WHENEVER WE UNDERTAKE ANY DIVING PROJECT in the UK, we have to meet the approved code of practice laid down by those who govern us, as represented by the Health & Safety Executive. One of its conditions is to have an oxygen therapy unit available close to the surface of where we’re diving. We bought a Marinox unit for that purpose.
In simple terms, the delivery of pure oxygen to a diving casualty increases the pressure gradient of the problem gas, the nitrogen that has been absorbed.
It may be forming bubbles, and this helps to shrink the bubbles, and allows the body to shed the nitrogen through natural respiration.
At the same time, the oxygen respired delivers plenty of oxyhaemoglobin in the blood to what may be cells damaged by such bubbles.
It is not necessary to wait for the onset of decompression-illness symptoms. A typical scenario for the use of oxygen therapy would be if a diver was known to have made a fast ascent, or had surfaced and missed some mandatory decompression stops.
The one thing I took on board from an oxygen-administration course was that administering oxygen via a therapy set needs no particularly special skills. The limited supply available from a typical therapy set is not enough to cause problems, so the best rule appears to be to give oxygen without delay, and give plenty.
Recently, I was far from home waters when I surfaced and decided that I needed to take advantage of the O2 set available on the boat.
It was swiftly made available to me, but it reminded me of another time when I was attending to a far more seriously affected casualty, and needed to ask a third person on the boat we were on to assemble the kit while I got on with other matters in hand.
Few were even prepared to try, even though I told them I would instruct them how to do it.
I have religiously carried the Marinox Marine Oxygen Therapy Unit around with me, but as I’m one of the people most likely to need it, should the worst happen, I thought I’d better find out how easy it would be for a casual observer to get it up and running.

What You Get
Designed for the hostile marine environment, this unit comes in a heavyweight plastic tube with screw-on lid and gasket forming a watertight seal to keep out salt spray and dirt. There is also an over-pressure valve to prevent an ineffectively closed-off cylinder venting gas, causing the tube to explode.
Oxygen can be an extreme fire-hazard, so it should be treated with respect. Always ensure that the cylinder is turned off effectively, and the unit stored in a well-ventilated place.
Inside the tube is a 2.7-litre, 200bar aluminium oxygen cylinder with a pin-index valve. The first stage of the regulator is fitted to this.
There is either a demand-valve second stage for a conscious casualty or a continuous-flow oral-nasal mask for one who is unconscious. Both are connected via a hose.
The demand valve is connected to the first stage just as an mp hose is screwed into a normal regulator first stage, except that this first stage has an A-clamp and unique two-pin connection.
The demand valve plugs into an oral/nasal mask that has an inflatable skirt. The valve has
a purge or flush button at the front to establish that there is a gas flow.
A pressure (contents) gauge is mounted to the body of the first stage, and its dial is phosphorescent to make it easier to use in poor light. Using the demand valve ensures a supply of pure oxygen to the user.
There is also a take-off for the constant-flow supply. This has a connection rather like that
of a direct-feed hose to a BC, except that the male and female parts are reversed.
A flow-restrictor limits the constant flow of gas to 10 litres/min, when the narrower hose of the constant flow supply is connected, and this in turn is plugged into an extra intake on an otherwise regular oral/nasal mask.
This is less effective as therapy, but may be the only choice if a casualty is unconscious.
A full cylinder could be good for more than 50 minutes, even with the constant-flow set-up.

In Use
The whole package is quite large and cumbersome – the equivalent of another scuba cylinder to pack into your car.
Friends have laughed at me because there are oxygen sets available in a much smaller format, but I like the fact that this unit can be transported set up and ready to go.
When oxygen therapy is needed, it is invariably needed quickly, so I decided to take the Marinox kit and see how someone who had never seen it before could assemble it ready for use. My 11-year-old daughter, a new Junior Open Water Diver, was an ideal candidate.
It took her a moment to unscrew the lid and heave out the contents, but she was quick to understand how to fit the valve to the cylinder.
This meant, for a demand-valve set-up, that she needed only to fit the mask by pushing it onto the demand-valve, and then open the tank valve. Righty-tighty, lefty-loosey! Job done.
Fitting the tube for a constant-flow application fooled her to begin with. She didn’t twig that it was just like a hose on a BC, but it didn’t take long for her to figure it out. It really is child’s play. It is entirely possible to use both systems simultaneously for two divers.

Oxygen Administration
Oxygen should be administered only by people trained to do so and, in a diving context, only in accordance with approved Diver Oxygen Therapy Course instructions.
However, every certified diver should be aware of the properties of pure oxygen when inhaled, and be prepared to administer it to themselves should they fall victim to circumstances in which DCI symptoms might present or be about to present themselves.
If an oxygen set is available (and it always should be at any dive site), don’t be afraid to ask – use it. If there are any symptoms of DCI, transfer to a hyperbaric facility without delay.
Because of the hazardous nature of pure oxygen, the unit should be used only in a well-ventilated area, such as the open deck of a boat or a shoreline.
Some cylinders may not have been refilled after previous use, so it is essential to check that there is sufficient supply available before anyone needs it.
If the cylinder has been used, clean the masks with the appropriate disinfectant afterwards. The demand valve unscrews into three parts for easy application of something like Dettol.
The heavy-duty Marinox container keeps everything clean and safe, and will even float should it fall overboard.

COMPARABLE O2 THERAPY UNITS TO CONSIDER:
Life Support Services DOTU, £531