S.C.U.B.A. = Self Contained Underwater Breathing Apparatus. Here is all the information you need to learn and be safe while enjoying this great sport. Explore the last frontier and uncharted depths in the S.C.U.B.A. category.

2,926 Questions

Can you scuba dive by using a garden hose?


Years ago, when I took my very first scuba course, the instructors had us walk from the shallow end of a pool to the deep end, wearing a weight belt and breathing through a very long snorkel. Nobody got all the way to the deep end before it became impossible to breathe against the increasing water pressure. It was a very effective exercise in that it taught us very quickly about the effects of ambient water pressure, which doubles in the first 33 feet of sea water.

If the intent of the question is to ask if one can breathe underwater through a garden hose used as a snorkel, the answer is "not deeper than a few feet". In fact, breathing through a snorkel deeper than about two feet is extraordinarily difficult. Your diaphragm simply isn't strong enough to displace the water at deeper depths.

One could use a hose like a garden hose with surface supplied air. The "snuba" systems used at some resorts use this approach. "Scuba", however, is defined as Self Contained Underwater Breathing Apparatus. It's a fair argument that any system which involves a surface gas supply is no longer "self contained".


How do you reduce drag while scuba diving?

Reducing drag is usually referred to as improving your "trim" in scuba diving. There are several ways you can try and do it.

  • Pay attention to body positioning. Generally, the more horizontal you are, the more streamlined you are. Avoid the "bicycle" position.
  • Use more streamlined gear. For example, consider using a backplate and wing rather than jacket style BCD. If you carry a pony, mount it rather than sling it.
  • Cut down on any unnecessary gear.
  • Avoid "danglies". Clip in everything, or stow it within pockets and holders.
  • Focus on neutrel bouyancy. Although unrelated to trim (at least in a physical sense), divers who maintain good neutral bouyancy are less susceptible to drag and resistance.

What type of oxygen is in a scuba tank?

Unless you've been specially trained to use any other form of air, it's the same as normal air, just compressed with impurities removed.


What is the material used in a scuba diver's suit?

All scuba wetsuits are made out of neoprene which is an elastic synthetic material having great insulation properties. The neoprene itself is impregnated with nitrogen bubbles (neoprene foam) which are not interconnected. This is what contributes to the wetsuit's insulation properties. Because of the nitrogen gas bubbles which are present within the wetsuit's lining, bodily heat loss is further prevented, therefore allowing you to stay warm in colder waters.

Whilst neoprene is a pretty good insulator, one of the properties that make it useful for a wetsuit is that is flexible and can move with the body and be tight fitting. This reduces drag through the water. Although wetsuits are great because they are not bulky, they are not as effective in keeping you warm as dry suits. Dry suits stop you getting wet completely and can be made out of a number of waterproof materials. Originally dry suits were made of oiled canvass and leather and as natural rubbers were developed these were used. Today there are two main types of suit. One is made of neoprene and combines the thermal efficiency of the material and the air gap and clothing to the skin and the other uses a thinner material and largely relies on the thermal undergarments to keep you warm. These suits are called membrane suits and can use a number of rubberised or waterproof materials. Seals to stop water getting in are used at the wrists and neck and are usually made out of either neoprene or latex.

Navy SEALs

What do scuba diver down flags look like?

There are two types of "Diver Down" flags: the well known US version and an international version.

The US version is a rectangular red flag with a single, wide white stripe running diagonally from the top left corner to bottom right corner.

The international "Diver Down" flag is blue and white. It has a vertical white strip with two blue swallow tails. This flag is International Flag Code A (pronounced phonetically as 'alfa' or 'alpha'.) When flown as part of a message, this flag represents the character "A". When this flag is flown independently, it takes on the meaning of the "Diver Down" flag.

Both flags are intended to send the following message to other vessels: "I have a diver down. Keep well clear at slow speed." Check the links for images and specifications.


Why can't you scuba dive after a plane trip?

It is up for debate, but there are some studies that have shown divers are more likely to get decompression sickness after a plane trip. The thinking is that they become dehydrated on the plane trip - which is a contributing factor to DCI. Another possibility is that the reduction in cabin pressure is enough to generate some small asymptomatic bubbling as the 8,000' cabin pressure may be just past the threshold to cause bubbling.

Navy SEALs

Is compressed air in a scuba diver's tank a pure substance?

No it is not by any means. it is atmospheric air compressed with the high amounts of carbons and other gases lowered or removed.


What does the B stand for in SCUBA?



Is scuba diving one word or two?



What is the maximum depth a human can dive to?

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.

(see related links)

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.


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.

Air Compressors

Can you fill a scuba tank from a dental compressor?

No, even though dental compressors have very clean air, it is still not water-free enough to go in a steel tank, though it shouldn't cause problems in an aluminum, but mainly, even the high pressure dental pumps only go up to 175 psi, and even the lowest pressure scuba tanks are 2400psi, going up to 3300 in North America and 5000 in Europe.


How deep is 5 bars?

5 bars = 40 meters if you are looking to buy a watch you would not be able to take this one scuba diving but you would be fine in the bath tub
50 metres H2O 164.0 ft H2O 4.903 bar


What is the definition of a repetitive dive?


A repetitive dive is any dive that occurs before off-gassing of nitrogen has completed. This time will vary depending on the dive, and the dive table used. US Navy Dive tables give a maximum length of time for this to occur as 12 hours, while NAUI dive tables put it at 24 hours. Under PADI tables you only have 6 hours to off gas completely. When in doubt being conservative does not hurt but pushing the boundaries certainly can.

For comparison purposes, a side-by-side exam will easily show U.S.Navy Dive Tables to be the 'safest', or most conservative, giving the longest decompression /out gas times, next safest are the (sadly) now-defunct NAUI tables, which are only slightly less 'safe', or conservative, while the resort/hotel/rental industry-sponsored PADI 'tables' are simply designed to let a diver belt down a couple more beer on the 'safety' boat before diving again.


As far as what is most conservative, it depends on the profile. For a single dive, the U.S. Navy is not the most conservative. But for repetitive dives, it can be more conservative. The question should be simplified to what is the time needed before previous dives do not need to be considered. For some mild moderate dives, PADI's 6 hour surface interval with the RDP works very well. But if many dives are being made, then 6 hours may not be long enough to be considered "clean."


What kind of regulator works with an IDI Ballistic BCD?

The BCD (buoyancy compensator/control Devise) low pressure line is connected to the second stage of the regulator. International Divers Incorporated devises are compatible with other manufacturers of two stage diving equipment.


Any regulator will work. It is not the regulator, but the size of the low pressure inflator hose. The low pressure inflator hose can simply be changed if there is a size (fitting) issue. This should not be an issue unless you bought a used regulator where the previous owner used a different inflator on their BCD such as an inflator you can breath from (which often has a larger diameter inflator connection).

Sigmund Freud

Can you use a ScubaPro MK16 first stage and a S550 second stage for nitro?

You can use any 1st and 2nd stage combo with nitrox up to %40.

Additional comment

The contributor is correct that the scuba industry as a whole considers no modification is needed to a regulator if the nitrox is not greater than 40%. There are some pros and cons to this. However, a titanium regulator is NOT considered nitrox compatible by many. So be careful with that.

Navy SEALs

What are the origins of scuba diving?

Diving, using trapped/contained ambient pressure air with no air-supply connection to the surface, likely began many centuries ago. With enough weight to counteract the buoyancy of the trapped air, almost anything is possible, and was probably attempted. Breath-hold or 'free' diving's origins, however, can be traced back to several thousand years BC, most likely attempts to salvage sunken treasure from wrecked ships. Both commercially and recreationally, free diving is still, by far, the most common and frequent. Cheapest, too. Strictly speaking, however, Self-Contained Underwater Breathing Apparatus, or SCUBA, using pressurized (150 atmospheres/approx 5300(!!!)lbs) air with a downstream user-demand regulator valve can be very closely dated. In his (highly reccomended) 1953 book, "The Silent World", Capitaine Jacques-Yves Cousteau describes how, in June, 1943, he first tested (his own design of) the world's first (23kg) 'aqualung', accompanied by Phillipe Taillez as (surface) dive-boat 'tender' and Frederic "Didi" Dumas as 'safety' (skin) chase diver. Capitaine Cousteau's wife, Simone was to observe only, using mask and schnorkle.

Oceans and Seas

How much does water pressure increase per vertical foot?

The pressure increase is dependent on density of the water. Pure water at 60F has about 27.78 inches of water column (INWC or INWG) per psi or approximately 0.43197 psi/ft. This is from memory; but it should be close.

Fresh water: 0.43 psi per foot Sea water: 0.44 psi per foot.

So, for each additional 10 feet of depth, figure about 4.3 to 4.4 psi increase in pressure.

You can calculate this yourself by using the fact that fresh water weighs about 62.4 pounds per cubic foot (pcf) and sea water weighs about 64 pcf. Divide those numbers by 144 (the "footprint" of one cubic foot, 12 x 12) and there you go.

It's interesting to note that this pressure is independent of volume or expanse. i.e. the water pressure behind a fresh water dam at 100 feet deep is about 43.3 psi regardless of whether the dam's reservoir is 25 miles long or 10 feet long. Depth and density are the only relevant parameters needed to determine pressure.

Dive pressure, however, would be the water pressure of 43.3 plus the air pressure above the water. So the net pressure on your ears & body would be 43.3 plus 14.7 (one atmosphere)totalling 58 psi,or about 4 atmosphers. That's four times our normal experience. Worthy of careful consideration.

Regarding diving - internal pressure inside ones body EQUALS the atmospheric pressure (14.7 psi). [Otherwise we would be squashed by the athmospere.]

Therefore, the net result is still dependent on depth ONLY - in example given it would be around 2.95 atmospheres.


What is the maximum age limit for Saturation diving?

Frankly, speaking to all of you what i had been told by one of the saturation diver that the maximum age doesn't matter atAl's long our medical is pass and fit. Because some of the saturation divers in UK overthrow their ages is 65 years old there still doing the saturation diving. As long you all who get involve in saturation diving operation is fit for your medical fitness you can still continue the job. Kathi's is what i can share the information to all of you.

Mathematical Finance

What is the volume of air at 15psi?

The qustion should be rephrased to "What is the DENSITY of air at 15 psi." Volume is independent of mass, i.e. one cubic foot is one cubic foot regardless of pressure. Density refers to how much mass there is per unit volume. At 15 psi or, more accurately 14.7 psi, (atmospheric pressure at sea level) the density of air is 0.0805 pounds per cubic foot (pcf). Not much. This is commonly called one "atmosphere." Compare that with 62.4 pcf for fresh water and about 64 pcf for sea water. I ran some quick numbers and found that for each 33 feet of sea water depth the pressure increases by one atmosphere (14.7 psi.) The common recreational dive depth limit of 60 feet corresponds to just under 3 atmospheres, including 27 psi water pressure plus 14.7 air pressure above the water for a total of about 42 psi.

Units of Measure
Snow and Ice
Weight and Mass

How much does fresh water weigh per cubic foot?

1cu ft = 12 * 12 * 12 = 1728 cu in = 1728 * (2.54*2.54*2.54) cc = 28316.85 cc = 28.3 liters = 28 kg or 62.4 pounds

Navy SEALs

Can you hear voices in a submarine while scuba diving?

It's just barely possible you could under the right conditions. You'd need to be quite close to the submarine, and they'd be distorted and difficult to understand, the same way you can hear your neighbors in an apartment building but not necessarily be able to understand what they're saying. It doesn't seem likely you could hear conversational voices; they'd probably have to be shouting.

Navy SEALs

Do dental fillings crush from scuba diving?


It's unlikely that fillings would ever crush, but theoretically an extremely badly made filling could crush from the pressure of a deep descent. A more common dental issue associated with diving is empty pockets of air in a filling expanding as you ascend and causing pain.

It's worth mentioning that you're a scuba diver to your dentist, and check out DAN(.org?) (Divers Alert Network) for dental health related issues.


No, fillings do not crush, and no, they do not trap air. This is an urban myth. There has never been even one authenticated case of either ever recorded. If you think its your teeth, its most likely your ears, believe it or not, its really hard to tell the difference.

Answer Improvement.

Far more frequent than problems with dental work are sinus problems. One old, hoary way of testing if your toothache is really a sinus problem is to hop on the heel of one foot on the side that hurts. If it throbs every hop, it's sinus and not dentistry.

I realize this sounds like voodoo. The science of it is that a swollen sinus cavity will press down on the same nerve plexus that hurts when an upper tooth gets problematic. However, that bouncing motion will really throb with a swollen sinus but won't do a thing to a tooth ache.

Doubt me? Try it :}

Another answer

I don't think a filling can be crushed, but if it is fitted badly and there is a pocket of air underneath the filling there is a possibility that as you ascend the air will expand causing the filling to pop out, however I think this rarely happens. Someone mentioned telling your dentist that you are a diver, but unless they are a diver themselves they will have no idea why you are telling them that so you will probably jut get an answer along the lines of'oh really? ? That'snice'

Periods while Pregnant

Can a woman on her period scuba dive without attracting unwanted marine life?

sharks generally do not care that much for human blood.. now put a few drops of fish blood in the water and that is a different story...

For what it's worth..."There is no evidence of increased shark interest in a menstruating female. The hemolytic blood associated with menses may instead act as a shark deterrent (Edmonds, et al., 1992, p. 65)."

I found the following reference particularly helpful. It is on the Divers' Alert Network and is titled, "Diving Medicine FAQs, Menstruation During Diving Activities"


Are scuba foam and neoprene same?

Neoprene or polychloroprene is a family of synthetic rubbers that are produced by polymerization of chloroprene.[1] Neoprene in general has good chemical stability, and maintains flexibility over a wide temperature range. It is used in a wide variety of applications, such as laptop sleeves, orthopedic braces (wrist, knee, etc.), electrical insulation, liquid and sheet applied elastomeric membranes or flashings, and car fan belts.

"Scuba Foam" or "High Density Scuba Foam" (HDSF) is commonly used in consumer products such as Koozies®, Laptop sleeves, Cell phone holders, etc.

This material can be anything from open celled foam, to polyester, to foamed neoprene with gel cells for insulation (most wetsuits are made of this material, most consumer goods are not)


What is the average price on a good scuba set?

Approx $1500 - $2000


Copyright © 2020 Multiply Media, LLC. All Rights Reserved. The material on this site can not be reproduced, distributed, transmitted, cached or otherwise used, except with prior written permission of Multiply.