Why cant a scuba filled with oxygen only?

Answer 1

Scuba tanks get hot when you fill them. Putting them underwater keeps them cool. If they overheat, the burst disk may blow. But even if it doesn't, a "hot" fill will cool down to a lower pressure, so if you think you have filled the tank to 3,000 PSI, when it cools down you will find that you only have, say, 2,750 PSI in your tank.

Answer 2

As compressed air is added to a scuba cylinder the air entering the valve and moving within the cylinder creates heat. Cylinders are placed in water to dissipate this heat and keep the cylinder from overexpanding while still allowing the tank to be filled to its rated cylinder pressure.

As a cylinder expands with the heat from air entering the valve, if not placed in water, as the cylinder cools once the incoming air has stopped the pressure within the cylinder will decrease as cooler air molecules take up less space and therefore the pressure of warmer air once cooled will be a much lower rates psi within the cylinder.

Answer 3

The air you breathe in the atmosphere is about 70% Nitrogen and 12% Oxygen, You do not need 100% oxygen at any time unless you are injured or have trouble breathing. 100% Oxygen can scar your lungs, but when diving you need regular air to breathe. The problem with Nitrogen in the air we breathe while SCUBA diving is once you dive deeply enough, usually around 40M or 130 ft. you begin to suffer from Nitrogen Narcosis, a condition caused by breathing under extreme pressure. As 40M is not a 'Normal' dive. The way to alleviate the problem is to ascend to a shallower depth, that's why it is always Best to have a Dive Buddy.

The Bends is another factor, usually caused by ascending too quickly from a deep dive.

Improved Answer

The answer above is wrong and diverts from the question. Air is roughly 79% nitrogen and 21% oxygen. A scuba cylinder cannot be filled with pure oxygen because oxygen is toxic when it is breathed under pressure (i.e. at depth underwater). The depth and time limit for pure oxygen is 45 minutes at 20 feet and this is only used during special technical decompression dives. Exceeding this depth (or time limit) can result in underwater convulsions and result in drowning. Any extra percentage of oxygen used in a dive (including pure oxygen) requires special training.

Answer 4

The air we breathe is about 21% oxygen and 79% nitrogen. Less that one percent of our air is composed of trace gases like carbon dioxide and helium. This normal surface air is the breathing gas used by the vast majority of scuba divers.

There are a number of reasons why recreational scuba divers do not dive using pure oxygen. The first, and most important, of these is that oxygen is toxic to humans at the elevated pressures experienced in diving. While the exact depth limit varies with a diver's physiology, a good rule of thumb us that pure oxygen should not be used below about 27 feet of sea water. At that depth, the partial pressure of oxygen makes it toxic to most divers.

Pure oxygen IS used as the breathing gas in shallow water rebreathers like the Drager LAR V. These special purpose scuba rigs are used for combat swimmer delivery by highly trained combat divers such as US Navy SEALs. The oxygen toxicity depth limit still applies, even with these highly trained divers.

Pure oxygen is also used as a decompression gas at shallow depths by technical and commercial divers who have used other breathing gases during the dive.

Mixed gas rebreathers use pure oxygen as one of the two breathing gases which are mixed throughout a dive. Another diluent gas such as air is used to maintain optimum oxygen partial pressure for the diver to minimize both oxygen toxicity and decompression illness risk.

Another reason standard surface air is typically used to fill recreational scuba tanks is convenience and expense. Normal air is easy to obtain and inexpensive. Oxygen is difficult to work with and expensive.

Some recreational scuba divers do use a breathing gas called "Enriched Air Nitrox" (EANx). This is air to which oxygen has been added, increasing the percentage from 21% to as much as 40%. The increased oxygen reduces the amount of nitrogen, allowing longer dives without the risk of decompression illness.

It is important to note that pure oxygen can be very dangerous to work with due to the risk of fire and explosion. Diving gear that is to be used with breathing gases containing elevated levels of oxygen is designed with special seal materials and non-petroleum-based lubricants.

Answer 5

Because oxygen is toxic at high concentrations. If you breathed in pure oxygen, you would eventually get very sick.

Answer 6

they don't