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 £2.50, or £5.00 for non-members (plus 20% for delivery outside Europe). Copies can be ordered online, or from publications@imca-int.com.
Full information on IMCA is available from www.imca-int.com and from the association at 52 Grosvenor Gardens, London SW1W 0AU, UK. Tel: +44 (0)20 7824 5520; Fax: +44 (0)20 7824 5521.
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About IMCA
• IMCA is an international association with over 850 members in more than 60 countries representing offshore, marine and underwater engineering companies. IMCA has four technical divisions, covering marine/specialist vessel operations, offshore diving, hydrographic survey and remote systems and ROVs, plus geographic sections for the Asia-Pacific, Central & North America, Europe & Africa, Middle East & India and South America regions. As well as a core focus on safety, the environment, competence and training. IMCA seeks to promote its members’ common interests, to resolve industry-wide issues and to provide an authoritative voice for its members.
• IMCA publishes some 200 guidance notes and technical reports – many are available for free downloading by members and non-members alike. These have been developed over the years and are extensively distributed. They are a definition of what IMCA stands for, including widely recognised diving and ROV codes of practice, DP documentation, marine good practice guidance, the Common Marine Inspection Document (CMID) – now available electronically as e-CMID, safety recommendation, outline training syllabi and the IMCA competence scheme guidance. In addition to the range of printed guidance documents, IMCA also produces safety promotional materials, circulates information notes and distributes safety flashes.
