What depth do divers get the bends?

Question

What depth do divers get the bends?

Answer 1

As Boarder127 pointed out, it is not the depth, but a function of how fast you ascend.  Rocketing to the surface from a deep dive does run a greater risk of the bends than rocketing to the surface from the bottom of a swimming pool, but both can run the risk of the bends.

As you are diving due, your body is absorbing the nitrogen from the compressed air in your tank due to the increased pressure of the surrounding water.  The nitorgen is inert meaning it does not do anything to your body (i.e. your body doesn't use or metabolize it); however, the nitrogen is being absorbed into your body tissues.

At deeper depths, the rate of absorbtion is greater because of the greater pressures.  As you ascend, the nitrogen comes out of your tissues in the form of bubbles.

If you come up slowly enough, the nitrogen bubbles will remain tiny and will pass from the tissues to your blood stream to your lungs and will be expelled from the body through normal breathing.

If you come up too quickly, the nitrogen bubbles will be larger and either remain in the tissue or pass to the blood stream (but not the lungs).  The larger bubbles in the tissue is what causes the bends.

The ananlogy that I use for my students is a shaken bottle of soda.  How hard you shake it reflects how deep you are diving.  Once shaken, if you open the bottle slowly enough, some bubbles will form; however, it won't bubble over.  If you open it quickly, large bubbles will form and foam out.

Answer 2

First, I'm disappointed no one posted what "the bends" is officially called-- DCS or DCI.  Meaning:  Decompression Sickness or Decompression Illness.

Your body did NOT decompress the nitrogen saturation in your body correctly-- so you become "ill" or "sick".  The term "the bends" was more of a misnomer by US Navy volunteers conducting the first dive table standards.  One of the most obvious physical symptoms was a diver experiencing "DCI" would be in pain in the arm or chest and bend over-- so thus "the bends".  There are 3 main recreational dive tables-- PADI, NAUI and US Navy (which all rec. dive tables are based on US NAVY and then PADI and NAUI added a more conservative analysis on top of the US NAVY)  130 ft depth according to US NAVY dive tables can only be limited to 28 minutes for sport divers.   PADI has 12 minutes for bottom time -- far more conservative-- and safer-- due to the law of Physics-- Boyle's law-- a 3300 PSI 80 cubic cylinder would be out of air in 28 minutes!

But really a diver does NOT bend over from DCI -- usually they just lay down or sit down and become quite irritable (I had a dive student that refused anyone's assistance upon ascent and stated he had a severe headache... and wanted to isolate himself from any assistance.  I ignored this, as he was my responsibility as my student.  I pressed on to find that he had smoked cigarettes  and drank alcohol the night before.  Our deepest depth was only 5 meters/17 feet and water temps were 17 c/58 F.   In this case-- it was not DEPTH;  but having RESIDUAL nitrogen that would NOT decompress due to his lungs filled with carbon monoxide and carbon dioxide in the lung tissues (alveoli)  and nitrogen from smoking.  Also his wetsuit was 2 sizes SMALLER than he needed.  I called DAN- Divers Alert Network.  And he was driven to a local hyperbaric chamber for precaution.  I administered pure O2(oxygen) until the ambulance arrived.  He stayed in the chamber for 8 hours until the pain in his head and chest disappeared.  And he went back 3 days later due to a recurring pain--again for 12 hours in the chamber.  And then he felt better; but he was excluded from more Rescue Dive cert. class for 3 weeks and having a thorough medical approval)

So you see-- not releasing ALL gases in our body are due to DCI/The Bends.   Even having too much carbon dioxide-- if you watch some 1950 movies and even more current ones-- they show divers HYPERVENTALATING before SCUBA diving.  THIS IS A HUGE NO- NO.  Due to the reasons I wrote above--- you are NOT clearing your lungs by hyperventalating but INHALING AIR (which is a mixture of many variety of gases in our atmosphere-- where as in a SCUBA cylinder the air is compressed-- at great pressure therefore greater purity and quantity.  Also your lungs are like a sponge--our lungs are about the size of a normal watermelon and compress to the size of a small grapefruit at depth-- so at depth this "sponge" compresses but is FILLED with the gases at a great pressure (Air-78%N2, 20%O2,.9%Ar, .03%CO2 and smaller parts Neon, Helium, methane, hydrogen and others-).  So upon ascent if you hold your breath and do NOT exhale or breathe normally-- again you may experience DCI  or an AIR embolism due to NOT releasing any gases and the molecules increase in size as the lungs "sponge"-- enlarges again;  and some gas molecules are bigger than others-- nitrogen.. and it works to escape throughout the body-- thus can create an aneurysm or bubble in the bloodstream and cut off circulation-- thus causing the pain and malfunction of the heart, brain, and appendages (the pain you instantly feel);  and without proper release (decompression chamber) will block off all circulation and the organs stop functioning -- brain, lungs, heart,  then slowly the rest-- liver, kidneys, eyes and skin... and the diver will die.  This can happen in a matter of 2 hours if there is no assistance.  Giving pure O2 allows oxygen to circulate in the areas of the body where there is no blockage by a 'bubble' but does NOT cure the problem at all.  Just a precaution until the diver can properly decompress!  On land-- in a hyperbaric chamber.  NOT go back down to the same depth and correctly decompress on ascent all over again .. Why?  Because 1) the diver does not know the exact depth he was at when he did not properly decompress 2) to descend one must equalize the cavities of the human body properly  -- and one can not do this if there is a symptom of DCI  3)The diver will have to REFILL his body with the same EXACT amount of nitrogen, oxygen, and variable gases at the exact depth of DCI occurence-- one could NEVER approximate this exactness.  

So to do so under medical supervision in a decompression chamber is done slowly, accurately, and can be observed without other problems of being underwater-- no weight of the water/pressure on the cavities, no exposure gear, weights, other gear and marine life to distract the diver.

Hyperventalitng PRIOR to a dive is best used for FREE DIVERS-- who fill their lungs with Atmospheric AIR-- our "regular air" in the earth's atmosphere.  NOT pressurized.  Thus there is NO danger of getting DCI-- but can have many other problems since the human is diving with ONE BREATH.  The most current deepest dive by a human on a FREE DIVE on ONE BREATH on atmospheric air is :  A man recently went 348 ft in 3 1/2 minutes one breath and a woman did 80m/262 ft in 3 minutes using ballast (personal additional weights to help descend faster)   A freediver does NOT have to worry about any DCI because they are NOT breathing compressed air.  But their lungs do decrease in size, heart rate slows down tremendously and all other kinds of factors due to a human being's ancient ability (which as land dwellers we do NOT utilize.. but we still have capability)  of "diver's response" muscles and actions-- the human body is a wonderful thing!

The soda can is a great display to present the law of physics for presenting what occurs to a diver while ascending-- Boyle's Law-- where P1 V1 = P2 V2-- so a sponge with water absorbed and squeezed out along with the soda can is a great presentation.

More than you wanted to know-- just kind of wanted to see if I remembered everything;-)

Answer 3

Becoming susceptible to the bends is a function of depth and time at depth. The deeper you go, the less time it takes for your blood to get 'saturated' with nitrogen (your blood has dissolved as much nitrogen as it can hold at that depth). Once your blood has achieved saturation, you must rise slowly, often stopping for periods of time at various depths (decompression stops) to allow that gas to come out of solution in a controlled manner through your lungs. If you fail to do so, the nitrogen can come out of solution IN your bloodstream which causes 'the bends'.

That said, to answer your actual question you can get saturated as shallow as one atmosphere (33 ft/10 meters) if you stay down long enough (I don't have my tables handy but it's around 200 minutes - you'll probably run out of air in your tank before you reach that time). At 60 ft., you have 60 minutes, and at 130 ft. (the 'sport diving limit'), you have 5 minutes before you get into the 'danger zone'. The effects of the bends usually don't manifest until you reach the surface.

Answer 4

Divers don't get the bends from a certain depth they get it from ascending to fast and not giving time for the nitrogen in their bodies to be released at a safe pace. Divers can get nitrogen narcosis from going to deep but that depth can change with each diver and each dive.