So you think you can take the cold?
Diving all year round in Britain or other Northern climes requires dedication, and the right clothing, regulator and attitude. John Bantin tears himself away from the icy waters to share his thoughts...
The temperature of the sea stays constant. If it were to drop only a few degrees we would face an Ice Age. But the temperature of freshwater dive sites can be very close to freezing, even in summer. Although you will be ready for this during the depths of winter, keeping warm can be very relevant to UK divers at any time of year.
There is a science to keeping warm. It's more than having a steaming beverage and taking a hot shower after a dive, both of which can lead to problems of their own making. For instance, a hot shower, can provoke the onset of decompression illness and draw blood away from the body's core
- a bad thing in the case of a near-hypothermic diver.
Being warm, well-rested and well-nourished before entering the water makes sense, and having warm clothing to put on afterwards is sensible too.
Drysuits are intended to keep you dry; they don't keep you warm. The insulating clothes you wear underneath establish a gap between your body and the outer shell of the drysuit, and it is the air in this gap that stops your body heat escaping through the walls of the suit to the cold water beyond.
The name's Bond
You could wear your everyday clothes, but the old idea of Sean Connery stepping out of his drysuit to reveal a dinner-suit in the James Bond film You Only Live Twice has been superseded by high-tech undersuits specifically designed for diving.
Nature has provided excellent examples of perfect thermal insulation in the form of feather and down, and fur. This is replicated in modern undersuits using materials with microfibres. Thinsulate is a popular example of this.
Because the fibres are so fine, they provide a very high surface area per unit volume, so they can retain more insulating air than older materials like that used in a traditional woolly bear. Modern undersuits are probably twice as efficient as the fibre fill in your loft.
Laminating this material to a carrier fabric (a fleece, for example) maximises this efficiency. Quilting fabrics together can cause a reduction in insulation quality of up to 30 per cent, because quilting causes compression of the insulation and cold "bridges".
Even when you're not too hot you sweat, so the inner surface of the undersuit must have a suitable "wicking" characteristic to ensure that moisture is spread evenly throughout. This avoids uncomfortable damp patches.
Undersuits come in various weights. A 250gsm suit will insulate rather better than a 100gsm suit but you will need to wear more lead to counteract its buoyancy. It is important to wear an undersuit that fits well, because this avoids the build-up of excess pockets of air. These might be hard to evacuate during an ascent.
Some divers have expressed problems with dump valves (usually cuff-dumps) getting blocked by the undersuit material. Some undersuits come with uninsulated mesh areas at the wrists which, ironically, have a big blood supply near the surface, causing chilling as a side-effect.
This is often more of a problem with the underside of the valve than with the suit. It is important
to avoid the excessive amounts of material associated with an over-sized undersuit.
Body parts
However, there are parts that even an undersuit cannot reach. Latex neck seals are a particularly cold area, but a soft woollen scarf (cashmere for those who can afford it) proves a simple solution.
Foot mitts made of a similar material to the undersuit keep the feet warm, although many divers opt for several pairs of low-tech woollen socks.
Much body heat is lost through the head, and years ago dry hoods were popular. However, a great many incidences of "reversed ear", that condition caused when the outer ear is blocked and expanding air within the middle-ear cavity pushes the eardrum outwards. This led to a revival of the use of neoprene wet hoods by most drysuit divers.
Full-face masks also reduce the amount of heat loss, because less of the head is exposed. Dry gloves, like dry hoods, can cause problems associated with the effects of pressure - in other words, squeeze.
More importantly gloves, whether dry or wet, can make it difficult to manipulate your diving equipment. Many photographers opt to go in with a single glove and sacrifice the other hand to the cold in return for its use during the earlier part of a dive. Keeping the rest of the body warm can mean that the hands don't get cold - providing the blood supply to them isn't restricted by over-tight wrist seals.
Seals and seams are known to be less than watertight, and many divers make do with damp suits rather than drysuits. This might be OK in the summer months, but damp areas conduct heat away from the body and getting cold can be the start of many problems.
A cold diver doesn't think quickly and might not react efficiently if things go wrong.
Breathing the very cold air from an open-circuit scuba system can chill the inner core of the body; after all, the lungs are a major area of blood supply.
Rebreathing expired air neatly gets around this problem and the exothermic reaction in the rebreather's scrubber unit can actually warm up the air in the system, so rebreathers, both semi- and fully closed circuit, provide an important alternative means by which a diver can keep warm.
Free-flow risk control
What diver relishes the idea of a regulator running out of control in the cold? But the chances of a free-flow happening can be minimised, and even if one does occur you should be able to handle it.
Every winter, divers get into trouble - some fatally - because their regulators freeze up. Why does this happen?
When a gas is compressed, a by-product is heat. A recently filled scuba cylinder is warmer than you might expect.
Conversely, when air is depressurised it suffers a drop in temperature. You might have noticed that the air you inhale from your regulator is often a lot cooler than you would like.
When air from a scuba cylinder under-goes a drop in pressure as it passes through the regulator first-stage - with a further drop in pressure at the second-
stage - it gets colder. The sea around Britain is rarely colder than 8°C, but that's not true of inland freshwater sites.
Much lower temperatures can be encountered, and if the ambient temperature of this water is at 5°C or less,
the very cold air caused by temperature drops in each stage of the regulator will cause any water droplets within the mechanism to form ice crystals, which
in turn can cause a malfunction.
Modern down-stream valves jam open rather than shut, but, if they jam, a catastrophic free-flow will always be the result.
Go with the flow
If your regulator suddenly goes into an uncontrollable free-flow, what should you do? The confusion and chaos caused by the roaring bubbles will startle even the most cool-headed and experienced diver, but what you must do is stay exactly that cool-headed.
Your priority is to make your way to the surface. Free-flows, like broken cylinder O-rings, often occur when you have the maximum tank pressure, in which case you will have time - provided you know how to breathe from the air that is escaping.
It's not that you have no air - you have too much! Hold the regulator second-stage in your mouth but angled upwards so that it is pressed against your top lip. Excess air will be free to escape from below the mouthpiece and you'll find that no water enters your mouth as you breathe.
Practise this in safe conditions, simulating a free-flow by holding in the purge button of your regulator.
It is extremely unlikely that your downstream regulator will jam closed, but even if it does so just after you exhale you will still need to vent off more air from your lungs while you ascend. The residual air held in "empty" lungs is likely to expand to such an extend that it causes an embolism during a breath-held ascent from 30m.
You should not need air for any other function, provided you were neutrally buoyant to start with. Expanding air in your suit or BC
will need venting as you ascend. Be careful not to overdo this. Know how to drop your weightbelt if, as a last resort, you need to.
FIVE ways to avoid a free-flow
ONE Make sure your cylinder is dry inside and filled with dry air. Don't leave it anywhere that might chill it.
TWO Avoid heavy air- flows from your regulator, which includes breathing heavily from it. Before diving, take test breaths when submerged in shallow water, rather than
in the air, and never press the purge button either above or below the surface.
THREE Blow away any entrapped water (or ice) that might be around your cylinder valve or regulator orifices with dry air from your cylinder.
FOUR Restrict yourself to no-stop diving at depths from which you are confident you could make a free ascent.
FIVE Be aware that water at less than 5°C can cause regulator icing, and that can include any fresh water outside the obvious winter period.
Design solutions
Some regulators have been designed to resist the effect of jammed valves caused by cold. The idea of environmentally sealed first-stages is to keep water out. Examples of regulators with this advantage are the Apeks TX100, Aqua-lung Titan D and Cousteau Supra D, Dacor 360XP AER Pacer, Ocean Reef Polar Enterprise and Oceanic Delta II Sub Zero.
Some regulators, like the Poseidon Cyklon 5000 and Jetstream, and Beuchat VS8 and VS10, can be adapted with cold-water kits that use silicone grease.
Certain second-stages have specially coated moving parts to stop any ice from sticking. Examples include the Beuchat VS8 and VS10, Dacor 360XP AER Pacer, and Spiro Cousteau Arctic. Some plastic regulator second-stages such as the Apeks TX100, Spiro Cousteau Arctic, Aqua-lung Cryo, Mares V16 SCS-XTR and Sherwood Blizzard have additional metal heat-sinks.
It is strange to think that what might feel like very cold water is, in fact, warming up the much colder air coming from the scuba cylinder, but regulators with plenty of metal in their design to conduct this small amount of heat to the air tend to be less prone to freezing. Examples include the Mares Ruby and Dacor 960XLE.
Other manufacturers say their regulators are designed not to freeze. Scubapro says its Thermal Insulation System works, and that the cold air never cools down any water that might enter the regulator. TIS is fitted to all the latest Scubapro designs.
You never know how close your regulator comes to failing because of icing, even if it has the latest cold-water technology, because the cir-cumstances that make that subtle difference are so varied.
The only regulator now approved by the US Navy for cold-water use is the Poseidon Jetstream, which is quite an old design.
It's a good idea to practise the technique of making an ascent, breathing from a free-flowing regulator. This is a technique routinely taught by many training agencies.
Appeared in DIVER - January 1999
