Standard diving helmet (Copper hat)
Historically, deep sea diving helmets ranged from the no bolt to two bolt to four bolt helmets; helmets with six, eight, or 12 bolts; and Two-Three, Twelve-Four, and Twelve-Six bolt helmets. Bolts being the method of securing the helmet to the diving suit. The helmet could also be secured to the breastplate (corselet) by bolts as in the case of US twelve-four helmets (12 bolts to the suit, four bolts seal helmet to corselet). The no bolt helmet used a spring-loaded clamp to secure the helmet to corselet over the suit. Swedish helmets were distinctive for using a neck ring instead of a corselet, a pioneer of modern diving euipment but hugely cumbersome and uncomfortable for the diver. This equipment is commonly referred to as "heavy gear."Lightweight demand helmets
Open circuit helmets
Notable modern commercial helmets include the Kirby Morgan Superlite-17 from 1975 and developments from that model. These helmets are of the demand type, built on a fiberglass shell with chrome-plated brass fittings, and are considered the standard in modern commercial diving for most operations.Kirby Morgan dominates the new helmet market, but there have been other notable manufacturers including Savoie, Miller, and Swindell. Many of these are still in use; a new helmet represents an investment of several thousand dollars, and most divers purchase their own or rent one from their employer.
Oceaneering bought out the Ratcliffe helmet, often known by its nickname "Rat Hat". It can function in either free-flow or demand mode.
- Inside view of a Kirby Morgan 37 showing the oro-nasal mask, the mcrophone and a loudspeaker of the communications system
Reclaim helmets
Reclaim helmets use a surface supply system to provide breathing gas to the diver in the same way as in the open circuit helmets, but also have a return system to reclaim and recycle the exhaled gas to save the expensive helium diluent, which would be discharged to the surrounding water and lost in an open circuit system. The reclaimed gas is returned to the surface through a hose in the umbilical which is provided for this purpose, passed through a scrubber to remove carbon dioxide, and can then be repressurised and blended with oxygen to the required mix before storage for later use.In order to allow the exhaust gas to be discharged from the helmet safely, it must pass through an exhaust regulator, which works on a similar principle to the demand valve for supply gas, but is activated by the pressure difference between the interior of the helmet and the ambient pressure.
Free-flow helmets
The Desco "air hat" is a metal free-flow helmet, designed in 1968 and still in production. Although it has been updated several times, the basic design has remained constant and all upgrades can be retrofitted to older helmets. Its robust and simple design (it can be completely disassembled in the field with only a screwdriver and wrench) makes it popular for shallow-water operations and hazardous materials diving. The Desco is secured to the diver by means of a "jock strap" which runs between the legs, and its buoyancy can be fine-tuned by adjusting intake and exhaust valves.Light-weight transparent dome type helmets have also been used. For example the Sea Trek surface supplied system, developed in 1998 by Sub Sea Systems, is used for recreational diving. Also the Lama, developed by Yves Le Masson in the 1970s, has been used in television to let viewers see the face and hear the voice of the presenter speaking underwater.
