Why do deep-sea divers use a special mixture of gases and not just air to breathe?

Answer 1

Well, for starters, air is 79% Nitrogen/inert gas which will cause the decompression sickness if breathed at pressure over time as nitrogen levels build up in your body, then expand as you come up. This is known as the bends - following the Recreational Dive Planner tables, you can avoid staying down too long on normal air, but the tables for gas mixtures with higher oxygen levels give more time. However, oxygen becomes toxic at 1.4-1.8 bar/atm(atmospheres of pressure) which is about 15 feet down on pure oxygen. This can cause convulsions, which are bad on land but really bad underwater. So, finding a balance and knowing your depth and time limits is critically important. Adding other gases like Helium can extend both depth and time, but get very expensive very fast and require years of training.

Answer 2

Well, one needs to be clear about how oxygen is used.

You cannot actually breathe pure oxygen below a depth of about 20 feet. If you tried to do so, eventually you suffer from oxygen toxicity, which can result in a potentially fatal seizure.

However, when you engage in deep sea diving, your body absorbs various gases like nitrogen and helium. When you ascend, you need these gases to come out of your body before you get the surface, or you will suffer decompression sickness (the 'bends'). Using oxygen-rich mixtures to accelerate this process is now common practice, although as noted above, you normally don't breathe pure oxygen until you are close to the surface. However, divers can start decompressing on oxygen-rich gas mixtures as deep as 100 feet (which might contain, say, 36% oxygen - as opposed to the 21% oxygen found in air).

When divers use pure oxygen to accelerate decompression, we are really talking about dives much deeper than recreational sporting limits of 100 feet. We are talking about 200 foot, 300 foot and deeper dives, using specialised equipment.

Answer 3

Most divers just use air - which is made up oxygen and nitrogen. Many dives are now being done with oxygen added to the air which is commonly known as enriched air or nitrox. Helium is also being used in diving gasses when divers go deeper. Other gasses have been experimented with and used, but they can be very expensive or even dangerous such as hydrogen. So the common gasses are air, nitrox or trimix (a combination of helium and nitrox).

Answer 4

Lots of divers do dive on normal air, however some use nitrox, which has an increased concentration of oxygen because it lowers the risk of DCI (decompression illness or the bends) and also allows the diver to spend longer at a certain depth, however, the increased concentration of oxygen means that the depth is limited. Some technical divers use trimix gasses because this allows them to dive deeper than they would be able to on air, as normal air is toxic at around 60m

Answer 5

Compressed air has nitrogen in it. The "Bends" are caused by nitrogen bubbles in the blood that expand when a diver comes to the surface.

Answer 6

Divers need air and can't get it from the water so they take it with them.

Answer 7

so that more air can be stored in the tank for longer stay underwater.

Answer 8

Deep sea divers use a self contained breathing apparatus (SCBA). This device has an oxygen tank that can be worn on the back and a breathing tube connected to the mouth.

Answer 9

Because it needs to be watertight. Imagine if the equipment wasn't water tight and a diver went down deep, there would be some serious consequences to it.