Published on 12 June 2012
One of the most recent publications from the International Marine Contractors Association (IMCA) is ‘Surface Supplied Diving Operations Using Nitrox’ (IMCA D 048). Surface supplied diving is sometimes carried out using a breathing gas mix of nitrogen and oxygen, with a higher percentage of oxygen in the mix than in natural compressed air. The common industry terminology for such a gas mix is nitrox.
“Diving while breathing nitrox reduces the required decompression time for any particular dive in comparison to the same dive using natural compressed air,” explains IMCA’s Technical Director, Jane Bugler. “The technique is normally used to ensure that particular dives can be carried out without the diver needing any decompression, but in other cases is used to ensure that very lengthy decompression is not required. The dive plan for the use of surface supplied diving using nitrox needs to consider all the relevant safety implications of using this technique instead of natural compressed air. One of the main risks, not normally present when breathing compressed air, is the increased risk of oxygen toxicity problems, particularly those occurring while the diver is still under water. IMCA guidance states that any gas mix containing a percentage of oxygen greater than 25% should be handled as if it is pure oxygen. This means that any nitrox mix which is over 25% oxygen will require the use of oxygen compatible greases and equipment components throughout the system, special cleaning procedures etc ”
The new guidance identifies what is generally regarded in the diving industry as good practice to achieve safe working during surface supplied diving operations using nitrox. National regulations may exist in some parts of the world that restrict or exclude the use of this technique (for example by restricting depth or oxygen partial pressures). In such cases these regulations must always take precedence over this guidance.
Sections of the new publication deal with safety considerations, personnel, equipment, and decompression tables. The safety considerations section includes information on operational limits, risk assessment, equipment failure, fire and explosion risk, maximum partial pressure of oxygen, bail-out bottle, secondary surface gas supplies, surface standby diver, oxygen toxicity, and breathing apparatus. The personnel section looks at the role of divers, supervisors, equipment technicians and manning levels. And, the equipment section of the guidance covers diving equipment, decompression facility, marking of gas storage cylinders/quads, on-site gas mixing, use of gas blender or membrane compressor, gas purity, and charging of storage cylinders.
Like all IMCA guidance documents IMCA D 048 can be downloaded via both the public and members-only websites free of charge, with printed copies available to members at Â£2.50, or Â£5.00 for non-members (plus 20% for delivery outside Europe). Copies can be ordered online, or from [email protected].