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How Full Face Masks Benefit Tech Divers

by Aron Arngrimsson, Team Blue Immersion:
full face mask tdi diverIt has been a common perception that full-face masks belong to specialized areas of the scuba industry like public safety divers, commercial divers, research teams and underwater film crews alike. In recent years the use of full face mask in sport diving has become more common where the public has found the advantages of greater field of vision, the ease of breathing and being able to breathe through your
nose.

Now the full-face mask is finding its way into mainstream technical diving both for open and closed circuit, and rightfully so – if you have a good mask and the right configuration this is a great benefit in terms of risk management for your mission specific diving. There are three points in particular for technical divers.

Cold Water Durations
In some places in the world, the temperature of the water becomes the limiting factor on a technical dive rather than decompression, gas management and CNS.

The dive industry has progressed immensely the last years developing new and innovative dry suits and undergarments to battle this limitation, but it can be easy to forget if you also have a full face mask how much difference it can actually make.

The University of Manitoba recently conducted a study with volunteers immersed with scuba gear in a cold pool and found that having your head immersed in cold water only adds 10% to your overall heat loss.

However when the body is effectively insulated through thermal protection and the head is not, the body´s core temperature drops a lot more rapidly. This is because the surrounding environment cools the hot blood flowing from your warm body as it passes through your head, which will decrease your core
temperature.

It is also a physiological fact that people do not shiver when only their head is exposed to the elements. Shivering slows your rate of cooling and therefore in technical diving thermal protection does not become a question of comfort; it becomes a question of real decompression safety.

Today more and more divers are going deeper and staying longer which requires increased protection that “only” a dry suit and a good set of undergarments can maybe not deliver. If you have a flooded dry suit and a lot of deco to do, the mask will certainly do more good than bad in trying to help you cope with the thermal stress. It also feels nice not to have a numb face!

Utilizing Gas Switch Block
Wearing a full-face mask in technical diving introduces a new method of gas switching; there are some different procedures and skills to learn to be able to conduct them safely. Here we will cover how to use the switch block.

The switch block is a manifold that from one point connects straight into the full face mask, and from the other points has two quick connections where you can attach your bottom and decompression stages.
When you are on the bottom phase of the dive you only have one connection plugged in between the two ports with your bottom gas. Doing this prevents accidentally switching to your decompression gas during the bottom phase, which could have disastrous consequences.

When the decompression phase starts, you plug in the decompression cylinder quick connection into the manifold, go through the gas switching procedure and disconnect the bottom gas. The reason to disconnect the bottom gas is in case you would switch to bottom gas during decompression phases without knowing and therefore compromising your decompression.
Using the switch block in essence gives you the peace of mind of always having access to gas. Some people prefer the quick connection method, taking the bottom gas hose of the mask and connecting the next one straight over, but this procedure if it fails can lead into a dangerous error chain. Here at least if you are having trouble connecting you are not fighting your most valuable asset, time.

Safety in Relation to Longer Durations/CNS Loading
Having an oxygen toxicity hit underwater is a life-threatening scenario in diving, because when using regular open circuit regulators there is a very big risk of drowning during the seizure. The seizure can occur without warning, with no symptoms prior, and the convulsions are followed by unconsciousness which will very likely drown the victim, or get him bent breaking his decompression ceilings to get him to the surface.

Using a full-face mask in technical diving prevents the loss of regulator in the event of a seizure by breaking your max pp02 or switching to the wrong gas, so in the event you have an oxygen toxicity hit with a full face mask, you will not drown and your buddy or support diver will be able to help you through the phases of the hit without fear of having you drown.

Amount of exposure before onset is unpredictable because people, depending on their personal physiology, have a wide variation of tolerance but with the ease of breathing of the full face mask decreasing CO2 retention, and the increased thermal protection, it decreases the risk of a hit.

There are many other benefits to FFM in technical diving, communication being integral for support divers and surface on expeditions and being able to hydrate or even eat underwater on long decompression stops.

In conclusion I think it is safe to say that integrating a full-face mask into your equipment kit while technical diving can have enormous benefits in terms of safety and communication. It is very important you seek the proper training when using this for technical diving, so contact TDI for more information about an Instructor in your area.

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