PARADISE HUNTER:
Cerich,
What do you mean by "technique"?
The problem with a diving in cold weather is that the temperature of the first stage can fall below freezing causing ice to form on it, or in the ambient chamber where it can in turn block the movement of the piston or diaphragm causing the reg to freeze open and free flow (popularly known as a "freeze flow").
As the air in your tank expands, it has to draw heat from somewhere to gain the energy needed to expand. (Tanks get warm when filled as the air has to give up heat when compressed, and when it is released and re-expands, it needs all that heat back). During the dive, the air draws this heat from the valve and first stage that it is passing through which in turn have to draw heat from the surrounding water to remain above the freezing point. In warm water, there is a much larger gradient between the water temp and freezing point, but the closer you get to the freezing point, the less temperature differential you have to work with and the less gradient you have to work with for heat transfer and the longer it will take to transfer a given amount of heat.
So a cold water first stage is designed to keep water out of the internal areas (where water flow and heat transfer are minimal) and a cold water first stage will often incorporate fins or another means of increasing surface area to help the heat transfer occur.
Good diver technique builds on this in a few ways:
1. Testing and dive preparation - A smart cold water diver will test the reg at home and then not mess with it at the dive site, where the air and the regulator way be near or even already well below the freezing point. You can tell the cold water newbies as they are the ones testing their regs and filling their BC's on the boat or on the beach just like they would in the summer - actually some do so even more than normal due to needing additional assurance their reg will work on a cold water dive.
What all this testing and BC filling does is supercool the first stage and virtually guarentees that it will freeze up a minute or two into the dive as ice accumulates on both the inside and ouside of the regulator. (ice on the exterior of the reg is also bad as it acts an insulator and once it starts to form, it accellerates the cooling of the regulator as the ice covered parts are now far less effective at transferring heat.)
A. So...test the reg at home and you can still be assurred it will work an hour or two later at the dive site.
B. Orally inflate your BC, and if you are wearing a dry suit do not fill it until you are in the water with the first stage submerged (as once in the water, heat transfer is about 80 times more efficient than it is in air).
C. Do not breathe off the reg until you are in the water with the first stage fully submerged. It should be placed in your mouth just before you do your giant stride entry if boat diving, and inhale from the atmosphere before you place the second stage in your mouth. Obviously you want to be careful to ensure your valve(s) are on and that your BC is inflated. If the reg does not deliver air, you'll bob to the surface where you can breathe anyway so there is no need to inhale from the reg before you hop off the boat. On a shore entry the same thing applies, except you just stand up if you discover the valve was inadvertantly closed.
D. Metal surfaces transfer heat. So help the first stage out by pulling back any hose protectors so that they do not cover and insulate the metal hose connections which significantly increase the area where heat transfer can occur. This includes the little trim boots over the second stage low pressure fitting where the low pressure hose enters the second stage - this is often the only place where heat can transfer efficiently from the water to the poppet inside the regulator on today's craptastic plastic second stages. The poppet assembly inside the second stage is also cooled as the air drops 120-140 psi from intermediate to ambient pressure.)
2. In water technique - The more air you use the more cooling occurs in the first stage. Heat transfer however is fairly constant, so any extra air use/cooling that you inflict on the first stage will require more time to allow the first stage to return to the temperature of the surrounding water.
A. Do not inflate and inhale at the same time if at all possible.
B. Do not over breathe the regulator or place yurself in a situation where you will need to breathe more air than normal from the regulator (over exertion, etc.)
C. Use short blasts on the inflator. Dropping to the bottom quickly with a near empty BC or drysuit and then filling it with a long blast on the inflator is a good way to ice up your first stage. Inhaling during this long blast will often push it over the edge. Obviously several small additions of air to the BC or suit during a slower ascent will keep the first stage warmer when you arrive on the bottom as it has a longer time to transfer heat from the water and can also accomplish much of this transfer at shallower depths where the water may be warmer water at some dive sites.
D. Flowing water increases heat transfer. If you are motionless in water with no current flowing past the first stage, the water near the first stage becomes much cooler and heat transfer is reduced as heat has to pass through more of the now cooler water where the temperature gradient is lower to reach the first stage. In extreme cases, the cooler water is more likely to freeze on the first stage. If you keep swimming even slowly to maintain some flow past the regulator, heat transfer is improved.
3. Other factors
A. Less adibatic cooling occurs if the pressure drop is less. Low pressure tanks put less heat transfer demands on a first stage as the drop from 2250 or 2400 psi to 140 psi is a lot less than the drop from 3000 or 3300 psi to 140 psi.
B. Freeze flows are less likely near the end of a dive due to the lower amount of cooling occurring as the air drops from a tank pressure of 1000 or less psi to 140 psi. However, the cautionary disclaimer is that if the reg has been slowly bulding up a coating of ice, you may still encounter a freeze flow near the end of the dive as the heat transfer ability may be dropping faster than the adibatic cooling is decreasing.
C. Moist air can cause problems with ice forming inside the regulator. Compressed air is normally very dry - keep it that way. Leave any moisturizing attachments at home and if you own your own tanks, have an annual VIP to ensure the tank remains dry and ensure proper use and fill techniques are used to keep it moisture free.
D. More air flows though the first stage at depth, for reasons that should be obvious to anyone who remembers their certification training. So be especially careful about over breathing the reg or inhaling and inflating at the same time while at depth.
4. If a freeze flow occurs, don't panic, just notify your buddy and either:
A. Begin your ascent breathing off either the free flowing regulator or your octo. (if you breathe off the freeflowing reg, be sure you don't let your front teeth get excessivley chilled (frozen). It usually takes at least a couple minutes to drain a tank that is freeze flowing and you should have adequate air for an ascent from a recreational dive. Unless surfacing immediately will cause difficulty in exiting, meeting the boat, etc. this is the preferred approach. (If you are doing overhead diving, your training and equipment redundancy will dictate another approach.)
B. Or...if you trust your buddy and have practiced this before, switch to the buddy's octo (or primary if you adhere to the donate the primary school of thought) and have your buddy shut off your tank valve for a minute or so. Then turn it back on. The odds are very good that the ice causing the problem will melt during this brief shut down period and you may be able to continue the dive or at least make a more normal ascent depending on the pressure remaining. The disclaimer here is that you are also placing an extra cooling load on your buddy's first stage and increasing the potential for his reg to freeze flow as well.
I don't recommend doing this unless the buddy has a very reliable cold water first stage - and you have both discussed and practiced this contingency. Obviously if the buddy bolts, you are left with a closed tank valve. Configuring your gear and increasing your flexibility so that you can reach your own valve increases the safety of this approach. If you carry a pony bottle and can reach all the valves, you can also execute this thawing process independently.
The Canadian Forces used to (still may) do cold water testing of gear in the Gaspe Peninsula, where the fresh and salt mix, water temps of 29 degrees in Jan/Feb and air temps -20 to -40....
