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The quick answer is that a diver breathing air should descend no deeper than about 218 feet of seawater due to concerns of oxygen toxcity.
Here's the longer answer:
Oxygen can become toxic to a diver as the partial pressure of the gas increases with increasing depth. The point at which this occurs varies based on the metabolism of the individual diver and time at depth. A general rule of thumb is 1.6 atm PPO2. The NOAA Diving Manual quotes the following maximum times at various oxygen partial pressures:
1.6 45 minutes
1.5 120 minutes
1.4 150 minutes
1.3 180 minutes
1.2 210 minutes
It is important to understand that these are not fixed limits. An individual diver's reaction to high pressures of oxygen varies greatly. Most mixed gas rebreathers are set to maintain 1.2 to 1.4 PPO2, allowing for this variability.
To understand what this means to a diver in terms of maximum depth, we need to understand how depth affects the partial pressure of oxygen. The partial pressure of any gas is the total pressure the gas is under, times the fractional percentage of the gas. Each foot of seawater increases the total pressure of the breathing gas by .030303 atm. This means that the total pressure at 33 feet is 2 atm (1 at the surface plus one of water). Total pressure at 66 feet is 2 atm, 99 feet is 3 atm, and so on.
Since air is about 21% oxygen, the PPO2 of air is .21 at the surface, where the total pressure is 1 atm. At a depth of 33 feet of seawater, the total pressure is 2 atm, making the PPO2 (2 X .21) or .42. Accordingly a PPO2 of 1.6 is reached at about 218 feet of sea water. This depth, 218 fsw, is generally considered the maximum safe depth for a diver breathing air.
The same formula can be used for other breathing gases. A diver breathing pure oxygen reaches 1.6 PPO2 at about 20 feet of seawater. A diver breathing Nitrox32, containing 32% oxygen, reaches 1.6 PPO2 at 132 feet.
Note that much of this is moot for most recreational divers. Recreational dive training agencies set a maximum depth of 40 meters (130 feet) for a variety of reasons including avoidance of decompression illness.
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How do rebreathers work?
In simple terms, a rebreather has a breathing loop, and the air that the diver exhales goes back through the loop and a CO2 scrubber removes the carbond dioxide from the exhaled air. The system then injects additional gas (either pure oxygen or a dilutent) to deliver breathable gas around the far side of the loop back to the diver. If the CO2 scrubber fails, then the CO2 in the breathing gas will build up until the diver blacks out. Some modern models include CO2 sensors, but most of the popular models still do not.Rebreathers also monitor the diver's depth, and deliver the maximum safe level of oxygen to the diver for any particular depth (if divers breathe too high a concentration of oxygen at depth, then the diver can black out from oxygen toxicity). The system senses the oxygen content using O2 sensors, and can either enrich it (by injecting oxygen into the looop) or dilute it (by injecting the dilutent). A diver will use a "set point" to determine their oxygen exposure, usually about 1.2 ATA. When the diver is shallow, the system will inject more oxygen. When the diver is deep, the system will inject less oxygen. By maximising the safe level of oxygen, the diver can dive for much longer without the need to engage in decompression (or alternatively, the diver can consirably shorten the amount of time that they need to decompress).
Why is there a limit to the depth a diver can go?
there are several reasons. One is the effects of nitrogen narcosis, which is when you go below 100 feet in the water, you get the effects of laughing gas. the other is caused by oxygen toxicity, which is when you are breathing pure oxygen deeper than 130 feet. These are all caused by Boyle's law, I think.
Why do free-divers sink at depth?
The cartesian diver sinks because the diver wants to get to a place of low pressure
The stunt diver used an oxygen tank until he reached the surface?
The stunt diver
What is meant by the sick term divers diseases?
Scuba diver's diseases include decompression sickness, pulmonary embolus or emboli, oxygen toxicity, nitrogen narcosis, and other afflictions associated with scuba diving, working under different pressures, at sea, or underwater.
What is the name of a diver that does not use an oxygen tank?
Shark Bait
What partial pressure of oxygen is a scuba diver breathing if the total pressure is 6.3 ATM and 20 percent of the air is oxygen?
The answer to the question what partial pressure of oxygen is a scuba diver breathing if the total pressure is 6.3 atm and 20 % of the air is oxygen is 1.26 atm (atmospheres).
What helps a diver breathe under water?
Oxygen Tank + mask
Why scuba diver wear oxygen tank?
so they can breath underwater
How is the frog like a scuba diver?
Well, it needs oxygen like a human scuba diver but it lasts a pretty long time underwater just like a human would if he used an oxygen tank.
Can you scuba dive to 6000 ft?
220 feet is about 67 metres. The pressure of air at this depth is about 8 bar (or atm). Using standard air the partial pressure (20%) of oxygen is 1.6 bar. This is the boundary where oxygen begins to become toxic and can cause serious health problems (and lead to death). I am a diver with BSAC and the recommended maximum depth is 50m on air which is about 164 feet. The alternative is to use other mixes of gas which usually require more advance training but they contain less oxygen so it is safer to diver deeper. Summary, it is NOT safe to dive to 200ft on standard air
What is the common depth for beginner scuba divers?
As a beginning diver, you will be certified in an open water course. Upon completion, the diver is cleared to go down 60 ft. It is advisable to get more training such as a deep diver certification if you wish to go farther. The recreational limit is 130 ft. with proper training. Personally, I like 30 ft. depth in the Caribbean waters.
