The body of the mask is constructed of fiberglass molded to fit the contours of the face. A faceplate and regulator are part of the mask. The faceplate is constructed of acrylic plastic. An adjustable nose pad is available to assist the diver in clearing his ears and sinus cavity during descent. All free-flow/demand masks are similar and may include a side valve assembly, demand regulator, oral-nasal mask, exhaust assembly, emergency air supply, and communications system.

The side valve assembly on some masks has two control valves. One valve, when closed, directs breathing gas into the regulator assembly and on to the oral-nasal cavity upon demand. When open, it additionally allows breathing gas to free flow across the face plate to prevent fogging. The second valve controls the source of the breathing gas which would either be primary or emergency.

The demand regulator is a modified second-stage scuba regulator. It will accept breathing gas at pressures between 50 to 200 psi above ambient pressure and has a control which allows the diver to manually adjust the breathing resistance. The regulator is secured to the fiberglass frame directly in front of the diver's mouth, and admits air into the oral-nasal cavity upon demand. Gas is supplied to the regulator from the side valve assembly. A manual purge button on the front of the regulator allows the diver to quickly switch to a free flow of air through the regulator.

An oral-nasal mask may be located inside the fiberglass frame and is used to create a partial seal around the diver's nose and mouth, thereby effec

tively reducing dead space and the chances of a CO2 buildup. Air enters the cavity directly from the regulator, and is exhausted through the regulator exhaust when the demand mode is in use. When the mask is set to free-flow, the gases enter the oralnasal cavity directly from the side valve, through a check valve, and are exhausted through the regulator exhaust. The oral-nasal cavity is an important safety device and it is recommended that it be used.

WARNING

If the Oral-Nasal Mask Is Absent There Is a Danger of CO2 Buildup. Therefore the Diver Must Ventilate at Frequent Intervals.

Free-flow/demand masks generally have two exhaust assemblies located near the bottom of the fiberglass frame, below the regulator. These one-way valves are constructed of neoprene rubber, are of the mushroom design and function automatically when the pressure inside the mask is greater than ambient pressure. Because of their location, the exhaust valves function as a purging system, automatically maintaining the water level in the mask below the oral-nasal cavity if the mask is in a relatively upright position.

A partially or completely flooded mask can be quickly purged by placing the exhaust valve in a downward position and opening the free-flow valve or depressing the manual purge button on the demand regulator.

Lightweight Helmet

Photo General Aquadyne

A self-contained emergency gas supply system (or bailout unit) is used in conjunction with surfacesupplied diving equipment for work in excess of a 60 foot depth or when working in tunnels, pipes, etc., or where there is specific danger of entanglement. The unit consists of a scuba cylinder assembly, a reduction regulator (first stage of a standard singlehose regulator), and a backpack-harness assembly. The capacity of the scuba cylinder assembly will vary from 10 ft3 to 140 ft3, depending on the diver and the situation. The self-contained emergency gas may be fed directly into the mask through a special attachment on the side valve or directly into the diver's air hose assembly. In the latter case, a check valve should be located between the intersection of the emergency gas supply hose and the primary surface supply hose. A completely separate bailout system may be used in which a scuba tank and regulator are carried. Upon loss of the umbilical air supply, the full face mask is removed and the diver ascends using the scuba tank and mouthpiece. If this system is selected, a face mask should also be carried. The advantage is complete independence. The disadvantage is loss of communication, difficulty in putting on the face mask and locating the regulator.

One of the primary advantages of the free-flow/ demand mask is the availability of reliable voice communications. The microphone is located inside

the oral-nasal cavity. The earphones are located in pockets in the hood or attached to an adjustable boom which can be placed over the ear.

Head protectors are used with the free-flow/ demand mask to prevent injury to the diver's head. The helmet-style protector is generally constructed of fiberglass and designed to absorb shock either through internal padding or special attachment to the mask. Head protectors are recommended when working under boats or other types of obstructions.

4.5.3 Lightweight Helmets

Several lightweight helmets are commercially |

available. These helmets (Figure 4-15) are compatible with the variable volume dry suit, the standard wet suit and heated wet suits. Unbreakable faceplates and improved visibility are additional advantages. Many models are designed for use with an emergency air supply and for use with mixed gases.

The modern lightweight helmet is commonly constructed of copper, brass, or a tough, rigid fiberglass. Improved air control and exhaust valves are easy to operate and are corrosion and clog resistant. Most have a large primary viewport and a smaller port for looking upward. The majority of helmets | incorporate a neck ring which can be connected to the neck seal of all types of dress.

The lightweight helmet is equipped with communications and may be the safest choice of equipment for conducting very strenuous underwater tasks.

4.5.4 Diver Umbilical

The umbilical is that combination of hoses and lines from the support platform or habitat required to support the diver. A scuba diver may have an umbilical consisting solely of a lifeline. Surfacesupport umbilicals usually have a minimum of two lines (gas hose and communications line), but may have as many as five (gas hose, communications line. pneumogauge hose, hot water hose, and lifeline).

4.5.4.1 Gas Supply Hose

The gas supply hose is the primary source of life support gas and is the most important part of the umbilical. A synthetic rubber, braid-reinforced hose with an inside diameter of 3/8-inch is normally used. The hose must be extremely tough and durable; weather, abrasion, and oil resistant: and capable of withstanding a minimum internal

pressure of 200 psi. The hose must be easy to handle, flexible and kink resistant. Only high quality hose insuring minimum shrinkage properties should be used.

If possible the hose should be of one-piece construction to reduce the chances of separation; however, if necessary, special connectors can be used. The hose itself should be frequently inspected for wear, cracking, abrasion, or other deterioration.

4.5.4.2 Communications Line

The communications line must be durable enough to prevent parting due to strain on the umbilical assembly, and have an outer jacket that is waterproof and oil and abrasion resistant. A two, three, or four size 16 or 18 conductor shield wire with a neoprene outer jacket is satisfactory. Although only two conductors are in service at one time, the extra conductors may be used for rapid field repairs in the event of one of the conductors breaking while in service. The wire-braid shielding adds considerable strength to the umbilical assembly. For example, spiral 4 communications line with four #18 plastic-coated conductors embedded in a vinyl filler surrounded by stainless-steel wire braid and synthetic cover has a breaking strength rating in excess of 1,460 pounds.

The wire is fitted with connectors compatible with those on the mask or helmet and the surface communicator. When joined together, the electrical pin connections are established and a watertight seal is formed, insulating the wire from the surrounding sea water. Many masks and helmets are equipped with post binders instead of socket-type connectors. As a backup, the conductor wires may be attached directly to these terminals; however, the quality of communications is lowered and the wires are easily pulled loose.

4.5.4.3 Lifeline

The use of a separate lifeline for umbilical diving is optional and at the discretion of the Dive Master. An umbilical assembly consisting of high quality hose (i.e., SAE100R3 or equivalent specification) and shielded communications wire is generally considered of sufficient strength for free-flow/demand mask and lightweight helmet diving. For those who wish to incorporate a lifeline into the umbilical assembly the use of limited stretch synthetic line or lightweight aircraft cable is recommended. Avoid

nylon or other similar synthetic materials which stretch under tension and put unnecessary strain on other components of the umbilical. Some divers use a combination communications wire-braided polypropylene synthetic line. The communications wire may be fed through the hollow core of the braided line to form a strong, compact single unit.

4.5.4.4 Pneumogauge Hose

The pneumogauge is used to accurately monitor the diver's depth. It consists of a durable, lightweight flexible hose attached to a low pressure air supply source on the surface, and open at the diver's end. The hose should be attached to the umbilical with the open end terminating at the diver's chest. Although the open tube is not subjected to high pressure, it should have a working pressure capacity of 200-250 pounds per square inch. Lightweight air hose (0.25 inch inside diameter), extruded seamless nylon tubing (0.17 inch inside diameter, 0.25 inch outside diameter, with a 250 pound per square inch maximum working pressure), or thermoplastic tubing with external open polyester braid (0.25 inch inside diameter, 0.456 inch outside diameter, with a 250 pound per square inch maximum working pressure) have been found satisfactory (Somers 1972).

4.5.4.5 Hot Water Hose

When diving with hot water wet suits, a specially insulated hose is required. This can be obtained in either 2 or 3/4 inch inside diameter depending upon the depth and volume of water to be supplied to the diver. The insulation reduces heat loss to the open sea allowing a lower boiler operating temperature. The hose should be equipped with a quick-disconnect female fitting compatible with the manifold attached to the suit. The hot water hose should be joined to the diver's gas and communications umbilical to prevent handling problems.

4.5.4.6 Assembly of the Umbilical

The various components of the umbilical are assembled and taped at approximately 1-foot intervals with 2-inch wide, polyethylene cloth, laminated tape (duct tape) or the equivalent. Prior to taping, the various components (gas hose, communications wire, lifeline if used, pneumohose, and hot water hose) are laid out adjacent to each other and inspected for damage or abnormalities. The gas supply hose is plugged at one end and pressurized to the

Umbilical Attachment Assembly

working pressure (generally 120-200 pounds per square inch) to ensure that the shrinkage factor will not cause "looping" when the umbilical is in use. When assembling the umbilical, take into account the length of gas hose whip, communications wire whip and the hot water hose connection location. Generally, the communications wire is longer than the rest of the assembly at the diver's end. This provides an extra length of wire in the event that repairs must be carried out. The excess is looped around the umbilical and secured with tape. The diver's end must be assembled first so as to prevent excess looping and bulk; the umbilical should not interfere with the diver's movements. It is best to start taping at the diver's end and work toward the surface end.

A quick-release type swivel snap shackle or special air hose clamp is secured to the umbilical to facilitate attachment to the diver's harness and prevent pull on the helmet or mask. The shackle may be tightly secured to the umbilical with several wraps of nylon line or a specially constructed cable saddle. Attachment location will depend on the harness assembly worn by the diver, but should never be attached to the weight belt in case it needs be dropped (Figure 16).

4.5.4.7 Coiling and Storage of Umbilical Hose

After the umbilical hose is assembled, it should be stored and transported with protection provided for hose and communications fittings. The hose ends should be capped with plastic protectors or taped closed to keep out foreign matter and to protect threaded fittings. The umbilical hose may be coiled on take-up reel assemblies, "figure-eighted," or coiled on deck (Figure 4-17) with one loop over and one loop under. Incorrect coiling, all in the same direction, will cause twist and, subsequently, handling problems. The tender should check the umbilical assembly at the end of each dive to ensure that there are no twists. The coil should be secured with a number of ties to prevent uncoiling during handling. Placing the umbilical assembly in a large canvas bag or wrapping it in a tarp will prevent damage during transport.

4.5.4.8 Umbilical Maintenance

After a day's diving, the umbilical should be washed with fresh water, visually inspected for damage and carefully stored to prevent "kinks."

If the umbilical is to be stored for a long period of time, the hoses should be blown dry and the connectors capped, to prevent foreign matter from entering. Connectors should be lubricated with silicone spray after capping.

4.5.4.9 Harness

The diver should wear a harness assembly to facilitate attachment of the umbilical assembly. The harness should be designed to withstand a minimum of 1000-pound pull in any direction and must prevent strain from being placed on the diver's mask or helmet when a pull is taken on the hose assembly.

WARNING

Never Attach the Diver's Umbilical Directly to His Weight Belt. A Separate Belt or Harness Is Recommended

4.6 SUPPORT PLATFORM EQUIPMENT

The equipment installed on a support platform depends heavily on the type and duration of the diving activity and the physical limitations of the platform itself. Support platforms encompass surface ships

and barges as well as underwater habitats and submersibles. The primary equipment in the support platform is that associated with the diver's breathing medium. Air compressors or banks of compressed gas cylinders constitute the major diver support items in all platforms. Saturation diving complexes and recompression chambers require a significant allotment of deck space when installed on diving barges or ships. A habitat, while requiring some surface support equipment, especially air compressors or mixed gas supplies, may, in an emergency, utilize internal compressed gas sources for maintenance of its atmosphere. Submersibles carry sufficient gas in cylinders to maintain their atmosphere for long periods of time as well as support divers who may make excursion dives from the submersible. This paragraph discusses various aspects of low pressure air compressor equipment as well as compressed gas cylinders, whether they support a diver directly, or are ancillary to the habitat or submersible. For a discussion of high pressure air compressors see Paragraph 5.1.3.

4.6.1 Air Compressors

The air compressor is the most common source for diver's breathing air. The compressor is generally backed up by a bank of high pressure gas storage cylinders to reduce the possibility of interrupting the diver's breathing gas supply due to loss of power or compressor malfunction.

The low pressure air compressor is the most frequently used source of breathing air for the umbilical supplied diver supported from the surface, a diving bell, or habitat. Of the several different de

signs of air compressors available, the reciprocating model is the primary type used for diving operations. These compressors are capable of compressing gases to the pressures required for scuba operations, or in the quantities required for low pressure surface supplied operations. The gas is compressed to the desired pressure by a series of pistons. Coolers are used to reduce the temperature of the compressed gas and the water vapor in the compressed gas.

The centrifugal compressor will provide a large volume of air, but compact size and high RPM complicate maintenance so that they are not readily adaptable to diving operations. Rotary compressors are compact units, but normally limited to one stage and an output of only 100 psi.

A compressor is rated at the pressure at which it will unload or the unloading switches will activate. A compressor must not only have the volumetric capacity to provide sufficient breathing medium, but must also provide the pressure above the range equivalent to the ambient pressure the diver will experience at his planned depth. A practical minimum allowable margin for dives less than 120 feet is 50 psi over bottom pressure. For dives over 120 feet, a compressor rating of 100 psi over bottom pressure is the accepted standard.

All air compressors used for diver's air supply must have an accumulator (volume tank) as an integral part of the system. The accumulator will provide a limited emergency supply of air should the compressor fail and will provide air for the diver while the surface crew switches to the backup air supply.

4.6.2 High Pressure Cylinders

Occasionally it is advantageous to use a series of large, high-pressure cylinders as the source of gas in lieu of a compressor. This is particularly advantageous in areas where convenient access to a highpressure compressor for recharging is available. Using cylinders as the gas source will reduce the chances of losing the primary supply as the entire volume of gas required for a dive is compressed and stored prior to the dive. The cylinders can be stored out of the working area. Most lock-out submersibles carry the diver's gas supply in high-pressure cylinders built into the body of the submarine. It is important to note that cylinder banks may be used to store mixed gases for diving operations as well as compressed air. Mixed gas cylinders are usually taken to the dive site prior to the diving operation. The