January 2005

Vol. 20, No. 1     What's this?

All I Need Is the Air That I Breathe

— what’s in your tank?

from the January, 2005 issue of Undercurrent  

We in the U.S. have come to expect the quality of the food we eat, the water we drink, and the air we breathe to be monitored by various governmental agencies and independent organizations. Nonetheless, there is no regulating organization in the U.S. to insure that the air put into divers’ tanks meets any airquality requirements whatsoever. Only PADI Five-Star centers require quarterly analysis, and there are no regulations at all on Nitrox quality.

To determine whether U.S. divers were getting good air, researchers employed TRI (Texas Research International in Austin, TX) to measure the percentage of oxygen, carbon monoxide, hydrocarbons, methane, carbon dioxide, and nitrogen in air and EAN Nitrox samples from newly-purchased tanks filled at 13 different dive stores. They ordered 27 air samples and 11 EAN Nitrox samples ranging from 32 to 36 percent.

The EAN Nitrox measurements were at unacceptable levels for 3 of 11 samples acquired from two different stores. At one store, researchers purchased 32.3% EAN Nitrox, but when the sample was evaluated at TRI, the EAN was determined to be 30%. At another shop, what was sold as EAN 32% Nitrox was actually 34.9% when evaluated by TRI, while the EAN 36% was actually 39.4%.

In one EAN sample, TRI measured 25.2 ppmv carbon monoxide, two and a half times the CO levels deemed acceptable for scuba according to the Grade E standards. For air, Grade E standards range from 20 to 22% oxygen, but TRI found one shop’s air to be 24.3% oxygen, another’s 22.2%. All remaining samples met Grade E specs.

In this random sampling of 27 air and 11 Nitrox fills from local dive shops, three air-quality discrepancies were found. Additionally, there were three significant discrepancies between store-measured EAN and actual TRI-measured oxygen percentage. Two of the three discrepancies would have decreased the acceptable maximum depth of the dive.

Editor’s Note: What is apparent here is that air from some compressors does not meet air-quality standards and that gauges testing EAN Nitrox mixes can be inaccurate. Keep in mind that these are American stores, where one would expect air and Nitrox quality to be superior to that purchased in many remote locations.

Information was gathered from Recreational Scuba Air and EAN Nitrox Quality. Haiti K. MD; Weaver LK. MD, Churchill S. NP: Department of Internal Medicine, Pulmonary/Critical Care Medicine, LDS Hospital, Salt Lake City, Utah.