Shallow diving, is there a time limit.....

[JP]

I have my open water scuba license. I have been trying to find the answer to a question that I have been wondering about.

The dive tables for recreation diving start at 35 feet. When calculating to figure your pressure group, the chart says to use the closest available depth.

What if you were diving at 10 or 15 feet? Are there time limits? At what point does one worry about too much nitrogen in the blood.

I have looked over all my PADI books and can't find the answer to my question.

I received my certification back in 1987. I don't remember if we went over this type of question.

 

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[desertfox]

J, I've had my open water since 1974 and like you, I can't remember the limits. Just call a local dive shop they should be able to tell you the limits. I really don't think there are any for that shallow of a depth tho. I hope your not diving by yourself as even at only a few feet Sh** happens!

Happy Hunting and good luck

Desertfox

 

[trikikiwi]

My First Advice is to seek the answer from your local dive school professional.
Just like 'How To Do CPR' does change every few years, so can 'the dive tables'.
My Certificates are well outdated, so I speak from memory

35 feet is about 10 metres - and each 10 metres of diving (in water ) provides an additional one atmosphere of pressure on the body.
I suggest the answer to your query will differ depending on whether you are at 5 metres for 15 minutes, or 10 metres for 5 hours.

Mike

 

[wreckdiver1715]

Remember that for each 33 feet of depth underwater is equal to one atmosphere of pressure. If you are operating at 10 to 15 feet, stay all day or until you run out of air. You should have no real bottom time concerns operating at that shallow of a depth.

Tom

 

[wwwtimmcp]

any time you are in the water using scuba you are on gassing. you could theoretically get bent from staying in shallow water for an extended period of time but you would have to have lots of tanks and time. if only using a single 80 you are probably safe.

in the early 1990's we did tests using an edge computer and a pressure testing pot. they left the edge on over a weekend in the pressure pot and it did show saturation. depth was about 20 feet. quite frankly my skin would probably fall apart after being in the water that long.

I've spent 9 hours in the water swinging my metal detector but was up and down in 4-5 feet of water with no ill effects. I always exhale before getting up from digging an object. our instructor told us that first 5 feet can cause an embolism or pneumothorax.

 

[JP]

Thank you everybody for replying. There are several of us planning a shallow dive for next month. I, like most that are certified, don't go often and have forgoten some of these things that they may have talked about in class (21 years ago). I've been reading up a lot these past few months to bring myself up to where I was. I know from the minimum that the recreational dive tables show is 35 feet 244 minutes. I know from working in the past with a tank strapped to my back in a pool that an 80 really didn't last that much time, may have been 40 minutes (I don't remember, may have been less). So I assume with a metal detector it should be close to the same time, depending on how you work. I know to surface still with 500 psi in the tank.

I have always continued to snorkel and once every couple of years scuba. That's been since 1987. 90% of the time it was for sight seeing. The summer that I worked for the New Port Richey pool was different, it was work.

My brother is starting his class this week. I will send the question along with him and post the answer from the instructor.

I am sure too that even with surfacing and trading out tanks that it would be an all day thing. I'm also sure my hands will be so wrinkled that I won't be able to close them.

Thanks DessertFox, I know and will keep to that gordon rule. But still thank you for saying it just in case there are some here reading this that have never gone in for lessons, were taught by a friend, etc. I was talking with one person the other day that was talking about scuba and metal detecting. He had been scuba diving a couple of times, never certified, and didn't know about the concept of constant breathing. I explained to him there are many dangers involved that are simple to avoid with scuba and that he should get lessons.

 

[JP]

I've spent 9 hours in the water swinging my metal detector but was up and down in 4-5 feet of water with no ill effects.  I always exhale before getting up from digging an object.  our instructor told us that first 5 feet can cause an embolism or pneumothorax.

Wow 9 hours, I was thinking it might be a 4 hour trip for us.  But from what your instructor wrote about the 5 feet and possible embolism is why I posted the question, to find out if there were any other possible internal problems that could happen from staying under for an extended period of time even at a shallow depth.  I know that nitrogen enters ones blood stream at any depth.

I feel bad to ask you this question, but, why do you exhale before getting up from digging an object?  The reason I feel bad is just in case the answer is obvious, I don't want to look that bad.

Thanks again everybody.  I will post the answer that the instructor gives me this weekend.

Wreckdiver you probably are the one that would have worked the most with the scenario of the question. Thanks.

 

[pcolaboy]

Last fall I set a new personal record of 3 hours at 15-20 feet on a hookah system.. Aside from a dry mouth/throat and chilly body, we came up only to refill the gas tank and go back down for another hour and a half. Of course a few days later I came down with an upper respiratory infection probably because my body temp got so low .

Pcola

 

[wwwtimmcp]

1. you always exhale coming up.
2. the greatest pressure change is in shallow water IE water is more dense than air.
3. your body is not indestructable and it is very easy to burst a lung or alveoli in your lung. in shallow water you can spend a load of time and it is easy to forget the things you need to do in order to dive safe. especialy when you are metal detecting and find something good. get into the habit in order to prevent an accident.


I was in the water 9 hours not under it. I've been walking in shallow water and diving on hits. I used up 2 80 cubic foot tanks that day and the last one was almost empty. that last 150-250 psi is hard to get, you really have to breathe hard. total bottom time was probabl 4-5 hours. I dug up alot of barbed wire and sinkers.

 

[dive4it]

Just some simple thoughts on the subject. You should be able to spend a whole lot of time at a ten to fifteen foot depth. Your body is absorbing nitrogen through respiration at depth while breathing compressed air. The way it works is....(I'll try to keep it simple) a given volume of air at the surface, say 1 cubic foot, has "X" amount of molecules in it, it's comprised of oxygen and nitrogen (with a few trace gases like argon and stuff too small amount to mention). Aprox. 22% is oxygen, the rest is nitrogen (unless breathing enriched gas like nitrox). For purely an example and for simple math, say....at the surface, for every cubic foot of air breathed....it has 100 molecules of oxygen and 800 molecules of nitrogen. If you go down to depth, the air is more compressed, lung volume is the same but it takes more air to fill them (it's compressed). At 33 feet, it will take twice as much air to fill the same lung space....same size, more compressed. That means that at 2 atmospheric pressures, you are breathing (example of 1 cubic foot) 200 molecules of oxygen and 1600 molecules of nitrogen. Your body can't exhaust that much nitrogen so it starts to absorb it in it's tissues. Now, if you're not confused enough yet, the body's tissues have different densities throughout it, meaning they absorb and release it at different rates. Some are slow "compartments" and some are fast. You are certainly absorbing nitrogen, even at the shallow depths of 10 - 15 feet. It's the different tissue compartments in the body that determine the amount of time you can spend at any given depth. You have a "controlling" tissue compartment that may absorb and saturate with nitrogen at any given depth, it may be a different compartment at a different depth that controls the amount of bottom time.
To put it all in easy terms, there is a limit at how long you can spend at any given depth, no matter how deep or shallow. At ten to fifteen feet though, I can almost guarantee that your energy level, bladder limit, and cold factor will most certainly give out before you will absorb too much nitrogen. I've spent up to thirteen hours at a depth of ten feet (I am a commercial diver and instructor). Every two hours I'd come up from underneath the structure to either change out tanks or take a wiz. I don't recommend it, but you can stay down even longer with re-breathers and cathider suits. Another thing to think about, after most any dive to depths of 45 feet or more, where do you do your safety stops? At fifteen feet, I think you'll be ok. When in doubt, take a dive computer along and see what it suggests, they are usually pretty conservative and will take into account any surface "credit" time that you take while switching out tanks or eating lunch, etc.

JT
Underwater ops. LLC

 

[JP]

Thanks everybody for the replys. I figure that I would give out anyway with metal detecting underwater within a few hours. I know the cramps will set in, I know one gets exhausted over time. I also thought it was a good subject to start here because there are people on the forum and others out there that scuba dive or want to without training and don't even realize the dangers of simple (but deadly important) issues like constant breathing.

Thank you all again.

JP

 

[Real de Tayopa Tropical Tramp]

Good morning: In basic words, as you ascend, the air in your lungs, now being under lesser pressure, expands. Your lungs can only expand so much before they are damaged, ruptured. = R.I.P.

The last 5 ft or so, are particularly dangerous since a small depth change equals a relatively large air volume change.

Calculate the difference in pressure from say 100 ft to 90 ft. Then from 5 - 10 ft to the surface. Notice the great relative difference in the residual compressed air volume for a 5 ft change in depth.

Sooo, "always" breath out on the ascent. Divers have been killed by ignoring this thumb rule for compressed air, even in swimming pools.


This problem does not occur with free diving, i.e.diving from the surface holding your breath, since the air in your lungs can only expandback to the surface volume.


Joseph Curry

 

[nudels]

I have my open water scuba license. I have been trying to find the answer to a question that I have been wondering about.

The dive tables for recreation diving start at 35 feet. When calculating to figure your pressure group, the chart says to use the closest available depth.

What if you were diving at 10 or 15 feet? Are there time limits? At what point does one worry about too much nitrogen in the blood.

I have looked over all my PADI books and can't find the answer to my question.

I received my certification back in 1987. I don't remember if we went over this type of question.

IIRC I was told that you use the 35 foot numbers for dives less than 35 feet, as part of the "better safe than sorry" philosophy.

Also found this snippet about shallow dives and taking flights:

http://www.scubaboard.com/forums/ba...flying-20-hrs-after-shallow-dive-15-safe.html

 

[allen_idaho]

Basically, diving in 35 feet of water or less places you in one bar of pressure as long as you are at least one foot below the surface. If you go by the basic dive chart, you can stay under for around 3.5 - 4 hours without any surface interval. However, going by a dive computer will give you a lot more safe time without risking nitrogen problems.

So if you are using scuba tanks, and need to switch out every couple of hours or so, you should be just fine. If you are using a hooka system, you might want to take a break every now and then.

 

[abacopirate]

Several years ago was doing some underwater work in 15 feet of water. We were building a fence a lot of heavy work. Went throught 6 tanks in 8hours of work. At the end of the day computer showed 20% most body zones and 30 % in one. Your still takeing up nitrogen, just at a lower rate.

 

[FireRescue]

You shouldn't really worry about narcing out, you're gonna build up nitrogen very slowly at that depth.
What you should really look out for is dehydration, sounds stupid but we spent 6 hrs in the water the other day and one of the less seasoned fellows collapsed when we were finishing up.

 

[JLatham]

Even with shallow water you can end up with the bends, this happens only because of the "it cant happen to me factor" be carefull of shallow water dives they can and will kill you if you don't follow the rules, if you friend or relative is taking a class to become certified, why don't you go and take a Scuba tune up class offered by PADI or any other cert. agency, this will not only refresh your knowledge but also make you sure of your basic skill's. Diving once in a while over almost 20 years is not allot of experience, you may not only save your own skin but that of your dive buddies also, remember there is a BIG difference between recreational diving and WORKING underwater (this includes swinging a detector).

John

 

[harryuk]

HI, THERE IS A LIMIT ON HOW LONG YOU STAY DOWN UNDERWATER METAL DETECTING, IT ALL DEPENDS ON WHAT YOU ARE FINDING? HAHAHAH SORRY ABOUT THAT..HARRY

 

[rgecy]

HI, THERE IS A LIMIT ON HOW LONG YOU STAY DOWN UNDERWATER METAL DETECTING, IT ALL DEPENDS ON WHAT YOU ARE FINDING? HAHAHAH SORRY ABOUT THAT..HARRY

Eventually you will have to come up to change batteries every now and then!

 

[pcolaboy]

A big limiting factor besides available air supply, dehydration, hunger, etc. is the loss of body heat. Even in 80 degree water at depth, you can theoretically run into hypothermia issues. I've been down nearly 3 hours on a hookah at 22 feet in 80 degree water and was literally chilled to the bone towards the end. Of course a wetsuit or diving skin would have made things much better

Pcola