- Full face diving mask
A full-face diving mask is a type of
diving maskthat seals the whole of the diver's facefrom the water and contains a mouthpiece or demand valvethat provides the diver with breathing gas.cite journal |author=Norfleet WT, Hickey DD, Lundgren CE |title=A comparison of respiratory function in divers breathing with a mouthpiece or a full face mask |journal=Undersea Biomed Res |volume=14 |issue=6 |pages=503–26 |year=1987 |month=November |pmid=3120386 |doi= |url=http://archive.rubicon-foundation.org/2456 |accessdate=2008-08-31] The full face mask has several functions: it lets the diver see clearly underwater, it provides the diver's face with some protection from cold and polluted water, it increases breathing security and provides a space for equipment that lets the diver communicate with the surface support team.
Full face masks can be more secure than breathing from an independent mouthpiece; if the diver becomes unconscious or suffers an
oxygen toxicityconvulsion, the diver can continue to breathe from the mask unlike a mouthpiece which must be always gripped between the teeth.
Full-face diving masks are often used in
professional diving. They are relatively rarely used in recreational diving, where they protect the face from cold water or stings, such as from jellyfishor coral, and prevent the discomfort derived from gripping a mouthpiece between the teeth for long periods.
This type of gear is also referred to as a Jack Browne rig, named for a
Descoengineer who designed an early version of a full-face mask with an integrated air-supply attachment. [cite journal |author=Middleton, JR |title=Evaluation of the U.S.N. Lightweight Diving Mask (Jack Browne). |journal=US Naval Experimental Diving Unit Technical Report |volume=NEDU-14-78 |date=1978 |url=http://archive.rubicon-foundation.org/3511 |accessdate=2008-08-31 ]
Full-face diving mask have these features, with these results:
traps firmly fasten it to the head
It takes longer to remove the mask when needing to switch to breathing from atmosphere. To avoid this, most full-face masks have a valve to switch between breathing from the set and breathing from atmosphere. That set/air valve should be easily operated by the diver, including if he has thick diving
gloves, but not projecting so that it can be easily knocked against things. An excess of bulky projecting valvework may cause water resistance in swimming and moving his head about.
Most full-face masks can be knocked off much less easily than an ordinary scuba mouthpiece or an ordinary eyes-and-nose
diving mask; but an excess of bulky projecting valvework may act as a lever for his head to be pushed around by. These risks can happen in these circumstances:
*When working or moving about in zero
visibilitywater or in the dark. This often happens with underwater work, as a work diver cannot choose time and place of diving as easily as a sport diver.
*If he is involved in a hand-to-hand fight underwater. This risk may happen with combat / patrol frogmen in war conditions, or with diving sea-police arresting suspects underwater. In this case, his set/air valve should be where an opponent cannot easily grasp it, either to operate it, or to use it as a handle to pull the mask off or to pull the head about.
*If there is a risk of him becoming unconscious underwater. (For the same reason, many
industrial breathing setsand a few scuba sethave a mouthpiece with a strap that fastens behind the back of the neck.)
Much less risk of water leaking in past a mouthpiece
Some divers accustomed to open-circuit scuba get into a habit of casually letting small amounts of water leak in between the lips and the mouthpiece and blowing it out the next time the diver exhales. If by force of habit the diver does the same with a
rebreatherthat has a plain mouthpiece instead of a full-face mask, that water will get into the breathing circuit.
Without a mouthpiece inside the full-face mask
Here, the diver can talk clearly without removing his mouthpiece, including talking with other divers underwater. This allows communications equipment (usually an
intercomwire or by modulated ultrasound) to be installed in the mask and is very useful for working divers.
If a full-face mask floods underwater, it is more difficult to clear it, than with a mouthpiece.
There also is the problem of "dead space" inside the mask causing risk of carbon dioxide retention.
With a small mouth-and-nose (ori-nasal) breathing mask inside the full-face mask
Here, the dead space is less, and there is less space to needing to be blown empty if the mask floods. But the smaller space around the mouth increases the "gasmaskyness" distortion of speech.
With a mouthpiece inside the full-face mask
Here, if the mask floods, the diver can breathe again before clearing the mask, and many
Royal Navyand frogman's rebreathers have this mask arrangement; but the full-face mask plus mouthpiece combination acts like a strapped-in gagmaking clear talking impossible.
The inside of the mask window may get misted/fogged, and need to be treated with a demister. Some
British Armyand Russian gas masks are designed so that when the wearer breathes in, the inflow of air blows over the inside of the mask window and tends to evaporate any mist deposit on it.
The mask window should be a modern strong
polymerand not glass.
*Industrial breathing sets (SCBA): many of them are full-face masks.
Gas mask: most gas masks are full-face masks.
* shows a smoothly rounded full-face mask with no projections to cause friction or catch on things.
* [http://www.apeks.co.uk/products/Full%20Face%20Mask%20Tech%20Spec.pdf Photos and description of a full face mask for open and closed circuit breathing equipment]
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