Something about diving you need to know （2）

About Use

😀😀The strap can be adjusted to suit the diver's head. Too loose may not provide an effective seal and the mask may dislodge easily, and too tight may result in discomfort or pain. Correct positioning of the strap around the back of the head will reduce the risk of dislodging and facilitate clearing.

When entering the water while wearing the mask, the diver may need to manually prevent water impact from dislodging or knocking off the mask. Alternatively, a diver can enter the water with the mask off and then put it on or use an entry method which does not result in fast water flow over the mask. Wearing the mask pushed up onto the forehead while out of the water or on the surface increases the risk of the mask falling or being knocked off.

To prevent a mask from fogging up due to condensation on the glass many divers spit into the dry mask before use, spread the saliva around the inside of the plate and rinse it out with a little water. The saliva residue allows condensation to wet the glass and form a continuous film, rather than form droplets. There are commercial products that can be used as an alternative to the saliva method, some of which are more effective and last longer.

Standard maintenance is to rinse inside and out with clean, fresh water after each day's use, and allow to dry out of direct sunlight before storage. Ultraviolet light degrades the synthetic materials of the skirt and frame. A well-maintained mask should last for several years. The strap is the most stressed component and is often the first part to fail, but can usually be replaced. Inspection of the strap for cracks and tears before use can reduce the risk of failure during a dive.

Mask removal and refitting underwater and clearing are basic skills that all divers must learn so that they can deal with flooding and leaks or the mask being dislodged without panic.

Snorkel Mask

Mask clearing

Practicing mask clearing during entry level training

It is quite common for water to leak into the mask, which can be annoying, or interfere with clear vision, and the diver needs to be able to get rid of the water quickly and effectively. Reasons for the leakage include poor fit or fitting, leaking via head or facial hair, movement of the facial muscles causing temporary leaks, or impact of external objects against the mask, which may distort it temporarily, or move it so that it leaks, or in extreme cases dislodge it entirely from the diver's head.

The methods of clearing differ between the half mask, which covers the eyes and nose, and the full-face mask, which also covers the mouth. If the mask has a purge valve and the strap tension is correct, the diver holds the head so that the valve is at the lowest point and exhales through the nose. If the mask is a good fit on the diver's face and the strap is correctly placed, exhaling through the nose will usually drive water out along the bottom edge of the skirt. It may be necessary to press the upper part of the mask against the face to improve the seal if the diver is rolled to one side. If the fit is not perfect, or the strap is too low, contact pressure of the top edge against the forehead may be insufficient to maintain a seal when the head is upright.

Equalizing

Pinching the nose while clearing the ears on descent

See also: Ear clearing

The pressure changes during ascent and descent may affect gas spaces in the diver and diving equipment. A change in pressure will cause a pressure difference between the gas space and environment which will cause the gas to expand or compress if that is possible, and constraining the gas from expanding or compressing to balance the pressure may cause damage to the surrounding material or tissues by over-expansion or crushing. Some gas spaces, such as the mask, will automatically release excess gas as it expands during ascent, but have to be equalized during compression of descent.

Equalising of the mask is an essential skill for any form of diving. Goggles that do not cover the nose can not be equalised and are unsuitable for diving. The mask is equalised by exhaling sufficient air through the nose to provide a balanced internal pressure. Any excess will simply leak out around the skirt. Equalising (or clearing) the ears is necessary to prevent barotrauma to the middle and inner ear. Some divers need to pinch the nostrils closed as part of their equalisation technique, and this must be allowed for in the design of the mask skirt.

You will enjoy the experience better brought by snorkel mask only if you know the snorkel mask better. Avoid the trouble and irritation, Just smile it ! We're going to talking about the type of the snorkel mask next time !

Good day ~😀😀

  Something about diving you need to know.

😀😀Nearly 3/4ths of the world is covered in water and what lies beneath is a sea life experience you can only enjoy if you’re looking. When you start this journey, you maybe need to know something about diving mask.

A diving mask (also half mask, dive mask or scuba mask) is an item of diving equipment that allows underwater divers, including, scuba divers, free-divers, and snorkelers to see clearly underwater. Surface supplied divers usually use a full face mask or diving helmet, but in some systems the half mask may be used. 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 to focus the light. By providing an air space in front of the eyes, light enters normally and the eye is able to focus correctly.

🌴🌴When the diver descends the ambient pressure rises and it becomes necessary to equalize the pressure inside the mask with the ambient pressure to avoid the barotrauma known as mask squeeze, This is done by blowing sufficient air out through the nose into the mask to relieve the pressure difference. This requires that the nose is included in the airspace of the diving mask. Equalisation during ascent is automatic as excess air easily leaks past the seal from inside.
Corrective lenses can be fitted to allow normal vision for people with focusing defects, or contact lenses may be worn inside the mask.
A wide range of viewport shapes and internal volumes are available, and each design will generally fit some shapes of face better than others. A good comfortable fit is important to the correct function of the mask.

Function:

🍡🍡Light rays bend when they travel from one medium to another; the amount of bending is determined by the refractive indices of the two media. If one medium has a particular curved shape, it functions as a lens. The cornea, humours, and crystalline lens of the eye together form a lens that focuses images on the retina. Our eyes are adapted for viewing in air. Water, however, has approximately the same refractive index as the cornea (both about 1.33), so immersion effectively eliminates the cornea's focusing properties. When our eyes are in water, instead of focusing images on the retina, they now focus them far behind the retina, resulting in an extremely blurred image from hypermetropia.By wearing a flat diving mask, humans can see clearly under water. The scuba mask's flat window separates the eyes from the surrounding water by a layer of air. Light rays entering from water into the flat parallel window change their direction minimally within the window material itself. But when these rays exit the window into the air space between the flat window and the eye, the refraction is quite noticeable. The view paths refract (bend) in a manner similar to viewing fish kept in an aquarium. Linear polarizing filters decrease visibility underwater by limiting ambient light and dimming artificial light sources.

Refraction of light entering the mask makes objects appear about 34% bigger and 25% nearer when underwater. Also pincushion distortion and lateral chromatic aberration are noticeable. As the diver descends in clean water, the water acts as a colour filter eliminating the red end of the visible spectrum of the sunlight entering the water leaving only the blue end of the spectrum. Depending on the depth and clarity of the water, eventually all sunlight is blocked and the diver has to rely on artificial light sources to see underwater.

Construction:

👀👀Scuba diver with bifocal lenses in half mask
There are two basic categories of diving mask: The half mask covers the eyes and nose, and the full face mask covers eyes, nose and mouth, and therefore includes a part of the breathing apparatus. The half mask is described here.

Diving masks may have a single, durable, tempered glass faceplate, or two lenses in front of the eyes. These may be supported by a relatively rigid plastic or metal frame, or they may be permanently bonded to the rim of the skirt, in a construction known as "frameless". In the case of freediving masks, which need to have a low internal volume to minimize the amount of breath needed to equalize the change of pressure that occurs with depth, the lenses may be made of polycarbonate plastic. There is usually a "skirt" of synthetic rubber or silicone elastomer to support the frame and lenses and create a watertight seal with the diver's face. The skirt material may be almost transparent, translucent or opaque. A nearly transparent skirt provides a greater peripheral vision, though somewhat distorted, and may reduce the feeling of claustrophobia in some divers, but in some cases the light entering through the sides may cause distracting internal reflections. The skirt also encloses the nose, usually by means of a nose pocket, so that air can be exhaled through the nose into the mask to equalise the internal pressure during descent and thereby avoid possible barotrauma of the enclosed area of the face. The section of the mask covering the nose must allow the wearer to block the nostrils while equalising pressure in the middle ear. All diving masks have means to keep them in position, usually an elastomer strap of similar material to the skirt,[1] but occasionally an expanded neoprene pad with velcro straps is used. Mask straps are usually wider at the back or split into an upper and lower strap at the back of the head for stability and comfort.
Some masks had a one-way purge valve under the nose to let water out, but this is no longer common as they were neither necessary nor reliable, and often leaked
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Visual correction

👧Diving masks can be fitted with prescription lenses for divers needing optical correction to improve vision. Corrective lenses are ground flat on one side and optically cemented to the inside face of the mask lens. This provides the same amount of correction above and below the surface of the water. Bifocal lenses are also available for this application. Some masks are made with removable lenses, and a range of standard corrective lenses are available which can be fitted. Plastic self-adhesive lenses that can be applied to the inside of the mask may fall off if the mask is flooded for a significant period. Contact lenses may be worn under a mask or helmet, but there is some risk of losing them if the mask is dislodged in turbulent water.

Fit:

😊😊A mask is considered to fit well when it seals comfortably and effectively all around the skirt, and provides a good field of vision, without pressing on the nose or forehead while in use underwater. A low internal volume is considered desirable by freedivers, as less breath is wasted to equalise, and by scuba divers, as there is less tendency to press up under the nose due to buoyancy, which becomes uncomfortable quite quickly.

Divers may test whether a mask is a good fit by placing it on their face, without using the straps, and gently inhaling through their nose. If the mask stays on without any help this indicates that no air is being drawn in and that the skirt is in sufficient contact with the facial skin all the way round the mask. Optimum sealing requires that hair strands do not cross under the edge of the seal, as they can provide a path for water to leak into the mask. This is more a problem with the forehead hairline than with lower facial hair, as water from the top tends to run in

to the eyes, while water pooling at the bottom is easily purged by exhaling a small volume of air through the nose. Most bearded divers learn to manage the slight leakage without difficulty, inconvenience, or greasing the moustache. Other factors affecting a comfortable fit are sufficient space for the nose in the nose pocket, no contact between the rigid mask frame and the bridge of the nose, and no excessive pressure on the forehead. There should also be sufficient space between the mask lenses and the face that the eyelashes do not contact the glass noticeably when blinking.

👄👄😀😀Next time, we'll share something about type of diving mask, using and make clearing.

Touch the sea in different way：Top 10 perfect diving places

A little wave is bobbing along in the ocean, having a grand time. He is enjoying the wind and the fresh air until he notices the other waves in front of him, crashing against the shore. "My God, this is terrible,the wave says ."Look whats going to happen to me! Then along comes another wave .It sees the first wave, looking grim, and it says to him, “Why do you look so sad?”

The first wave says,You don’t understand! We`re all going to crash! All of us waves are going to be nothing! Isn`t this terrible ?”The second wave says ,No , you don`t understand.You`re not a wave, you`re part of the ocean.

So，today , I will show you 10 perfect diving places 

1. Diving with great whites, Gansbaai , South Africa. 

 Everyone knows how the Jaws theme music goes. Diving with great white sharks is up there with base-jumping in the adrenaline top 10, and Gansbaai in the Southern Cape is the ideal place to swim with the big fish

Fortunately, there`s an aluminium cage-or for the brave, a clear plastic tube-between you and the ocean`s greatest killing machines. Numerous companies offer dives in Gansbaai`s “Shark Alley”, but look for operators who invest their profits back into shark conversation .

2. Getting married underwater in Trang , Thailand.   

If you fancy making a splash on your wedding day, consider an underwater wedding at Trang in southern Thailand

Every Valentine`s Day, dozens of couples don scuba tanks and descend to an altar 12m beneath the Andaman Sea for a full Thai wedding ceremony .

Wedding dresses are de rigueur and even the marriage certificate is signed underwater; the ceremony ends with the happy couple releasing one million baby shrimps and a giant clam onto the reef to gain Buddhist merit

Of course, it`s tricky saying “I do” with a regulator in your mouth

3. Sleeping with the fishes in Fiji

Travelers with plenty of cowrie shells to spare can swap a night under the stars for a night with the starfish at the sparkling Poseidon Undersea Resort in the Fiji islands. Suites are housed in futuristic pods on the sea bed, covered by acrylic domes and linked to the surface by a high-speed elevator. There`s even a private submarine that guests can pilot aroune the lagoon. It`s all very James Bond, and the prices would make a super villain wince

4. The ultimate fish supper in the Maldives.

Taking the heights of luxury to the depths of the ocean, the Conrad Rangali Maldives resort offers every imaginable indulgence, including an eatery at the bottom of the briny. Covered by a curving glass canopy; the restaurant floats beneath a curtain of swirling tropical fish, 5m below the surface of the Indian Ocean. Stingrays, groupers and sharks are regular visitors-think of it as an aquarium where the fish get to watch you eat. If you can see past the obvious contradiction, the menu runs to spiced scallops, tuna sashimi and lobster fricassee.

5. Swimming to your room in the Florida Keys    

The only hotel in the world where you have to scuba dive to reception, Jules`Undersea Lodge is housed inside a converted maring laboratory off the coast of Key Largo. Just six people fit inside this futuristic space, which opens directly onto the seabed through a pressure-balanced wet room. The compact quarters might deter the claustrophobic, but the sea=delivered from the surface in waterproof containers-as well as dives in the lagoon.

6. Snorkelling with whale sharks , Ningaloo Reef , Australia  

Swimming with sharks feels a lot less scary when the sharks in question don`t eat meat. Whale sharks grow to more than 12m in lengh-sa long sa a double decker bus-but these gentle giants live off a diet of microscopic plankton.

Whale sharks spook easily and the ideal way to get close is with a mask , snorkel and fins ,so the best place to swim with the world`s biggest fish is Ningaloo Marine Park on the west coast of Australia

7. Submarine cocktails in Eilat，Israel

According to Jules Veme, Captain Nemo Frowned on alcohol and anything else associated with the surface of the earth , but the Red Sea Star would still be his kind of bar . Nestling on the seabed off the coast of Eilat, this wacky watering hole offers the rare opportunity to sip a cocktail at the bottom of the sea . 这家Okay, so the décor-wobbly windows , starfish lanterns, jellfish chairs-is as tacky as an octopus`s tentacles ,but you can`t fault the views over a coral garden teeming with fish.

8. Wreck diving in Truk Lagoon ，Micronesia

The world of wreck diving owes a lot to WWII-whole fleets of warships were sent down to Davy Jones at Coron in the Philippines and in Scapa Flow in Scotland. But nothing compares to wreck diving in the tiny state of Chuuk in Micronesia. The sandy seabed of this coral atoll forms an eerie graveyard for more than 300 Japanese battleships, freighters, submarines and aircraft, sunk in a single devastating American assault in February1994. However, dive carefully-the wrecks still carry their original cargoes of tanks, ammunition, torpedoes, depth charges and mines.

9. Freshwater frolics in Lake Malawi    

Landlocked Malawi might seem an unlikely destination for a dive trip , but Lake Mlawi has hidden depths . One of the world`s top spots for freshwater diving, this African Great Lake is home to at least 1500 species of tropical fish , but significantly , no crocodiles (for some reason , they stick to the rivers feeding the lake ) . On the southern lakeshore, Monkey Bay is a prime spot to learn to dive: for one thing , the - 5 -  “pool” training takes place in the warm , current-free waters of the lake.

10. Disappear into a sinkhole in Mexico  

The polar opposit

e of open-water diving ,sinkhole diving offers the eerie experience of dropping into the dark unknown . Hidden away in the jungles of Yucatan ,Tamaulipas and Quintana Roo, Mexico`s cenotes-from the Mayan word for “sacred well”- plunge to dizzying depths . Divers have descended to 282m in the still, silent waters of Zacaton in Tamaulipas without ever reaching the bottom. Leave your fear of confined spaces at the surface-the average sinkhole is a tangle of stalactites, stalagmites and winding limestone passages.

What a amazing world! Let’s go together !