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Open Water 20 - Equipment

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EQUIPMENTwww.diveRAID.com

Open Water 20 - Equipment

INTRODUCTION ................................................................................................. 2

SECTION OBJECTIVES ..................................................................................... 2

MASKS ................................................................................................................. 2

SNORKELS .......................................................................................................... 4

FINS ..................................................................................................................... 4

EXPOSURE SUITS .............................................................................................. 6

BUOYANCY COMPENSATION DEVICE .......................................................... 9

BCD TERMINOLOGY ......................................................................................... 11

REGULATORS ..................................................................................................... 12

CYLINDERS ......................................................................................................... 14

GENERAL RULES FOR CYLINDERS ................................................................ 15

INSTRUMENTS ................................................................................................... 16

DIVE COMPUTERS ............................................................................................. 17

WEIGHT SYSTEMS ............................................................................................ 19

ACCESSORIES .................................................................................................... 20

EQUIPMENT MAINTENANCE ........................................................................... 22

REBREATHERS .................................................................................................. 24

A FINAL WORD ON EQUIPMENT .................................................................... 25

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RAID OPEN WATER 20 www.diveRAID.com

INTRODUCTIONYou may not be too familiar with the features or the differences between the different types of equipment as there are many types and designs. The most important feature is comfort and whether it is functional for the type of diving activities that interest you. Your RAID Instructor and/or Dive Centre can help you with your purchases and offer advice on different types of equipment needed for the different areas.

They will help you personalise your fit and meet your diving needs.

RAID Note: With all equipment generally the most important thing is comfort and fit!

SECTION OBJECTIVES• Describe the equipment scuba divers use• List helpful hints on maintaining your equipment• Describe the operation of your equipment• List the general rules for using scuba cylinders• List the main rules for using a dive computer

MASKSOur eyes were not designed to see well in water and a mask provides an air space between the water and our eyes so that we can see clearly.

For diving, a good mask is absolutely essential. It is the difference between a great diving experience and an average one. A good mask must fit well, not leak and provide good vision underwater.

Single Lens MaskDouble Lens MaskWhat’s the difference between goggles and a mask? Why do scuba divers wear masks that cover the nose and eyes, not just goggles, which only cover the eyes? The reason is that the nose pocket of a diving mask is needed to compensate for increasing pressure as you dive deeper. The nose pocket allows the diver to blow air into the mask, equalising the pressure.

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What does a diving mask consist of?It consists of a lens made of tempered glass, a double skirt, made from surgical grade silicone which holds the water out, and the mask strap which must be easily adjustable.

A diving mask is made robustly and is thus more expensive than the children’s mask one can buy in a supermarket.

How do you make sure it will fit you?There are as many masks on the market as there are different shaped faces! So try as many as you like to get the “right one”.

Firstly hold your head back and look up. Take the mask (after folding back the mask strap) and place the mask on your face.

Now without breathing in, and causing a vacuum, ask a friend to look at the skirt to make sure that there are no gaps around the mask. Next place a snorkel in your mouth as this will change the shape of your face, and check the skirt again to see that there are no gaps between your skin and the skirt. Try not to inhale as most soft silicone masks will suck on to the face and this does not necessarily mean it will not leak.

If you find a mask that fits without the need to inhale through the nose then you have found the “right one”.

Prepare For UseFollow the manufacturer’s guide lines as they coat new masks with a protective chemical that you need to scrub off before use. If not, you won’t be able to defog the mask effectively. You can use an appropriate cleaner to clean the inside of the glass, in order to remove the coating, although this might take a few attempts. Adjust the strap for a comfortable fit. Should your mask mist up while underwater, you will get lots of practice to clear this in your confined water session.

Equalising Your MaskYou will find that as you descend the air in your mask will be compressed by the water pressure and the mask will suck on to your face much harder. You need to equalise this pressure so the mask becomes comfortable on your face. The simplest way is to breath out through your nose into the mask until it feels comfortable. You will have a chance to practice this in the water sessions.

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Maintaining Your MaskRinse as soon as possible with fresh water after using your mask in the pool and sea. Keep out of sunlight. Do not leave it on the floor for someone to stand on!

SNORKELSScuba divers use a snorkel as a safety device in case they have to float for extended periods of time while locating, or being located by, a boat. The snorkel is also used to swim, on the surface, to and from dive sites without using up precious gas from your cylinder.

So what does a snorkel consist of?There’s the tube, of course, and that varies in length, bore diameter, and shape. Let’s look at how each of those factors influences the snorkel.

The inside bore diameter of the snorkel tube is important. A large-bore tube with an inner diameter of about a 2.5cm/1 inch is easiest to breathe through.

There is a huge range of designs to choose from and it is a good idea to test them first in water before you decide which one is for you.

Do I really need a snorkel?The type of diving will dictate whether you need a snorkel or not. Your RAID Instructor or Dive Centre will advise you if the dive site requires a snorkel. Even though it is a small item of equipment it can be very useful in certain situations. So if in doubt, do not dive without!

You will be able to practice your snorkel skills in your first confined water session.

FINSWith the extra drag of the scuba equipment, fins are essential for scuba diving. The necessity to move in the water and control movement requires having the right set of fins. So knowing what is out there, what options are available, and what works best under what conditions is important.

Snorkel with purge valve

Dry top

Snorkel keeper

Mouthpiece

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Leading scuba equipment manufacturers are doing an enormous amount of research and development to develop new and more efficient designs, with space-age materials, new manufacturing techniques, and entirely new concepts in order to provide the best thrust in the most efficient way for the least amount of energy expended by the diver.

So let’s take a look at the two standard types:

Closed Heel / Full Foot FinsThey have a foot pocket and a blade attached. They come in all sizes and are primarily designed for most applications where there is no scuba equipment and/or where the scuba equipment is light weight for warm waters.

When the diver is wearing heavy scuba equipment with plenty of drag, most divers will choose Open-heel fins as they provide more thrust. Closed heel fins are good for warm water boat scuba diving, but not for shore entries when walking over hot sand and sharp rocks. They are also less durable and harder to use in strong currents. So again, consult the RAID Dive Centre and/or your instructor for advice.

Open Heel Adjustable FinsThey are worn with scuba booties. The foot pocket allows for the foot and bootie, and tightens with a heal strap. This allows a few different sizes of foot and bootie for each fin. Generally, these are the fins chosen by the majority of divers as they are designed to cater for the drag that all the scuba equipment creates. The foot will be much warmer with the bootie on and provide protection when walking around without the fin.

The two types of fin have not changed in principle for over 40 years, although what has changed are the types of material used and the blade design.

The most important feature is that you find a fin that is suitable for your type of general diving, is comfortable to wear and does not tax your calf muscles!

Consult your RAID Dive Centre to get the best advice on the fins that will be suitable for you. Remember that you not only want an effective fin but one that is comfortable and fits correctly.

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EXPOSURE SUITSOK, who would go to the Arctic with shorts and a shirt, or to the Caribbean in heavy woolen clothing? Nobody would, right? So we dress for the occasion. We learn that water conducts heat away from the body 20 times faster than air. So an air temperature of 25°C / 77°F means that in the water, with the same temperature, you will not be there for very long before you start to chill.

Further, even with exposure protection the length of submersion will eventually cool the body down to the extent it becomes uncomfortable. As soon as this happens get out the water and warm up!

Overheating can also be a problem before diving.

Your exposure suit should be put on after getting your dive gear ready, just before the actual dive, and taken straight off after exiting the water, because a suit limits the normal emission of heat in the air.

Remember if you are not feeling comfortable for the environmental conditions that you are in then advise your buddy/Divemaster/Instructor and take appropriate action to either cool down or in the case of cold, warm up.

Consult with the RAID Dive Centre about the exposure suit that is used for their waters, as local information is always the best.

The other reason why divers wear exposure suits is that they protect against cuts, stings, abrasion, infection and sun burn if bare skin is exposed.

Different kinds of exposure suitsThere are three conceptually different kinds of exposure suits: dive skins, wetsuits, and dry suits. Each kind comes in several varieties, and each is designed for specific environments.

Dive SkinsDive skins are the thinnest, lightest exposure suit and offer the least amount of protection. Some consist of Lycra, others use very thin neoprene or technical fleece. Dive skins are very elastic, form-fitting, and come in numerous colours.

Technical fleece is the new standard in tropical dive suits and undersuits for wetsuits. A technical fleece has all the warmth qualities of a thin wetsuit but none of the buoyancy issues. It is often much more abrasion resistant and comes in many forms from tops to full body suits. Some divers use their standard wetsuit in summer and add the technical fleece for more warmth in winter.

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Dive skins generally have a zipper upfront for under dry suits and back for tropical diving, stirrups to keep the pant part from riding up, and a loop that goes around the thumb so the sleeves stay in place. Dive skins provide protection from corals, blisters and sunburn when out of the water.

Dive skins are almost exclusively worn in tropical waters with friendly underwater environments. The exception is that they can also be worn under wetsuits. In fact, wearing a dive skin makes donning a thick wetsuit a lot easier.

WetsuitsWetsuits are the most common type of exposure suits. They are made from a closed-cell foam neoprene material. The term “closed-cell” refers to the fact that neoprene contains separate gas bubbles. The bubbles, as well as the rubber material itself, provide thermal insulation as well as protection. The wetsuit does not absorb water, but the suit is also not sealed at the extremities to keep water out. In fact, it is designed to allow a thin layer of water between the suit and the skin. The water warms up without easily giving up its heat due to the neoprene suit, which has tiny ‘bubbles’ (gas filled closed cells) that conduct heat slowly providing a layer of insulation. Note: The air bubbles inside the wetsuit compress as water pressure increases, so the suit becomes thinner and provides less insulation at depth.

The term “wetsuit” is somewhat generic as wetsuits come in many configurations, styles, and thicknesses.

When little protection is needed, a “shorty” may do. Shorty suits are one-piece suits with short sleeves and legs (though some have long legs). They provide some insulation and protection, but should generally be worn only in water 27°C / 80°F or higher. Shorties are usually made of thin neoprene, not more than 2-3 millimetres.

Full body suits are one-piece affairs with a zipper in the front or back. They come in thicknesses of 3 to 7 millimetres, fit skin tight, and offer much more protection than a shorty or dive skin. These suits provide enough insulation in water that’s more temperate and some good quality suits can be used in water that is much colder.

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Below that, a third variation of the wetsuit is the two-piece suits, also called “Farmer Johns”. That design provides a double layer of protection to the diver’s midsection. Two-piece suits are usually made of thicker neoprene, and are easier to put on and take off.

When selecting a wetsuit, whatever style you choose, do make sure it fits well. There’s nothing worse than an ill-fitting suit where the water sloshes around instead of generating the desired thin insulating film. The suit must fit as tight as comfortably possible.

Wetsuits can be worn with a number of accessories. Those include gloves of various types and thicknesses, booties in many styles and designs, protective knee pads, special insulating vests worn underneath the wetsuit, hoods that can be separate or attached, spine pads to keep water from flowing where it shouldn’t, pockets for special things, and even integrated or strap-on heat-packs that employ re-usable chemicals to provide half an hour’s worth of heat.

Dry SuitsDry suits are what divers wear in cold water and help extend your bottom time compared to a wetsuit. As dry suits improve in design and are made with new materials, more and more people are using them in even warmer waters up to 20°C / 68°F. Dry suits stay dry inside and allow no water in. It is what you wear under the suit that keeps you warm, and various layers of 100% wool clothing are highly recommended. There are also other materials specifically designed for dry suit undergarments.

To compensate for the increase in pressure as the diver descends, air from the cylinder via a hose to the dry suit connection on the front and released on descents and ascents. Due to this extra task loading and for buoyancy control, a separate training programme is required. This can be incorporated within the level you are doing or afterwards as a separate specialty programme.

Unlike wetsuits that come in various configurations, all dry suits are full body suits.

They are fully sealed, and there are special waterproof zippers. Obviously, in order for a dry suit to truly stay dry, every seal must be perfect. Seals are made of latex or neoprene, with large contact areas to provide the best possible seal.

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Each type of seal has its pros and cons. Latex seals are thinner and seal better, but they are somewhat fragile and some people are allergic to latex. Neoprene seals wear better, but are thicker and need to be stretched to fit.There are now silicon seals that offer the same sealing characteristics as latex but are allergy free and last much longer. Seals are usually the first thing to break on a dry suit. They can be replaced, and some dry suits even have seals that can be zipped on.

RAID Note: To stay safe, learn better buoyancy and get the best out of your dry suit you should enrol in a RAID Dry Suit Specialty

To find out about which type of suit you should get, ask the advice of the local RAID dive centre where you plan to do most of your diving and then hire a suit first, complete a few dives and then make your decision. Custom made dry suits are available too. That little extra time spent will be worth it!

BUOYANCY COMPENSATION DEVICE Buoyancy Compensation Device (BCD) or Buoyancy Control Device. The BCD is a body harness with an integrated air bladder that can be inflated and deflated, either manually or by the power inflator (see below). The reason why we wear a BCD is to compensate for the loss of buoyancy as the diver descends, due to the effects of increased pressure on the exposure protection suit. Without the BCD, most divers would be negatively buoyant and sink. By adding air the BCD allows you to be neutral at any depth and positive on the surface.Remember the Archimedes principle. If we make ourselves bigger by inflating the BCD we will displace more weight of water making ourselves more buoyant.What do we want from a BCD? It must be comfortable to wear; easy to get on and remove, and have enough lift to be able to hold you positively buoyant on the surface. Remember the BCD is NOT a life jacket and is not designed to hold an unconscious person face up on the surface.Most BCDs are designed to hold you in the correct position while swimming underwater. There are many makes and styles of BCD, with advantages and disadvantages. The best way to see what is suitable for you is to dive first with a couple of different designs and then decide. There are not many designs that cater for a rebreather (rebreathers are explained on page 24) as the majority of designs are for open circuit divers. Some rebreathers are sold separately from the BCD, which gives the diver a choice of BCDs to choose from, or adapt your own BCD to fit. Don’t forget that you can contact your chosen RAID dive centre and find out what choice they have on offer.

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Types of BCD’s1. Standard/Stabilising JacketsThese are a “waist coat” design, with air cell under the arms, in the front, at the back and sometimes over the shoulder. This type of design has been the choice of the majority of open circuit (OC) divers and OC dive schools.This design allows air to move anywhere inside the jacket. Air will gather at the highest point and thus provide very good stability. It is important to know that to release the air in the BCD you have to hold the inflator hose higher than the BCD because of the air wanting to move higher.2. Back Mount BCD’sThese are sometimes called “wings” that have the air bladder located on the back only. There are two types of wings/bladders. The doughnut style, where the bladder is circular, allowing air all the way round. This is preferred by recreational divers who want the “clean front” feel, uncluttered sides and front as well as the stability of a standard “jacket BCD” The other wing design is the horseshoe style bladder. The design allows air to be trapped on one side to counter balance the weight that a Technical diver would have, while carrying stage cylinders on the side. Air movement from one side to the other is restricted and takes some time to learn to dive with and they generally have a much larger lift capacity to cater for the additional weight of technical diving. It is generally not a choice for the recreational diver. Both style “wings” have oral and power inflators, and dump valves. 3. The Platform HarnessSome of the RAID registered rebreathers are sold without a BCD or sold without a harness and bladder/wing system. If you don’t have a BCD, or the use of one, and you haven’t yet decided on what to purchase, then the Platform Harness together with a choice of bladder is a good decision to integrate into a RAID registered rebreather. It can also be used to adapt to many types of technical diving. There is also a version of this design made for sidemount diving. This is where the cylinders are on your side making you more streamlined for diving in wrecks and caves.

RAID Note: Take the RAID Sidemount program to learn how to dive in the sidemount configuration.

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RAID Note: BCDs should be rinsed inside & out with fresh water then dried and stored away from sunlight in a dry, cool place.

BCD TERMINOLOGYPower Inflator

This is a low-pressure direct feed of gas from the first-stage regulator. You press a button to inflate the BCD, and deflate with another button.

Some power inflator systems have their own separate air source (demand valve) which might also serve as a backup air supply. Oral inflating: Inflate the BCD by pressing a button, then physically blow into the power inflator’s small mouthpiece (either system works).

Dump Valve This is to let air out of the BCD and is located on the left shoulder where the inflator hose is and also can be found at the bottom of the bladder. The valves are activated by pulling a cord. Some BCD’s have two or more dump valves, and they can be in varying locations. These are quick and easy to use so that you can dump air to descend or dump air in case you are ascending too fast.

Pressure Release Valve This valve is there to keep the BCD from bursting due to over inflation, which could happen during a rapid ascent. The pressure release valve and the dump valve are often combined into a single system.

Waistband/CummerbundThis is a fairly thick waist band as part of the abdominal harness strap that keeps the BCD in place.

Integrated WeightSome BCDs have pockets for weights in various locations, to help with body trim. The main sections for the weights have a quick release system that can easily be pulled free for positive buoyancy.

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Quick-release Shoulder StrapsThese make it easier to get in and out of the BCD.

Accessory Rings

Generally located in the front, you can clip on additional items i.e. camera, torch.

LiftAmong the main purposes of any BCD is providing lift. Lift depends on how much air the bladder of the BCD can hold. Manufacturers provide these details on the BCD.

REGULATORSYour first stage regulator attaches to the cylinder valve and reduces the gas pressure from your cylinder to an intermediate working pressure of about 8 to 9 bar/116psi to130psi.

Your second stage regulator supplies you with breathing gas at ambient pressure (surrounding pressure) from the first stage regulator.

You will often hear the words “secondary regulator”, “regulator”, “second stage”, “octo”, “octopus”, ”alternate air source” and “demand valve” (DV) used interchangeably, but basically it is the part of a regulator that delivers gas to your mouth.

Open circuit divers have two secondary regulators: The primary regulator and the alternate air source sometimes known as the “octopus” or “octo”.

The octo is for the unlikely event that your buddy is low on air or out of air and needs air. You will get lots of practice breathing on both the mouthpiece and octo in your first confined water session.

The location of the alternate air source/octopus, for both OC and rebreather divers, is in the front of the diver, between the chin and the end of the rib cage.

1st Stage (DIN) 1st & 2nd Stage Octopus Complete Regulator Set

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Choosing your regulatorThere are many types available and you should consult you dive centre to determine the best regulator for the type of diving you plan to do.

When choosing your regulator a few considerations include:• The type of regulator for the diving you plan to do. Will you be

doing deep diving where you need a high performance regulator for example? Can your regulator adapt for technical diving if you plan to do further training?

• Ease of breathing. Your regulator should be the best performing regulator you can afford. An easy breathing regulator makes diving so much more enjoyable.

• Do you plan to dive nitrox and is the regulator suitable for this?• Ease of maintenance and availability of spares and service.• Warranty and support considerations.• Can you get support in most parts of the world?

RAID Note: Whatever type of diving you plan to do, your RAID Dive Centre is the best place to get advice on the most suitable equipment for you.

How does the regulator attach to the cylinder valve?There are two ways of attaching the First Stage regulator to the cylinder valve:1. By a Yoke fitting (below left).2. By a DIN (Deutsche Industrie Norm) fitting (below right).

Yoke DIN

The yoke fitting is the ‘normal’ method of fitting a regulator to a cylinder valve. As well as being known as a “yoke” fitting the same system is often called an “A-Clamp” or sometimes an “international” fitting.

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This system is well tried and tested; it does work, but in some areas is being slowly replaced by the superior DIN fitting, which is a screw in type attachment.

Because of the superiority of DIN attachments, divers are turning to this method to attach the regulators.

CYLINDERSScuba cylinders also referred to as “tanks” or “bottles” are subject to periodic inspection and testing. Once every 12 months all cylinders have to be visually inspected for corrosion and condensation. Cylinders also need to be hydro-statically tested for the integrity of the metal.

RAID Note: It is important to check your local laws regarding the frequency of cylinder testing requirements. Please check with your RAID Dive Centre.

A qualified gas blender will inspect each cylinder a series of codes stamped into the neck and inspection and testing stickers. If those are out of date, no responsible, reputable dive shops or gas blenders will refill the cylinder.

All Scuba cylinders serve the same purpose: to hold gas. They come in various shapes, sizes, materials, colours, and pressure ratings. While most recreational open circuit divers carry a single bottle, there are also twin cylinder configurations for OC divers needing more gas. Check out this video showing how cylinders are made:

http://www.youtube.com/watch?v=qAgSU6BCpsY

Cylinders are most commonly made from either steel or aluminium and fitted with cylinder valves. The cylinder valve allows the First Stage to be connected to the cylinder and more importantly keeps the gas inside the cylinder.

Side Sling CylinderThis is generally a small cylinder that has been configured/set up to enable divers to carry the cylinder on their side while underwater. In sport diving this is mostly carried to provide emergency air in the unlikely event that another diver needs assistance. The side sling cylinder is not used in this program and will be introduced in other RAID programs.

http://www.youtube.com/watch?v=qAgSU6BCpsY

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Cylinder ValvesEach scuba cylinder has an on/off valve. Valves are usually made of chrome-plated brass. Some countries require the valve to have a thin copper “burst disk” that’s designed to burst and release pressure if the cylinder is overfilled by a certain percentage, or if it gets very hot and builds up pressure. Burst Disks have various pressure ratings.Most valves today are ’K-valves’ which have a simple on/off valve, allowing gas in or out; with or without a burst disk. In the past when submersible gas pressure gauges were not available, the cylinders were fitted with a ‘J-valve’. This valve was designed to close when the pressure within the cylinder reached a pre-determined level, at which time the valve would close. The OC diver would be alerted that they were low on air. By pulling the lever, it would open the valve again and the diver could ascend to the surface with the last remaining air/gas in the cylinder. The standard DIN thread size is 5/8”The new EU regulations SS-EN 144-3 require all Oxygen and Nitrox cylinders, with an oxygen content of more than 22% to have the new DIN thread connection size of M26 x 2.Cylinders with compressed air will have the standard DIN M25 thread.

RAID Note: There is variation to this depending on what part of the world you are in. So as a tip: before your dive holiday, check with the dive centre if they have filling adapters, should you require them.

GENERAL RULES FOR CYLINDERSThere are a number of general, common sense rules and guidelines when dealing with scuba cylinders. 1. Only get your cylinder filled by a reputable Dive Centre.2. Don’t have them overfilled. If the “+” indicator is stamped on a

steel cylinder, 10% over the rated pressure is okay. Aluminium cylinders must never be overfilled.

3. Never fill a dedicated oxygen cylinder with any other gas. ONLY fill with oxygen. If you do fill with any other gas by mistake, empty the cylinder. DO NOT re-fill with oxygen before it has been oxygen cleaned, by qualified certified personal.

4. Don’t completely empty a cylinder during a dive. Leave some remaining pressure inside as this keeps moisture, along with the increased likelihood of corrosion, out.

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5. Have all inspections, tests, and repair work certified by formally trained and certified technicians (once a year).

6. Personally inspect your cylinder before every dive. 7. Store cylinders upright with 20 to 30 bar / 300 to 500 psi, of

pressure in them. 8. When assembling equipment, never leave an unattended cylinder

standing up.9. Handle cylinders carefully so they don’t drop or fall over.10. Inspect the valve outlet O-rings. 11. After diving, once you remove the regulator, partially open the

cylinder valve to blow out water droplets that may accumulate. 12. Keep the cylinder away from heat as much as possible. 13. Always analyse your gas before equipment assembly to verify

cylinder content.RAID Note: Your RAID Dive Centre can help you with any issues with your cylinder. Further professional training is required to do any maintenance work on the valve or cylinder.

INSTRUMENTSIn this section most of the instruments used for scuba diving are described and discussed.

Timing DevicesUnderwater timing devices are watches that are waterproof up to a pre-determined pressure. Look at the manufacturer’s specification regarding the absolute pressure rating, and ask if it can be used for scuba diving.

Cylinder Pressure GaugeSubmersible Pressure Gauges (SPGs) show, either in digital or analogue form, the remaining pressure in the cylinder. Pressure gauges can be mechanical or digital.

Depth GaugeDepth gauges work similar to pressure gauges and are based on the same technologies. There are digital ones with transducers, and mechanical ones.

CompassAn underwater compass works just like a land unit, except that it must be waterproof. Select one that has a rotating bezel and is oil-filled to dampen the movements of the needle. You will be learning basic compass navigation in your open water dive.

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You should have your own compass when you learn navigation in the RAID Navigation Specialty or the RAID Advanced 35 or Explorer 30 programs.

The ThermometerIt’s not necessary to have a thermometer, but it’s nice to know the water temperature in order to properly dress and plan ahead. Thermometers may be separate instruments, but more often they are built into one of the other instruments, such as the computer or SPG.

Underwater, you need additional instruments to give you vital information. That information includes: 1. The maximum depth reached. 2. The current depth. 3. The time spent underwater. 4. The current gas pressure in the cylinders.5. The partial pressure of oxygen (rebreather divers).

All this information can be obtained from various instruments or from your dive computer.

What is Partial Pressure (Pp)?Pressure is made up of the sum/total of partial pressures. For example, the pressure of air/gas at sea level is 1 bar/ata and it is made up of 0.21 oxygen (21%) plus 0.79 nitrogen (78% N2 +1% inert gas). So the partial pressure of oxygen is 0.21.

DIVE COMPUTERSOn land the only instrument most people wear is a watch, you have to know what time it is.

Dive computers have revolutionised diving by making information available that wasn’t available during a dive before. That’s because a computer can sense and process a wealth of information continuously and display it for the diver. A computer can also warn a diver of dangerous situations.

There are basic dive computers and very advanced ones with numerous features. However, they all do one very important thing; they use depth (PpO2 for the rebreather diver) and time information to keep track of nitrogen dissolved into your body via a mathematical model, and they display how much time you have remaining without acquiring decompression obligations.

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Gas-integrated computers also calculate remaining air pressure and based on that, remaining dive time. Dive tables calculate allowable dive profiles only on an assumed square profile (that is a dive that goes straight down to a set depth, remains there for a set time and then ascends directly to the surface); but since computers continually monitor depth and surface intervals, every few seconds, the computer is far more accurate. They store the divers’ actual profile, for future reference. (Top right: computer with transmitter which plugs into first stage. Bottom right: gas integrated computer, attaches to first stage).There are dive computers for open circuit divers that can be switched over to provide information to the rebreather diver when diving closed circuit. These dive computers are growing in numbers although at present they are limited to a small section of the dive industry.

Which is the best dive computer to use?Open circuit divers should look for a Nitrox compatible computer. Overall, the minimum functions a dive computer should include: 1. No-decompression time and recognised decompression

algorithms. 2. Max Depth and actual depth 3. Altitude compensation.4. Nitrox for open circuit. 5. PC or PDA interface.6. Automatic freshwater/seawater adjustment or most conservative

setting.7. Rapid ascent warning.8. Required safety stops (if any).9. Decompression time required (if any).10. Surface interval.11. Profile storage.12. Various warnings; rapid ascent, required safety stop or

decompression violation etc.13. Battery state of charge.14. System status indication.

The most important information is displayed and the other information is in the background for use if needed.

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Remember: Before you dive, make sure you know what, where and how your computer is working!

How do you plan a computer dive? Follow the manufacturer’s guidelines within the manual to plan your dive on your computer.

Now for a few Don’ts that apply:1. Don’t share a dive computer, and open circuit divers must never

follow the dive times of a rebreather dive computer. 2. Don’t ignore the computer’s warnings!3. Don’t forget to input the correct Nitrox mix before diving if using

the Nitrox functions.4. Don’t dive on a computer with a low battery warning!

WEIGHT SYSTEMS The weight system helps offset your positive buoyancy to allow you to sink. During your practical sessions your RAID Instructor will help you determine the correct weight for you so you can sink without carrying too much.

The most important feature on any weight belt is the “quick-release system” which allows you to release your belt with one hand in an emergency. The most common type of weight belt is nylon webbing threaded with weights and a quick release buckle.

Wear your weight belt so it is clear of all dive equipment. They require little maintenance other than a quick rinse after a dive. Handle them carefully and don’t drop it carelessly which can cause injury.

It is standard practice with all scuba divers to ensure that the weight belt is Right Hand Release. This standardisation allows for rescuers to release the weight belt quickly and easily if necessary.

Before you buy a weight system, first decide which type of diving you’ll be doing, and then look around for a system that will suit. For example, if you have to do long walks for a shore entry dive then a soft lead pouch may be more comfortable on your hips.

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If you find wearing a belt is difficult and it keeps dropping off from around your waist then a weight integrated BCD may be the best option. The other aspect which needs consideration is balance.

It might be better for you to have small ankle weights to help with buoyant legs in a dry suit. As always, you can discuss the options with your RAID instructor and/or Dive Centre.

ACCESSORIESGloves, Hoods and Booties We wear gloves, hoods and booties for warmth, or protection against cuts, scrapes and stings.

Hoods: You can lose up to 75% of body heat through your head. Select a hood that is not too tight or it can compress the arteries in your neck (the carotids).

Gloves: Hands don’t have much insulation and are susceptible to heat loss. Do not treat gloves as a license to touch anything you want.

Booties: These are necessary when wearing open-heel fins, and are useful during shore entry dives to protect against cuts and scrapes, hot sandy entries, or hot boat decks.

Surface Marker Buoys (SMB)Surface floats are an essential accessory for marking your underwater position while diving. You may tow them behind you throughout the dive, or anchor them to the bottom or carry submersible marker buoys that can be deployed at the end of the dive.

For this you will need at least 15m / 50ft of polypropylene rope on a reel. (Never tie the line and/or float to your BCD or your body, you may get pulled up by the current or snagged up).

You will practice surface deployment in your last confined water session before going into open water. It is highly recommended you purchase your own SMB before going into the open water.

Tip: Mark your SMB with your name in Big Bold Letters.

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Dive FlagsFor your safety, and especially when required by law, you need to display a dive flag which is a blue and white pennant flag (Alpha flag) or a red rectangle with a diagonal white strip. This signals to any boats in the area that divers are in the water.

Shore entry diving: Attach the flag at least 1m / 3.3ft high off your float.

Boat diving: Attach the flag to the highest point for maximum visibility.

General rule of distance: The diver must stay within 15m / 50ft of the flag, and boats should stay about 50m / 164ft away from the flag (don’t assume boaters will do this, so therefore ascend carefully and listen for boat traffic). Check in your diving area as there may be marine laws that determine safe distances from boats and other hazards.

If you are not sure how far away you are from your anchored flag, carry a reel and SMB and inflate it well before you surface.

Underwater LightsIn certain locations these are carried on all dives and in others, only for night dives. They range in price and style, and you need to decide if your type of diving warrants purchasing an underwater light. Lights are useful even in clean water as they intensify colours when shining on the reef, in shallow depths or underwater overhangs.

Underwater SlateThese are used to communicate information or as memory aids.

KnivesDivers carry knives today not to protect themselves against sea creatures, but to be able to free themselves or others in case of entanglement.

Spare Parts Kit BoxThese can contain for example spare O-rings, fin straps, basic tools, spare oxygen cell, battery, mask strap, etc.

Alpha Flag

Diver Down Flag

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Dive BagsMesh dive bags are very useful to carry mask, snorkel, fins, hoodie, drinking water, camera, cap or any accessory required for the dive. They make it easy to rinse everything in one go at the dive site after your dive.

There are also larger dive bags designed for travelling with your dive gear. These may have many compartments, wheels, wet gear pockets and come in various sizes and styles.

EQUIPMENT MAINTENANCEAfter the end of each day’s diving complete the following equipment maintenance program: (your instructor will demonstrate for you while following the manufacturer’s recommendations):1. Rinse the complete diving unit in fresh water, level the pressure in

the cylinder. The cylinder valve also needs washing and it is best done when the equipment is still fully assembled.

2. Strip the equipment down and cover the first stage with the dust cap. This is to prevent water entering the first stage.

3. Wash complete regulator set with clean fresh water. 4. Wash all the other equipment including, dive computers, cameras,

wetsuits, mask, fins, booties etc.5. Hang up to dry out of the sun and protect against the

environment. Warm moist places will promote bacterial growth.6. Refill the cylinder or for long storage leave only 30 bar / 200 psi

pressure.7. Store electronics out of the sun and in a dry environment and

exposed to normal air.

Check the Following According To Manufacturer’s Recommendations

EQUIPMENT REGULATOR COMPONENTS1. Factory sealed components should not be opened for repair except

by qualified manufacturer’s technicians. If you suspect a problem with the regulator then take it to your RAID Dive Centre for checking.

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2. Check the computer battery is OK.

O-RINGS

Most O-rings are sealed inside your regulator but there is the external one that connects the regulator to the tank. This one you need to inspect and change if damaged. Here are some general rules to this process:1. Carefully inspect prior to scuba unit assembly. 2. Replace damaged O-rings with manufacturers recommended products.3. Check the O-ring groove for damage.4. Do not use sharp metal pics to remove O-rings as you can

possibly cause damage to the sealing surface.

HOSES 1. Check for visible damage after every dive.2. Do not carry and/or lift equipment by any of the hoses.3. Do not place heavy equipment on and/or store hoses under stress.4. Ensure all is completely dry to prevent mould inside.5. Protect the DIN threads from damage.

BCD1. Perform visual inspections regularly.2. Before each dive fully inflate and check for leaks and that the

dump valves are working.

Remember – Look after your equipment and it will look after you!

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REBREATHERS Why would an open circuit diver wish to know all this?As rebreathers become ever more popular there is a high possibility that you at some stage dive with a rebreather diver.

If you are diving with a rebreather diver it is important to understand some rebreather basics. What a warning light or an alarm looks like and how to react to one as a rebreather diver’s buddy.

All RAID rebreather divers participate in a workshop which teaches them how to explain the key points and safety procedures for their rebreather.

Although we say rebreathers, it is a generalisation covering a range of equipment that has two common similarities: • The exhaled gas is re-circulated within a breathing loop.• The carbon dioxide is removed by an absorbent.

REBREATHER EXPLAINEDA rebreather is made up of a breathing loop incorporating counter lungs, which allow gas to be moved around the breathing loop, breathing hoses, mouthpiece, oxygen monitoring electronics and an absorbent canister.

The rebreather recirculates the breathing gas and adds oxygen as required. It is controlled by electronics that give various warnings if there is a problem with the rebreather. As mentioned above, your rebreather buddy will explain their particular unit and all the warning signals generated by the rebreather.

Unless ascending or completing minor breathing adjustments, rebreathers do not generally emit any bubbles from the unit; if they do this could be a warning sign.

! CONSTANT BUBBLES FROM A REBREATHER DIVER COULD BE A SIGN OF DANGER, ASCEND!

You can learn more about rebreathers in some of the RAID rebreather training programs.

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A FINAL WORD ON EQUIPMENTYou should aim to purchase the equipment you need that fits you, is comfortable and is suitable for your environment and training level. You can buy a full set of equipment on a budget or spend more on the best life support equipment you can get.

At the very least you should get your own mask, fins, snorkel and a rash guard. These are easy to travel with, won’t break your budget and can be used for snorkelling sessions when you are not diving. Your mask is like a pair of shoes, they form fit to your face over time and get more comfortable. Meaning you will always have a correct fitting mask once you have your own.

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LICENSE AGREEMENT

End User License Agreement (Non-transferable) and Limited Warranty. Read carefully before using the License Agreement and Limited Warranty.

Your use of this product must be within strict accordance of the License Agreement. This means you may not copy this program for any purposes other than to maintain a backup copy for your own personal use.

It is against the License Agreement to sell, give, or lend this program, or a copy of it, to a third party.

© Copyright 2007

Reviewed and updated 2016

This document is the property of Rebreather Association of International Divers AB, Sweden.

All rights reserved.

ACKNOWLEDGEMENTS

Primary Author: Barry Coleman, Celia Coleman

Contributing Editors: Paul Toomer, Barry Coleman, Mark McCrum, Steve Bates, Karen White, Alex Woodhams, Lisa Toomer, Watson Devore, James Rogers

Images: Barry Coleman, Paul Toomer, Steve Anderson, A. Mathiesen-Oman, Poseidon Dive Systems

Graphics: Kristen Goldsworthy

Version 2.04

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