Masks

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 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.

Diving masks have a durable, tempered glass plate in front of the eyes and a "skirt" of rubber or silicone to create a watertight seal with the diver's face. A strap keeps the mask in position.

Masks that are used at depth must be constructed so that the diver can exhale through the nose into the mask to prevent the "squeeze" caused by increasing pressure during descent in water.

Some masks have a one-way purge valve under the nose to let water out. The diver simply holds the mask upright and exhales through the nose. While common in snorkeling, this feature is less favored by SCUBA divers because of the possibility of the valve failing at depth and leaving the user no means of clearing his mask. A simple and effective method for clearing a diving mask while underwater is to look down, place a finger on the top of the frame at either side, and slowly look up while exhaling through the nose.