EN 144-3

EN 144-3:2003 is now the new standard for "Outlet Connections For Diving Gases Nitrox And Oxygen", though until August 2008 valves may have been supplied either to this or the previous national standard. The standard now applies to the connection between a gas cylinder-valve and a first stage or compressor connection when the tank contains gas with an oxygen content greater than 22%. What it means is that your nitrox cylinder will have a dedicated outlet valve, your nitrox regulator will have a dedicated connection to your cylinder valve, and filling stations will have a dedicated nitrox filling connector.

Brussels decided that some new regulations were needed regarding the transport of gases under pressure. They decided that each gas should have its own individual tank valve fitting, so that the wrong gas could never be put into a particular cylinder.
There was already a DIN fitting for use with air cylinders (DIN being the German standards body), so they decided to stipulate an entirely different fitting for use with air mixes with a higher content of oxygen than normal - nitrox. They came up with the M26 valve thread, with a larger diameter than the now familiar DIN fitting.

The recommendation was not mandatory till August 2008, and a poll of Greek service providers indicated that no-one seemed aware of it.

As instructors and service providers we have a duty of care to our students and clients. Failing in our duty exposes us to both legal action and liability for any harm caused. Our 3rd party liability insurance may, or may not, decline to pay out, partly or fully, in an accident if the breach of duty of care is bad enough.