imperial metric scubaComing back to America, I never realized the horrible pain of the Imperial measurement system. Not to knockdown my fellow Americans, but why do we measure stuff like this? WHY?

Ok, that was my rant. Now here is some useful information that I have been noting between diving in Europe, Asia and America.

TANKS (and Pressure!)

This shouldn’t be complicated, but for some reason I found tanks to be a bit tricky. Tank measurements include the pressure fill amount, the actual tank size, Pressure rate (low, standard, or high) and the tank composition material.

A Bar, from wikipedia is “Atmospheric air pressure is often given in millibars where standard sea level pressure is defined as 1013 mbar, 101.3 (kPa), or 1.013 bar.”

Pounds per square inch (psi) is “Pounds per square inch absolute (psia) is used to make it clear that the pressure is relative to a vacuum rather than the ambient atmospheric pressure. Since atmospheric pressure at sea level is around 14.7 psi, this will be added to any pressure reading made in air at sea level.”

The conversion from 1 bar to psi is approximately 14.50377. When converting units (not scuba tanks): liters to cu.ft, you get 1 liter is 0.0353147 cu.ft.

In general, in Europe cold water diving, one can expect to get a 12 or 15L tank, steel composition, filled to about 200-220 bar, standard pressure.

In America cold water diving, one can expect to get a 80 cu ft or 100 cu. ft tank filled to a choice of  low (2400 to 2640 psi), standard (3000 psi), and high (3300 to 3500 psi).

In terms of conversion, I will show you how I converted between Liters and cu. ft for tanks with standard pressure:

larger tanks

—->    15Liter tank : 15L * 200 bar *14.5038 psi = 105.9441 cu.ft
—->    100 cu ft tank: (100 cu. ft./.0353147 cu.ft) / (3000 psi /14.5038 psi) = 13.69005 L

OR

smaller tanks:

—->    12Liter tank : 12L * 200 bar *14.5038 psi = 84.75528 cu.ft
—->    80 cu ft tank: (80 cu. ft./.0353147 cu.ft) / (3000 psi /14.5038 psi) = 10.95204 L

So these values show you about tank sizes from cu.ft to liters. Note: This equation doesn’t seem to solve the problem of the converting consumption rate at all.

DEPTHS

This one was pretty easy. 1 meter is 3.28084ft.  A safety stop is required at 5m or 15 ft. I can see why PADI rounded the numbers…. it would be annoying to do a stop at 16.4ft instead of 15ft.

The max depth for open water divers is 18meters or 60 ft.

The max depth for advanced open water divers is 30meters or 100ft.

If you get the PADI Deep Diver Certification, the max depth is 40meters or 130ft.

TEMPERATURE

The conversion formula is: Fahrenheit Temperature = (Celsius Temperature* 9/5) + 32.

Or the easy way to remember is to double the Celsius temperature and add 32.

Of course, that’s not going to give you the exact temperature, but at least you won’t have to bust out a calculator when some says its 17degC outside (Its 62.6degF).  The only crappy thing about temperature conversions is that you can’t say something is 5 degC cooler is directly 43degF difference. For differences, you need to calculate everything in both numbers first and then explain.

CONCLUSION

  • Just remember, when you go somewhere else, that 3000 psi is about 200 bar (14.5 psi is 1 bar).
  • A 12L tank is about the same size of an 80L tank.  A 15L tank is about the same size as a 100L tank.
  • For temps in Celsius, double the number and add 32 to get Fahrenheit.
  • Max depths in meters are 18m, 30m, and 40m; and safety stops are at 5m.  Max depths in Imperial are 60ft, 100ft, and 130ft; with a safety stop at 15ft.