Pressure and health

Question
QUESTION: Dear Mike,

My question is related to the side-effect of diving.

I know that while diving in a diving suit at some depth the diver has to maintain a higher pressure in his suit to counteract the pressure of the water. And then if staying long in this situation this causes certain illnesses if the diver goes out too quick (the decompression may even kill him). The longer he stays underwater before rapidly going out the stronger the affect is.

My questions is: How strong must the air pressure in the diver's suit be to cause such illness if, let say, he stays in his suit underwater for 12 hours before going out? Starting with what depth of diving do such side effect emerge?

Or let it formulate otherwise: Would the pressure of 2 or 3 atm already cause such illness - and after how much time spent underwater before instantaneous going up? (And how deep in water the pressure is 2 and 3 atm?)

Regards,

Mathew

ANSWER: Hi Mathew,

Good Question!!  However there are a couple of misconceptions that we need to clear up.  The diving suits worn by divers in cold water are called "dry suits".  The diver wears warm thermal underwear under a waterproof shell.  Air can be put into the suit through an air hose and valve located on the front of the suit.  Just enough air is introduced to keep the water pressure from compressing the waterproof shell against the thermal underwear.  This compression would prevent the suit from properly insulating the diver.  As the diver goes deeper, the air inside the suit compresses so more air is needed to maintain the space between the underwear and the outer shell.  The air inside the suit is at the same pressure as the water outside the suit and is adjusted as the diver changes depth.

The illness you're referring to is commonly called decompression illness.  It's caused by nitrogen bubbles.  As the diver breathes air under pressure (diving), nitrogen from his inhaled air dissolves in the tissues and blood.  The deeper the diver goes and the longer he stays will determine how much nitrogen is dissolved.  When the diver starts to come up, the pressure is decreased and this dissolved nitrogen starts to come out of the tissues.  As long as he comes up slowly, the nitrogen will be eliminated through his exhaled breath.  If he comes up too quickly, then the nitrogen will come out quickly in the form of bubbles in his blood and tissues.  This causes decompression illness.

In your question, you need to know how long the diver should stay underwater to get rid of the excess nitrogen accumulated after 12 hours underwater.  That would depend on how deep the diver has gone.  Remember, the deeper the dive, the greater the pressure so the deeper the diver has gone, the longer it will take to get rid of the excess nitrogen.  At the least, it will take about 2 hours and may take up to 14 hours...again depending on the depth.  Dive computers will calculate all this for the diver so they just read their computers and follow the instructions it gives on how fast to come up and how long to wait before surfacing.

Your third question asks how much pressure does water exert?  Thirty three feet (about 10 meters) of salt water will exert 1 atm of pressure.  That would be added to the atmospheric pressure at sea level (about 1 atm) to make a total pressure of 2 atm at 10 meters of depth.  Each additional 10 meters of salt water will add 1 atm of pressure.

Mathew, you can see that this is a very complicated subject and requires a lot of study to fully understand what's happening.  This is only a brief explanation but I hope it gives you an idea of how water pressure, nitrogen and dive suits work.

Thanks for writing!!

Mike
Mike's Dive Center

---------- FOLLOW-UP ----------

QUESTION: Dear Mike,

thank you very much for your long and very clear answer. Especially I am grateful for having cleared all my misconceptions - I suppose they might be quite common among people like who have never been diving in this kind of dry suit - only watching some TV documentary (I have always been thinking that the air pumped into the suit is exercising its pressure directly on the skin of the diver). Now I am happy I understand it better.

My follow-up question is: Do you know any website that does have such a "dive calculator/computer" so that I may calculate for myself various possibilities and gain theoretical knowledge of what I will never have an opportunity to experience in practice (I am already 73 and after several surgeries I don't think I will ever dive myself).

Best regards,

Mathew

ANSWER: Hi Again, Mathew

I know how age can factor into the activities we would like to participate in...I'm currently 69!!  Fortunately, I've  been diving for 58 years and enjoyed a lot of experiences.  At my age, I know better than to pursue more vigorous diving activities so will stick to recreational scuba from now on.  Thanks for sharing that information.

Your statement about air exercising it's own pressure directly on the skin of the diver is actually correct.  What you need to keep in mind is that water is actually transmitting the water pressure through the air inside the suit and then to the skin of the diver.  These pressures are actually equalized even though the two mediums (air and water) are different.  As an example, if you press an inflated balloon against your skin, the pressure of your hand is transmitted through the air in the balloon to your skin so you can feel the pressure.

I see you're located in Poland so I'll try to tailor this answer to cover that region.  The training and certification agency I'm affiliated with is named the Professional Association of Diving Instructors (PADI)and they have offices in Europe.  You should be able to find a PADI dive center fairly near your location.  I checked the main website, www.padi.com and see that there are several facilities in your country but, not being familiar with your specific location, I can't pick one for you.  PADI has an electronic device called the Electronic Recreational Dive Planner (ERDP)that will permit you to plan dives and see the limits on dive time and depth as well as the nitrogen accumulation we spoke of.  These inexpensive devices are designed to be used in conjunction with a scuba course but I'm pretty sure the dive center will be happy to sell you one and show you the basics of it's operation.  It comes with a detailed operations manual but it will still require some assistance to make its understanding easier for you.  Although you seem comfortable with English, I believe the device may be available in Polish as well.  Your dive center can tell you.  If I were closer, I'd be pleased to show you how it works and also to explain the physics behind it's development.  Hopefully, your local center will do so as well.

PADI has just released it's newest version of the Open Water Dive Manual for students but, unfortunately, it has dropped the theoretical sections on dive calculations in favor of showing students how to plug numbers into a dive computer.  I'm not in favor of that change but...they didn't ask me!!  If you can find an older version of the dive manual in a store or possibly online, you can gather much useful information on the physics of dive table calculations.  Again, your local dive center should be able to help you find a useful manual.  They may even have an old PADI manual laying around.  They can't use it any longer so you might be able to get it very inexpensively.  The principles of dive planning are presented in an easy to understand format since the students generally have no previous experience in diving.

I wish I could provide a detailed explanation of how dive physics works but it's just too much information to put in a column like this.  I would also like to have your feedback during instruction so I could make sure you're on the right track.

Mathew, try these suggestions and see if it provides satisfactory information.  If not, write back with specific questions and I'll be happy to answer them for you!!

Best Wishes,
Mike

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QUESTION: Hi Mike,

Once again, thank you very much for your detailed answer - and I hope that I could get the calculator or the manual (or both) you are talking about. Although the nearest PADI shop is located some 200 km from my town. I am only wondering why all of them are located in central Poland, and none of them is located on the seashore or in the great lakes area, where one would expect them?

You have written: "I see you're located in Poland". I wonder, how have guessed. From what I had read before writing to you I understood that all my personal data, including e-mail, are hidden to the expert. It's not that I necessarily want to hide my country, it's only that the information given to me by the AllExperts system does not appear to be 100% correct.

All the best,

Mathew

Answer
Hi again, Matthew,

First, let me apologize for the delay in answering your question.  I changed my email address and the AllExperts site didn't get the change so I haven't been aware that questions were awaiting me.

To answer your question regarding personal information being released by the AllExperts site, the only thing that identifies your location is the name of the country (Poland) where the question originated.  Nothing else except the name you provided appears.  You do not even have to provide your real name. It's very helpful for us to know your general location because some information will vary by country.  For example, I may put values in metric for those countries where it's use is common and use imperial values for others.  Additionally, if a question has to do with laws or standards, it will vary by country so what's valid in one country may not be valid in another.  Once again, no attempt is made to pinpoint your location, it just helps us provide relevant answers if we know where the question originated.

Thank you for your interest and, once again, I apologize for the delay in answering your question.