diving high risk ch 4 8-07.pdf

Chapter 4Surface-Supplied Diving Equipment

Surface-supplied diving is the preferred method for contaminated water diving operations. In the surface-supplied mode, the divers air supply is pumped through a hose from the surface. Other hoses and cables may be attached to the breathing air hose, including (but not limited to) a communications wire, a depth sensing hose (known as a pneumofathometer), a closed-circuit television cable, and a strength member. This bundle of hoses and cables may be referred to as the divers umbilical, the divers hose, or the divers tether. These terms are used interchangeably. Where I refer to a specific hose, such as a breathing air hose, which is part of the divers umbilical, I will identify it as such. Many scuba divers have the false perception that diving with surface-supplied equipment is more dangerous than using scuba. This is not true! Commercial diving, where the surface-supplied mode is used almost exclusively, is definitely more dangerous than sport scuba diving, search and rescue diving, and scientific diving. However, the danger has nothing to do with the diving equipment, but relates directly to the diving conditions, depths, and heavy construction work involved. Surface-supplied diving in itself is much safer than diving with scuba gear. For the working diver, surface-supplied diving has many advantages over scuba gear. These include:

t6OMJNJUFEBJSTVQQMZIn the surface-supplied mode, you can stay underwater for an indefinite period (subject to decompression limitations, of course). As a scuba diver, you must return to the surface when the limited air supply in your tank is gone. If you have an unexpected decompression obligation while on scuba you can be in very serious trouble if your air supply is gone.

t3FEVOEBOUBJSTVQQMZ In the rare event the topside air supply should fail, the wise surface-supplied diver always carries an emergency air supply (bail-out bottle) which is directly connected to the breathing system. The surface-supplied diver has an additional air hose, known as the pneumo hose, which is normally attached to the umbilical. This hose can be used in a non-contaminated water diving situation as another air source (see Chapter 6).

%JWJOHJO)JHI3JTL&OWJSPONFOUT

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Conversely, if you are using a full-face mask on scuba and have not rigged a special bail-out supply, with most masks, there is no way to breathe without removing your mask to access your buddys air supply, a Spare Air or similar system. While removing your mask is obviously not a good idea in a contaminated water diving situation, if you've got to breathe, you may not have a choice.

t"DDVSBUFDPOUSPMPGEFQUIBOEUJNF When you are working underwater on scuba, it is very easy to forget to look at your submersible pressure gauge, depth gauge, watch, or dive computer. In the surface-supplied mode, all these functions are monitored continuously on the surface by the dive supervisor.

t#VJMUJOTFBSDITBGFUZMJOF In a contaminated water diving operation, you should always use some type of safety line if you are limited to using scuba. In the surface-supplied mode, the divers umbilical is the search/safety line.

t$PNNVOJDBUJPOTCommunications greatly increase a divers safety and are essential for contaminated water diving operations. While wireless systems are much more reliable than they used to be, hard-wire communications are still the most reliable and provide the highest level of intelligibility.

t)FBEQSPUFDUJPOAll surface-supplied diving helmets incorporate a hard fiberglass or metal shell which provides superior head protection when working around docks, bridges, shipwrecks, and similar environments.

t)FMNFUTVJUJOUFSGBDF All surface-supplied diving helmets can be mated directly to a dry suit to totally encapsulate and keep the diver isolated from

the environment. This is the preferred mode for diving under ice or in contaminated water. When the helmet is locked onto the suit in this manner, it is almost impossible to accidentally dislodge.

t&GmDJFODZ Most underwater tasks can be accomplished easily by a single person. In surface-supplied diving, a single diver can operate eciently due to the number of backup systems employed and the use of communications. This is a far more productive use of manpower.

t%FDJTJPONBLJOH A diver who is at depth and suering from nitrogen narcosis may not always make the best decisions regarding an underwater operation. However, in surface-supplied diving, with direction and feedback from topside, the same diver has a better chance of completing the job safely and eectively.

The author, Steve Barsky, worked as a com-mercial diver in the North Sea using surface-supplied gear exclusively.

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Admittedly, there are some disadvan-tages to surface-supplied diving compared with scuba. These include:

t&YQFOTFSurface-supplied diving systems are more expensive than scuba systems.

t"NPVOUPGFRVJQNFOUAlthough some surface-supplied diving systems can fit in the trunk of a car or operate from an inflatable boat, there is still more gear involved than in scuba diving.

t5SBJOJOHDiving with surface-supplied diving gear requires additional initial and monthly training to maintain familiarity with the system. There are also fewer training facilities qualified to teach surface-supplied diving.

Despite these disadvantages, if you must dive deep, under the ice, in a potable water system, or in contaminated water, there is no substitute for a good surface-supplied diving system.

&WPMVUJPOPG4VSGBDF4VQQMJFEDiving Gear The surface-supplied diving gear available today is similar in many ways to the first commercial equipment developed in the late 1800s. From the 1800s to the late 1950s, helmets were made of copper or bronze. In the early 1960s, two inventors, Bob Kirby and Bev Morgan, began designing their own diving helmets. Kirby was a former Navy and abalone diver. Morgan had been a lifeguard, surfer, commercial abalone diver, and commercial oilfield diver. Morgan also developed the first organized public scuba instruction program in the United States, the Los Angeles County Underwater Instructors program. Kirby and Morgan recognized that

a free swimming diver would be more versatile and could get more work done than the same diver equipped with a copper heavy gear helmet and lead boots. They began development of a series of swimmable lightweight fiberglass masks and helmets which are the basis for all of the diving helmets available today. Although most divers consider the diving helmet the central part of the system, other components are equally essential to conduct a surface-supplied dive.

All diving helmets today evolved from early designs like this U.S. Navy helmet.


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$PNQPOFOUTPGUIF4VSGBDF4VQQMJFE%JWJOH4ZTUFN Every surface-supplied diving system must include the following minimum components:

t$PNQSFTTFEBJSTVQQMZThe compressed air supply can either be a low-pressure compressor or a series of high-pressure bottles.

t%JWFSTBJSNBOJGPMECPYSome type of control system is required to monitor the air pressure to the diver, to regulate high-pressure air at the correct pressure for the breathing system, and to provide a connection for a topside backup supply. The pneumofathometer for checking the divers depth is usually incorporated in this box. The manifold also provides a method for switching from one gas supply to another.

t5PQTJEFDPNNVOJDBUJPOCPYThe topside communications box provides the power and amplification for communications between topside and the diver. The communications box may be a stand-alone unit or may be built directly into the divers air manifold box.

t%JWFSTVNCJMJDBMThe umbilical includes the divers breathing hose, communication wire, and pneumofathometer hose. It may also include a strength member of polypropylene line. These components may be fastened together with plastic fasteners, at a distance of every 8-12 inches. Twisted umbilicals that are assembled without tape are also available that are excellent for diving in biologically contaminated water. High-pressure surface-supplied diving systems may use only a high-pressure hose and depend on a wireless communications system. This provides a very low-profile

umbilical which is light weight. If a high-pressure umbilical is used, there must be two first stages at the diver. One first stage is used to reduce the pressure supplied from the surface. The additional first stage is used to reduce the pressure in the bail-out system worn by the diver.

t%JWFSTIFMNFUNBTLThe helmet (or mask) provides breathing air and a cavity into which the diver can speak.

t#BJMPVUTZTUFNEvery diver should be equipped with an independent air supply, carried on his back, to provide emergency breathing air.

$PNQSFTTFE"JS4VQQMZ Compressed air for surface-supplied diving may come from either a low-pressure or high-pressure supply. Most commercial

Some surface-supplied diving systems are designed to solely use a high-pressure supply of air and supply high-pressure to the diver.

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This diver is using a high-pressure surface-supplied diving system. The main gas supply is from the two high-pressure cylinders resting on the deck. The gas then feeds to the high-pressure manifold and from there to the umbilical. The diver wears a small manifold block on his buoyancy compensator. This block is where the first stage regulator reduces the pressure from the topside supply, and also allows the diver to select his bail-out cylinders (4500 p.s.i.) as the emergency gas supply. Communications for this system are wireless rather than hard wired.

High-pressure gas supply

High-pressure manifold

High-pressure umbilical

Emergency gas supply

Full-face mask

First stage regulator (behind diver's hand, see photo below)

With a high-pressure surface-supplied diving umbilical, the pressure from the surface must be reduced at the regulator on the manifold worn by the diver. Note the hose connected from the surface at the diver's right, which connects to the manifold, tying together the bail-out cylinder and the full-face mask. The diver can turn on the reserve cylinders at the manifold block.

Manifold

Regulator

H.P. umbilical

Pressure gauge

Bail-out cylinders


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diving operations use a low-pressure gasoline or diesel-driven compressor to supply breathing air for their divers. These compressors are very reliable and will run for many hours with a minimum of maintenance. Unfortunately, they produce fumes and are extremely heavy, bulky, expensive, and loud. For the majority of public safety and scientific diving operations, a high-pressure compressed air source is a better alternative. This can take the form of either large high-pressure cylinders or ordinary scuba bottles. Whichever type of cylinders are used, they are generally filled at a remote station (such as a dive shop) and transported to the dive site. In formulating your dive plan, you must ensure that you have a sucient quantity of high-pressure air on hand to complete the diving operation, and enough extra on hand to cover unforeseen emergencies.

Low-pressure compressors like this are used for commercial diving operations.

High-pressure bottled air has a decided advantage during contaminated water diving operations, particularly if the hazards are chemical and fumes are present. High-pressure compressed air that has been bottled o site will generally be free of all contaminants. The use of a low-pressure compressor on-site presents the distinct possibility that noxious fumes will be sucked into the divers air supply. Some types of diving helmets operate in the free-flow mode only, in which a constant stream of air flows through the helmet and diving suit. If you use this type of diving helmet you must use a very large, low-pressure diesel-driven compressor to supply a sucient volume of air, or have an extremely large supply of bottled compressed air on hand. For most professional diving, a diving helmet that operates in the demand mode is preferred. This type of helmet must have a low-pressure gas supply and a high-performance second stage regulator mounted on the helmet.

5IF%JWFST"JS.BOJGPME#PY4VSGBDF4VQQMJFE%JWJOH The divers air manifold box includes a number of valves and gauges to control the air supply to the diver. These boxes will generally accept air from one or more high-pressure sources and a low-pressure source at the same time. At any given time, however, the diver will only be breathing o one of the sources. If a high-pressure supply is used, the box must include a valve to permit the operator/dive supervisor to change out high-pressure bottles as each cylinder is drained. A high-pressure regulator is also required somewhere in the system to break down the high pressure from the source to an intermediate pressure acceptable for satisfactory operation of the second

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H.P. cylinder connection

Communications box

Diver #1 pneumo-fathometer gauge

L.P. air supply connection

Diver #2 Pneumo hose connection

Umbilical pressure control knob

H.P. cylinder selection valve

H.P. supply pressure gauge

Diver #2 pneumo-fathometer gauge

Diver #1 umbilical connection

Diver #2 umbilical connection

Layout of a typical diver's air manifold box. This system will accept both high-pressure and low-pressure air supplies, but only supplies low-pressure air to the diver.

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Charging Port Power Indicator

RemoteSpeaker

TapeOut

Speaker

Push toTalk Switch

On/OffVolume

HeadsetMic Jack

HeadsetEarphone

Jack

Diver 1

Diver Earphone

Diver Mic Jacks

Diver 2

Diver Earphone

Diver Mic Jacks

Diver Select Crosstalk

Yanmar

Surface-Supplied Air System

1999 S. Barsky

Bail-out bottle &harness

Low pressurecompressor; including volume tank and filtrationHigh-pressure supply

Umbilical

Communicationsbox

Full-face mask

AirManifoldBox

Diagram of a typical surface-supplied system. Note that this system can use either low-pressure or high-pressure air, but the air pressure sent to the diver is always low-pressure.

stage regulator on the diving helmet (if so equipped). Usually this pressure will be at least 115 p.s.i. over the bottom pressure at the divers depth. The regulator will be manually adjusted by the dive supervisor/manifold box operator. A gauge connected to the low-pressure side of the box gives an exact reading of the air pressure as it is reduced by the regulator. Think of the high-pressure regulator in the manifold box as equivalent to a first stage scuba regulator, the divers umbilical as the hose coming from the first stage, and the regulator on the helmet performing like a scuba second stage regulator.

1OFVNPGBUIPNFUFS4ZTUFN The pneumofathometer system, or pneumo, is usually contained in the divers air manifold box. It uses a small volume of the low-pressure air to measure the divers depth. The system includes a valve that is connected to a gauge by a T fitting. The other end of the T fitting connects to the pneumofathometer hose, which is part of the divers umbilical. The divers end of the pneumo hose is open. By opening the valve for the pneumofathometer system, the dive supervisor/manifold operator flows air through the gauge and down the hose, since air pressure in the hose is the same as the pressure from the divers regulator. When the air bubbles out the end of the hose the diver will usually notice and tell topside that he has bubbles. Once the valve is closed, the air pressure trapped in the hose will read out on the gauge and give a constant

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reading of the divers depth. When moving deeper, the diver must inform the topside crew and a new pneumo reading must be taken. At the end of the dive, as the diver ascends, the air will expand in the hose, bubble out the end, and automatically track the diver moving toward the surface. Pneumofathometer systems are very simple, but quite accurate. The gauges usually are accurate to within 1/4 of 1 percent of the full scale of the gauge. Accuracy to 1/10thof 1% of scale 200

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Air bubbles out of the end of the hose

Pneumofathometer hose

Depth gauge

Needle valve controls air flow

Compressor or other air supply

Topside

Underwater

Schematic of a typical pneumofathometer system.

Diver's manifolds are available in many dif-ferent configurations. These models all accept both low-pressure and high-pressure air.

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If the diver is using a high-pressure surface-supplied system there may be no pneumo hose and the diver must rely upon a dive computer. In this situation, the diver should always carry a back-up dive computer.

5PQTJEF$PNNVOJDBUJPOT#PY The hard-wire communications boxes used with surface-supplied air are identical to those described in Chapter 3. The system may be of either two-wire or four-wire design. Wireless communications are less commonly (but occasionally) used when diving with surface-supplied equipment, since the diver is always connected by an umbilical to topside.

%JWFST6NCJMJDBM Divers umbilicals can be delivered in any length your dive team may need, but as the hose grows longer it becomes more expensive, requires more deck space, and is much heavier. Beyond the basic fittings on the hose, you pay for diving hose by the foot. The minimum length umbilical for practical operation is probably 250 feet, although commercial diving companies use hoses 600 feet long or longer. The length of your diving hose is determined by identifying your maximum diving depth and your distance to the divers work site from the divers air manifold box. In a contaminated water diving operation, the divers air manifold may be located quite a distance from the water, requiring many feet of hose to be laid out topside and unavailable to the diver. The most critical element in your selection of a diving umbilical is the type of hose for the divers air supply. The breathing hose is usually the single heaviest component of the umbilical. Another important consideration is the change in length of the hose when pressurized (some hoses get longer). This should be minimal. Hoses are typically specified by their inside diameter (I.D.), their rated pressure, and their operating temperature range. The internal diameter determines the volume of air that will flow through the hose. It must be large enough to supply you with air at the maximum depth you will be diving without leaving you starved for something to breathe. To provide an adequate volume of air to a hard working diver at depth will usually mean a 3/8-inch hose must be used. The rated pressure of the hose should be at least 50 percent higher than the maximum pressure your regulator will require at your maximum diving depth. Oil resistance is another important consideration for any hose that will need to be used around running machinery. The hose should not kink shut when twisted to its minimum bend radius. In particular, any hose used for breathing purposes must not contain, or o-gas, any material which could be toxic. In the past, the commercial divers hose of choice has typically been a Gates hose, 3/8-inch I.D., with the designation C3 or 33HB. The industry specification for this hose is the Society of Automotive Engineers 100 R3 (SAE 100 R3). This is a very heavy, bulky, sinking rubber coated hose which can be dicult for the novice surface-supplied diver to use. Since the hose is negatively buoyant, it lays on the bottom and the diver must be constantly aware of obstacles which could cause the hose to entangle. (See Appendix C for chemical compatibility testing of hoses.) Today there are several alternatives to sinking hose, including polyurethane hoses. Some of the new hoses are much lighter and actually float. Floating umbilicals are much easier for the novice diver to use since the hose usually will be suspended directly above

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the diver in an arc, provided there is sucient umbilical length for the hose to lay on the surface. If you are at the end of your umbilical at a fair distance from the divers air manifold box, the hose will be stretched in a diagonal line through the water. Floating hose can present a hazard if there is unexpected or uncontrolled boat trac through your diving area. Divers have died as a result of a propeller entangling or severing a diving hose. Floating hose is normally much lighter weight than sinking hose. While older versions of floating hose did not usually have the same kink resistance or high operating pressures as sinking hose, many newer hoses oer more satisfactory characteristics in these areas. Twisted umbilicals are a good choice for working in biologically contaminated water. No tape is used to assemble the umbilical which includes a breathing hose, communications wire, and a pneumo hose. The hoses are made from polyurethane, which is a very rugged material. Depending on the configuration, the hoses will float in salt water. Whatever hose you choose must be approved for breathing air purposes. The fittings on the divers breathing hose are normally brass and are reusable. Some divers prefer oxygen fittings, which are specified as a 9/16-inch thread, 18 threads per inch. The fittings seal with a metal-to-metal seat; no O-ring is required. The quill that helps lock the fitting inside the hose must be appropriate for the internal diameter of your hose.

Note the twisted umbil-ical that is being used by this diver. This type of umbilical is excellent for use in contaminated water. It is not as-sembled with tape and the hose has excellent chemical resistance.

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Other divers prefer to use J.I.C. fittings, which have a 37 degree flare to the metal-to-metal seat where the male and female fittings join. J.I.C. fittings are specified in 16ths of an inch. For example, a #6 J.I.C. fitting for a 3/8-inch internal diameter diving hose is actually 6/16 (3/8) of an inch. Both types of fittings are designed to swivel on the hose for attachment. Your choice of fittings may be determined for you by what fittings are supplied as standard with your divers air manifold. Whichever type of fittings you select, be sure to have extras on hand and the tools required to attach them. Fittings do crack and need to be replaced on occasion. Oxygen fittings and J.I.C. fittings do not mate properly with each other to form an airtight seal. Despite the fact that the threads are similar and a male oxygen fitting can be joined to a female J.I.C. nut, they are not to be used together. Pipe threads (plumbing fittings) that are tapered and require Teflon tape for assembly are also not acceptable for joining the divers hose to the manifold or divers helmet. If you are diving in chemically contaminated water, you will need to ensure that your diving hose, and every other piece of equipment that goes in the water, is compatible with the chemicals you will encounter. Some dive teams have experimented with smaller diameter hoses for the divers breathing air. While 1/4-inch I.D. hoses have been used for this purpose, they should be employed with caution, particularly in longer length umbilicals (over 250 feet). If you need to work very hard underwater, you could find yourself starved for air with a small I.D. umbilical.

Pneumo Hose

Communications Wire

Air Supply Hose

Non-absorbent waterproof tape

J.I.C. fitting (left) and oxygen fittings (right) are not interchangeable.

For surface-supplied diving with a low-pressure system, the umbilical will typically include an air supply hose, communications wire, and a pneumo hose. The umbilical may be twisted or assembled with non-absorbent waterproof tape.

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The pneumo hose is most commonly a 1/4-inch I.D. low-pressure, thermoplastic hose. Synflex is the brand name of the hose most commonly used, with a part number of 3600-04. Similar hoses will perform just as well. The working pressure of pneumo hose need be no higher than 250 p.s.i. Synflex 3600-04 is not compatible with aromatic hydrocarbons, ketones, and chlorinated solvents. The topside end of the pneumo hose should have a brass fitting attached to it to provide the connection to the pneumo system. This fitting will normally be a #4 J.I.C. fitting, either reusable or crimp-on.

The communications wire and connectors are as described in Chapter 3. A strength member of polypropylene is a wise addition to the divers umbilical. In the event the diver becomes unconscious, it may be necessary to lift him from the water by the umbilical hose. Adding a strength member of polypropylene also increases the buoyancy of the umbilical for those teams who desire a floating hose. Approximately four feet from the divers end of the hose there should be a stainless steel ring attached to the umbilical bundle. This ring provides an attachment point for the divers hose to the divers harness. A stainless steel snap shackle on the left D ring of the harness hooks into the ring on the divers hose. The snap shackle may be attached to the divers hose with a special hose block. The snap shackle then hooks into the D ring on the divers harness directly. Either location is acceptable. When the divers tender pulls on the divers hose, he will be pulling against the harness and not directly on the hose attachment to the mask (or helmet). If this shackle is not installed, the tender could pull the divers mask o, if he is equipped with just a mask.

'VMM'BDF.BTLT"QQMJDBUJPOTJO4VSGBDF4VQQMJFE%JWJOH Lightweight masks can very readily be used for surface-supplied diving. For safety, you must also use an auxiliary bail-out block since neither mask is equipped to directly accept a bail-out supply. The bail-out block serves as a junction point for the divers umbilical, the bail-out supply, the low-pressure inflator hose for the dry suit, and the divers mask. The lightweight masks are generally not recommended for diving in contaminated water except where Level C protection is acceptable. This confines their use principally to waters with only low-level biological contamination. For high levels of biological contamination, or any chemical environment, it is much safer to use a helmet.

.BOJGPMECMPDLGPSGVMMGBDFNBTLEJWJOH If you plan to use a light-weight full-face mask for surface supplied-diving, you will need to use some type of manifold block to enable you to properly access your emergency breathing gas or "bail-out" supply. Typically, this manifold block will be mounted on

A snap hook like this one is essential to con-nect the diver's umbilical to his harness. By using this device, you can avoid having a direct pull on the diver's mask or helmet by the tender.


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your diving harness. The bail-out block is designed to be a connection point for the diver's umbilical, dry suit inflator hose, and supply hose for the full-face mask.

%JWJOH)FMNFUT1SPWJEFUIF.PTU1SPUFDUJPOJO$POUBNJOBUFE8BUFS%JWJOH Many commercial diving companies use free-flow diving helmets for contaminated water diving operations. Their rationale for this is that a free-flow helmet will keep any contaminants from entering the helmet. These types of helmets require greater skill to use, particularly when used in conjunction with a dry suit, since the helmet is open to the interior of the suit. Varying the flow of air in and out of the helmet controls your buoyancy since this changes the volume of the suit as well. This type of gear is much more complicated to use than a helmet equipped with a demand regulator, which is the principal subject of this book. It is also more expensive and requires more logistical support. Demand diving helmets, i.e., those which incorporate a demand regulator, are preferred by some commercial diving companies, public safety divers, and scientific dive teams using high-pressure bottled air as their compressed air source. These helmets enable the dive team to economize their air supply and are much simpler to learn to use than a free-flow helmet when used with a dry suit. Although these helmets operate in the demand mode, all of them include a free-flow valve to provide a continuous stream of air if desired. Communications systems with any diving helmet are typically of better quality and more reliable than with a full-face mask. This is because the communications components in the helmet are always kept completely dry and the earphones are not transmitting sound through a hood or water. Communications with a demand helmet are superior to those with a free-flow helmet since the diver need not compete with the air flow in the helmet to be heard. It is not uncommon for a diver in a free-flow helmet to shut o the air supply at the helmet to hear or be heard.

Umbilical hose connects here

Emergency gas supply valve body

Mounting plate

Low-pressure port

Emergency gas supply connects here

Emergency gas supply control knob

This bail-out block is designed to be used with a full-face mask for surface-supplied diving.

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The major disadvantage of a demand helmet in contaminated water diving is that every time you inhale, you create a slight negative pressure inside the diving helmet. This can allow water to leak into the helmet. Contaminants can also enter the helmet through the exhaust valve unless it has been specially modified. To prevent any back-flow of contaminants into the helmet, a redundant exhaust system must be used. The redundant exhaust system most commonly used is a series of exhaust valves in which two exhaust valves are placed in line with each other. Any contaminant that makes it past the first exhaust valve will usually be stopped by the second one. When you select a diving helmet, you should look for the following features:

t/FVUSBMCVPZBODZBOECBMBODFThe helmet should be designed to be neutrally buoyant in the water. Helmets that are negatively buoyant will cause neck strain. The helmet should be well balanced in the water.

t/POSFUVSOWBMWFThe helmet must include a non-return valve in the breathing system. This prevents air from rushing back out of the helmet if there is a break in the diving hose.

t&NFSHFODZ(BT4VQQMZWBMWFThe helmet must be equipped with a valve for the connection of a bail-out system for emergency breathing air.

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cushionFace port

Portretainer

Demand regulator

Rear weight

Helmet shell

Redundant exhaust system whisker

Free-flow valve

Emergency gas supply valve

Non-return valve

Sideblock

Locking pin

Regulator adjustment knob

Features of a demand diving helmet.

Equalizing deviceknob


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t%FGPHHFS'SFFnPXWBMWF

The helmet should be equipped with some means of directing air across the lens to defog it underwater.

t4IBUUFSSFTJTUBOUGBDFQMBUFThe lens should be made from a material such as Lexan to resist breakage.

t/FDLZPLFBTTFNCMZThe helmet should be equipped with a mechanism to prevent accidental removal.

t3FHVMBUPS1FSGPSNBODFThe helmet should be able to provide sucient air for heavy work loads with no carbon dioxide build-up.

tEqualizing deviceThe helmet should be equipped with some mechanism for equalizing air pressure in the divers ears.

t$PNNVOJDBUJPOTRVBMJUZThe helmet must provide excellent communications.

Adjustable locking collar

Head cushion

Exhaust whisker

Helmet sealing surface where neck dam and suit yoke interface with helmet

Chin strap

Rear hinge

Bottom end of a demand diving helmet

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Regulator body

Diaphragm

Exhaust valve

Starboard Whisker

RegulatorMount Nut

Water DumpValve

Exhaust Main Body

Port whisker

Exhaust valve

Valve seat

Tie wrap

Washer

Cover

CoverRetaining Ring

WhiskerClamp

Thrust Washer

HelmetShell

t3VHHFEFYUFSJPSTIFMMThe shell of the helmet must be made from a rugged material to withstand physical impact and chemicals. Fiberglass and stainless steel are two very popular materials used to build diving helmets.

t3FEVOEBOUFYIBVTUTZTUFN Every diving helmet should be equipped with either a redundant exhaust system or a "reclaim system" (see the latter part of this chapter). A redundant exhaust system is particularly important for divers who are using a demand diving helmet. When the diver exhales, there is always the possibility that some contaminants will back-flow into the helmet during the very short time period when the exhaust valve seals between exhalation and inhalation. By having a secondary exhaust valve, this helps to prevent any contaminants from entering the breathing system.

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Redundant exhaust systems like the one used in this helmet help to prevent a back-flow of contaminants into the breathing system.


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&WFSZ%JWFS/FFETB#BJM0VU4ZTUFNFor surface-supplied diving with a demand helmet, a bail-out is considered standard equipment. The bail-out system consists of the following items:

t#BJMPVUCPUUMFThe bottle should be of a sucient size to provide a minimum of five minutes of breathing air at your maximum dive depth.

t'JSTUTUBHFSFHVMBUPSA high-flow, high-performance scuba first stage regulator is mounted on the valve of the bail-out bottle.

t%JWFSTIBSOFTTThe harness serves as an attachment point for the divers hose and bail-out bottle. In function, it is similar to a scuba backpack but is

Diving helmets come in a variety of dierent styles, finishes, and designs. The top two helmets here are both made from stainless steel and are demand hel-mets. The helmet on the lower right is made from fiberglass and is a free-flow helmet.

Most diving helmets weigh about 30 pounds and can be uncomfortable to wear out of the water, par-ticularly if they are not well balanced. Underwater, a helmet should have neutral or slightly negative buoyancy.

The bail-out bottle size should be appropriate for your diving depth. Bail-out bottles can't supply sucient air for free-flow helmets.

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both more flexible and more rugged. The harness is also equipped with an additional D ring to give the diver a place to hang tools, lights, or other equipment. Many public safety divers wear a buoyancy compensator along with their divers harness. This is not a common practice in the commercial diving field.

t3FMJFGWBMWFThe bail-out bottle is normally left on at all times while the diver is in the water, but the auxiliary (emergency) valve on the helmet is turned o. To breathe the emergency air, the diver opens the auxiliary valve on the helmet. This allows the bail-out supply to flow into the breathing system. If the bail-out regulator develops a first stage leak into the low-pressure whip connecting it to the emergency valve, pressure will build continuously as long as the emergency valve is turned o. If this pressure is not relieved, the whip will burst and the diver will lose the entire bail-out supply almost instantly. In addition, the whip will swing about wildly and could injure the diver. A small relief valve is normally attached to one of the low-pressure ports on the first stage regulator. This valve is pre-set to bleed o high pressure before the whip ruptures. The valve will reset itself once the pressure drops below its adjustable relief point.

#BJM0VU4ZTUFNBOE)FMNFU"DDFTTPSJFTt3FTUSJDUPS This device screws into the sideblock on most diving helmets and the dry suit inflator hose attaches here. In the event of a dry suit inflator hose failure, the restrictor will help to prevent the air supply from being rapidly depleted. Most modern dry suit hoses have restrictors built into them so you may not need this device on your system.

t4VCNFSTJCMFQSFTTVSFHBVHFA submersible pressure gauge should be connected to the bail-out regulator so the diver can monitor the bail-out supply.

t2VJDLEJTDPOOFDUXIJQMPXQSFTTVSFXIJQA low-pressure whip with a quick disconnect fitting (similar to a BC low-pressure hose connection) links the bailout regulator to the emergency valve on the divers helmet. The hose should have a locking sleeve to prevent accidental disassembly. Quick disconnects make the system easier to assemble and disassemble.

Every surface-supplied diver must be equipped with some type of harness.

This relief valve is designed to vent the first stage bail-out regulator to prevent the hose from rupturing.

Dry suit hose restrictor.

Quick disconnect fittings.


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Helmets mate to dry suits with special yokes. Each helmet requires its own style of yoke. This is a free-flow helmet used by many com-mercial divers for contaminated water dives.

.BUJOH%SZ4VJUT Mating dry suits are equipped with special yokes to attach the diving helmet directly to the suit to keep the diver completely dry. The suits are basically the same as the suits used with full-face masks or scuba, but are almost always of the thickest material available. Dry suits used with helmets equipped with demand regulators must include a neck seal to isolate the suit from the helmet. Without a neck seal, you would need to breathe all of the air out of the suit before the demand regulator would operate. Since the helmet is separate from the suit, the system must provide a means to inflate the dry suit.

Note the dierent shape and configuration of each of the helmet yokes on the suits shown on this page.

Heavy duty dry suits used for contaminated diving are typically made from thick material. Note the attached boots.

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3FDMBJN4ZTUFNT In deep diving, over 190 FSW, rather than using air, commercial divers use special mixtures of helium and oxygen or heli-ox. Since helium is very expensive, and logistically dicult to transport to distant operations, divers searched for a means to reuse the helium, which is not metabolically consumed during respiration. Reclaim systems were originally designed as a method for conserving expensive helium-oxygen mixtures. A helium reclaim system operates very much like a topside mounted rebreather.

When you exhale, instead of your exhalation venting to the water, a special hose connected to the diving helmet carries the exhaust gas topside. On the surface, special pumps circulate the gas through a scrubber that removes the carbon dioxide and adds fresh oxygen. The mixture is then pumped back down to the diver. You may also hear these systems referred to as push-pull systems and return-line systems. Since most contaminated water diving operations take place in relatively shallow water, if you use a reclaim system designed for shallow water, there is no need to reclaim the breathing mixture, which would normally be ordinary air. However, special hardware is needed on the helmet and topside to help prevent the possibility of the diver suering from a squeeze if the system accidentally vented to atmospheric pressure topside. This could kill a diver.

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Reclaim helmets completely isolate the diver's breathing system from the environment.

4UFFMUPFECPPUT Commercial divers who work on the bottom and don't do much swimming, or those who work in particularly viscous environments, sometimes prefer to wear steel-toed boots rather than fins. The boots provide better support and toe protection from heavy objects. Steel-toed boots help provide protection from crushing injuries. Commercial divers who use high-speed water blasters should be equipped with "metatarsal guards" which may extend further up the foot than a normal steel-toed boot. More than one commercial diver has punched a hole in their foot while using a high pressure water blaster.


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Breathing Air Manifold

Bail-Out System

Reclaim Helmet

1998 S. Barsky

Inlet Inlet

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Outlet Outlet

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Vacuum Pump Vacuum Pump

Reclaim System

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Reclaimed gas is vented to atmosphere

Reclaim systems provide the most protection for the diver's breathing apparatus from contami-nated water. This system is designed for shallow water, where the "reclaim" hardware is not designed to reuse the diver's exhaled gas. Instead, the "reclaim" hardware provides a system to exhaust the gas to topside without subjecting the diver to a squeeze.

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$BTF)JTUPSZo%JWJOHJO.FYJDP$JUZT4FXFSTIn Mexico City, there is a team of divers whose job it is to dive in the citys sewers

on a daily basis, to ensure that the sewers do not stop flowing. Four divers work each day to unplug the pipes, repair pumps, and pull bodies, shopping carts, car parts, and plastic bottles from the black waters.

Unlike most U.S. cities that have separate waste and storm water systems, Mexico city has a single system that can fill to the bursting point during heavy summer rains. This fact makes it essential that the sewer system must run freely at all times. In ad-dition, with little environmental enforcement, factories and hospitals regularly dump hazardous materials down the sewers.

Some of the items that the divers have recovered include half of a Volkswagen, furniture, trees, mattresses, and the bodies of dogs, pigs, cows, and people.

Most human wastes that enter the system have not been properly treated. Of course, this is an overhead environment where the diver must navigate long stretches of pipe in zero visibility. There are over 6,000 miles of pipes and canals that the divers must maintain.The divers wear vulcanized rubber dry suits, attached dry gloves, and full-cover-

age surface-supplied diving helmets. Despite the dangerous nature of their work, they have managed to do their jobs for many years with only minor injuries and eye infec-tions, and one fatality. The divers are paid about $300.00 per month.

The sewers in Mexico City would overflow all the time if divers did not keep them clear.


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The dive supervisor should review the dive plan with the other members of the team prior to setting up any gear.

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