Nitrox & Mixed Gas Diving

Project Type
Projects Icon - Technical Services

Project Description

Used on a variety of projects to increase stay times and enhance safety (Applicable to all industries)

The plan called for divers to work at a depth of 90 feet.  Diving work at this depth can be conducted safely using surface supplied air, but time on the bottom is limited.  The no decompression limit at 90 feet on air is 30 minutes.  After 30 minutes, the decompression obligation quickly escalates and work times beyond one hour are impractical and unsafe.

To allow increased bottom while minimizing decompression, it was decided that Enriched Air, or Nitrox, would be used.  Nitrox is a mixture of nitrogen and oxygen where the percentage of oxygen is varied to reduce the amount of inert gas in the breathing mixture.  Breathing gas with a higher partial pressure of oxygen allows a shallower equivalent air depth to be used when calculating decompression time.

In this case, the breathing gas was mixed using 65% oxygen and 35% nitrogen resulting in an equivalent air depth of 70 feet.  This increases the bottom time to 50 minutes without any required decompression.  However, to work productively, a diver needs to be able to spend two to three hours on the bottom.  Two and one half hours at 70 feet would require over seventy minutes of in-water decompression time.  At three hours bottom time, the decompression would approach two hours.

Using a procedure called surface decompression on oxygen, or SurD-O2 it is possible to dramatically reduce the decompression times and permit the diver to spend all or a portion of his decompression time in a decompression chamber making the process more comfortable and much safer in a controlled environment.  In the case of a 70 foot dive for 2.5 hours, SurD-O2 reduces the decompression time by 40% all of which can be spent in the decompression chamber.

All other things being equal, most diving contractors would prefer to work a twelve-hour day. This usually allows them to establish a dive rotation that includes at least three dives. Table 1 illustrates the productivity gained by utilizing Nitrox and surface decompression on oxygen.  In each case, the three divers would spend a collective nine hours involved in diving, but the divers using Nitrox and SurD-O2 would enjoy an additional two and one half hours of productive time over the air divers.  They would also reduce their decompression time by 62% and spend no time decompressing in the water.