It was an average March day. Sue and Martin entered the water of the lake, snug and warm in their drysuits, hoods and gloves. Only the shock of it, contacting the exposed parts of their faces, reminded them that the water was very cold.
Soon the two divers were down at 20m. Everything was routine, until Sue suddenly disappeared in a violent cloud of bubbles, which free-flowed uncontrollably from her regulator. Sensibly close at hand, Martin offered her his octopus-rig mouthpiece.
Sue spat out her own mouthpiece, which, continuing to disgorge the contents of her aqualung cylinder, thrashed around at the end of its medium-pressure hose, adding a degree of chaos to the situation. Being careful to keep control of their buoyancy, the divers began to head for the surface. Then Martin's own regulator suddenly went into free-flow too.
Martin expertly tilted the device in his mouth in order to allow excess air to escape harmlessly away. Sue was not so aware of this technique, but she still managed to reach the surface safely with her buddy, no worse for the experience, save for the effects of severe intestinal wind.
Many British divers have suffered experiences similar to this. In this case, it was annoying that the dive had to be abandoned - but at least no one was hurt. In reality, there are cases every year in which the divers concerned are not so lucky. Some end up severely injured; others end up dead. Why does it happen? Winter is a time for dive training and, with inhospitable seas, it's no surprise that inland sites are so popular. However, British lakes and rivers can get very cold, even well outside the obvious winter months. The reasons for this are the absence of the warming currents which are present in our coastal waters, and, sometimes, a lack of surface sunlight. The most important consequence, as far as divers are concerned, is that it's not uncommon to hear about regulators freezing open in fresh water. It is this which causes the sudden and unstoppable free-flows which can so rapidly empty a diving cylinder.
How exactly does the freezing inside the regulator occur? When air flowing from the aqualung cylinder is subjected to a dramatic reduction in pressure - from a possible 230 bar to around 10 bar - by the regulator 1st stage, it loses a lot of heat. The water surrounding the metal parts of the regulator is cooled and, if this water is already very cold, it can freeze, affecting operation.
Environmentally sealed designs prevent the cold water from coming into contact with the working parts of the 1st stage. Often, this is done by filling the regulator cavity with silicone oil. Other models are environmentally dry-sealed. However, water vapour, which might be present in a less-than-perfect air supply, can still sometimes cause ice crystals to form and affect the working parts. Research undertaken by Diver has shown that it's very common for water vapour to be present in quantities close to the limit in air supplied by British air retailers. This must be blamed primarily on this country's humid climate.
Even if the 1st stage is unaffected, the cold air passing down the medium pressure hose has a second chance to cause problems if there is any water present near the working parts of the 2nd stage. There often is.
How can the 2nd stage be warmed up? Ironically, it needs to take heat from the water, which may seem cold but is actually a lot warmer than the air supply at this point.
The metal parts of the regulator act as a heat sink, and today many manufacturers of regulators with modern plastic 2nd stages find themselves adding metalwork (as heat exchangers) to their designs, as one of the ways to tackle the problem of freezing. Another method is to use Teflon-coated components so that ice crystals won't stick to them.
A further possible aid is the simple air control device marketed by Apeks Marine Equipment. When inserted in-line in the medium pressure hose next to the 2nd stage, this enables a diver to cut down or stop the air supply to a free-flowing regulator. The idea is that you allow the regulator to absorb heat from the surrounding water for a few seconds before letting the air-flow return (or changing to your own octopus second stage).
What do you do if you are unable to halt a free-flow during a dive? First, be well-practised at breathing from a free-flowing regulator. Then, if the worst actually happens, be prepared to head for the surface, accompanied by your buddy. Since your buddy's regulator will have been subject to similar water conditions, it might be about to fail too. If you try to share air by exchanging regulators, your buddy's is likely to ice up too. The same might happen if you double the air flow on his 1st stage by using his octopus rig.
There is a new European standard (EN250) for the cold water performance of diving regulators and, if you are about to buy a model for this type of diving, it may be wise to make sure your choice is certificated. This does not necessarily mean that a regulator is environmentally sealed. At the time of writing, the following were some of the models claimed by their UK distributors to conform to the EN250 standard:
Fresh water in Britain can often be close to freezing, even outside the obvious winter period. Our ten tips for preventing regulator freeze-ups are: