oxygen cylinders

Question
QUESTION: Can we use 100% oxygen in diving cylinders at grater depths.
If not what are the possible complications. If yes for how much depth can we use them.

ANSWER: Hi Veeru

The short answer to your question is "No".  Although oxygen is necessary to support metabolism (life), it can also be toxic when breathed under high concentrations and while the body is under pressure.  Pure oxygen is used in hyperbaric (pressurized) chambers to treat wounds and also for diving related injuries but it is used under very tightly controlled conditions.  The patient is monitored constantly while in the chamber.  This would not be possible for a diver submerged under water.

Air which has increased amounts of oxygen added is called Enriched Air or Nitrox.  Nitrox is commonly used in diving but it is not 100% oxygen.  It is typically 32 to 50% oxygen with the remainder of the gas composed of nitrogen, helium or some other inert gas.

Nitrox does not permit the diver to dive deeper.  It will permit the diver to remain at a safe depth for a longer period of time without an unnecessarily high probability of decompression illness.  Generally speaking, the higher the oxygen concentration, the shallower the maximum depth to which the diver can safely descend.

The calculations involved are too complicated to describe in this letter so I'll give you a brief example of what a higher concentration of oxygen will permit the diver to do.  The maximum depth for a diver on 32% oxygen is about 130 feet.  The maximum depth for a diver on 50% oxygen is about 70 feet.  While at those depths, the diver can safely remain for a much longer period of time as long as his air supply is sufficient to permit the longer times.

As you can see, this can get complicated.  That's why specialized training courses must be taken by divers wishing to use any breathing gas other than standard breathing air.

Veeru, I hope this answers your question.  If not, please write back and I'll be happy to provide more information.

Sincerely,
Mike Giles
Mike's Dive Center
mikescuba.com

---------- FOLLOW-UP ----------

QUESTION: Thanks for the previous answer
As the nitrogen causes narcosis can the he+o2 mix can be cosidered the better option, or there is any betterone than this except ne+02.

Answer
The question of which one is "best" does not have a clear-cut answer.  It depends on the depths for the planned dive as well as the duration of the dive.  Nitrox (nitrogen and oxygen)is well suited for shallow depths (above 100 feet).  It is also relatively inexpensive and readily available.  Heliox (helium and oxygen) is better suited for deeper depths.  Helium is less dense than nitrogen so the mix (Heliox) is not as "thick" as Nitrox at deeper depths and is easier to breathe.  There are also mixtures of all three gases (Trimix) which incorporate the properties of each gas to provide the relative benefits of each.  Heliox and Trimix aren't readily available at most dive sites and are much more expensive.  As previously stated, the use of these exotic gases requires specialized training and properly prepared equipment.  The presence of high concentrations of oxygen in contaminated equipment poses a risk of excessive heat generated by oxidation.  This heat can cause equipment failure during use.

Thanks for the follow-up question!!

Mike