Copper and brass three bolt Soviet diving helmet.
|Uses||Provision of breathing gas, communications, underwater vision and head protection to underwater divers|
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 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, although this does not apply to a full face mask, which also continues to provide air if the diver is unconscious).
Before the invention of the demand regulator, all diving helmets used a free-flow design. Gas was delivered at an approximately constant rate, independent of the diver's breathing, and flowed out through an exhaust valve against a slight over-pressure. Most modern helmets incorporate a demand valve so the helmet only delivers breathing gas when the diver inhales. Free-flow helmets use much larger quantities of gas than demand helmets, which can cause logistical difficulties and is very expensive when special breathing gases (such as heliox) are used. They also produce a constant noise inside the helmet, which can cause communication difficulties. Free-flow helmets are still preferred for some applications of hazardous materials diving, because their positive-pressure nature can prevent the ingress of hazardous material in case the integrity of the suit or helmet is compromised. They also remain relatively common in shallow-water air diving, where gas consumption is of little concern, and in nuclear diving because they must be disposed of after some period of use due to irradiation; free-flow helmets are significantly less expensive to purchase and maintain than demand types.
Most modern helmet designs are sealed to the diver's skin at the neck using a neoprene or latex "neck dam" which is independent of the suit, allowing the diver a choice of suits depending on the dive conditions. When divers must work in contaminated environments such as sewage or dangerous chemicals, the helmet (usually of the free-flow type or using a series exhaust valve system) is directly sealed to a special dry suit (commonly made of a fabric with a smooth vulcanised rubber outer surface) to completely isolate and protect the diver. This equipment is the modern equivalent of the historic "Standard diving dress".
The first successful diving helmets were produced by the brothers Charles and John Deane in the 1820s. Inspired by a fire accident he witnessed in a stable in England, he designed and patented a "Smoke Helmet" to be used by firemen in smoke-filled areas in 1823. The apparatus comprised a copper helmet with an attached flexible collar and garment. A long leather hose attached to the rear of the helmet was to be used to supply air - the original concept being that it would be pumped using a double bellows. A short pipe allowed breathed air to escape. The garment was made of leather or airtight cloth, secured by straps.
The brothers lacked money to build the equipment themselves, so they sold the patent to their employer, Edward Barnard. In 1827, the first smoke helmets were built, by German-born British engineer Augustus Siebe. In 1828 the brothers decided to find another application for their device and converted it into a diving helmet. They marketed the helmet with a loosely attached "diving suit" so that a diver could perform salvage work, but only in a fully vertical position (otherwise water entered the suit).
In 1829 the Deane brothers sailed from Whitstable for trials of their new underwater apparatus, establishing the diving industry in the town. In 1834 Charles used his diving helmet and suit in a successful attempt on the wreck of Royal George at Spithead, during which he recovered 28 of the ship's cannon. In 1836, John Deane recovered from the discovered Mary Rose shipwreck timbers, guns, longbows, and other items.
By 1836 the Deane brothers had produced the world's first diving manual, Method of Using Deane's Patent Diving Apparatus, which explained in detail the workings of the apparatus and pump, and safety precautions.
In the 1830s the Deane brothers asked Siebe to apply his skill to improve their underwater helmet design. Expanding on improvements already made by another engineer, George Edwards, Siebe produced his own design; a helmet fitted to a full length watertight canvas diving suit. The equipment included an exhaust valve in the helmet, which allowed excess air to escape without allowing water to flow in. The closed diving suit, connected to an air pump on the surface, became the first effective standard diving dress, and the prototype of hard-hat rigs still in use today.
Siebe introduced various modifications on his diving dress design to accommodate the requirements of the salvage team on the wreck of HMS Royal George, including making the helmet be detachable from the corselet; his improved design gave rise to the typical standard diving dress which revolutionised underwater civil engineering, underwater salvage, commercial diving and naval diving.
Commercial diver and inventor Joe Savoie is credited with inventing the neck dam in the 1960s, which made possible a new era of lightweight helmets, including the Kirby Morgan Superlite series (an adaption of Morgan's existing "Band Mask" into a full helmet.) Savoie chose not to patent his invention because of his desire to improve diver safety. The neck dam seals the helmet around the diver's neck in the same way that a dry suit neck seal works, using similar materials. This allows the helmet to be carried on the head and not on a corselet, so the helmet can turn with the head and can therefore be a much closer fit, which considerably reduces the volume, and as the helmet must be ballasted for neutral buoyancy, the overall weight is reduced.
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 equipment but hugely cumbersome and uncomfortable for the diver. This equipment is commonly referred to as Standard diving dress and "heavy gear."
The US Navy Mk V helmet is still in production to order. In 2016 DESCO Corporation purchased the assets of Morse Diving International and began producing Morse helmets under the A. J. Morse and Son brand. The US Navy Mark V Helmet is available in either make with the minor manufacturing differences intact. While the Mark V is a US Navy design and all helmets should have been identical, models from Morse, Schrader, DESCO, and Miller Dunn all had differences. Brails from a Miller Dunn are difficult to fit on another maker's helmet. Early Miller Dunn Mark V helmets had gussets on the interior radius of the air and communication elbows. Schrader Mark V helmets used yellow brass castings instead of red brass like other makers. Schrader also canted their spitcock body. The standard Mk V weighs approximately 55 lb (25 kg) complete.
A small number of copper Heliox helmets were made for the US Navy by the Second World War. These helmets were Mk Vs modified by the addition of a bulky brass carbon dioxide scrubber chamber at the rear, and are easily distinguished from the standard model. The Mk V Helium weighs about 93 lb (42 kg) complete (bonnet, scrubber canister and corselet) These helmets and similar models manufactured by Kirby Morgan, Yokohama Diving Apparatus Company and DESCO used the scrubber as a gas extender, a form of semi-closed rebreather system, where helmet gas was circulated through the scrubber by entraining the helmet gas in the flow from an injector supplying fresh gas, a system pioneered by Dräger in 1912.
Four companies produced Mark V diving helmets for the US Navy: Morse Diving Equipment Company of Boston, Massachusetts, A Schrader's Son of Brooklyn, New York, Miller-Dunn Diving Co. of Miami, Florida and Diving Equipment and Salvage Co. (later Diving Equipment Supply Co.) of Milwaukee, Wisconsin.
The shallow water helmet is a very simple concept: a helmet with viewports which is fitted by lowering over the diver's head to rest on the shoulders. It must be slightly negative when filled with air so that it does not float off the diver in use. Air is supplied through a low pressure hose and escapes at the bottom of the helmet, which is not sealed to the suit, and can be lifted off by the diver in an emergency. The helmet will flood if the diver leans over or falls over. The shallow water helmet generally has a handle on top to help the tender lift it onto and off the diver when out of the water. The structure is variable, and ranges from relatively heavy castings to lighter sheet metal shells with additional ballast.
The concept has been used for recreational diving as a breathing system for use by untrained tourists in the direct care of a dive leader in a benign diving environment, marketed as the Sea Trek diving system.
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, Gorski 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.
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 discharged from the helmet through a back-pressure regulator and returned to the surface through a hose in the umbilical which is provided for this purpose, passed through a scrubber to remove carbon dioxide, blended with oxygen to the required mix and repressurised for immediate re-use or stored for later use.
In order to allow the exhaust gas to be discharged from the helmet safely, it must pass through an exhaust back-pressure regulator, which works on the same principle to a built-in breathing system exhaust valve, activated by the pressure difference between the interior of the helmet and the ambient pressure. The reclaim exhaust valve may be a two-stage valve for lower resistance, and will generally have a manual bypass valve which allows exhaust to the ambient water. The helmet will have an emergency flood valve to prevent possible exhaust regulator failure from causing a helmet squeeze before the diver can bypass it manually.
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. Concept and operation are very similar to the standard diving helmet.
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.
"Diving helmet" may also refer to a rigid safety helmet like a workman's helmet that covers the top and back of the head, but is not sealed. These may be worn with a full-face mask to provide impact protection.