Diving helmets are worn by divers who need to speak and hear underwater. A normal diving mask and diving regulator prevent the diver from effectively communicating. Diving helments are mostly used with surface supplied diving: the helmet acts as a firm anchor point on the diver for the umbilical supplying the breathing gas. Divers do heavy or dangerous work underwater also benefit from the head protection provided by the helmet.
There are several types of diving helmets :
An alternative to the diving helmet that allows communication with the surface is the full face diving mask.
"Diving helmet" sometimes means a hard safety helmet like a workman's helmet that covers the top and back of the head but not the face and does not keep air in and water out.