Full face diving mask - AbsoluteAstronomy.com

A full-face diving mask is a type of diving mask

Diving mask

A diving mask is an item of diving equipment that allows scuba divers, free-divers, and snorkelers to see clearly underwater. When the human eye is in direct contact with water as opposed to air, its normal environment, light entering the eye is refracted by a different angle and the eye is unable...

that seals the whole of the diver's

Scuba diving

Scuba diving is a form of underwater diving in which a diver uses a scuba set to breathe underwater....

face from the water and contains a mouthpiece

Mouthpiece (scuba)

In breathing sets, a mouthpiece is a part that the user grips in his mouth, to make a watertight seal between the breathing set and his mouth. It is composed of a short flattened-oval tube that goes in between the lips, with on its free end a flange that fits between the lips and the tooth and gums...

or demand valve that provides the diver with breathing gas

Breathing gas

Breathing gas is a mixture of gaseous chemical elements and compounds used for respiration.Air is the most common and only natural breathing gas...

. 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

Unconsciousness

Unconsciousness is the condition of being not conscious—in a mental state that involves complete or near-complete lack of responsiveness to people and other environmental stimuli. Being in a comatose state or coma is a type of unconsciousness. Fainting due to a drop in blood pressure and a...

or suffers an oxygen toxicity

Oxygen toxicity

Oxygen toxicity is a condition resulting from the harmful effects of breathing molecular oxygen at elevated partial pressures. It is also known as oxygen toxicity syndrome, oxygen intoxication, and oxygen poisoning...

convulsion, 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

Recreational diving

Recreational diving or sport diving is a type of diving that uses SCUBA equipment for the purpose of leisure and enjoyment. In some diving circles, the term "recreational diving" is used in contradistinction to "technical diving", a more demanding aspect of the sport which requires greater levels...

, where they protect the face from cold water or stings, such as from jellyfish

Jellyfish

Jellyfish are free-swimming members of the phylum Cnidaria. Medusa is another word for jellyfish, and refers to any free-swimming jellyfish stages in the phylum Cnidaria...

or coral

Coral

Corals are marine animals in class Anthozoa of phylum Cnidaria typically living in compact colonies of many identical individual "polyps". The group includes the important reef builders that inhabit tropical oceans and secrete calcium carbonate to form a hard skeleton.A coral "head" is a colony of...

, 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

DESCO

DESCO is an underwater diving equipment maker which was first organized in 1937 in Wisconsin in the USA as Diving Equipment and Salvage Co.It was founded by:-...

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 glove

Glove

A glove is a garment covering the hand. Gloves have separate sheaths or openings for each finger and the thumb; if there is an opening but no covering sheath for each finger they are called "fingerless gloves". Fingerless gloves with one large opening rather than individual openings for each...

s, 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

Scuba set

A scuba set is an independent breathing set that provides a scuba diver with the breathing gas necessary to breathe underwater during scuba diving. It is much used for sport diving and some sorts of work diving....

mouthpiece or an ordinary eyes-and-nose diving mask

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 visibility
Visibility
In meteorology, visibility is a measure of the distance at which an object or light can be clearly discerned. It is reported within surface weather observations and METAR code either in meters or statute miles, depending upon the country. Visibility affects all forms of traffic: roads, sailing...

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
Frogman
A frogman is someone who is trained to scuba diving or swim underwater in a military capacity which can include combat. Such personnel are also known by the more formal names of combat diver or combatant diver or combat swimmer....

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
Scuba set
A scuba set is an independent breathing set that provides a scuba diver with the breathing gas necessary to breathe underwater during scuba diving. It is much used for sport diving and some sorts of work diving....

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

Rebreather

A rebreather is a type of breathing set that provides a breathing gas containing oxygen and recycled exhaled gas. This recycling reduces the volume of breathing gas used, making a rebreather lighter and more compact than an open-circuit breathing set for the same duration in environments where...

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

Intercom

An intercom , talkback or doorphone is a stand-alone voice communications system for use within a building or small collection of buildings, functioning independently of the public telephone network. Intercoms are generally mounted permanently in buildings and vehicles...

wire or by modulated ultrasound

Modulated ultrasound

Ultrasound can be modulated to carry an audio signal . This is often used to carry messages underwater, in underwater diving communicators, and short-range communication with submarines; the received ultrasound signal is decoded into audible sound by a modulated-ultrasound receiver.-Range...

) 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

CO2 retention

CO2 retention is a pathophysiological process in which too little carbon dioxide is removed from the blood by the lungs. The end result is hypercapnia, an elevated level of carbon dioxide dissolved in the bloodstream. Various diseases may lead to this state; disturbed gas exchange may lead to...

With a small mouth-and-nose (oronasal) breathing mask inside the full-face mask

With a small mouth-and-nose (oronasal

Orinasal mask

An orinasal mask is a breathing mask that covers the mouth and the nose only. It may occur independently, as an oxygen mask, or on some anaesthetic apparatuses, or it may occur inside a fullface mask on a scuba set or an industrial breathing set to reduce the amount of dead space...

) 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 "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 Navy

Royal Navy

The Royal Navy is the naval warfare service branch of the British Armed Forces. Founded in the 16th century, it is the oldest service branch and is known as the Senior Service...

and frogman

Frogman

A frogman is someone who is trained to scuba diving or swim underwater in a military capacity which can include combat. Such personnel are also known by the more formal names of combat diver or combatant diver or combat swimmer....

's rebreather

Rebreather

s have this mask arrangement; but the full-face mask plus mouthpiece combination acts like a strapped-in gag

Gag

A gag is usually a device designed to prevent speech, often as a restraint device to stop the subject from calling for help. This is usually done by blocking the mouth, partially or completely, or attempting to prevent the tongue, lips, or jaw from moving in the normal patterns of speech. They are...

making clear talking impossible.

With a removable pod carrying the moutpiece

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.

Other features

The inside of the mask window may get misted/fogged, and need to be treated with a demister

Demister (SCUBA)

A demister is a substance applied to transparent surfaces to stop them from becoming fogged with mist deposit, often referred to as fog. Scuba divers often spit into their masks and then wash the surface quickly with water to prevent mist buildup that can impair vision. Several products are...

. Some British Army

British Army

The British Army is the land warfare branch of Her Majesty's Armed Forces in the United Kingdom. It came into being with the unification of the Kingdom of England and Scotland into the Kingdom of Great Britain in 1707. The new British Army incorporated Regiments that had already existed in England...

and Russian gas masks

Gas mask

A gas mask is a mask put on over the face to protect the wearer from inhaling airborne pollutants and toxic gases. The mask forms a sealed cover over the nose and mouth, but may also cover the eyes and other vulnerable soft tissues of the face. Some gas masks are also respirators, though the word...

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

Bailout arrangements

There are several approaches to bailout air supply which can be used with a full-face mask:

Bailout gas may be supplied via a bailout block. This is the same system used for diving helmets. The main gas supply to the mask passes through a non-return valve to a bailout block and then to the demand valve. An alternative gas supply is connected to the bailout block through a valve which may be opened by the diver to allow use of the bailout gas. This does not allow supply of bailout gas to another diver. This system is used for most full face masks, as they have no other option.
For scuba diving with a full face mask, a gas-switching block is sometimes used to supply different gas mixes to the second stage in the mask. A bailout or reserve supply is then available via the switching block and a buddy's block may be connected via an intermediate pressure hose to share gas. This has the advantage that both divers are always breathing the same mixture in an emergency, reducing the chance of one diver inadvertently breathing a mix beyond its maximum operating depth.
A secondary demand valve cabn be fitted to some full-face masks. The Draeger Panorama (and the Apeks Panorama) have a port (P-port) on each side which can be used for this purpose. The demand valves of these masks can be unclipped on the surface to allow breathing of atmospheric air, and can also be removed underwater to clip in a secondaty supply carried either by the diver of by a buddy carrying compatable equipment. This system also allows for gas switching for decompression if enough of the appropriate demand valves are available.
The Kirby Morgan 48 Supermask allows the demand valve pod to be unclipped and another clipped on, or a standard demand valve can be used if the pod is left off while it is in use. When this is done the diver inserts the mouthpiece into his mouth in the usual way though the large opening left by the removal of the pod.

Potential problems with full-face masks

The mask window (faceplate) should be a modern strong polymer

Polymer

A polymer is a large molecule composed of repeating structural units. These subunits are typically connected by covalent chemical bonds...

and not glass

Glass

Glass is an amorphous solid material. Glasses are typically brittle and optically transparent.The most familiar type of glass, used for centuries in windows and drinking vessels, is soda-lime glass, composed of about 75% silica plus Na2O, CaO, and several minor additives...

, 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.