M26 Connection Guidance
The European Standard which introduces the M26 connection is BS EN 144-3. The scope of the standard states, “ This European Standard is applicable to a thread connection used for the connection between a gas cylinder valve and a pressure reducer for respiratory equipment for diving containing breathable nitrox gas with an oxygen content greater than 22% or oxygen”.
The aim of BS EN 144-3 is to reduce the potential hazards posed by the high oxygen content in Nitrox (> 22% O2) and pure oxygen by ensuring the clear identification of equipment intended for use with these gases. The Standard’s status as a harmonised Standard means that it has been accepted (by majority decision) across the EU as one accepted means of meeting the safety requirements of the applicable European Directives in relation to that type of equipment Such Standards are not mandatory but observing them provides a means of demonstrating that appropriate risk controls have been applied - this may of course be achieved in other equally effective ways. Where a standard such as this exists for respiratory devices, it is open to manufacturers to produce those devices according to different standards (including their own standards) provided that the manufacturer can show that those other non-standardised devices meet the requirements of European Directives. Approved bodies, which are the organisations that check that equipment conforms with these European Directives, take account of such harmonised standards when assessing new diving equipment for CE marking.
EN 144-3 was published in 2003 but allowed a 5 year transition period before its implementation date of August 2008. During this interim period other standards could still be used for the manufacture and CE marking of these cylinder connections. After August 2008, those at work involved in diving or the filling of diving cylinders may choose to continue to use the connections that were made to these other standards. However, whichever connections are employed, those at work will still need to be able to demonstrate that any safety arrangements they use are adequate.