Diving mask
Snorkeler wearing a clear silicone diving mask
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| Uses | Provides clear underwater vision for divers |
| Related items | Full-face mask, Swimming goggles |
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 equalise 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.
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.
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Wikipedia