Over 10 years ago, from my diving center in Egypt, I wrote a short article on the problems that the country was experiencing with rebreather divers from Europe arriving in Egypt and finding that in many locations the rebreather oxygen cylinders being supplied were not fitting their oxygen regulators on their rebreather unit. The number of instances of this problem in Egypt today is considerably less, but it is worth-while to provide a reminder, especially to new rebreather divers who might be looking to travel outside of Europe with their rebreather unit for the first time…
In 2008 it had been decided in Brussels that some new regulations were needed regarding the transport of breathing 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 the wrong cylinder. The Deutsches Institut für Normung (DIN) fitting for use with air cylinders (DIN being the German standards body) was already being used, so they decided to stipulate an entirely different fitting for use with gas mixes with a higher content of oxygen than normal – nitrox or oxygen. The M26 valve thread and its corresponding regulator first stage was born. With a slightly larger diameter than the familiar DIN fitting this is the type of cylinder valve that must be fitted to any new cylinder that is going to be used with any gas greater than 22% oxygen. This is a European directive that came into force in August 2008 and these valves will match any regulator supplied in the European Union (EU) which has been designated for use with gas containing an oxygen content greater than 22%.
In simple terms, if you buy a rebreather in the EU it will come with a M26 fitting on the oxygen regulator and if you buy a new rebreather cylinder for oxygen use then it will also come fitted with a M26 valve. Both the regulator and the valve look similar to the DIN type of valve, just slightly bigger. The cylinder valve should have the information stamped or etched on the valve itself.
It is important for extended range divers and rebreather divers travelling outside of the EU who have these M26 regulators to recognize that this directive is purely within the EU. When you travel to other continents such as Africa or Asia it is strongly advisable to check with the diving operator to ensure that either; there are cylinders available with M26 threads or they can supply an adaptor. In many countries outside of EU it is very difficult even, on some occasions not possible to purchase the specific M26 cylinders or adaptors. If this is the case you will need to remember to take with you your own adaptor.
So, remember if you have a M26 regulator check with your diving operator what the options are before you travel!