...I find myself being anxious about what if I (or my daughter) get into an uncontrolled ascent. ...
Chickweed, you have had lot of great advice (and a few debates) here. So let me try to summarize it all.
1. It is normal to have some concerns. Buoyancy control is more difficult the shallower you are as small amounts of air make big changes at shallow depths.
2. Causes of uncontrolled ascents are:
A: Failure to control your decent on the way down and waiting too late to add air and then adding too much (Huh? yes, that is corrrect, more on that later under prevention).
B: Ascending without venting when appropriate. Failure to notice subtle signs you have ascended now need to vent air are a popping in the ears or a floaty feeling.
C: Equipment malfunction - inflator hose gets stuck ( this is a rare situation. Prevention flush the inflator valve with fresh water by pouring fresh water in through the inflator hose both the power inflator and the oral inflator and out through a differnt dump valve and properly clean your BCD inside and out after each dive day). Note, there should be no ocean/pool water or just a 1/8 of a cup of water in the BCD at the end of the dive day. If there is say a cup or two, you are dumping air when the bcd is empty. Check your legs on decent and stop moving your legs back and forth (finning) as this is swimming you up when you are trying to go down. Almost all diver do this unconciously when in the water and on decent for the first few (like 50) dives until they learn to think about it and stop their legs. Crossing your legs before you start your decent helps.
D: Being overweighted - This causes you to have more air in your BCD at depth, more air equals more to expand.
Actions on ascent or uncontrolled ascent:
1. Exhale, hard if it is not the first small feeling of being floaty but actually ascending - your lungs are under your immediate control and you don't have to waste time trying to find your inflator hose and grabbing your snorkel instead (hint, when grabbing inflator hose bring left hand to waist and then up your chest, the inflator hose will be the first hose you come to, the snorkel the second. Most people grab in an arc from the head to the torso and hit the snorkel first
2. Get horizontal, you probably already are if you are in normal swiming position. This will help slow you.
3. Locate the vent closest to the surface. This is inportant as you have to use the vent where air is. Air will be at the point closest to the surface. Using the inflator hose to dump if your shoulder is lower than your hip will not work, or if your right shoulder is higher and your inflator hose is on your left.
4. If using the inflator hose to dump air (if it has a pull on the hose shouder dump, use that) be sure the hose is fully extended. Most people inspite of being taught to fully extend the hose (up towards the surface by the way) hold it next to their ear or face for some reason. This creates a J or U in the hose. In plumbing that call that a trap (every sink has one) and its purpose is to keep sewer gas out of your house. In short the J or U will trap air and prevent complete venting of the BCD. A completly (allegedly) empty BCD with a U in the inflator hose will magically dump more air when you fully extend the hose to make a straigh | towards the surface.
5. I use, and demonstrate to my students, my lungs to control my buoyancy over a range of 9 or 10 feet of water. As one poster stated, once you are neutral and properly weighted, you can move from the bottom of the pool (9 feet) to the surface and back with only your lungs taking biger or smaller breaths to control your buoyancy. My students sit in the lotus position, legs crossed, hands on knees for 5 minutes 1/2 way between the surface of the pool and the bottom before we graduate to the ocean.
Prevention -
1. Situational Awarness - note when you are changing your depth. Pay close attention to the subtle signs. Ears popped - you have either decended more or ascended. Either
may require an adjustment to the amount of air in the BCD. Starting to feel floaty on the exhale (you will move up and down a little with each inhale and exhale), could be time to dump a little air.
2. Proper weighting - Empty BCD, full lung, floating with water at eye level, Exhale and sink. If diving ALumimum tank, add 4 pounds for the end of the dive buoyancy of the tank. At end of dive recheck weight with 500 PSI in tank you should be able to hold 15 feet with empty BCD.
2.
BCD Inflator hose is
NOT and
elevator button.
Do NOT put air in your BCD to start your ASCENT (note, paralyzed divers may have do this to bring up an unconcious diver but they are trained to do so and are therefor the exception). When doing a deliberate ASCENT, you should be negative and vent often (Inflator fully extended making a straight line from shoulder to surface, other arm up in the Superman pose, looking around 360 for signs of obstructions (embarising and painful to run into the bottom of the anchored boat or worse the prop) such as kelp, rocks, other divers or a boat esepecially a boat that is under power. Remember sail boats are a delight to sail and part of the enjoyment is no motor noise. Sail boats have a center board sticking under the boat up to 10 feet (big sail boat) and are silent moving through the water so you need to be on the look out.
3. Control the decent (the problem you described in the pool is usally from an uncontrolled decent). When you add air, work to ad as little as possible. Barely touch the inflator button until it makes a Psst sound, not a Pssssssssst sound. Pssst is ok but Psst is better.
3A: Controlling decent: On decent, signal dive buddy decend, clear ears, cross leggs, hit deflator button on inflator hose to dump air and decend. Once the water is over your head LET GO OF THE DEFLATOR BUTTON and stop dumping air. If you continue to dump air after the water is over your head (your head is underwater ergo you are sinking and therefore are negative) you are only dumping air you will have to immediatly add back to get neutral (and also a sign you are overweighted). Start adding air at about 10 feet of depth (or before). A small Psst, clear ears, wait 1 or 2 seconds, add air Psst repeat as you decend. You should be floating down slowly. You may need to check your depth guage to verify you are decending. The objective is to be negative, but just barely negative, say 2 pounds or so. This will allow you to stop your decent at any time by simply taking a large breath (but not closing the airway and holding your breath). you should be able to stop at any depth before you reach the bottom. Handy later when you are diving a wall over a 1000 foot bottom and want to stop at 60 feet. When you are aout 15 feet from your desired depth or the bottom add air in several Psst, Psst, Psst to get neutral. This techniuqe will keep you from doing the lawn dart crash into the bottom most new divers do.
3B: How does the controll decent prevent an uncontrolled ascent you may be asking. The answer is this. Uncontrolled fast lawn dart decents cause the diver when they finally add air to their BCD to have a lot of momentum. Momentum is the answer to the question of "Why when I add air to my BCD does nothing happen for a while but when I dump air the affect is almost instant?". Due to the speed of your decent (working with gravity and going faster and faster) when you add air it takes a while to overcome momentum. Just like when you take your foot off the gas and put the car in neutral it does not instally stop, but keeps on going for a while. When you apply the breaks (add air) you don't stop instatly either. The fast you are going (more momentum) the longer it takes to stop. Since you added air to the BCD but are still decending, you add more, and then more. Evenutally the first bit of air you added overcomes the downward momentum and now you have too much air in the BCD. Now you have an out of control ascent. If you are going too fast by the time the air you added overcomes the downward momentum, you are deep enough that it is time to add more air. If you wait too late to add the first air, you could be going fast enough that you would not be able to get ahead of it and have an out of control decent. For ascent, gravity helps you overcome momentum which is why air dumped appears to have a quicker response. On ascent, if you wait too late to dump, the upward speed gets ahead of your ability to dump air. In short you can't dump air quick enough to make up for the speed of the ascent and you do a polaris missle ascent.
So for the readers digest version. Buoyancy control (stopping uncontrolled ascents is buoyancy control) you need proper weighting, controlled decents, and controlled adding of air (add a little and wait a couple of seconds), and dumping air early in the ascent (exhale, and bcd) and staying ahead of the momentum curve by dumping early and often (or adding air on decent early and often).
Other people get through them - so can you.
