A full-face diving mask is a type of diving mask that seals the whole of the diver's face from the water and contains a mouthpiece or demand valve that provides the diver with breathing gas.[1] 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 toxicity convulsion, the diver can continue to breathe from the mask unlike a mouthpiece which must be always gripped between the teeth.[1]
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 jellyfish or coral, and prevent the discomfort derived from gripping a mouthpiece between the teeth for long periods.
This type of gear is also sometimes referred to as a Jack Browne rig, named for a Desco engineer who designed an early version of a full-face mask with an integrated air-supply attachment.[2]
Contents |
Full-face diving mask have these features, with these results:
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:
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 rebreather that has a plain mouthpiece instead of a full-face mask, that water will get into the breathing circuit.
Here, the diver can talk clearly without removing his mouthpiece, including talking with other divers underwater. This allows communications equipment (usually an intercom wire 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 can be 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 (oronasal) breathing mask inside the full-face mask, 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 gas mask like distortion of speech.
Here, if the mask floods, the diver can breathe again before clearing the mask, and many Royal Navy and frogman's rebreathers have this mask arrangement; but the full-face mask plus mouthpiece combination acts like a strapped-in gag making clear talking impossible.
Kirby-Morgan makes a unique configuration of full-face mask, the KM-48 Supermask, which has some charcteristics of a half mask, while retaining many of the advantages of the full face mask.
The rigid plastic main frame of the mask has a rubber skirt which seals around the eyes and nose like a standard half-mask, and the nose may be held through the rubber nose pocket to equalise in the same way as with a half mask, and there is an extension to ths skirt which seals around the lower part of the face and encloses the mouth.
This mask has a clip-on pod section which carries the regulator, and this part seals against the main frame, allowing the diver to remove the regulator pod when on the surface, or to use an alternative gas supply, which can either be mounted on another pod, or be an ordinary Scuba regulator second stage with a standard mouthpiece. This feature makes it possible to use bailout gas supplies by a dive buddy with a standard regulator with the supermask. An optional pod with a dive/surface valve for use with rebreathers is available to military users.[3]
The inside of the mask window may get misted/fogged, and need to be treated with a demister. Some British Army and 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. This feature is also found on the original Kirby Morgan EXO-26 mask, but the later EXO-BR uses an oro-nasal inner mask to reduce dead space[4]
There are several approaches to bailout air supply which can be used with a full-face mask:
The mask window (faceplate) should be a modern strong polymer and not glass, and must be very securely attached to the skirt. A failure of the faceplate can be a life threatening incident with some full face masks, as the water will flood into the oro-nasal inner mask and compromise the air supply. This problem is avoided by the masks which include a mouthpiece.