Why cant scuba divers go 300 feet under the water?

Answer 1

Nothing other than training. Technical diver do it all the time, but recreational divers are limited by either air or nitrox which is narcotic at 40 meters (131 feet) and a very short time limit where technical divers can be trained in using helium as well as how to perform decompression stops.

Answer 2

Scuba divers breathing ordinary air are prevented from descending deeper than about 40 meters because of a condition known as nitrogen narcosis. At high pressures, nitrogen becomes toxic and causes a condition similar to drunkenness, which leads to loss of consciousness and drowning if the diver does not ascend.

Breathing mixtures of exotic gases, such as nitrox and oxygen-helium mixes, among others, scuba divers have descended to much greater depths. The current record is 313 meters, but the limit for most divers under normal conditions is much less.

Answer 3

To dive deeper than this requires specialised equipment and gas mixes called tri-mix which allows a diver to avoid oxygen narcosis as the air they are breathing becomes more and more compressed and therefore richer in oxygen.

Helium is mixed with the gases in a divers tank to 'dilute' the air as Helium is one of the few gases which does not have a narcotic effect at depth.

Addition

The above is not really correct. A diver can obviously go deeper than 40 meters (130 feet), but narcosis does become an issue. However that narcosis is mostly from nitrogen (and not oxygen). Also, a recreational diver really does not have enough gas in a standard cylinder to do a dive safely beyond 40 meters since gas is needed for the dive, the ascent, safety stops as well as the ability to bring 2 divers to the surface if one has a gas problem underwater.

Answer 4

Using standar air, below about 70 metres, the partial pressure of oxygen is so high (about 1.6 bar) that oxygen becomes toxic.

Most recreational diving organisations recommend a maximum depth much less than this. For BSAC the maximum (with training) is 50. I think for some other organisations it is 40m.

If you are using a gas mix with a higher oxygen content such as Nitrox, the maximum depth would be lower (probably about 40-50m) because of the higher partial mix of oxygen.

There is also the problem with nitrogen narcosis where the presence of nitrogen in the breathing gas impacts the divers ability and can give the effects of euphoria for example.

In terms of standard air, the limit is about 70m but a safe limit is usually set much shallower than this

Answer 5

Three main reasons:

1) The Bends. You may have heard of this. It's the accumulation of nitrogen in the blood when divers rise too fast to the surface. When you go deeper, it gets more and more dangerous and complicated because you have to take a lot of time to surface to avoid the bends, so if there is an issue with your equipment or if you get injured, you may not be able to surface in time.

2) Water Pressure. As you dive deeper, there is more water weighing down on you. Before that, however, the water pressure will crush you. You can start to feel water pressure if you swim to the bottom of the deep end, but hundreds of feet down it can crush you.

3) Oxygen Poisoning/Nitrogen Narcosis. At about 200 feet, the water pressure makes oxygen toxic. This makes it necessary to use special blends, but they have their limits, because they all have to have oxygen, despite prolonging the "life," per se, of the oxygen. Also a factor is nitrogen narcosis. After about 100 feet, divers experience a sensation very similar to alcohol intoxication. They may also experience dulled senses and tunnel vision. This can make it difficult to maintain your equipment and manage their dive.

All of these issues, plus more I'm sure (I'm no expert on deep diving), make it much more complicated and dangerous to go deeper than normal depths. Although some technologies exist to try to get around these issues (such as military diving suits that are like suits of armor and are pressurized), they are a constant problem for divers.

Answer 6

They can. It just requires special training.