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Given a solid suit or vehicle, where pressure is maintained near normal sea-level (1 atmosphere), there is obviously no limit, except that we haven't yet built a machine that can with-hold that type of pressure yet. But for humans without such protection, the pressure levels in water below 1000 feet (300 m) present severe problems.
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Modern recordsA Navy diver submerged 2,000 feet (609.6 m), setting a record using the new Atmospheric Diving System (ADS hardshell suit), off the coast of La Jolla, CA, on Aug. 1 2007.The deepest open circuit Scuba dive was accomplished by Pascal Bernabé (Ralf Tech/WR1 Team) who on July 5, 2005 descended to 1,083 feet (330 m). The dive took place near Propriano, Corsica.
Re-Breather UseThe options for modern exploration are most commonly open circuit scuba and re-breather. Diving is limited by the correct mixture of breathable gases. On open circuit "classic" scuba the gas must be mixed ahead of time, while on re-breathers a diver always has the right mix of gas for the depth. Australian diver David Shaw successfully used a modified recreational re-breather to reach a depth of 888 ft (270 m) in fresh water in 2004. (Shaw died on an attempt to recover a fellow diver's body in 2005.) Oxygen RequirementsThe maximum depth that you can dive safely on air is dependent upon the partial pressure of oxygen. The air that we breathe at the surface is at a partial pressure of 0.2 bar .The partial pressure increases as your depth increases : at 10 metres it will be 0.4 bar and at 20 metres it will be at 0.6 bar. Oxygen becomes toxic at approximately 1.6 bar partial pressure, giving a maximum safe diving depth on ordinary air of around 70 metres (230 ft) . Diving to this extreme depth is not recommended, as individuals tolerances may vary. Deep-diving Gas MixturesThe maximum depth someone can dive will be directly related to the percent of oxygen in the breathing mixture. The air mixture we as humans breath is mostly made up of oxygen and nitrogen. The ratio is around 80% nitrogen and 19% oxygen and 1% other gasses. The same gas, oxygen, that keeps us alive can become toxic and kill us under high pressure. But one way to prevent oxygen toxicity is to reduce the concentration of oxygen and replace it with a different gas, such as helium. Since our bodies only use about 5% of the 19% of oxygen in air, we can replace a portion of the gas with something that is relatively safe under pressure. This is called a tri-mix gas. It can be used to dive much deeper than the recreation limit of 130 feet (40 m). Another physiological problemAs the previous answers all indicate in one way or another, the primary limiting factor in most cases at least is PPO2 (partial pressure of oxygen) and various gas results including hypothermia, which gases like helium exacerbate. However, in super-high pressures, there is a problem with denaturing of various proteins in the human system. This rare and unlikely problem is still in the books and not reality, as human descent to such depths and ambient pressures has never been tried. When the Trieste descended to 36,000 ft (10,900 m) in 1960 (Marianas Trench), the people inside were protected at one atmosphere. It's likely that with exposure to extremely high pressure, human physiology may fail, for reasons unrelated to gas problems.Proteins denaturing is detectable by increased neuropathy. Given a "perfect" gas mixture, this could eventually prove fatal. Divers Alert Network (DAN) was the source of this, with the USC Catalina Chamber circa 1970, and may have indicated problems with the medullary sheath as well.
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Obviously the limit for recreational diving as it is defined by PADI (Professional Association of Diving Instructors) is 40m. This would be achieved using ordinary nitrox (a mixture of oxygen and nitrogen; basically air but with a slightly higher percentage of oxygen). For BSAC and SSAC (British Sub Aqua Club and Scottish Sub Aqua Club) the limit is 50m, but it is generally acknowledged that beyond 40m a decompression stop on ascent is required. BSAC and SSAC both teach deco as a part of their dive training courses. The purpose of decompression is to allow bubbles of nitrogen to escape from the blood and prevent DCI (Decompression Injuries); also to increase and decrease the air volume in the lungs and sinuses at a safe rate to minimise the effects of barotrauma on the air spaces (which are otherwise liable to implode). Technical divers scuba dive at greater depths, and one of the methods they might use is an open circuit rebreather as has been discussed above; alternatively multiple cylinders and pony bottles. Oxygen toxicity occurs as a result of the increased pressure and can result in seizures (the pressure increases with depth at a rate of one atmosphere per 10 metres) and for this reason the maximum depth at which air can safely be breathed is much debated. The general consensus is that it is around the 60m mark but of course it varies from person to person and it would be unwise to venture beyond the defined limits of recreational diving without appropriate technical training.
Through diving with various complex gas mixtures individuals have managed to reach maximum depths of around 300m, but would probably have to be taken straight to an onsite hyperbaric chamber afterwards. Pressure underwater increases at a rate of an additional atmosphere per 10 metres. The effect of this upon the lungs and sinuses is that they experience a 'squeeze' - the air volume within these air spaces in fact halves with every additional atmosphere! Divers are taught to 'equalise' (add air to the air space) their sinuses to maintain the same air volume and avoid discomfort or worse when diving. They are supposed to do this as they ascend or descend and it is achieved by pinching the nose inside the mask and breathing out, thus using the air from the lungs. The effect of the increased pressure on the lungs is less noticeable because the lungs are comparatively so large and flexible, but obviously there is little that can be done to equalise them. Generally speaking the lungs are not dangerously subject to barotrauma at depths safe to dive using air, but as you can imagine, at 300 metres the pressure has increased by 30 atmospheres, meaning the air volume of the lungs has been compacted 30 times! At greater depths than this the lungs would quite simply implode, or else could explode on returning to the surface due to excessive expansion.
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Maxine- June 2005, a South African called Nuno Gomes, had Reached the depth of 318.25m in the Red sea. The Guiness Book of World Records still records this as the deepest ever scuba dive.
- Later 2005, a French diver named Pascal Bernabe reportedly dived to 330m exactly, but for some reason that dive has never been officially recognised as a world record. I do not know the reason why.
- Previously Mark Ellyatt, a British technical diving instructor, had set a new world record for the deepest scuba dive when he descended to a depth of 313 meters (1,026.9 ft) off the island of Phuket in Thailand, beating the previous record by about 5 meters (16.4 ft). No independent verification of the record was immediately available.
- According to news reports, it took Ellyatt 12 minutes to reach the record-breaking depth, but six hours and 40 minutes to decompress and return safely to the surface. The Briton took six tanks down with him and had another 24 brought down by support divers. This dive took 10 years of preparation. Apparently his motive was to improve safety standards, not necessarily to set a world record. However, Ellyatt suffered serious decompression sickness as a result of his attempt.
- Another British diver, John Bennett, set the previous world record of 308 meters (1,010.5 ft) on November 6, 2001 off the island of Mindoro in the Philippines.
- Those are the only four known scuba dives below 1,000 feet (although it is widely accepted that military special forces may have dived deeper in classified dives). A summary of attempts to set ultra deep diving records (and the high number of fatalities) can be found at:
this actually has to be a multiple purpose answer because there are number of different ways to dive on a single breath of air and you didn't specify 'which' here are the details of free diving but it breaks down to: 6.1 Constant Weight Apnea (CWT)
6.2 Constant Weight Apnea Without Fins (CNF)
6.3 Free Immersion Apnea (FIM)
6.4 Variable Weight Apnea (VWT)
6.5 No-Limits Apnea (NLT)
6.6 Static Apnea (STA)
6.7 Dynamic Apnea With Fins (DYN)
6.8 Dynamic Apnea Without Fins (DNF)
you will also find the answer to the max for each there also found this interesting note which is what most folks think of when 'diving on a single breath'
Francisco "Pipin" Ferreras broke his own world record for "no-limits" free diving today, October 13, 2003 , descending 170m into Los Cabos Bay in Mexico on just one breath of air.
The historic dive took about two minutes and 40 seconds and saw Ferreras plummet to record-depth using a weighted sled, then rocket back up to the surface when his air tanks inflated.
Decompression wasn't needed because he didn't breathe in any air during the dive.
Ferreras, who was born in Cuba but lives in Miami, founded the International Association of Free Divers. He set the previous record of 162m in January 2000.
Today marked the one-year anniversary of the death of his wife, 28-year-old, French-born Audrey Mestre, who died after plunging into deep waters near La Romana, Dominican Republic with a target depth of 171m which tragically she achieved.
HOWEVER, Frenchman Loic Leferme has plunged to a depth of 162 meters unassisted reclaiming a world record in free diving for a fourth time.
He remained under water for 3 minutes, 35 seconds as he surpassed the 160-metre record mark set by Briton Tanya Streeter in August.
Tanya Streeter dived down to a depth of 160metres (525ft) riding on a weighted sled, then pulled and kicked her way to the surface after spending three minutes and 38 seconds underwater on a single breath.
Given apparent different parameters of descent and ascent Tanya potentially holds the record since her breath was held longer than the others.
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