face mask

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. Full face masks can be more secure than breathing from a mouthpiece if the diver becomes unconscious, as a mouthpiece must be always gripped between the teeth.

Full-face diving masks are used in professional diving, to allow the diver to communicate with the surface and to protect the diver's face from polluted water. In recreational diving, they are also used to protect the face from cold water or stings, such as from jellyfish or coral, and to 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 Desco engineer who designed an early version of a full-face mask with an integrated air-supply attachment.

Features

Full-face diving mask have these features, with these results:

Straps 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.

Most full-face masks can be knocked off much less easily than an ordinary scuba mouthpiece or an ordinary mouth-and-nose diving mask, a risk that can happen in these circumstances:

• When working or moving about in zero visibility water 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 sets and a few scuba set have 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 rebreather that 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 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 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 British naval 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.

Other features

The inside of the mask window may get misted/fogged, and need to be treated with a demister. Some British Army and Russian gasmasks 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 polymer and not glass.

See also

• industrial breathing sets: many of them have full-face masks.
• gasmask: most gasmasks have full-face masks.
• diving helmet.
• This link shows the older British Navy Clearance Diver's and British SBS frogman's full-face mask with a big front window and a mouthpiece inside made by Siebe Gorman.
• This link shows a smoothly rounded full-face mask with no projections to cause friction or catch on things.

External links

• Photos and description of a full face mask for open and close circuit breathing equipment