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.
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.
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).
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
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.
Divers need air and can't get it from the water so they take it with them.
so that more air can be stored in the tank for longer stay underwater.
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.
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.
They don't breathe normally on their own.They have to use pressure regulators to breathe naturally, overcoming the extreme pressure deep underwater.A snorkel and oxygen tank help the divers breathe when they are underwater.
You can breathe underground by using submersible breathing aparatus similar to scuba gear used by divers.
Skin divers are people who dive into the ocean without using special equipment, unlike Scuba divers.
The air mixture in scuba diving tanks is typically compressed air, which consists of about 21% oxygen and 79% nitrogen. This mixture allows divers to breathe at depth without experiencing adverse effects of high pressure.
Scuba - self contained underwater breathing apparatus
By oxygen tanks - similar to SCUBA divers.
Clearance Divers
A mixture of oxygen with nitrogen or helium.
In recreational diving, most divers use compressed air (as in the normal air we breather at the surface). Some divers are also trained to use special gas mixes called Nitrox which have a higher oxygen content and lower Nitrogen. Professional (or commerical) divers tend to use more advance mixes such as Heliox or Trimix which combine Oxygen, Nitrogen and Helium.
If a diver's tank is filled with a helium-oxygen mixture to a specific pressure at the surface, the same pressure will be maintained at depth to prevent nitrogen narcosis. This is because helium is less narcotic than nitrogen, allowing the diver to breathe at higher pressures without experiencing detrimental effects. The specific mixture and pressure are carefully calculated to ensure the safety and well-being of the diver during deep-sea operations.
Sea Divers - 1958 TV was released on: USA: 2007 (DVD special edition)
the risks the diver most was holding their breathe using nose clips for long time