Appeared in DIVER February 2007

NITROX CONNECTIONS Which way will the M26 take us
SOME TIME AGO, THE BUREAUCRATS IN BRUSSELS decided that some new regulations were needed regarding the transport of gases under pressure. In their infinite wisdom, 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.
Mike Harwood of the UKs Health & Safety Executive told DIVER that his organisation had voted against this move, on the basis that the scuba-diving industry was mature, and that there was no evidence to suggest that significant mistakes with cylinder filling were being made.
The HSE was out-voted, however, and the proposal became a recommendation. The standard is not mandatory yet, and as far as we were concerned in the UK, the idea had simply gone away. A straw poll of a few UK dive centres indicated that no-one seemed aware of it.
However, a visit to a state-of-the-art dive centre in France recently indicated that the idea had not gone away on the Continent. All the nitrox tanks I saw there carried valves complying with the new Euro standard.
Not only that, but they were designed such that it is not possible to insert an adaptor and fit an A-clamp regulator either. It looks as if the unique M26 nitrox valve thread is a fact of life within Europe.
This may impact on UK divers travelling to any areas in which European divers form the majority of the customer base. If they want to use their M26-fitting nitrox regulators, the locals will supply them with tanks to suit.
In Egypt, they got round the problem of A-clamp versus the original DIN valve by using DIN fitting tank-valves with
a removable slug that instantly converted them to A-clamp. This will not be possible with the new DIN M26 nitrox fitting.
Boats and dive centres in Egypt that accommodate divers from all over Europe will now have to stock two different kinds of tank valve, and divers will have to double-check that tanks to suit their regulator fittings are available.
That, or international diving resorts will ignore the problem and tell their European visitors simply to bring standard air-fitting regulators. A quick check with some dive centres in Egypt serving both British and continental European clients seemed to indicate that this may well be what happens.

BS EN 144-3:2003 IS NOW THE NEW STANDARD for Outlet Connections For Diving Gases Nitrox And Oxygen, though until August 2008 valves may be supplied either to this or the previous national standard. The standard 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.
2008 may seem a long way off, but a few of us will be in for a surprise if this regulation is enforced. We may find it difficult to get our cylinders fitted with their existing valves filled with any gas mix other than air, and we may even have trouble finding a nitrox cylinder with a valve that fits our regulator when we travel.