Using Nitrox for Shallow Water, Commercial Diving

The job to be performed normally dictates the time required for a diver to be underwater.   Unlike recreational divers, commercial divers must often work underwater for longer periods of time. Commercial divers will often make dives requiring decompression to eliminate excess nitrogen from the body, which is because of the longer bottom times. As a diver stays longer and descends deeper, the inert nitrogen gas making up 79% of the breathing air, is absorbed in the tissues of the diver’s body at a higher rate because of the increased surrounding pressure. There is a limit to how much excess nitrogen the body can absorb before the dive requires decompression, a process by which the excess nitrogen is released from the tissue.

Commercial diving operations have had the option of decompressing the diver in the water or using a decompression chamber to decompress the diver above water, which is known as surface decompression. Using this method, the diver exits the water and quickly enters a chamber, returning to pressure and breathing pure oxygen for 30-minute increments. The pure oxygen helps to purge the excess nitrogen from the body faster. Also, with in-water and surface decompression, as the bottom time increases, the decompression time also increases. Either method of decompression allows the body to slowly and safely eliminate the excess nitrogen that has been absorbed through expiration. Failure to do so can cause the excess nitrogen to come out of solution in the body’s tissues resulting in nitrogen bubbles in the bloodstream. These nitrogen bubbles manifest as decompression sickness causing symptoms ranging from pain in the joints to more severe symptoms that can affect the central nervous system, respiratory and cardiac systems.

Decompression diving is inherently more dangerous than no-decompression diving. Personal diver susceptibilities and many factors (which can vary on a daily basis) may pre-dispose a diver to an increased risk of decompression sickness. In previous years, there were not any practical alternatives to decompression diving for commercial divers needing lengthy bottom times.

In the last 15 years, interest in an alternative breathing gas known as Nitrox has gained in popularity among recreational SCUBA divers. Due to recent equipment innovations, Nitrox diving is now an alternative for commercial diving operations. What is Nitrox and what makes Nitrox diving a better alternative?

Nitrox is a manufactured gas, with less than 79% nitrogen and a higher amount than 21% oxygen. The oxygen range can be adjusted from 22% to 40% thereby decreasing nitrogen content from 78% to 60% respectively. By decreasing the nitrogen content of the breathing gas, the diver absorbs less nitrogen, allowing him to stay longer at depth without decompression.

In the commercial diving business that equates to more time with a diver spent working underwater and less time spent decompressing.

Examples  dives to 60’ using the US Navy Air Decompression Table.

Dive Profile 1 – 60’ air dive – No decompression limit – allowable bottom time of 60 minutes

Dive Profile 2 – 60’ air dive – 120 minutes bottom time – requires 75 minutes of in-water decompression.

Dive Profile 3 – 60’ air dive – 160 minutes bottom time – requires 60 minutes of chamber decompression breathing oxygen.

 Dive Profile 4 – 60’ Nitrox dive (39% oxygen mix) – allowable bottom time of 163 minutes with no decompression.

Dive Profile 1 only allows 60 minutes of bottom time.

Dive Profile 2 only allows 120 minutes of bottom time with 75 minutes of in-water decompression required.   Today, the practice is to limit in-water decompression to 15 minutes or less[1].

Dive Profile 3 allows a longer bottom time of 160 minutes but requires a chamber decompression of 1 hour. In Dive Profile 1 and 2 there is a trade-off of increasing bottom time at the expense of lengthy decompression time. Decompression time is unproductive time that is costly and riskier from a safety aspect.

Dive Profile 4 makes the advantages clear with 163 minutes of bottom without decompression.

Nitrox diving is not the panacea for all problems associated with diving. As a matter of fact, it is most useful in shallower depths. It practicality diminishes as the depth increases past 90 feet. This is due to the increasing pressure of the oxygen in the breathing mix becoming toxic with combinations of higher percentages and deeper depths. So it is necessary for proper calculations to be made before nitrox is used, in order to determine the optimum oxygen percentage and the bottom time limits to be used on the job[2].

For years, Glenn Underwater Services, Inc. has been recognized as an innovator in inland diving, using technology to solve problems and to accomplish underwater tasks. Today, nitrox diving has become an important technological addition to Glenn Underwater Services resources and their surface-supplied diving operations. A specially designed Nitrox compressor is used to blend nitrox gas mixtures on demand. For more information on Nitrox Diving and how Glenn Underwater Services is using Nitrox to benefit our clients, please visit our website at www.glenndiving.com.

[1] As per US Navy Decompression Tables Revision 6, 9-8.4 In-water decompression on air is most suitable for dives which require less than 15 minutes of decompression

[2] Diving physiology, decompression tables, and breathing mixtures are all complex subjects requiring a working knowledge in order to ascertain what method and dive profile is best for a specific commercial diving application. The intent here is to provide a lay explanation of decompression diving requirements and possible alternatives. It is not to be used for dive planning. Only competent and trained commercial divers should carry out dive planning.