page_title: Diving mask
section_title: Related equipment
hierarchical_section_title: Diving mask / Related equipment
caption_attribution_description: English: An Engineer-Diver with KB Bandmask
context_page_description: A diving 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 on the retina. By providing an air space in front of the eyes, the eye is able to focus nearly normally. The shape of the air space in the mask slightly affects the ability to focus. Corrective lenses can be fitted to the inside surface of the viewport or contact lenses may be worn inside the mask to allow normal vision for people with focusing defects.
  When the diver descends, the ambient pressure rises, and it becomes necessary to equalise the pressure inside the mask with the external ambient pressure to avoid the barotrauma known as mask squeeze, This is done by allowing sufficient air to flow out through the nose into the mask to relieve the pressure difference.
context_section_description: There are several specialised types of diving headgear or outerwear:
  full face diving mask - often worn by working divers who need underwater verbal communication ability.
  Lightweight diving helmet - usually worn by divers using surface supplied diving equipment.
  Copper hat - part of the old fashioned standard diving dress.
  fluid filled mask - the need to equilibrate the internal pressure in the mask by exhaling air through the nose reduces the freediver capacity to dive deep. Masks or swimming goggles with high power lenses (40-200 diopters) have been developed in this view: they are filled with water or saline fluid.
caption: Diver wearing heavy duty Kirby-Morgan band mask
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