Atmospheres (ATMs) versus ATAs

[dougchartier]

I'm still not certain of which is appropriate to use when. Can someone please explain the difference and proper usage? Thanks!

 

[Jax]

Pressure, Depth and Scuba Diving - The Basic Consequences of Water Pressure in Scuba Diving

Yes, air actually has weight. The weight of air experts pressure on your body - about 14.7 psi (pounds per a square inch). This amount of pressure is called one atmosphere of pressure because it is the amount of pressure the earth's atmosphere exerts. Most pressure measurements in scuba diving are given in units of atmospheres or ATA.

ATA is the proper acronym for the measure of atmospheres, and stands for Atmospheres Absolute.

ATM is a slang-ish acronym for atmospheres, not scientific.

 

[Cave Diver]

It depends on your usage.

ATM is a relative term. When you descend to 99' you've increased the pressure by 3 ATM's over what you were at the surface (one for every 33' of depth) but you will be at 4 ATA of pressure (3 ATM's for depth + 1 for the surface).

Pressure, Depth and Scuba Diving - The Basic Consequences of Water Pressure in Scuba Diving



ATA is the proper acronym for the measure of atmospheres, and stands for Atmospheres Absolute.

ATM is a slang-ish acronym for atmospheres, not scientific.

Assigning a value of 14.7 psi to 1 ATM isn't scientific?

 

[scjoe]

An ATM is 14.7 PSI or 1 BAR of pressure. Each 33 feet in seawater adds 1 ATM of pressure. An ATA is the total pressure at a given point and includes the 1 ATM of air pressure. Your SPG gives you a reading of ATM, not ATA.

 

[DazedAndConfuzed]

You think dive watch makers would use ATA instead of ATM so that they could add an extra atmosphere to their depth rating. But maybe people wouldn't know what ATA stands for.

 

[mrsrobinson27]

ATM - used to express relative pressure; for example, atmospheric pressure at sea level is 1ATM, or gauge pressure at 66 feet of water is 2ATM.
ATA - used to express absolute pressure, which is the sum of atmospheric pressure and gauge pressure. In diving, absolute pressure is also called ambient pressure.

Example of usage: At the depth of 99 feet of water the gauge pressure is 3ATM and absolute (ambient) pressure is 4ATA (1ATM of atmospheric pressure at sea level + 3ATM of water pressure at 99 ft).

 

[Jax]

An atmosphere is defined as the normal pressure of air at sea level (normal pressure does not include such factors as barometric pressure).

When we use the term atmosphere (atm), we aren't necessarily considering the pressure that is already being exerted on the body. To correctly state the total amount of pressure being experienced we use atmospheres absolute (ata).

Mild Hyperbaric Oxygen Therapy - ATA, ATM, PSI, PSIG