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Sorry for the confusion. I was referring to modern, fiberglass, fully enclosed, air filled helmets (as opposed to the old brass helmets for use with constant volume suits or diver's safety type hard hats). There are quite a few of these units currently being manufactured. Bob Kerby and Bev Morgan who now do business under Diving Systems International produce two demand type helmets, the Superlite 17 and Superlite 27. General Aquadyne makes the demand hat DMC-7 and freeflow hats AH-7 and GH-8. Miller Diving Equipment makes a demand hat. Desco makes a freeflow hat (actually the Desco and Miller hats happen to be made out of brass but are of modern design). There are others that don't come to mind at the moment. Bandmasks are units that use a metal band to affix a neoprene hood to a front fiberglass frame. A face seal keeps water out of the front portion of the unit. They fall into a category between helmets and full face masks (FFM). An important distinction between them and FFMs is that a bandmask has valves to allow a constant free flow of gas to the unit and the attachment/control of an emergency gas supply. Diving Systems International, General Aquadyne, US Divers and others currently supply these units. For contaminated water diving, dry suit manufactures make special yokes that attach the helmet to the suit. These yokes are glued directly to the suit in lieu of a hood. A neck seal is also used to seal the hat from the suit. These yokes are specific to the helmet in use. A suit with a Superlite yoke can't be used with a Miller helmet for example. A special contaminated water exhaust system must be installed on the hat to keep water from coming in through what is normally a single mushroom valve. I guess theoretically, freeflow hats are better suited for use in contaminated water but much of this type of diving is done in demand hats. I personally use a demand Superlite-17 with a Viking or Nokia suit. Vulcanized suits are generally used due to the relative ease of decontamination compared to neoprene or nylon shell suits. Cheers- Rob --------------------Reply Separator-------------------- > There are several advantages to using helmets and bandmasks over FFMs. ... (1) Re divers' helmets, is there a usual expression to distinguish between (a) the old brass helmets, (b) modern sorts of air-filled helmet such as the Kirby-Morgan, (c) underwater safety helmets that let water in and serve merely to protect the head from cuts and bumps? (2) What sorts of type (b) diver's helmets are around, except Kirby-Morgan? (3) I have dived 3 times with type (a). (4) What is a bandmask? (I take it that `FFM' means `fullface mask'). > For real contaminated water diving, a full helmet ... Including for diving in alphabet soup, I suppose :-) (such as FFM, BCD, NSS, IANTD, etc etc etc) > ... that <connects directly to> a vulcanized dry suit is a must. Does this mean merely that the helmet's neck seal should overlap the drysuit's neck seal when in use? Or what? (I once saw on the TV a Russian front-entry spacesuit with the helmet permanently attached to the suit. The helmet had an opening front plate.) --
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