Why are SCUBA divers taught not to hold their breath while ascending in water?

Answer 1

To prevent decompression illness (usually shortened to dci, non divers commonly refer to it as the bends as ur limbs flex and bend, my Biology teacher, also a diver, told me so a while ago). When u go deep, the air breathe is at a higher pressure, as the water pressure tries to squash ur lungs, u just take in more air-compressed. Because the air is compressed, u r actually breathing more of it, meaning ur also taking in more nitrogen. As it is inert, it just dissolves into ur blood, but as the pressure is released, the dissolved nitrogen rushes out in bubbles, like when u open a bottle of fizzy drink. The body can only cope with so much bubbles in the blood, so our ascent is always slow. Dives deeper than 40 metres, using air (i.e. not using a special blend of gas) usually require staged decompression - where u go to one depth, stop, go to a shallower one, and stop and so one, to let the bubbles slowly escape. It is common practice that we make a 'safety stop' no matter what depth we dive to just to be on the safe side. It is a stop at 5 metres, and if all has gone well, it is for 3 minutes. We also have time limits for depths, deeper u go, the shorter the limit, as the body cant cope with too much dissolved nitrogen, known as residual nitrogen. If u go over this time limit by no more than five minutes, the safety stop is made at 5m again but for 8 minutes. Ifu exceed a time limit by more than 5 minutes, the safety stop must be 15 minutes - air/breathing gas supply allowing. Obviously if you're running out of air, you surface and seek medical attention before its too late.

Answer 2

This is because you have no time to outgas as you ascend, so you can get the Bends.

Addition

The goal of course is to not get decompression sickness (a.k.a. the bends). Proper diving techniques will reduce this chance. While underwater time controls how much gas a diver absorbs or on-gasses during a dive, the way a diver ascends will affect the way the gas leaves the body or the off-gassing.

The starting point in answering this question is to understand that virtually every dive will result in bubbles in the diver even though decompression sickness does not occur. An initiating point of the bubbles are micro bubbles or micro nuclei. If these micro bubbles can be controlled then the amount of bubbling in a diver after a dive can also be controlled - which will help prevent decompression sickness. These micro bubbles have a surface or skin on them. This creates a surface or skin tension that tries to pull in or shrink the microbubble. An example of this is when you try to blow up a balloon. The balloon is hardest to blow up when you are just starting and it is easier the bigger the balloon. The same is true of a microbubble. The skin tension creates more of a shrinking pressure the smaller the nuclei. When this skin tension is exceeded, then it will grow and start expanding - which is what divers want to prevent. If a diver ascends slowly towards the surface (i.e. 30 ft./min or slower), the microbubbles have a better chance of staying small due to being under pressure and the slow release of the pressure which lets their skin tension stay higher. You can see this with a simple experiment at home. Take 2 equal soda bottles and open as slow as you can. Then when you are done, release the second one rapidly. You will notice the one you opened slowly has far fewer bubbles in it even though it has the same dissolved gas in it as the one you opened rapidly. This is because the slow release allowed the micronuclei to "self-collapse" more due to the skin tension not being exceeded. Of course nuclei will still expand with resulting bubbles, but you can see a significant difference in this experiment. So, always ascend slowly and know that this does your body good and of course perform safety stops since this stop under pressure also helps the body eliminate gas before surfacing.

Answer 3

Well when you go up there's air air in your lungs and as you go up, your lungs will literally explode or blow up. It's hard to explain. And also just common sense. By the way, it's called air embolism.

The above answer is correct. Holding your breath while diving could lead to an air embolism as as well as other serious problems. Holding your breath will cause the air in your lungs to expand as you ascend which can cause them to over expand and cause these problems. This is prevented by simply breathing so any air expanding is simply exhaled. This occurs due to the pressure caused by the water. Air compressing under pressure in a flexible container (and your lungs are flexible). Visualize holding a drinking glass upside down and taking it underwater. The air trapped in the glass will start compressing and you will see water enter the bottom of the glass. The farther you take the glass down. the more the air will be compressed. At 33 feet or 10 meters, the surface pressure doubles and air is compressed by a factor of 2. So the air in the glass will have been compressed by a factor of 2 and will now only take up half the glass. When you take the glass back to the surface, the air will start re-expanding until it reaches the surface where it will have re-expanded all the way to its original volume. Now picture this same glass at 33 feet, but fill the glass completely with air. If this glass is taken to the surface you will see the air in it expanding and overflowing and escaping out the bottom of the glass. Now picture this glass as your lungs. When you are underwater breathing, you take full breaths and your lungs will be full underwater. If you hold your breath while ascending to the surface, the air in your lungs will start expanding and if you do not exhale it, it must go somewhere and it will work its way out of your lungs by expanding your lungs causing some rupture. But again, this is very easy to prevent by simply breathing (and exhaling). This does not occur in snorklers since they don't take a breath while underwater.

Answer 4

In order for a diver to be able to breath the air from the Scuba tanks, it must enter their lungs at a pressure equal to or higher than the pressure in the water around them - otherwise they would not be able to expand their chest to breath in. At higher pressures, however, more air dissolves into their blood. As long as they remain under pressure, this is no problem, but if they rise to the surface quickly, the surface pressure is not sufficient to keep the gasses dissolved into their blood.

Think about all the little bubbles that start to form at the bottom of a pot of water as you start to heat it up. The tiny bubbles you see forming before it actually starts to boil is the air coming out of solution, not steam bubbles. In the same manner that air bubbles start to come out of the water, air bubble start to form in the blood. As the pressure drops, those air bubble expand - and it becomes very, very painful - and you get "the bends". It can cause people to black out - at which point they aren't going to come the rest of the way up on their own. If the pressure drop is severe enough it can rupture blood vessels causing all sorts of damage - including brain damage and even death. For this reason divers try to ascend a bit slowly - to allow the extra air to come out of their blood slowly rather than all at once in big painful bubbles.

Answer 5

Because nitrogen gas which is dissolved in the bloodstream converts back to gas if you come up too quickly (caused by the rapid change in pressure) The nitrogen bubbles travel along the blood vessels to the heart - causing a heart attack.