By Peter Steinhoff

Breathing the wrong gas at the wrong depth will kill you
This is a simple procedure yet it can cause big problems for those trying to do it fast and mess
it up. Remember, slow and deliberate is always fast. Also keep in mind that all deco and stage
tanks are turned off when not in use. That prevents us from loosing gas without knowing it
and is also an additional safety step preventing us from breathing the wrong gas.
Common mistakes

These are the most common mistakes for those relatively new to this:
- It’s easy to float up or down while changing regs. The solution is to check the depth
between each step of the procedure.
- It’s easy to get the hoses wrong. Make sure you have a clear mental picture of where
everything goes and what is behind or crosses when you switch.

Switch to stage or deco tank
1. Wait until you reach the switching depth.
2. Hang up you primary light (turned on, pointing down).
3. Choose the proper tank by looking at the MOD label and show it to your buddy who
verifies it with an OK (depth and gas is correct).
4. Grab the second stage with your right hand and route the hose around your neck.
5. Open the valve and purge the second stage.
6. Remove the long hose (with left hand) and put the stage/deco reg in your mouth and breath.
7. Clip the long hose on the right chest D-ring.
8. Unclip your light and signal you buddy that you are ready with an OK.

Switch back to the long hose
1. Hang up you primary light (turned on, pointing down).
2. Unclip the long hose and hold it in your right hand.
3. Remove the reg from your mouth with your left and pull the hose over your head.
4. Put the long hose in your mouth and start breathing.5. Close the valve on the tank you were breathing.
5. Close the valve on the tank you were breathing.
6. Lift the inner tube with your left hand (thumb) and push the hose in there.
7. Pull on the hose and make sure the second stage is secured under the inner tube.
8. Unclip your light.

Switching between multiple tanks
If you need to switch from one stage to another, from a deco tank to another or any
combination, you go to the long hose first. Like this:

1. Switch back to the long hose and stow the tank you are breathing.
2. Move tanks around if it makes things smoother.
3. Switch to the new stage or deco tank.
And you can have the light clipped off until you have completed the whole process.
If you are switching deco gases, let’s say from 50% to Oxygen, you switch to back-gas (long
hose) at 9m/30ft for the last couple of minutes. That gives you time to stow the 50% and
move things around. Then ascend to 6m/20ft and deploy the oxygen. This is the cleanest and
safest way to do it.

Gas breaks
When doing more than 20 minutes on oxygen you have to do a gas break to keep the gas
exchange effective. When you go to breathe the long hose you can stow the reg on the oxygen
tank just by clipping the second stage to one of the bolt snaps or the handle. Anyway you
chose to stow it, you NEVER let regs hang around your neck. Why? Because when something
happens you will not know what you are breathing or even if it is turned on.
Team switching
When you switch deco gases it’s best to do it one at a time, especially if you’re not very
experienced. The chance of something going wrong is always bigger at the gas switches so it’s
a good idea to supervise each other. I have stopped people from breathing oxygen at the
wrong depth or choosing the wrong tank several times. Also it’s easy to get something into the
second stage, like small sticks, sand, clay and if you breathe that you may need some help to
recover. By the way that’s why you need to purge the second stage before breathing it. But we
all make mistakes, right?

Stage diving
When you are using stages in the ocean you often suck them dry or almost dry. Then you
switch to the back-gas (unless you have several stages which is uncommon). If you want to,
you can signal your buddies, show them the switch sign and everybody can do the switch.
Nice if you have similar gas consumption since everybody’s stages should be getting close to
empty. If you are experienced you can switch on the fly though.

Source

by Marius Clore
Equipment and Technology Chair, NACD

Cave diving is critically dependent on lighting, hence the absolute minimum requirement of one primary light and two backup lights. The primary light must be sufficiently powerful both to signal appropriately and to view the cave, while the backup lights, which must be very reliable, need be only sufficient to follow the guideline out of the cave.

The advent of HID lighting has led to considerable improvements in both the quality of light and burn time over the older halogen lights. HID stands for High Intensity Discharge, and HID bulbs consist of two electrodes a short distance apart in a gas-filled chamber. A high voltage (low current) pulse across the electrodes creates an initial spark that results in the formation of a small plasma arc which produces a very broad band of high intensity light extending from the infrared to the ultraviolet.

In this brief article, I will summarize the basic features of HID lights, and compare HID lights in the 18/21W range from a number of manufacturers, including Salvo, Halcyon, Dive Rite and Sartek (see Table for summary of features and specifications).

In terms of components, an analogy between a HID light and a tank and regulator is useful. Every HID light comprises a battery canister, a battery, a ballast and a light head which are analogous to the tank, air supply, regulator 1st stage and regulator second stage, respectively. It is also worth considering that HID light usage should be considered in the same vein as air usage. Just as one turns a dive on 1/3rds, one should never plan a dive where the total possible duration of the dive is going to exceed half the burn time. Moreover, one should be conservative in this estimate since, in contrast to one’s air supply where one has a direct read out of remaining air pressure, it is impossible to know exactly what the total burn time is going to be, since this is obviously dependent on how well the battery has been charged (see below).

Given that HID lights are built from standard components, the variations in design are rather limited, and consequently, the choice of light is to a large extent a personal one based on preferences relating, for example, to the size of the canister, the packaging of the light head and the materials employed.

The canister. The canister should be robust and water tight. Salvo and Halcyon use Delrin, Dive Rite uses PVC and Sartek uses acrylic. Delrin is a more reliable material under extreme conditions, is not susceptible to cracking when dropped, and doesn’t become brittle in extreme cold. This may be important when diving in the Arctic, but under the environmental conditions found in Florida and Mexico, there is little to distinguish between the three materials. The dimensions of the canister are governed by the choice of battery pack configuration. The dimensions of the Salvo and Halcyon 9 Ah canisters are identical, while Dive Rites’ is wider, and Sartek’s is both wider and shorter. Indeed, the dimensions of Dive Rite’s wreck canister is the same length as the Salvo and Halcyon’s 13 Ah canister and only minimally narrower (3.5″ versus 3.75″).

The batteries. Modern HID lights are generally powered by nickel metal hydride (NiMH) rechargeable batteries. NiMH batteries provide the same energy (measured in Wh) as lead acetate batteries in a much smaller package (about half the weight and size for equivalent power capacity), they have a relatively long life with no cell memory, and withstand high charge/discharge currents. Generally, the nominal voltage of the pack is 12V and the total energy is given by the capacity in Ah times the nominal voltage. Thus a 9Ah 12V battery pack has a total energy of 108 Wh. If the ballast consumes 24 W (for an output of 18 W dues to losses), the total burn time can be estimated at 4.5 hours. However, the capacity of NiMH batteries is usually 10% lower than the rated capacity, yielding an actual burn time of about 4 hours. A 9 Ah pack can be built from either twenty 4.5 Ah 4/3 Fat A batteries comprising two strings in parallel, each comprising 10 batteries in series which easily fits into a 2.75″x10.5″ canister, as in the case of the Salvo and Halcyon lights. Alternatively, a more reliable pack in terms of obtaining a full charge (see below) can be built from a string of ten 12V, 9Ah D batteries in series, but the dimensions of this pack are quite a bit larger and can therefore only fit in either the 13.5 Ah Salvo and Halcyon canisters (3.75 x 10.75″).
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