IMCA publishes info note on divers’ gas supplyPublications // June 29, 2011
The International Marine Contractors Association (IMCA) has published an information note (IMCA D 04/11) on Divers’ Gas Supply.
“In the early days of saturation diving, a number of situations arose when divers working in the water lost their main gas supply,” explains IMCA’s Technical Director, Jane Bugler.
“Upon investigation it was found that the cause, in some of these cases, was that the gas supply system was set up in such a way that a failure of one diver’s umbilical or supply pipe work also removed the gas supply to another diver.
“A requirement was therefore introduced that each diver’s gas supply needs to be arranged so that if one line fails then this does not interfere with another diver’s gas supply.
“This requirement has been in existence since 1976. It was repeated in 1983 in the UK Department of Energy’s Diving Safety Memo 10/1983 and AODC issued formal guidance in November 1984 as information note AODC 028 – Divers’ gas supply. This requirement is also included in the document IMCA D 024 – Diving Equipment Systems Inspection Guidance Note (DESIGN) – in section 5, item 7.13 and in IMCA D 014 Rev. 1 – International code of practice for offshore diving – in paragraph 4.6.3.
“Our recently published information note, which updates and replaces AODC 028, has been developed to clarify the requirement, and circulated to all members of our diving division,” she adds.
The information note sets out the general principles explaining that it is necessary to ensure that the loss of gas supply to one diver will not compromise another diver by depriving him of his supply.
This could happen if two divers are fed from a common supply and one diver’s umbilical is cut or ruptured resulting in the second diver potentially losing his supply through the gas taking the path of least resistance into the water.
The Diving Safety Memo 10/1983 stated this requirement as: "‘The air supply system to a diver should be designed in such a way that in the event of the diver's umbilical being cut or severed, it should not deprive any other diver or standby diver of their air supply. It should be noted that it is impractical for the affected gas supply to be isolated by manually shutting a valve."
“Although the memo refers to ‘air supply’, the problem is the same for air or mixed gas diving, and is equally applicable to surface orientated or bell diving,” explains Jane Bugler.
“It needs to be stressed that the standby diver (or bellman) should also be considered. If there are two working divers in the water, plus a standby diver (or bellman), then the breathing mixture supply needs to be such that the rupture of one diver's umbilical and the consequent escape of gas does not deprive either the other diver, or the standby diver, of his supply.
“There are numerous ways of meeting this requirement, including totally separate supply systems (from separate sources) and complex valving arrangements with automatic shut down of the line in which pressure is lost. Most of these arrangements meet the requirement, and provided the basic intent of the requirement is understood then it is possible to check whether any specific system is suitable. Our information note sets out three ways of checking the system.”
Further information on the information note is available from IMCA at firstname.lastname@example.org or from IMCA, 52 Grosvenor Gardens, London SW1W 0AU, UK. Tel: +44 (0) 20 7824 5520; Fax: +44 (0) 20 7824 5521.