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IMCA guidance on Minimum Quantities of Gas Required Offshore

Published on 18 June 2012

The International Marine Contractors Association (IMCA) has published ‘Minimum quantities of gas required offshore’ (IMCA D 050) to address the minimum amount of emergency breathing medium (air or mixed gas) required to be kept at an offshore dive site before the dive commences, and during it. Helpfully , the new publication includes a useful equation for determining the minimum quantity of oxygen required to maintain the desired oxygen partial pressure levels in a system during decompression.

“In preparing this document, which supersedes AODC 014 which has been in existence since July 1983 we had four objectives in mind,” explains IMCA’s Technical Director, Jane Bugler.”We wanted to assist the diving contractor in preparing the diving project plan; ensure that the amounts of emergency air and gas held at the site have been carefully considered and calculated; ensure that these amounts are displayed in dive control and in saturation/chamber control; and, lastly, to make sure that supervisors do not start a dive and have to call a halt to it if these amounts are reduced to below the identified minimum level.

“The new IMCA D 050 provides operational guidance based on sound safety principles highlighting the need for an adequate safety management system; hazard identifications and an appropriate level of risk assessment; and failure modes and effects analyses (FMEA).”

The guidance is applicable worldwide. A number of countries have national regulations and/or standards that apply to diving operations, if these are more stringent than the IMCA guidance they need to take precedence over it.

“Attempting to formalise the minimum levels is difficult as they are heavily dependent on individual circumstances,” says Jane Bugler. “These include the breathing mixtures used; decompression schedules used; depth of diver; work rate; and the environmental conditions at the site. Our guidance only provides information on the absolute minimum levels to be carried out.”

‘Minimum quantities of gas required offshore’ (IMCA D 050) contains sections devoted to surface orientated diving (air, nitrox or heliox) and closed bell diving (bounce diving and saturation diving) and an appendix devoted to gas calculations and encompassing diver’s gas consumption (in water); maintenance of oxygen partial pressure during decompression; volume of chambers; oxygen metabolic consumption (in chambers); and BIBS gas consumption (at surface pressure).

The revised publication can be downloaded free of charge from the IMCA website at by members and non-member alike, with additional printed copies available to members at £10, and to non-members at £20 (plus 20% for delivery outside Europe). Copies can be ordered online or from [email protected] and from IMCA at 52 Grosvenor Gardens, London SW1W 0AU. Tel: +44 (0)20 7824 5520; Fax: +44 (0)20 7824 5521.