Premature surfacing

[IvIcYrusIvI]

a little bit of background info: havent dived in 2 years, but took my refresher course, and am now doing my wreck and digital photography spec.

ok so i was doing my 3rd dive this holiday, and i used up my air VERY quickly, (probably from chasing fish in circles to do my digital photography spec), but at 800psi i let my DM know of my air situation. he said ok and continued going along.

anyways a little time passed and i noticed that i was becoming positivly boyant and had to dump all the air from my BCD to stay neutral, so i checked on my air and it was down to 300psi :11:.

now i should mention the dive was at a max depth of 60ft, but mostly at around 40ft. this was following a 110ft dive with 1hr SI.

i started to get a little paniky so i caught up with my DM and told him i need to assend ASAP, he said ok, so i started to assend with the group. As i got to around 30ft i noticed that i became positivly boyant again, as my tank was getting very low, i was unable to keep myself from surfacing, (my dive computer didnt complain about my assent rate), but this meant i missed my saftey stop.

now sorry about the length of this post, but i have some questions:

1. when ur tank is very low how do u stop urself getting positivly boyant? i had already dumped my air from my BCD. if this was from a deeper level im sure i would have suffered from DCI, and even possibly overexpansion problems

2. i know a safety stop is not necessary if im not within 3 groups of my NDL ( i think thats right) but i did deep dive about an hour before, so i probably should have done the saftey stop! obviously i didnt feel any of the symptoms of DCI, but how long should i leave it before diving again? is 24 hours generally ok?


thanks a ton!

 

[grow-n-gillz]

Maybe more weight would keep u down. I'm not an avid diver, but if you cannot control your bouyancy, then you may not be wearing enuogh weight. If you can't stay at 15-20 ft., then yourtoo bouyant. Right?

 

[IvIcYrusIvI]

i was taught that the correct weighting is that on the surface the water level should come to mid-mask, but obviously this is with a full tank, so im not so sure?

 

[VooDooGasMan]

wrong the weighting is suit only

 

[JahJahwarrior]

I actually weight myself without gear on. I am perfectly weighted for diving with only a wetsuit. My gear is negative when full, and I never ever dive it to empty, so it never becomes bouyant. My aluminum 100s are a few pounds bouyant when empty, but I usually don't dive below 1000 psi, and I have enough weight at that point to stay negative if I need to.

The real thing here is that you did not seem to have a plan. You did not plan to go down to 300psi...you need to plan at what psi you will turn your dive and begin an ascent. Also,a scending along a line in open water situations can help, you have something to hold on to if you need to.

A fast ascent is something we've all done. Personally, I found I struggled with sharing air and keeping a safe ascent rate without a long hose. As soon as I'd rocketed to the surface from 15 feet once, I ordered a long hose. Not something I want to happen from any deper than my safety stop. Glad you are ok!

 

[VooDooGasMan]

depends on tank also, Your al is positive, never should got under 500. now you no the bouyancy is under 500, youl catch on (always monitor gauge)

 

[BKP]

a little bit of background info: havent dived in 2 years, but took my refresher course, and am now doing my wreck and digital photography spec.

ok so i was doing my 3rd dive this holiday, and i used up my air VERY quickly, (probably from chasing fish in circles to do my digital photography spec), but at 800psi i let my DM know of my air situation. he said ok and continued going along.

anyways a little time passed and i noticed that i was becoming positivly boyant and had to dump all the air from my BCD to stay neutral, so i checked on my air and it was down to 300psi :11:.

now i should mention the dive was at a max depth of 60ft, but mostly at around 40ft. this was following a 110ft dive with 1hr SI.

i started to get a little paniky so i caught up with my DM and told him i need to assend ASAP, he said ok, so i started to assend with the group. As i got to around 30ft i noticed that i became positivly boyant again, as my tank was getting very low, i was unable to keep myself from surfacing, (my dive computer didnt complain about my assent rate), but this meant i missed my saftey stop.

now sorry about the length of this post, but i have some questions:

1. when ur tank is very low how do u stop urself getting positivly boyant? i had already dumped my air from my BCD. if this was from a deeper level im sure i would have suffered from DCI, and even possibly overexpansion problems

2. i know a safety stop is not necessary if im not within 3 groups of my NDL ( i think thats right) but i did deep dive about an hour before, so i probably should have done the saftey stop! obviously i didnt feel any of the symptoms of DCI, but how long should i leave it before diving again? is 24 hours generally ok?


thanks a ton!

If you're dubious about your computer's stated SI, then use the tables, and your max depth for the profile of the dive. 24 hours even clears you for flying after any recreational dive.
A safety stop (while should be adhered to), is still that... a safety stop. Not mandatory deco. So, I wouldn't be too concerned.

Of more concern is taking your own ascent in hand, if you think you're low, instead of depending on someone else to give you thumb up signal. Even at 40 feet, you should be on your way up, long before you hit 500psi. I did something similar once on the Grove... I was still at 90 some odd feet at 700 psi. Dumb. (I know I won't allow it to happen again, however, shouldn't have happened in the first place -- I was waiting for someone else to tell me to head up).

As for the buoyancy, you should be neutrally weighted at 500psi (float at eye level). Run your tank down to 500psi, *completely* empty your BC, take a breath (on the surface). If you sink, you're overweighted... floating above eye level, you need more weight. Actually, sounds like you might have been ok, weight wise, if you didn't suck your tank almost dry.

Good luck...

 

[douglasville diver]

Glad your O.K., but don't let these things keep you out of the water!
I don't know alot of factors like what type of tank your were diving,fresh or salt,etc,etc.
The way I read your racall,for a second it sounded like the inflator botton on your bc may have stuck open. Alot of air seemed to have went fast went fast! Maybe maybe not the cause but one thing for sure,when a diver signals -LOW ON AIR-it's NOT a question.
Any diver can call any dive at any time for any reason

 

[rawls]

Your question should be how do I keep from letting my tank get so low on air that I became positively buoyant and therefore had trouble staying underwater at the hang line. One thing you need to keep in mind...No matter who it is...DM...Instructor...Buddy...you are on your own to a large degree and can never rely that someone else is going to save your behind. You seemed to have let the ball drop by following IMHO a very inept DM and not taking the responsibility of managing your gas on your own...
As far as being too buoyant...again...it goes back to the amount of gas you had left. If you determined your neutral buoyancy based on a full tank or 1/2 tank then you are going to be positive with 300psi...The only way you can compensate for that is to overweight yourself and you don't want to do that...Better to practice responsible gas management....

wrong the weighting is suit only

Well...he's not completely wrong....but you are right in that you can get a determination of neutral buoyancy by weighting yourself with wetsuit on and putting just enough weight on to be able to sit comfortably on the bottom holding a normal breath.

The other method is, as IvIcY....dude you gotta get another moniker...stated is with full gear on, you should float at eye level to the surface holding a normal breath with BC fully defalted, with ideally a half tank of gas.

IvIcYrusIvI......man that's a tough moniker...I have seen some doozies but I think you take the cake on this one

 

[jimdiverman]

1. when ur tank is very low how do u stop urself getting positivly boyant? i had already dumped my air from my BCD. if this was from a deeper level im sure i would have suffered from DCI, and even possibly overexpansion problems

2. i know a safety stop is not necessary if im not within 3 groups of my NDL ( i think thats right) but i did deep dive about an hour before, so i probably should have done the saftey stop! obviously i didnt feel any of the symptoms of DCI, but how long should i leave it before diving again? is 24 hours generally ok?

thanks a ton!

Short answer: All tanks are going to swing more positively buoyant during the entire dive. Some may not get as positive as Aluminum 80s, and some don't even get positive, but they all get less negative. Easiest fix: Add more weight if you plan to run the tank down. Preference: dive with a dive plan that does not include running the tank down and includes a preplanned turn pressure (or time limit) and/or ascent pressure. Requires: understanding your surface air consumption rate and how much gas you will use on your dive.

1. In a recreational dive, if you are healthy (not diving with congestion) and don't have any physical deformities in your lungs, your chances of getting lung overexpansion injury from a proper and normal emergency ascent are very low. Depending on the speed of your ascent, you could increase the size of the microbubbles floating in your blood stream, and potentially have problems with skin bends or worse, still an unlikely yet possible scenario. Your dive is considered a recreational dive, but that includes following the rules for ascent rate. If you go beyond those rules, as your training has taught you, then you introduce higher risk for decompression symptoms at some point post dive. A good conservative ascent rate is 30 feet per minute, as opposed to some other published ascent rates.

All divers have this problem at some point in their diving experience. You have the opportunity to learn from it. If this is a drift dive and you notice that you are running low on air, then you did the right thing when you notified the dive master, but then you need to start your ascent right away. Getting back on the boat with 500 psi is not a dive plan; it is an end point, but on a drift dive, you need to understand how much gas you need for ascent from your depth and your safety stop, and then have 500 psi or more left. I understand what it is like on a boat drift dive. The dive master is leading and you are following or keeping everyone in sight as you take pictures and float along. You still need to keep track of your SPG, and depending on your SAC rate, you need to start your ascent at a pre-planned gauge pressure (depending on your depth and time on the dive, also watching your NDL). Keep everyone in sight below you as practical, but maintain your depth so you can perform your safety stop mid water. If you have a lift bag (and know how to use it, recommended), you can greatly ease the safety stop in mid water especially in low visibility conditions.

If there is a ladder at 15 feet for the safety stop at the end of the dive, then usually it is weighted and it helps to hold on to that. Many times on these dives, others are underweighted at the safety stop as well, so it becomes a struggle to stay at 15 feet at the safety stop with everyone hanging on the bar counteracting the weight on the bar. If you are going to make this kind of dive and want to use up the air in your tank, then I would weight myself a little heavier at the start of the dive so you can get in your last 3 minutes at 15 feet without having to struggle increasing your exertion and compounding your susceptibility to DCS symptoms.

If there is no ladder at the safety stop, maybe there is an anchor line. You can hold on to that at 15 feet. If there is no ladder and no anchor line, then you can try to hold on to a buddy that may be able to offset your buoyancy. Finally, as a last resort, you may be able to get some extra weight from someone that is exiting the water because their dive is over. Careful you don't drop the extra weight on someone else, or to the bottom.

2. A safety stop should be required on every dive; I know what the RDP says, but it is just good practice to do it on every dive no matter what. All recreational dives, according to Hoyle, don't REQUIRE decompression. That is what makes them recreational NDL (NO DECOMPRESSION LIMIT) dives. But by the same token, the safety stop is there as insurance just in case something on the dive like your ascent rate was too high, or you stayed too deep for too long, or you are a little dehydrated today doesn't put you in a DCS situation because you may be teetering on the brink based on your dive profile and your personal physiology on that given day and on that given dive.

Are you diving with a computer? Check the nitrogen absorption bars on your dive computer to determine when it is safe to get back in the water. All computers don't operate the same, but they use the same principles. With experience at different exposures and different conditions, you will come to understand what your body feels like if you get close to your personal limits.

Check your tables to see what they say about surface intervals. Unless you exceed an NDL, you don't have to sit out for longer than 3 hours according to the RDP. The PADI RDP table doesn't cover missing a safety stop as far as how long to sit out as far as I can tell. To be conservative, you should end the day's dives, but that may be too conservative depending on the situation. Always use good judgment and dive conservatively.

Have fun diving, and be safe.