Snorkeling (British and Commonwealth English spelling: snorkelling) is the practice of swimming on or through a body of water while equipped with a diving mask, a shaped breathing tube called a snorkel, and usually swimfins. In cooler waters, a wetsuit may also be worn. Use of this equipment allows the snorkeler to observe underwater attractions for extended periods with relatively little effort and to breathe while face-down at the surface.
Snorkeling is a popular recreational activity, particularly at tropical resort locations. The primary appeal is the opportunity to observe underwater life in a natural setting without the complicated equipment and training required for scuba diving. It appeals to all ages because of how little effort there is, and without the exhaled bubbles of scuba-diving equipment. It is the basis of the two surface disciplines of the underwater sport of finswimming.
Snorkeling is also used by scuba divers when on the surface, in underwater sports such as underwater hockey and underwater rugby, and as part of water-based searches conducted by search and rescue teams.
A snorkel is a device used for breathing air from above the surface when the wearer's head is face downwards in the water with the mouth and the nose submerged. It may be either separate or integrated into a swimming or diving mask. The integrated version is only suitable for surface snorkeling, while the separate device may also be used for underwater activities such as spearfishing, freediving, finswimming, underwater hockey, underwater rugby and for surface breathing with scuba equipment. A swimmer's snorkel is a tube bent into a shape often resembling the letter "L" or "J", fitted with a mouthpiece at the lower end and constructed of light metal, rubber or plastic. The snorkel may come with a rubber loop or a plastic clip enabling the snorkel to be attached to the outside of the head strap of the diving mask. Although the snorkel may also be secured by tucking the tube between the mask-strap and the head, this alternative strategy can lead to physical discomfort, mask leakage or even snorkel loss.
To comply with the current European standard EN 1972 (2015), a snorkel for users with larger lung capacities should not exceed 38 centimeters in length and 230 cubic centimeters in internal volume, while the corresponding figures for users with smaller lung capacities are 35 cm and 150 cc respectively. Current World Underwater Federation (CMAS) Surface Finswimming Rules (2017) require snorkels used in official competitions to have a total length between 43 and 48 cm and to have an inner diameter between 1.5 and 2.3 cm. A longer tube would not allow breathing when snorkeling deeper, since it would place the lungs in deeper water where the surrounding water pressure is higher. The lungs would then be unable to inflate when the snorkeler inhales, because the muscles that expand the lungs are not strong enough to operate against the higher pressure. The pressure difference across the tissues in the lungs, between the blood capillaries and air spaces would increase the risk of pulmonary edema.
Snorkels constitute respiratory dead space. When the user takes in a fresh breath, some of the previously exhaled air which remains in the snorkel is inhaled again, reducing the amount of fresh air in the inhaled volume, and increasing the risk of a buildup of carbon dioxide in the blood, which can result in hypercapnia. The greater the volume of the tube, and the smaller the tidal volume of breathing, the more this problem is exacerbated. A smaller diameter tube reduces the dead volume, but also increases resistance to airflow and so increases the work of breathing. Occasional exhalation through the nose while snorkeling will slightly reduce the buildup of carbon dioxide, and may help in keeping the mask clear of water. It may also increase fogging.
The simplest type of snorkel is a plain tube that is allowed to flood when underwater. The snorkeler expels water from the snorkel either with a sharp exhalation on return to the surface (blast clearing) or by tilting the head back shortly before reaching the surface and exhaling until reaching or breaking the surface (displacement method) and facing forward or down again before inhaling the next breath. The displacement method expels water by filling the snorkel with air; it is a technique that takes practice but clears the snorkel with less effort, but only works when surfacing. Clearing splash water while at the surface requires blast clearing.
Some snorkels have a sump at the lowest point to allow a small volume of water to remain in the snorkel without being inhaled when the snorkeler breathes. Some also have a non-return valve in the sump, to drain water in the tube when the diver exhales. The water is pushed out through the valve when the tube is blocked by water and the exhalation pressure exceeds the water pressure on the outside of the valve. This is almost exactly the mechanism of blast clearing which does not require the valve, but the pressure required is marginally less, and effective blast clearing requires a higher flow rate. The full face mask has a double airflow valve which allows breathing through the nose in addition to the mouth. A few models of snorkel have float-operated valves attached to the top end of the tube to keep water out when a wave passes, but these cause problems when diving as the snorkel must then be equalized during descent, using part of the diver's inhaled air supply. Some recent designs have a splash deflector on the top end that reduces entry of any water that splashes over the top end of the tube, thereby keeping it relatively free from water.
Finswimmers do not normally use snorkels with a sump valve, as they learn to blast clear the tube on most if not all exhalations, which keeps the water content in the tube to a minimum as the tube can be shaped for lower work of breathing, and elimination of water traps, allowing greater speed and lowering the stress of eventual swallowing of small quantities of water, which would impede their competition performance.
A common problem with all mechanical clearing mechanisms is their tendency to fail if infrequently used, or if stored for long periods, or through environmental fouling, or owing to lack of maintenance. Many also either slightly increase the flow resistance of the snorkel, or provide a small water trap, which retains a little water in the tube after clearing.
Modern designs use silicone rubber in the mouthpiece and one-way clearing and float valves due to its resistance to degradation and its long service life. Natural rubber was formerly used, but slowly oxidizes and breaks down due to ultraviolet light exposure from the sun. It eventually loses its flexibility, becomes brittle and cracks, which can cause clearing valves to stick in the open or closed position, and float valves to leak due to a failure of the valve seat to seal. In even older designs, some snorkels were made with small "ping pong" balls in a cage mounted to the open end of the tube to prevent water ingress. These are no longer sold or recommended because they are unreliable and considered hazardous. Similarly, diving masks with a built-in snorkel are considered unsafe by scuba diving organizations such as PADI, BSAC because they can engender a false sense of security and can be difficult to clear if flooded.
Snorkeling is mentioned by Aristotle in his Parts of Animals. He refers to divers using "instruments for respiration" resembling the elephant's trunk. Some evidence suggests that snorkeling may have originated in Crete some 5,000 years ago as sea sponge farmers used hollowed out reeds to submerge and retrieve natural sponge for use in trade and commerce. In the fifteenth century, Leonardo da Vinci drew designs for an underwater breathing device consisting of cane tubes with a mask to cover the mouth at the demand end and a float to keep the tubes above water at the supply end. The following timeline traces the modern history of the swimmers' snorkel during the twentieth and twenty-first centuries.
1927: First use of swimmer's breathing tube and mask. According to Dr Gilbert Doukan's 1957 World Beneath the Waves and cited elsewhere, "In 1927, and during each summer from 1927 to 1930, on the beach of La Croix-Valmer, Jacques O'Marchal could be seen using the first face mask and the first breathing tube. He exhibited them, in fact, in 1931, at the International Nautical Show. On his feet, moreover, he wore the first 'flippers' designed by Captain de Corlieu, the use of which was to become universal."
1932: First submerged persons' breathing tube patent application filed. On 30 July 1932, Joseph L. Belcher files a patent application for "breathing apparatus" delivering air to a submerged person by suction from the surface of the water through hoses connected to a float. His invention is granted US patent 1,901,219 on 14 March 1933.
1938: First swimmers' mask with integrated breathing tubes. In 1938, French naval officer Yves Le Prieur introduces his "Nautilus" full-face diving mask with hoses emerging from the sides and leading upwards to an air inlet device whose ball valve opens when it is above water and closes when it is submerged. In November 1940, American spearfisherman Charles H. Wilen files his "swimmer's mask" invention, which is granted US patent 2,317,237 of 20 April 1943. The device resembles a full-face diving mask incorporating two breathing tubes topped with valves projecting above the surface for inhalation and exhalation purposes. On 11 July 1944, he obtains US design patent 138,286 for a simpler version of this mask with a flutter valve at the bottom and a single breathing tube with a ball valve at the top. Throughout their heydey of the 1950s and early 1960s, masks with integrated tubes appear in the catalogues of American, Australian, British, French, German, Greek, Italian and Spanish swimming and diving equipment manufacturers. Meanwhile, in 1957, the US monthly product-testing magazine Consumer Reports concludes that "snorkel-masks have some value for swimmers lying on the surface while watching the depths in water free of vegetation and other similar hazards, but they are not recommended for a dive 'into the blue'". According to an underwater swimming equipment review in the British national weekly newspaper The Sunday Times in December 1973, "the mask with inbuilt snorkel is doubly dangerous (...) A ban on the manufacture and import of these masks is long overdue in Britain". In a decree of 2 August 1989, the French government suspends the manufacture, importation and marketing of ball-valve snorkel-masks. By the noughties, just two swim masks with attached breathing tubes remain in production worldwide: the Majorca sub 107S single-snorkel model and the Balco 558 twin-snorkel full-face model, both manufactured in Greece. In May 2014, the French Decathlon company files its new-generation full-face snorkel-mask design, which is granted US design patent 775,722 on 3 January 2017, entering production as the "Easybreath" mask (see Figure 3) designated for surface snorkeling only.
1938: First front-mounted swimmer's breathing tube patent filed. In December 1938, French spearfisherman Maxime Forjot and his business partner Albert Méjean file a patent application in France for a breathing tube worn on the front of the head over a single-lens diving mask enclosing the eyes and the nose and it is granted French patent 847848 on 10 July 1939. In July 1939, Popular Science magazine publishes an article containing illustrations of a spearfisherman using a curved length of hosepipe as a front-mounted breathing tube and wearing a set of swimming goggles over his eyes and a pair of swimming fins on his feet. In the first French monograph on spearfishing La Chasse aux Poissons (1940), medical researcher and amateur spearfisherman Dr Raymond Pulvénis illustrates his "Tuba", a breathing tube he designed to be worn on the front of the head over a single-lens diving mask enclosing the eyes and the nose. Francophone swimmers and divers have called their breathing tube "un tuba" ever since. In 1943, Raymond Pulvénis and his brother Roger obtain a Spanish patent for their improved breathing tube mouthpiece design. In 1956, the UK diving equipment manufacturer E. T. Skinner (Typhoon) markets a "frontal" breathing tube with a bracket attachable to the screw at the top of an oval diving mask. Although it falls out of favour with underwater swimmers eventually, the front-mounted snorkel becomes the breathing tube of choice in competitive swimming and finswimming (see Figure 4) because it contributes to the swimmer's hydrodynamic profile.
1939: First side-mounted swimmers' breathing tube patent filed. In December 1939, expatriate Russian spearfisherman Alexandre Kramarenko files a patent in France for a breathing tube worn at the side of the head with a ball valve at the top to exclude water and a flutter valve at the bottom. Kramarenko and his business partner Charles H. Wilen refile the invention in March 1940 in the USA, where their "underwater apparatus for swimmers" is granted US patent 2,317,236 on 20 April 1943; after entering production in France, the device is called "Le Respirator". The co-founder of Scubapro Dick Bonin is credited with the introduction of the flexible-hose snorkel in the mid-1950s and the exhaust valve to ease snorkel clearing in 1980. In 1964, US Divers markets an L-shaped snorkel designed to outperform J-shaped models by increasing breathing ease, cutting water drag and eliminating the "water trap". In the late 1960s, Dacor launched a "wraparound big-barrel" contoured snorkel, which closely follows the outline of the wearer's head and comes with a wider bore to improve airflow. The findings of the 1977 report "Allergic reactions to mask skirts, regulator mouthpieces and snorkel mouthpieces" encourage diving equipment manufacturers to fit snorkels with hypoallergenic gum rubber and medical-grade silicone mouthpieces (see Figure 5). In the world of underwater swimming and diving, the side-mounted snorkel has long become the norm, although new-generation full-face swim masks with integrated snorkels are beginning to grow in popularity for use in floating and swimming on the surface.
1950: First use of "snorkel" to denote a breathing device for swimmers. In November 1950, the Honolulu Sporting Goods Co. introduces a "swim-pipe" resembling Kramarenko and Wilen's side-mounted ball- and flutter-valve breathing tube design, urging children and adults to "try the human version of the submarine snorkel and be like a fish". Every advertisement in the first issue of Skin Diver magazine in December 1951 uses the alternative spelling "snorkles" to denote swimmers' breathing tubes. In 1955, Albert VanderKogel classes stand-alone breathing tubes and swim masks with integrated breathing tubes as "pipe snorkels" and "mask snorkels" respectively. In 1957, the British Sub-Aqua Club journal features a lively debate about the standardisation of diving terms in general and the replacement of the existing British term "breathing tube" with the American term "snorkel" in particular. The following year sees the première of the 1958 British thriller film The Snorkel, whose title references a diving mask topped with two built-in breathing tubes. To date, every national and international standard on snorkels uses the term "snorkel" exclusively.
1969: First national standard on snorkels. In December 1969, the British Standards Institution publishes British standard BS 4532 entitled "Specification for snorkels and face masks" and prepared by a committee on which the British Rubber Manufacturers' Association, the British Sub-Aqua Club, the Department for Education and Science, the Federation of British Manufacturers of Sports and Games, the Ministry of Defence Navy Department and the Royal Society for the Prevention of Accidents are represented. This British standard sets different maximum and minimum snorkel dimensions for adult and child users, specifies materials and design features for tubes and mouthpieces and requires a warning label and a set of instructions to be enclosed with each snorkel. In February 1980 and June 1991, the Deutsches Institut für Normung publishes the first and second editions of German standard DIN 7878 on snorkel safety and testing. This German standard sets safety and testing criteria comparable to British standard BS 4532 with an additional requirement that every snorkel must be topped with a fluorescent red or orange band to alert other water users of the snorkeller's presence. In November 1988, the Austrian Standards Institute publishes Austrian standard ÖNORM S 4223 entitled "Tauch-Zubehör; Schnorchel; Abmessungen, sicherheitstechnische Anforderungen, Prüfung, Normkennzeichnung" in German, subtitled "Diving accessories; snorkel; dimensions, safety requirements, testing, marking of conformity" in English and closely resembling German Standard DIN 7878 of February 1980 in specifications. The first and second editions of European standard EN 1972 on snorkel requirements and test methods appear in July 1997 and December 2015. This European standard refines snorkel dimension, airflow and joint-strength testing and matches snorkel measurements to the user's height and lung capacity. The snorkels regulated by these British, German and European standards exclude combined masks and snorkels in which the snorkel tubes open into the mask.
A snorkel may be either separate or integrated into a swim or dive mask. Usage of the term "snorkel" in this section excludes devices integrated with, and opening into, swimmers' or divers' masks.
A separate snorkel typically comprises a tube for breathing and a means of attaching the tube to the head of the wearer. The tube has an opening at the top and a mouthpiece at the bottom. Some tubes are topped with a valve to prevent water from entering the tube when it is submerged.
Although snorkels come in many forms, they are primarily classified by their dimensions and secondarily by their orientation and shape. The length and the inner diameter (or inner volume) of the tube are paramount health and safety considerations when matching a snorkel to the morphology of its end-user. The orientation and shape of the tube must also be taken into account when matching a snorkel to its end use while seeking to optimise ergonomic factors such as streamlining, airflow and water retention.
The total length, inner diameter and/or inner volume of a snorkel tube are matters of utmost importance because they affect the user's ability to breathe normally while swimming or floating head downwards on the surface of the water. These dimensions also have implications for the user's ability to blow residual water out of the tube when surfacing. An overlong snorkel tube may cause breathing resistance, while an overwide tube may prove hard to clear of water. A high-volume tube is liable to encourage a build-up of stale air, including exhaled carbon dioxide, because it constitutes respiratory dead space.
To date, all national and international standards on snorkels specify two ranges of tube dimensions to meet the health and safety needs of their end-users, whether young or old, short or tall, with low or high lung capacity (See Figure 1 and Figure 2). The snorkel dimensions at issue are the total length, the inner diameter and/or the inner volume of the tube. The specifications of the standardisation bodies are tabulated below.
|Snorkel standards and rules||Total length||Inner diameter||Total inner volume|
|British Standard: BS 4532 (1969)||500 mm - 600 mm||15 mm - 18 mm|
|British Standard: BS 4532 (1977)||300 mm - 600 mm||15 mm - 22.5 mm. An inner diameter exceeding 20 mm is child-inappropriate.|
|German Standard: DIN 7876 (1980)||Form A (Children): 300 mm max. Form B (Adults): 350 mm max.||Form A (Children): 15 mm - 18 mm. Form B (Adults): 18 mm - 25 mm.||Form A (Children): 120 cc max. Form B (Adults): 150 cc max.|
|Austrian Standard: ÖNORM S 4223 (1988)||Form A (Children): 300 mm max. Form B (Adults): 350 mm max.||Form A (Children): 15 mm - 18 mm. Form B (Adults): 18 mm - 25 mm.||Form A (Children): 120 cc max. Form B (Adults): 150 cc max.|
|German Standard: DIN 7876 (1991)||Form A (Users over ten years of age): 350 mm max. Form C (Ten-year-olds and younger): 300 mm max.||Form A (Users over ten years of age): 18 mm min. Form C (Ten-year-olds and younger): 18 mm min.||Form A (Users over ten years of age): 180 cc max. Form C (Ten-year-olds and younger): 120 cc max.|
|European Standard: EN 1972 (1997)||Type 1 (Users 150 cm or less in height): 350 mm max. Type 2 (Users exceeding 150 cm in height): 380 mm max. Competitive finswimming: 480 mm max.||Type 1 (Users 150 cm or less in height): 150 cc max. Type 2 (Users exceeding 150 cm in height): 230 cc max. Competitive finswimming: 230 cc max.|
|European Standard: EN 1972 (2015)||Class A (Users with larger lung capacity): 380 mm max. Class B (Users with smaller lung capacity, e.g. children): 350 mm max.||Class A (Users with larger lung capacity): 230 cc max. Class B (Users with smaller lung capacity, e.g. children): 150 cc max.|
|World Underwater Federation (CMAS) Surface Finswimming Rules (2017)||430 mm - 480 mm.||15 mm - 23 mm. Tube cross-section to be circular.|
The table above shows how snorkel dimensions have changed over time in response to progress in swimming and diving science and technology:
Snorkels come in two orientations: Front-mounted (see Figure 4) and side-mounted (see Figure 5). The first snorkel to be patented in 1938 was front-mounted, worn with the tube over the front of the face and secured with a bracket to the diving mask. Front-mounted snorkels proved popular in European snorkeling until the late 1950s, when side-mounted snorkels came into the ascendancy. Front-mounted snorkels experienced a comeback a decade later as a piece of competitive swimming equipment to be used in pool workouts and in finswimming races, where they outperform side-mounted snorkels in streamlining. Front-mounted snorkels are attached to the head with a special head bracket fitted with straps to be adjusted and buckled around the temples (see Figure 4).
Side-mounted snorkels are generally worn by scuba divers on the left-hand side of the head because the scuba regulator is placed over the right shoulder. They come in at least four basic shapes (see Figure 6): J-shaped; L-shaped; Flexible-hose; Contour.
A snorkel consists essentially of a tube with a mouthpiece to be inserted between the lips. See Figure 7 for snorkel parts location and nomenclature.
The barrel is the hollow tube leading from the supply end at the top of the snorkel to the demand end at the bottom where the mouthpiece is attached. The barrel is made of a relatively rigid material such as plastic, light metal or hard rubber. The bore is the interior chamber of the barrel; bore length, diameter and bends all affect breathing resistance.
The top of the barrel may be open to the elements or fitted with a valve designed to shut off the air supply from the atmosphere when the top is submerged (see Figure 5 and Figure 7). There may be a fluorescent red or orange band around the top to alert other water users of the snorkeller's presence. The simplest way of attaching the snorkel to the head is to slip the top of the barrel between the mask strap and the head. This may cause the mask to leak, however, and alternative means of attachment of the barrel to the head can be seen in Figure 8.
Attached to the demand end of the snorkel at the bottom of the barrel, the mouthpiece serves to keep the snorkel in the mouth. It is made of soft and flexible material, typically natural rubber and latterly silicone or PVC. The commonest of the multiple designs available features a slightly concave flange with two lugs to be gripped between the teeth (see Figure 9):
A disadvantage of mouthpieces with lugs is the presence of the teeth when breathing. The tighter the teeth grip the mouthpiece lugs, the smaller the air gap between the teeth and the harder it will be to breathe.
Snorkel design is only limited by the imagination. Among recent innovations is the "collapsible snorkel", which can be folded up in a pocket for emergencies. One for competitive swimmers is a lightweight lap snorkel; with twin tubes another is a "restrictor cap" placed inside a snorkel barrel "restricting breathing by 40% to increase cardiovascular strength and build lung capacity". Some additional snorkel features such as shut-off and drain valves fell out of favour decades ago, only to return in the contemporary era as more reliable devices for incorporation into "dry" and "semi-dry" snorkels; see Figure 5 featuring a modern snorkel topped with a splash guard.
In this section, usage of the term "snorkel" denotes single or multiple tubular devices integrated with, and opening into, a swim or dive mask, while the term "snorkel-mask" is used to designate a swim or dive mask with single or multiple built-in snorkels. Such snorkels from the past typically comprised a tube for breathing and a means of connecting the tube to the space inside the snorkel-mask. The tube had an aperture with a shut-off valve at the top and opened at the bottom into the mask, which might cover the mouth as well as the nose and eyes. Although such snorkels tended to be permanent fixtures on historical snorkel-masks, a minority could be detached from their sockets and replaced with plugs enabling certain snorkel-masks to be used without their snorkels (see Figure 10).
The 1950s were the heyday of older-generation snorkel-masks, first for the pioneers of underwater hunting and then for the general public who swam in their wake. One even-minded authority of the time declared that "the advantage of this kind of mask is mainly from the comfort point of view. It fits snugly to one's face, there is no mouthpiece to bite on, and one can breathe through either nose or mouth". Another concluded with absolute conviction that "built-in snorkel masks are the best" and "a must for those who have sinus trouble." Yet others, including a co-founder of the British Sub-Aqua Club, deemed masks with integrated snorkels to be complicated and unreliable: "Many have the breathing tube built in as an integral part of the mask. I have never seen the advantage of this, and this is the opinion shared by most experienced underwater swimmers I know". Six decades on, a new generation of snorkel-masks has come to the marketplace (see Figure 3).
Like separate snorkels, integrated snorkels come in a variety of forms. The assortment of older-generation masks with integrated snorkels in Figure 10 highlights certain similarities and differences:
Integrated snorkels are tentatively classified here by their tube configuration and by the face coverage of the masks to which they are attached.
As a rule, early manufacturers and retailers classed integrated snorkel masks by the number of breathing tubes projecting from their tops and sides. Their terse product descriptions often read: "single snorkel mask", "twin snorkel mask", "double snorkel mask" or "dual snorkel mask".
All existing new-generation snorkel-masks (see Figure 3) are full-face masks covering the eyes, the nose and the mouth. They enable surface snorkellers to breathe nasally or orally and may be a workaround in the case of surface snorkellers who gag in response to the presence of standard snorkel mouthpieces in their mouths. Some old-generation snorkel-masks (See Figure 10) are full-face masks covering the eyes, nose and mouth, while others exclude the mouth, covering the eyes and the nose only. The 1950s US Divers "Marino" hybrid comprised a single snorkel mask with eye and nose coverage and a separate snorkel for the mouth.
An integrated snorkel consists essentially of a tube topped with a shut-off valve and opening at the bottom into the interior of a diving mask.
Tubes are made of strong but lightweight materials such as plastic. At the supply end, they are fitted with valves made of plastic, rubber or latterly silicone. Three typical shut-off valves are illustrated in Figure 11.
Integrated snorkels must be fitted with valves to shut off the snorkel's air inlet when submerged. Water will otherwise pour into the opening at the top and flood the interior of the mask. Snorkels are attached to sockets on the top or the sides of the mask.
The skirt of the diving mask attached to the snorkel is made of rubber, or latterly silicone. Older-generation snorkel masks come with a single oval, round or triangular lens retained by a metal clamp in a groove within the body of the mask. An adjustable head strap or harness ensures a snug fit on the wearer's face. The body of a mask with full-face coverage is fitted with a chinpiece to enable a complete leaktight enclosure of the mouth.
Older proprietary designs came with special facilities. One design separated the eyes and the nose into separate mask compartments to reduce fogging. Another enabled the user to remove integrated snorkels and insert plugs instead, thus converting the snorkel-mask into an ordinary diving mask. New-generation snorkel-masks enclose the nose and the mouth within an inner mask at the demand end directly connected to the single snorkel with its valve at the supply end.
Snorkelers normally wear the same kind of mask as those worn by scuba divers. By creating an airspace, the mask enables the snorkeler to see clearly underwater. All scuba diving masks consist of the lenses also known as a faceplate, a soft rubber skirt, which encloses the nose and seals against the face, and a head strap to hold it in place. There are different styles and shapes. These range from oval shaped models to lower internal volume masks and may be made from different materials; common choices are silicone and rubber. A snorkeler who remains at the surface can use swimmer's goggles which do not enclose the nose.
Full face snorkel masks use an integral snorkel with separate channels for intake and exhaled gases theoretically ensuring the user is always breathing untainted fresh air whatever the respiratory effort. The main difficulty or danger is that it must fit the whole face perfectly and since no two faces are the same shape, it should be used with great care and in safe water. In the event of accidental flooding, the whole mask must be removed to continue breathing. Unless the snorkeler is able to equalize without pinching their nose it can only be used on the surface, or a couple of feet below since the design makes it impossible to pinch the nose in order to equalise pressure at greater depth. Trained scuba divers are likely to avoid such devices[clarification needed] however snorkel masks are a boon for those with medical conditions that preclude taking part in SCUBA diving.[clarification needed]
As a result of a short period with an unusually high number of snorkeling deaths in Hawaii there is some suspicion that the design of the masks can result in buildup of excess CO2. It is far from certain that the masks are at fault, but the state of Hawaii has begun to track the equipment being used in cases of snorkeling fatalities. Besides the possibility that the masks, or at least some brands of the mask, are a cause other theories include the possibility that the masks make snorkeling accessible to people who have difficulty with traditional snorkeling equipment. That ease of access may result in more snorkelers who lack experience or have underlying medical conditions, possibly exacerbating problems that are unrelated to the type of equipment being used.
Snorkeling is an activity in its own right, as well as an adjunct to other activities, such as breath-hold diving, spearfishing and scuba diving, and several competitive underwater sports, such as underwater hockey and finswimming.
In all cases, the use of a snorkel facilitates breathing while swimming at the surface and observing what is going on under the water.
A snorkel can be useful when scuba diving as it is a safe way of swimming face down at the surface for extended periods to conserve the bottled air supply, or in an emergency situation when there is a problem with either air supply or regulator. Many dives do not require the use of a snorkel at all, and some scuba divers do not consider a snorkel a necessary or even useful piece of equipment, but the usefulness of a snorkel depends on the dive plan and the dive site. If there is no requirement to swim face down and see what is happening underwater, then a snorkel is not useful. If it is necessary to swim over heavy seaweed which can entangle the pillar valve and regulator if the diver swims face upward to get to and from the dive site, then a snorkel is useful to save breathing gas.
Being non-competitive, snorkeling is considered more a leisure activity than a sport. Snorkeling requires no special training, only the very basic swimming abilities and being able to breathe through the snorkel. Some organizations[by whom?] recommend that for snorkeling safety one should not snorkel alone, but rather with a "buddy", a guide or a tour group.
Some commercial snorkeling organizations require snorkelers at their venue to wear an inflatable vest, similar to a personal flotation device. They are usually bright yellow or orange and have a device that allows users to inflate or deflate the device to adjust their buoyancy. However, these devices hinder and prevent a snorkeler from free diving to any depth. Especially in cooler water, a wetsuit of appropriate thickness and coverage may be worn; wetsuits do provide some buoyancy without as much resistance to submersion. In the tropics, snorkelers (especially those with pale skin) often wear a rashguard or a shirt and/or board shorts in order to help protect the skin of the back and upper legs against sunburn.
Experienced snorkelers may progress to amateur free-diving, which should be preceded by at least some training from a dive instructor or experienced free-diver.
The greatest danger to snorkelers are inshore and leisure craft such as jet skis, speed boats and the like. A snorkeler is often submerged in the water with only the tube visible above the surface. Since these craft can ply the same areas snorkelers visit, the chance for accidental collisions exists. Sailboats and sailboards are a particular hazard as their quiet propulsion systems may not alert the snorkeler of their presence. A snorkeler may surface underneath a vessel and/or be struck by it. Few locations demarcate small craft areas from snorkeling areas, unlike that done for regular beach-bathers, with areas marked by buoys. Snorkelers may therefore choose to wear bright or highly reflective colors/outfits and/or to employ dive flags to enable easy spotting by boaters and others.
Snorkelers' backs, ankles, and rear of their thighs can be exposed to the sun for extended periods, and can burn badly (even if slightly submerged), without being noticed in time. The wearing appropriate covering such as a "rash guard" with SPF (in warmer waters), a T-shirt, a wetsuit, and especially "waterproof" sunblock will mitigate this risk.
Dehydration is another concern. Hydrating well before entering the water is highly recommended, especially if one intends to snorkel for several hours. Proper hydration also prevents cramps. Snorkelers who hyperventilate to extend sub-surface time can experience hypocapnia if they hyperventilate prior to submerging. This can in turn lead to "shallow water blackout". Snorkeling with a buddy and remaining aware of the buddy's condition at all times can help avoid these difficulties.
When snorkeling on or near coral reefs, care must be exercised to avoid contact with the delicate (and sometimes sharp or stinging) coral, and its poisonous inhabitants, usually by wearing protective gloves and being careful of one's environment. Coral scrapes and cuts often require specialized first aid treatment and potentially, emergency medical treatment to avoid infection. Booties and surf shoes are especially useful as they allow trekking over reefs exposed by low tide, to access drop-offs or deeper waters of the outer reef - this is, however, ecologically irresponsible.
Contact with coral should always be avoided, because even boulder corals are fragile.
Another safety concern is interaction and contact with the marine life during encounters. While seals and sea turtles can seem harmless and docile, they can become alarmed if approached or feel threatened. Some creatures, like moray eels, can hide in coral crevices and holes and will bite fingers when there is too much prodding going on. For these reasons, snorkeling websites often recommend an "observe but don't touch" etiquette when snorkeling.
Snorkeling is possible in almost any body of water, but snorkelers are most likely to be found in locations where there are minimal waves, warm water, and something particularly interesting to see near the surface.
Generally shallow reefs ranging from sea level to 1 to 4 meters (3 to 13 ft) are favored by snorkelers. Deeper reefs can also be explored, but repeated breath-holding to dive to those depths limits the number of practitioners, and raises the bar on the required fitness and skill level. Risk increases with increased depth and duration of the breath-hold excursions from the surface.
Underwater photography has become more and more popular since the early 2000s, resulting on millions of pictures posted every year on various websites and social media. This mass of documentation is endowed with an enormous scientific potential, as millions of tourists possess a much superior coverage power than professional scientists, who can not allow themselves to spend so much time in the field. As a consequence, several participative sciences programs have been developed, supported by geo-localization and identification web sites, along with protocols for auto-organization and self-teaching aimed at biodiversity-interested snorkelers, in order for them to turn their observations into sound scientific data, available for research. This kind of approach has been successfully used in Réunion island, allowing for tens of new records and even new species.
Just then as divers are sometimes provided with instruments for respiration, through which they can draw air from above the water, and thus may remain for a long time under the sea, so also have elephants been furnished by nature with their lengthened nostril; and, whenever they have to traverse the water, they lift this up above the surface and breathe through it.