HSE publishes research on performance of 'octopus' regulators for scuba diving

HSE press release E057:05 - 21 April 2005

The Health and Safety Executive (HSE) has published the results of research carried out to review breathing performance of 'octopus' regulators.

Commenting on the research findings, Chris Sherman, HSE Chief Inspector of Diving, said: "This research highlights a potential problem that may be encountered in an emergency situation using an 'octopus' regulator."

Many recreational divers use an 'octopus' system which has two second stage regulators (or demand valves) attached to a single first stage regulator; thus enabling two divers to breathe from the same cylinder.

The breathing performance for a single demand valve and first stage regulator combination is set out in British Standard EN250. This, however, gives no indication as to how two demand valves would perform together when drawing on a single first stage regulator. This, along with evidence of divers struggling to use 'octopus' systems in genuine emergencies, prompted the research.

The results of test data show that SCUBA single demand valve systems capable of meeting the requirements of BS EN250 cannot necessarily be relied on to perform to the same standards when used as part of an 'octopus' system.

In particular, the research found that the performance of a first stage regulator is a vital factor when determining the performance of a complete system and that reduced breathing performance was experienced when using low cost/performance first stage regulators compared to high cost/performance models. In addition, tests showed that the poorer performing demand valve of any 'octopus' pair will experience a greater loss of performance with increasing depth and ventilation rate when compared to the better performance valve. Breathing in-phase as opposed to out-of-phase also affected performance.

The report recommends that a completely independent gas supply and demand regulator is the preferred system as an alternative air supply during an emergency situation. However, if divers choose to use a 'octopus' system, they should be aware that:

• although CE marked valves to BS EN250 may be considered as 'fit for purpose' when used alone, their performance cannot be assured when configured as part of an 'octopus' system;
• octopus systems should be based on a high-performance first stage regulator;
• systems should be configured with demand valves of similar performance; and
• older valves, or valves whose performance may have degraded should not be used.

Chris Sherman added: "HSE recommends the use of a completely independent secondary gas supply system; for example, a pony cylinder set-up. That way, if there is a problem with the 'octopus' system or if a buddy pair become separated, divers have a much increased chance of survival in the event of running out of air."

Note to Editors

1. 'Breathing performance of 'Octopus' demand diving regulator systems' can be viewed at: http://www.hse.gov.uk/research/rrhtm/rr341.htm
2. The research was carried out by QinetiQ Alverstoke using dual hyperbaric breathing simulators and associated equipment within their Life Support Systems Laboratory. Six 'octopus' configurations were tested, with over 2,500 breathing tests conducted at varying ventilation rates both in and out of phase at varying depths, with a supply pressure of both 150 and 50 bar.
3. BS EN250:2000 is the British Standard for Respiratory equipment - Open-circuit self-contained compressed air diving apparatus - Requirements, testing, marking.
   

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