicone masks for vision spear fishing, but as long as you use this method to get a good fit you are going to have fun.
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Old 20-09-2010, 02:30   #52
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Deep water blackout...

There is an interesting discussion of Deep water blackout in Wikipedia.

There does appear to be a need to be very conservative with regard to depth dived and time spent underwater. Hyperventilating before diving could be fatal.

For most snorkelers sunburn could be the biggest danger, followed by such hazards as stonefish stings and sea urchin spines.

I once had a small sea snake nibbling round my belly. Fortunately it was small and their fangs are at the back of their mouths.
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Old 20-09-2010, 04:33   #53
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BEFORE DIVING ONE TAKES A DEEP BREATH FILLING ONES LUNGS with air then dive beneath the surface (time and depth dependant on ability etc).

DO NOT WORRY ABOUT FORCEFUL EXHALLATION. THIS IS NOT CORRECT.

When you surface you need to expell air as rapidly as possible in order to take a breath and in doing so it simply expells the small amount of water in your snorkle vs your lung exhallation volume (say 3 litres). A rapid exhallation is not an issue.

SWB occurs when returning to the surface from a deep dive generally around 5-10 meters depth.

The diver at depth freediving may have exerted themselves spearfishing or in returning from the bottom overcoming negative bouyancy from the compression of air spaces in their wetsuit and lung volume. A 6 litre lung will lose 4 litres of bouyancy at 20m (4kg lead equilavent)

As one descends the pressure on the body is double atmospheric at 10 meters and 3 times at 20meters. The 20% oxygen in lungs and bloodstream is respectively increased X2 and X3 times nominally from the surface so that even as diver exerts themselves at depth depleting the blood oxygen level they remain concious because the blood oxygen is increased vs surface but as they surface the Partial pressure of Oxygen (PPO2) in the bloodstream reduces rapidly as the diver ascends. It will reduce by half ascending from 20m to 5m not allowing for burning any O2 from finning and whilst the diver is still concious and swimming at 20m if they have reduced their oxygen to a critical level as they surface the law of physics reduces the partial pressure of O2 below the critical level causing unconciousness on the at around the 5-10 meter level.

If they are over weighted and negativly bouyant when that ocurrs they will sink to bottom and drown.

Safety dictates a deep freediver weight themselves to be neutrally bouyant at around 8-10 meters if regularly diving 15-20 meters. If blackour occurs the diver ends up on surface and many experienced divers have ended up on the surface after blacking out and automatically exhale and come to on surface having automatially taken a breath. It is however recommended a freediver diving deep do so with a buddy.

A diver returning to the surface from a deep dive if they feel they might have overexteded themselves should consider tripping the release buckle on their weight belt such that it releases and drops free allowing the diver to float to the surface.

For shallow diving 10m or less add more weight.

Deep diving safety principles/
1. Dive with a buddy.
2. Weight yourself to be neutrally bouyant at 5-10 meters. Means a good duck dive required and need to swim down to that depth
3. Keep hand on a released weight belt buckle if you overexert.
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Old 20-09-2010, 07:51   #54
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Uh, IMHO, this is all rather overdone. Which is not to make light of the possibility of SWB. A suitable application of common sense, as in all things, will see folks right.

When otherwise just cruising over a reef or whatever, a couple of deep breaths and a lung clearing breath will do it. Get to the top, grab some air without the snorkel (most folks I know are too spent to blow out the tube anyway), catch your breath, and then head back down as desired. Rushing things is a bad idea in many ways - raising the chances of SWB included.
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Old 20-09-2010, 14:30   #55
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I've been snorkeling for years and have never heard of SWB or DWB. I think generally there are 3 things you can do - Snorkel, Free Dive or Scuba. I think its free diving that is the most prone for SWB and DWB just from what I've read here.

So if you want to keep it safe, just snorkel. That doesn't mean you can't dive down to get closer, but keep it reasonable and don't push it. If you really want to stay down or get deeper, learn to scuba dive.
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Old 20-09-2010, 15:34   #56
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There's some truth to the concern. The guy I did my SCUBA OW with has a story about a student who huffed and puffed until the lights went out. In short, it can be done. But... it takes some work. Some folks are quite comfortable in the water, and some folks are a little (or a lot) on the hyper side. Which can lead to hyperventilation which can lead to SWB.

The thing that makes us feel "uh-oh! outta air!!!" isn't a lack of oxygen, it's the carbon dioxide buildup in the lungs and in the blood that triggers the message. Three good lung clearing breaths will do a lot to purge residual carbon dioxide and add some fresh air (good ol' nitrox - free for the breathing). Anything past that and you're moving closer to hyperventilation and... boink - time for a nap.

But folks who're cruising the surface, checking things out, and heading down for an occasional closer look at the scenery, not to worry.

Freediving to 40-50' or beyond... whole other game with a whole other set of rules.
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Old 20-09-2010, 17:00   #57
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Uh, IMHO, this is all rather overdone. Which is not to make light of the possibility of SWB. A suitable application of common sense, as in all things, will see folks right.

Totally agreed – as I was saying above I could keep raving on about all kinds of “crap”, but the real point is to relax and have fun!

We all had to start somewhere and I can vividly remember having as much fun diving as a kid in 2’ of water in the lake as when I took up a short stint of competitive spear fishing with some of the types who really know how to take enjoyment out of the equation. Generally, the over-competitive types were in that much of a hurry to kill huge fish and dive to extreme depths that they really forgot the point about having a good time. Many in their haste either missed the basics or ignored commonsense and did end up having “accidents”.
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Old 20-09-2010, 17:40   #58
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Uh, IMHO, this is all rather overdone. Which is not to make light of the possibility of SWB. A suitable application of common sense, as in all things, will see folks right.

When otherwise just cruising over a reef or whatever, a couple of deep breaths and a lung clearing breath will do it. Get to the top, grab some air without the snorkel (most folks I know are too spent to blow out the tube anyway), catch your breath, and then head back down as desired. Rushing things is a bad idea in many ways - raising the chances of SWB included.
1. WRONG - THERE ARE RISKS INVOLVED IN DEEP DIVING AND MANY AROUND THE WORLD HAVE DROWNED. It is useful to understand the theory behind the practise and most have died in ignorance. There are nowdays texts and courses on snorkling to assist.

2. The reason snorklers use snorkles are to are to make it easy to breath and to save energy. There are no risks with a proper snorkle. If you don't blow water out through your snorkle you have to raise your head up clear of the water expending much more energy and oxygen doing so. A person will last much longer with their head down in the water breathing than a swimmer having to raise their head out of the water to breath.

For the average person who is a competent swimmer snorkling on surface enjoying the view and gradually developing their diving skills without hyperventilating there are no issues- enjoy but learn to use a snorkle - it is safer.

Your quote "When otherwise just cruising over a reef or whatever, a couple of deep breaths and a lung clearing breath will do it Rushing things is a bad idea in many ways - raising the chances of SWB included." is correct.

Please don't take me as an overbearing instructor but as someone who enjoys freediving and seeing others doing it safely. It takes time to learn to use a snorkle efficiently but is well worth the effort in persisting.

Start diving deeper as most kids do as their skills develop it's time to understand the physics involved in SWB. Most tourists don't need to but cruisers living on a vessel doing a lot of snokling may need to consider so.

Whilst I taught myself to scuba dive I eventually took instruction becoming a long time instructor reading all I could find. That was in the early days any whilst we may have survived I would not recommend it for anyone.

Enjoy your snorkling/freediving a great pastime and keep safe.
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Old 20-09-2010, 19:44   #59
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Hi all, I like the thread. Its plain practical for us about to go crusin'.

So what about fins. Those with split ends down the middle look like a scam for more money but what the hell do I know about that. Tell me you.
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Old 20-09-2010, 19:47   #60
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I don't use them since they didn't have them when I bought my fins, but apparently they move you along easier. I don't think it matters much snorkeling, but in scuba it could help you use less air.
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