Nitrox Mixes – Oxygen 100%
The MOD of 100% Oxygen is 6m.
This places you on the 1.6ata top limit. Do not go below for your own safety.

Pressure Equivalents
1 atm = 1.01325 bar = 10.337 meters (f w) = 33.9139 feet (f w) = 33.066 feet (s w)
1 bar = 0.986923 atm = 10.2018 meters (f w) = 33.4704 feet (f w) = 32.6336 feet (s w)
s w = Sea Water.
f w = Fresh Water

Approximate Pressure Equivalents Commonly Used in Diving
1 bar = 1 atm = 33 feet (s w ) = 10 meters = 14.7 p.s.i.

Re-Printed from www.thescubaguide.com website

Air is massive. All around and above us we are “swimming” in air and the weight of the air above us exerts pressure on everything in it. We do not notice or feel the air pressure around us because our bodies are compressed and exert an equal force back.

The weight of the atmosphere exerts a pressure of 14.7 psi at sea level. In other words, a 1 inch column of air as tall as the atmosphere (about 50 miles) weighs 14.7 pounds. This unit is called 1 Atmosphere of pressure or 1 ATM.

Scuba divers are concerned with pressures in tanks, in heads, in masks and under the water. We know that water is much heavier than air, so it exerts higher pressures with less volume. A cubic foot of water weighs 62.5 lbs, whereas a cubic foot of air weighs 1/12 lb. Sea water is even heavier – a cubic foot of sea water weighs 64 lbs. To exert 14.7 psi (1 ATM) it takes 50 miles of air, whereas it only takes 33 feet of water to exert the same pressure.

Let’s suppose you fill a balloon with 24L of air. Let’s take it scuba diving.

Depth Volume Air Density
sea level 12 1x
33′ 6 2x
66′ 4 3x
99′ 3 4x
132′ 2.4 5x

You see that the volume of the air changed the most between 0 feet and 33 feet, where it was squished to half of its previous size; a loss of 6L. Descending from 33 feet to 66 feet changed the volume by only 2L. As our air goes deeper the relative compression decreases. You will experience this effect firsthand when scuba diving; the first 15 feet is when you’ll feel “the squeeze” as all air spaces (lungs, sinuses, ear canals, the air in your mask, intestines and even bits of air trapped in your teeth) are compressed to half of their sea-level size. When descending you need to compensate for that loss of volume and “reinflate” your body by equalizing your ears, exhaling into your mask (which will literally suction itself to your face). You also need to add air to your BCD to maintain buoyancy. Once you’re past 15 feet it gets easier and once you’re below 40 feet you might hardly feel the difference in pressure at all.

The reverse holds true when ascending to the surface. All the air spaces will double in size in the last 33 feet; this means you need to leak out air as you ascend, bubbles will escape from your mask and you need to release air from your BCD; lest it inflate like a balloon and send you bobbing quickly to the surface (and probably give you the bends while you’re at it).

Scuba diving is not a dangerous sport. Scuba diving is riskier than a sport like hockey or baseball, but less dangerous than street luge or mountain climbing. Modern scuba diving equipment is easy to use, very reliable and with the proper training and a responsible attitude scuba diving can be enjoyed safely. In fact, almost all scuba diving injuries and casualties are the result of recklessness or bad judgment.

There are certainly risks involved in scuba diving. Part of certification training is learning about those risks and how to avoid them. The majority of possible health problems are forms of barotraumas, which are all caused in one way or another by changes in pressure. Other possible risks are associated with higher absorption of gases, while other risks are more mechanical and environmental in nature.

Here are some of the risks associated with scuba:

  • Barotrauma (explained by Boyle’s law)
    • alternobaric vertigo
      Dizziness or disorientation caused by unbalanced pressures in the inner ear. Most commonly experienced by stubborn scuba divers trying to dive with the common cold.
    • altitude sickness
      Headache caused by a quick ascent, usually associated with airplane travel.
    • barodontalgia
      Pain caused by tiny bubbles of gasses trapped in the teeth, usually in fillings or caps.
    • decompression sickness, a.k.a. “the bends”
      Nitrogen coming out of a solution in tissue which is caused by hastened decompression.
    • dysbaric osteonecrosis
      Rare bone lesions produced by long term exposure to high pressure environments.
    • embolism
      Nitrogen coming out of a solution in the body. It can be caused by accelerated decompression.
    • arterial gas embolism
      Gas coming out of a solution in the arteries. It can be potentially fatal.
    • cerebral embolism
      Gas coming out of a solution in the brain. It can be potentially fatal.
    • lung expansion injury
      It can be caused by holding breath while ascending.
    • pneumomediastinum
      Ruptured bronchus or alveoli in the lungs from excessive pressure. May be caused by holding breath while ascending.
    • pressure arrhythmias
      Abnormal heart rhythms caused by external pressure.
    • tinnitus, Eustachian & inner ear damage, Tympanic membrane rupture and/or hearing loss
      Inner ear damage can result from diving without equalizing air pressure in the Eustachian tubes. It is complicated or caused by water pressure and blocked sinuses and it can be extremely painful.

 

  • Non-Barotrauma (explained by Henry’s Laws and Dalton’s Laws)
    • co2 toxicity, a.k.a. hypercapnia.
      Too much CO2 in the body, usually caused by inadequate exhalation or air consumption during heavy exertion. Symptoms include shortness of breath, headache and/or confusion.
    • nitrogen narcosis, a.k.a. “rapture of the deep”
      The result of a toxic effect of high pressure nitrogen on nerve conduction. Symptoms are comparable to the effects of alcohol drunkenness.
    • o2 toxicity
      Toxic effects of absorbing too much oxygen. Symptoms include a burning sensation in the lungs, twitching, dizziness, vomiting and/or seizures.
  • Other physical and health hazards – Scuba Diving
    • dangerous marine life
      Most common injuries are the result of divers touching poisonous animals such as jellyfish, fire coral, urchins or stingrays. Attacks by large fish are extremely rare.
    • dehydration
      Dehydration is an inadequate bodily water level. Surprisingly common on boat tours; diving while dehydrated aggravates other health risks including nitrogen narcosis and hypercapnia.
    • hypothermia
      Hypothermia is a loss of body heat and early symptoms include fatigue and loss of judgment.
    • drowning
      An obvious risk if for any reason a diver breathes in water instead of air or just simply the loss of air.
    • running out of air
      Typically caused by irresponsible air management or scuba equipment failure.
    • underwater injury
      Common injuries include abrasions and cuts (from sharp coral), sprains, bumps and bruises. Studies show more serious injuries occur getting in and out of the boat than actually in the water.

Typical atmospheric air is mostly nitrogen (78%) and oxygen (21%) with only a small amount of carbon dioxide (0.03%). Other gases are present in trace amounts: Hydrogen, Argon, Neon, Helium and more.

When you breathe your lungs absorb oxygen from the air, but they also absorb all the other gases as well. The oxygen is used by your body for all its functions, but what about nitrogen? Air has more than three times more nitrogen than oxygen, so your body is dealing with quite a lot of it. The answer is that our body is saturated with inert nitrogen, it offgasses through your skin and quite a lot of it filtered by your organs and passed as nitrates in your urine.

When your tanks are filled for scuba diving they are usually filled with dry filtered air. Pumps and filters remove most of the particulates (dust, pollen, airborne pollutants). Water vapor is also present in air; the amount varying greatly depending on temperature, pressure and weather. Water condensation can rust the inside of a scuba tank, so water vapor is filtered as well. The result is a tank containing a normal mixture of dry atmospheric gases in normal proportions.

BAR to PSI

Reprinted from www.asknumbers.com

You may use this pressure conversion table if you are converting from bar to psi (pound per square inch) for the values listed in the table below.

For your information, Bar is the atmospheric pressure at the sea level, which equals to 100 kilopascals. Psi is 1 pound of force per square inch.

1 Bar = 14.5037738 Psi (Pound Per Square Inch)

To convert any other value, please go to website: Pressure Conversion

To convert pressure from psi to bar, please go to website: Psi to Bar

 

Bar to Psi Chart

Bar Psi Bar Psi Bar Psi Bar Psi
1 14.5037738 26 377.0981188 51 739.6924638 76 1102.286809
2 29.0075476 27 391.6018926 52 754.1962376 77 1116.790583
3 43.5113214 28 406.1056664 53 768.7000114 78 1131.294356
4 58.0150952 29 420.6094402 54 783.2037852 79 1145.79813
5 72.518869 30 435.113214 55 797.707559 80 1160.301904
6 87.0226428 31 449.6169878 56 812.2113328 81 1174.805678
7 101.5264166 32 464.1207616 57 826.7151066 82 1189.309452
8 116.0301904 33 478.6245354 58 841.2188804 83 1203.813225
9 130.5339642 34 493.1283092 59 855.7226542 84 1218.316999
10 145.037738 35 507.632083 60 870.226428 85 1232.820773
11 159.5415118 36 522.1358568 61 884.7302018 86 1247.324547
12 174.0452856 37 536.6396306 62 899.2339756 87 1261.828321
13 188.5490594 38 551.1434044 63 913.7377494 88 1276.332094
14 203.0528332 39 565.6471782 64 928.2415232 89 1290.835868
15 217.556607 40 580.150952 65 942.745297 90 1305.339642
16 232.0603808 41 594.6547258 66 957.2490708 100 1450.37738
17 246.5641546 42 609.1584996 67 971.7528446 125 1812.971725
18 261.0679284 43 623.6622734 68 986.2566184 150 2175.56607
19 275.5717022 44 638.1660472 69 1000.760392 175 2538.160415
20 290.075476 45 652.669821 70 1015.264166 200 2900.75476
21 304.5792498 46 667.1735948 71 1029.76794 250 3625.94345
22 319.0830236 47 681.6773686 72 1044.271714 300 4351.13214
23 333.5867974 48 696.1811424 73 1058.775487 500 7251.8869
24 348.0905712 49 710.6849162 74 1073.279261 750 10877.83035
25 362.594345 50 725.18869 75 1087.783035 1000 14503.7738

Atm (Atmosphere) To Bar Conversion

You may use this pressure conversion table if you are converting from atm (atmospheric pressure) to bars for the values listed in the table below.

For your information, Atm (atmospheric pressure) is the force per unit area by the weight of air above that point. Bar is the atmospheric pressure at the sea level, which is around 100 kilopascals.

1 Atm = 1.01325 Bars

To convert any other value, please go to Pressure Conversion

 

Atm to Bar Chart

Atm Bar Atm Bar Atm Bar Atm Bar
1 1.01325 26 26.3445 51 51.67575 76 77.007
2 2.0265 27 27.35775 52 52.689 77 78.02025
3 3.03975 28 28.371 53 53.70225 78 79.0335
4 4.053 29 29.38425 54 54.7155 79 80.04675
5 5.06625 30 30.3975 55 55.72875 80 81.06
6 6.0795 31 31.41075 56 56.742 81 82.07325
7 7.09275 32 32.424 57 57.75525 82 83.0865
8 8.106 33 33.43725 58 58.7685 83 84.09975
9 9.11925 34 34.4505 59 59.78175 84 85.113
10 10.1325 35 35.46375 60 60.795 85 86.12625
11 11.14575 36 36.477 61 61.80825 86 87.1395
12 12.159 37 37.49025 62 62.8215 87 88.15275
13 13.17225 38 38.5035 63 63.83475 88 89.166
14 14.1855 39 39.51675 64 64.848 89 90.17925
15 15.19875 40 40.53 65 65.86125 90 91.1925
16 16.212 41 41.54325 66 66.8745 100 101.325
17 17.22525 42 42.5565 67 67.88775 125 126.65625
18 18.2385 43 43.56975 68 68.901 150 151.9875
19 19.25175 44 44.583 69 69.91425 175 177.31875
20 20.265 45 45.59625 70 70.9275 200 202.65
21 21.27825 46 46.6095 71 71.94075 250 253.3125
22 22.2915 47 47.62275 72 72.954 300 303.975
23 23.30475 48 48.636 73 73.96725 500 506.625
24 24.318 49 49.64925 74 74.9805 750 759.9375
25 25.33125 50 50.6625 75 75.99375 1000 1013.25

You may use this length conversion chart if you are converting from meters (m, metre) to fathoms for the values listed in the table below.

1 Meter = 0.546806649 Fathoms

1 Fathom = 1.8288 Meters

To convert any other value, please go to Length Conversions

 

Meter To Fathom Chart

Meter Fathom Meter Fathom Meter Fathom Meter Fathom
1 0.546806649 26 14.21697287 51 27.8871391 76 41.55730532
2 1.093613298 27 14.76377952 52 28.43394575 77 42.10411197
3 1.640419947 28 15.31058617 53 28.9807524 78 42.65091862
4 2.187226596 29 15.85739282 54 29.52755905 79 43.19772527
5 2.734033245 30 16.40419947 55 30.0743657 80 43.74453192
6 3.280839894 31 16.95100612 56 30.62117234 81 44.29133857
7 3.827646543 32 17.49781277 57 31.16797899 82 44.83814522
8 4.374453192 33 18.04461942 58 31.71478564 83 45.38495187
9 4.921259841 34 18.59142607 59 32.26159229 84 45.93175852
10 5.46806649 35 19.13823272 60 32.80839894 85 46.47856517
11 6.014873139 36 19.68503936 61 33.35520559 86 47.02537181
12 6.561679788 37 20.23184601 62 33.90201224 87 47.57217846
13 7.108486437 38 20.77865266 63 34.44881889 88 48.11898511
14 7.655293086 39 21.32545931 64 34.99562554 89 48.66579176
15 8.202099735 40 21.87226596 65 35.54243219 90 49.21259841
16 8.748906384 41 22.41907261 66 36.08923883 100 54.6806649
17 9.295713033 42 22.96587926 67 36.63604548 125 68.35083113
18 9.842519682 43 23.51268591 68 37.18285213 150 82.02099735
19 10.38932633 44 24.05949256 69 37.72965878 175 95.69116358
20 10.93613298 45 24.60629921 70 38.27646543 200 109.3613298
21 11.48293963 46 25.15310585 71 38.82327208 250 136.7016623
22 12.02974628 47 25.6999125 72 39.37007873 300 164.0419947
23 12.57655293 48 26.24671915 73 39.91688538 500 273.4033245
24 13.12335958 49 26.7935258 74 40.46369203 750 410.1049868
25 13.67016623 50 27.34033245 75 41.01049868 1000 546.806649

Other useful sites for tables and pressure laws are:

www.engineeringtoolbox.com/pressure-d_587.html

Disclaimer: The information listed here is the best possible source and if you need to use this information during any sporting activity then it is incumbent on each individual to confirm it’s accuracy.