"A diving helmet is a rigid head enclosure with a breathing gas supply used in underwater diving. They are worn mainly by professional divers engaged in ...
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surface-supplied diving, though some models can be used with scuba equipment. The upper part of the helmet, known colloquially as the hat or bonnet, may be secured to the diver or diving suit by a lower part, known as a neck dam, breastplate, or corselet, depending on the construction and regional language preferences.
The helmet seals the whole of the diver´s head from the water, allows the diver to see clearly underwater, provides the diver with breathing gas, protects the diver´s head when doing heavy or dangerous work, and usually provides voice communications with the surface (and possibly other divers). If a helmeted diver becomes unconscious but is still breathing, the helmet will remain in place and continue to deliver breathing gas until the diver can be rescued. In contrast, the scuba regulator typically used by recreational divers must be held in the mouth by bite grips, and it can fall out of an unconscious diver´s mouth and result in drowning." - (en.wikipedia.org 14.12.2020)
