PADI Open Water Diver Course - Chapter Four · 2015. 12. 5. · both ﬂags, particularly when boat...

By now you’ve learned a great deal aboutrecreational diving, including dive equip-ment. Although you’ve focused on the majorequipment pieces and how they integrate, inusing them you’ve used items and acces-sories that contribute to making your dive gomore smoothly and efficiently. Beyond theseand the other major equipment let’s look atother commonly used accessories. As yougain experience diving and participate in dif-ferent underwater activities, you’ll learnabout others.

Surface Floats

FOUR

Dive AccessoriesDive Accessories

Health for Diving

Breathing Air at Depth

Dive Tables andDive Computers(Introduction)

Confined WaterDive Preview

Underline/highlight the answersto these questions as you read:

1. What are five uses for a sur-face float?

2. What do you do to avoidentanglement in a line con-nected to a surface float?

MAINObjectives

Handy.When shore diving, andoften when boat diving, youmay tow a surface float,which is any small float thatyou use for resting, markinga dive site, assisting anotherdiver, carrying things, and/orsupporting a dive flag.

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When shore diving, and often when boat div-ing, you may tow a surface float, which isany small float that you use for resting,marking a dive site, assisting another diver,carrying things, and/or supporting a dive flag(more about dive flags shortly). Over the

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years divers have managed to use just about every-thing that floats and that they can tow for this: surfmats, inner tubes, small rubber rafts and Styrofoamfloats are all common surface floats divers use.Covers over tire inner tubes make useful surfacefloats that provide lots of buoyancy and usuallyhave a space for storing accessories; your dive cen-ter or resort probably has a selection of these youcan choose from.

Depending on the dive site and the dive plan, youmay anchor a surface float or tow it throughout thedive. In either case, you’ll need a nylon orpolypropylene rope not less than 15 metres/50 feet

180 Open Water Diver Manual

1. Uses for a dive float include (checkall that apply):a. assisting another diver.b. resting.c. supporting a dive flag.d. carrying accessories.

2. To avoid entanglement with a lineto your surface float:a. don’t use a line — let it drift inthe general area.b. tie the line to your BCD.c. use a reel or line caddie.

How’d you do?1. a, b, c, d. 2. c.

QUICKQUIZ Self Assessment 1

Underline/highlight the answers tothese questions as you read:

3. Why should you use a diveflag when diving?

4. How close should you stay toa dive flag, and how far shouldboats, skiers and water craftstay away if there are no locallaws governing these dis-tances?

MAINObjectives

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long for towing or anchoring. Carry the line on areel or line caddie to avoid entanglement in slackrope. When towing a float by hand, don’t attach it toyour gear. This way, you simply let go if your floatgets snarled on something, or snagged by a boat or something.

Dive FlagsYou’ll find that many places where you like to dive,people enjoy other watersports, including boatingand water skiing. Boats and skiers zipping back andforth where you’re diving pose a hazard, and it’snearly impossible for boaters to see you while you’re
underwater. So for safety when boat traffic may be aproblem, and when required by law, you need to usea dive flag to warn off boaters.
The appropriate flag depends on where and underwhat conditions you dive. A dive flag is either a redrectangle with a white diagonal stripe or a blue-and-white double-tailed pennant (Alpha flag), andlarge enough to see from at least 100 metres/yardsaway. In some instances you may be required to flyboth flags, particularly when boat diving.

When diving from a boat, place the dive flag on amast, radio antenna or other elevated location formaximum visibility. If you’re diving from shore orhave a long swim from the boat, you’ll fly the flag

from a surface float. In this case, your flag should have a wire toextend it into the ``flying’’ position, and should ride at least ametre/three feet high so boaters can see it in choppy water.

Hey, we’re here.The appropriate flag depends onwhere and under what conditionsyou dive. In some instances youmay be required to fly both flags,particularly when boat diving.

Over here! In addition to staying near theflag, carry a surface signalingdevice, such as an inflatablesignal tube that allows you toalert boats to your presence in he water.

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Local laws regulate how close you have to stay to your flag, andhow far boaters and skiers must stay away. For areas where nolaws stipulate these distances, the rule of thumb is for you to staywithin 15 metres/50 feet of your flag and for boats to stay at least30 to 60 metres/100 to 200 feet away. Also, don’t display the diveflag unless divers are actually in the water. Your instructor will fillyou in on local dive flag laws.

Unfortunately, many boaters don’t know what a dive flag means,and sometimes they can’t see your flag (like when they’re comingfrom directly up wind so that it flies directly away from them).These boaters may come much closer to you and your flag thanthey should, so don’t assume that just because you have a flagthat all boats will stay away. Even with a flag, always ascend cau-tiously, and if a boat sounds particularly loud and close, staydown, deep enough to be safe until it clears the area. Remember,too, that as a diver, you have an obligation to remain in the areawith the flag. You can’t complain about a boat zooming directlyoverhead if you’re 300 metres/1000 feet from your flag.

As mentioned in Section Two, be careful of boat traffic. In additionto staying near the flag, carry an inflatable signal tube that allowsyou to alert boats to your presence in the water.

Surface Signaling DevicesYou should consider surface signaling devices like inflatable signaltubes standard in your equipment setup. You use these to attractattention when you need help in an emergency, so that boatersstay well away from you if you accidentally surface too far fromthe dive boat or your flag, and to help the dive boat crew trackyour position. The latter can be especially important if you inad-vertently end up too far down current and the boat must comepick you up.

There are both visual and audible surface signaling devices, andyou should have at least one of each. Visual signaling devicesinclude brightly colored inflatable tubes or balls that you can blowup to be seen more easily (inflatable signal tubes), as well as sig-nal mirrors, and for diving at night, signal lights and flashers.

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Most divers keep an inflatable signal tube and/orsignal mirror in their BCD pockets at all time.

Audible devices are primarily whistles you blow andthose powered by your low pressure inflator. Themost popular place for both is on your BCD inflatorhose, where it’s out of the way yet readily accessiblefor use in an emergency.

Collecting Bags

182

1. You should use a dive flag because(check all that apply):a. it warns off boaters.b. local law may require it.

2. If no laws stipulate otherwise, therule of thumb is that you shouldstay within ______of your dive flag,and boaters should stay ________away.a. 15 metres/50 feet, 30-60 metres/100-200 feet


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Sooner or later, you’ll find some thingsor need to carry several objects –equipment accessories, trash during an underwatercleanup, etc. – while diving. Doing that while tryingto operate your gear becomes an awkward jugglingact, so you’ll want a collecting bag, also referred toas a goodie bag or catch bag.

You can get various types and sizes, with the typicalcollecting bag made from mesh nylon, so it drains

quickly, and a wire frameto hold the top open orclosed. Most have a lockso they stay shut.

When you’re using a col-lecting bag, keep in mindthat once it’s full andheavy, you carry it in onehand so you can give itthe heave-ho if necessaryin an emergency. Don’tattach it to yourself oryour equipment. When

you’re not diving, you can use a large collecting bagfor carrying your mask, fins and snorkel.

Underwater Lights

b. 30 metres/100 feet, 60 metres/200 feetc. 30 metres/100 feet, 300 metres/1000 feetd. None of the above.

How’d you do?1. a, b. 2. a.


5. What three features does a typicalcollecting bag have, and whywould you have a collecting bag?

6. You might take an underwaterlight on a dive during the day forwhat two reasons?

7. What are two reasons for carryingan underwater slate as a regularpart of your dive gear?

MAINObjectivesOh, goodie.

You can get various types andsizes, with the typical collectingbag made from mesh nylon, so itdrains quickly, and a wire frame tohold the top open or closed. Mosthave a lock so they stay shut.

Besides their usefulness for diving in the dark atnight, you’ll find underwater lights have uses inbroad daylight. A compact underwater light is usefulfor illuminating and restoring color at depth(remember that water absorbs color), as well as for

Open Water Diver Manual

http://www.projectaware.org/

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looking into dark cracks and crevices (so you don’treach in without checking whether anyone’s home).

An underwater light is both watertight and pres-sure-proof; you can take an ordinary flashlightunderwater, but the water shorts it out and ruinsit, so don’t. (You were expecting something differ-ent?) Underwater lights remain watertight byusing an O-ring seal that you need to inspect, cleanand lubricate periodically (your PADI Dive Center,Resort or Instructor can show you how). Like mostflashlights, store underwater lights without theirbatteries if you’re not going to use them for anextended period to prevent possible damage frombattery leakage. Professional dive stores usuallystock a wide array of underwater lights, varying inpower source, size and brightness.

Underwater SlateIn the discussion about underwater communicationyou learned that you use hand signals and under-water slates as the two most common methods forcommunicating underwater. To use a slate, you

See? Besides their usefulness for diving in the dark atnight, you’ll find underwater lights have uses inbroad daylight.

1. You might use a collecting bag for(check all that apply):a. carrying several objects at once.b. gathering trash during an under-water cleanup.


have to have one. It’s an important communicationtool, but you also use it for carrying general infor-mation like time and depth limits, and makingnotes for your log book. They don’t cost much, nor
do they take up much space, so you probably want
to make one standardequipment.

Underwater slates are usu-ally made of plastic andtypically come with a pencilon a short cord (to preventloss). Most slates fit in yourBCD pocket, although someinstrument consoles acceptcustom slates on the back.Others strap to your wrist,and there are a few specialslates that erase easilyunderwater if you have to

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Right for writing.A slate is an importantcommunication tool, but youalso use it for carryinggeneral information like timeand depth limits, and makingnotes for your log book.

2. Reasons for taking an underwaterlight on a day dive include (checkall that apply):a. restoring lost colors.b. looking in cracks and crevices.c. unexpected solar eclipse.

3. You want to carry a slate as a reg-ular part of your gear (check allthat apply):a. to communicate.b. to carry information, like depthand time limits.c. None of the above.

How’d you do?1. a, b. 2. a, b. 3. a, b.

communicate a lot. You can also find specialized slatesthat carry information, such as the PADI Data Carriersthat come with The Wheel, and fish identification slatesthat show you the names of fish you might see.Regardless of which slate you choose, be sure to secure itso it doesn’t cause drag or pose an entanglement prob-lem. Generally, it’s best to carry it in a pocket.

Spare-Parts KitSave a dive.You make a spare-parts kit by collectingthose sundries that wear out, break orvanish and storing them with a few basictools, in a moisture proof container inyour equipment bag.

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There’s nothing quite so frustrating as missing an entireday’s diving because of something inane like breaking afin strap and having no spare. It doesn’t take mucheffort or investment to make a spare-parts kit, and withit, you minimize the probability of missing dives due tominor problems like a broken fin strap.


8. Why should you take aspare-parts kit with youwhen you dive?

9. What do you put in a spare-parts kit?

10. There are three primary rea-sons for keeping a log book.What are they?

MAINObjectives

You make a spare-parts kit by collecting those sundriesthat wear out, break or vanish at the worst time, andstoring them, with a few basic tools, in a moisture proofcontainer in your equipment bag. At first you won’t needmuch room for this, but as you gain experience, you’lladd to it — never throwing anything away — until it’sbasically an equipment locker you need a fork lift tomove. But that won’t happen for a few years, so here area few suggestions to get you started:

1. Mask strap — tip: fabric/Velcro™ type straps fit virtu-ally all masks, making them “universal”replacements

2. Fin strap — tip: When one goes, the other’s closebehind. Carry two and replace them at the sametime

3. O-rings — tip: different tank valves take slightly dif-ferent sizes; carry an assortment

4. Silicone lubricant — tip: carry silicone grease, notspray, and use it very sparingly according to themanufacturer of the particular equipment. A smallcontainer will last a decade or more, or until you lose it

5. Snorkel keeper6. Cement for exposure suit repairs — tip: different

suits require different cements


7. Waterproof plastic tape8. Quick-release buckle9. Pocket knife10. Pliers — tip: even better, a plier-tool, like the

Leatherman™ tool11. Adjustable wrench12. Screwdrivers13. Spare sunglasses, sunscreen (well sealed so it doesn’t

goop up your kit), motion sickness medication. (Thesearen’t spare parts, but things you really don’t want tobe without — so make them a permanent part ofyour kit.)

Your instructor can suggest other items for your spare-parts kits.

Log BookThe certification you earn in this course indicates thatyou’re a qualified scuba diver. It’s sort of like a diploma– it indicates that you’ve successfully completed the edu-cation. But if you were interviewing for a job, a prospec-tive employer would want to see what you’ve done withyour education – a resume listing your experiences sinceyou received your diploma. In diving, your “resume” isyour log book.

Your log book shows a divemaster or charter crew howfrequently you dive, what type of dives you’ve made, theenvironments that you have experience with and so on.It’s a proof-of-experience document often requested fordiver training, and when diving at resorts or on boats. Ithelps you assess how your experience contributes toyour diving ability and the dive opportunities open toyou. And, you can check it once in a while to see how farthe dive stories you tell depart from reality.

History of a diver.Your log book shows how frequently you dive,what type of dives you’ve made, the environ-ments that you have experience with and soon. It’s a proof-of-experience document oftenrequested for diver training.

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The three primary reasons to have a log book are toremember your dive experiences, to document your his-tory as a diver, and to note specific details about a divesite for future reference. Make a habit of filling out your
log book immediately after every dive, and having yourinstructor or buddy sign it (your instructor will signyour log book after each open water dive you make in
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this course). You can choose from log books rangingfrom simple ones with room for descriptions, to onessuch as the PADI Adventure Log with more featuressuch as space to record training, equipment purchasesand maintenance, air use, dive site maps, personalinformation, and more.

From what you’ve learned to this point, you know thatdiving is relaxing, but not sedate, and you need to be ingood health. You also realize that there are times whenstrenuous activity comes into play, so you need to havelevels of health, fitness and conditioning sufficient tohandle moderately strenuous activity, which couldinclude an emergency or other unanticipated physicaldemands. Being in good health helps assure that you can meet these demands, which in turn affectsyour safety.

General diving health recommendations follow thesame recommendations regarding rest and diet for

Health for Diving


In this subsection on Dive Accessories, you learned:

▲ You use a surface float to support your dive flag, for rest-ing and to carry accessories.

▲ Use an appropriate dive flag when diving where boatsmay be present and according to local law.

▲ Don’t attach a full collecting bag to your gear.

▲ Underwater lights have both day and night uses.

▲ A spare-parts kit can help you keep from missing a dive.

▲ Start and maintain a log of all your dive adventures.

▲ To communicate with an underwater slate, you have tohave one.

Summary PointsSummary Points

1. You want a spare-parts kit toreduce the chance you miss a divedue to something minor, like amissing O-ring or a broken strap.True False

2. Items you might put in a spare-parts kit include (check all thatapply):a. O-rings.b. straps.c. food.d. basic tools.

3. Reasons for keeping a log bookinclude (check all that apply):a. documenting your history as adiver.b. that it’s required to keep yourcertification.c. recording specific dive sitedetails.d. helping you remember yourexperiences.

How’d you do?1. True. 2. a, b, d. 3. a, c, d.


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Underline/highlight the answers to these questions as you read:

11. What three substances should youavoid using prior to diving?

12. How often is it recommended that youhave a complete physical examinationby a physician?

13. What two immunizations shoulddivers keep up to date?

14. What can you do to maintain your diveskills, or restore them after inactivity?

15. What effect does menstruation haveon diving?

16. Why is it recommended that pregnantwomen not dive?

MAINObjectives

Diving is generally relaxing, butat times it can cause elevatedphysical stress. Swimming hard,hot sun while in an exposure suitand other factors can strain yourheart and cardiovascular system.Like any other physical stress,this can cause a heart attack inpredisposed individuals. Be sureto discuss this concern with yourdoctor if you may have a predis-position to heart disease due toage, lifestyle, body composition,family history or other factors.

Heart HealthHeart Health

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everyday life. Never use alcohol, drugs or tobacco priorto diving. Alcohol and drugs, even in quantities thathave minimal effect on the surface, can impair yourjudgment at depth, where pressure can increase theireffects. Also, alcohol before or immediately after a divealso increases your risk of decompression sickness (dis-cussed later in this section). Be conservative if drinkingthe night before diving; alcohol tends to dehydrate you,which can also predispose you to decompression sickness.

If you’re taking a prescription drug, discuss its effectswith your physician prior to diving. If in doubt, don’tdive until you’re no longer using the medication.

Avoid smoking, which tends to interfere with having anactive lifestyle. Smoking is undeniably detrimental toyour health. If you do smoke, abstain for several hoursbefore and after diving because smoking significantlydecreases the efficiency of your circulatory and respira-tory systems. It can also promote air trapping withinyour lungs, theoretically raising your risk of lung overexpansion injury — even when breathing normally.

Don’t dive if you don’t feel well, including (as youlearned in Section One) diving with a cold. Doing so cancause ear and sinus squeeze or reverse blocks due toequalization difficulties. Diving with a chest cold canproduce air trapping, with a risk of lung over expansioninjury. No one wants to miss out on a dive, but youshould be in good health to dive safely. Don’t use med-ication to combat symptoms so you can make a divewhen you’re not well.

Maintain a reasonable degree of physical fitness andhave a complete physical examination when you firstenter diving, and at least every two years thereafter.
Ideally, you should be examined by a physician knowl- edgeable in dive medicine. Keep your immunizationscurrent; this is especially important for your tetanusand typhoid immunizations. Keep a well-balanced diet and get proper rest. Maintain a regular exercise pro-gram — you don’t have to be an Olympian, just in goodaverage health.
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188

1. Before diving, you want to avoid(check all that apply):a. drugs.b. eating.c. alcohol.


TunIf yoit hayouRevskilla mo

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Dive health also includes taking care of yourself inother ways — including keeping your skills andknowledge sharp. The best way to do this is to be anactive diver — dive — this helps maintain your diveskills. Take part in new underwater adventures, likedive travel and special activities and courses. You’llhave fun while developing new dive skills andimproving and refining those you have. If possible,swim with fins in a pool regularly to keep your legmuscles toned — and it’s a good aerobic exercise.Practice the skills you learn in this course frequently.

If you’re away from diving for awhile, no sweat — ithappens to all divers once in a while — refresh yourdive skills and knowledge. Review this manual, theOpen Water Diver Video and practice your skillswith a PADI Divemaster, Assistant Instructor or

Instructor. ThePADI ScubaReview programrefreshes yourknowledge andskills, and it’squick and easy —one evening or amorning is usu-ally all you need.

If you’re awoman, you havesome specialhealth considera-tions, includingmenstruation and

d. smoking.

2. It’s recommended that you have acomplete physical examinationevery _____ years.

3. Immunizations divers should keepup to date are ___________ and______________.

4. To maintain your dive skills, (checkall that apply):a. be an active diver.b. continue your diving education.c. participate in special divingactivities.

5. If menstruation doesn’t normallykeep you from other active recre-ations, it shouldn’t keep you fromdiving.True False

6. It’s recommended that pregnantwomen:a. not dive, because there is littleknown about the effects of divingon a developing fetus.b. dive only to 10 metres/30 feet,because there is little known aboutthe effects of diving on a develop-

e up, dive in.u’re away from diving for awhile, no sweat —ppens to all divers once in a while — refresh

r dive skills and knowledge. The PADI Scubaiew program refreshes your knowledge ands, and it’s quick and easy — one evening or rning is usually all you need.

pregnancy. As long as menstruation doesn’t nor-mally keep you from participating in other activerecreations, there’s no reason why it should keepyou from diving either. Diving while pregnant is

ing fetus.

How’d you do?1. a, c, d. 2. two. 3. tetanus, typhoid4. a, b, c. 5. True. 6. a.

another story. There’s not much known about howdiving may affect a developing fetus. It’s generallyagreed that it’s not worth the risk; so discontinuediving while pregnant, or if you’re trying to become pregnant.


You need to feel well to dive well. Maintain goodhealth, avoid habits that hurt your health, and stayin good mental and physical shape. Not just for div-ing, but for living.

So far, you’ve learned about the direct effects thatcome from breathing air underwater and yourresponses: volume reduction and the need to equal-ize, increased air density and breathing slowly anddeeply, volume expansion and never holding yourbreath while scuba diving.

Besides these direct effects, breathing air underpressure has indirect, more subtle effects. Like thedirect effects, these effects are pretty predictable,and you can avoid associated problems by followingsome simple guidelines.

Air To understand some of the indirect effects possiblefrom breathing air at depth, you need to under-stand what air is. As you may be aware, air con-sists of many gases, but

Breathing Air at Depth

In this subsection on Health for Diving, you learned:

▲ Don’t drink, smoke or take drugs before diving.

▲ Don’t dive when you don’t feel well.

Summary PointsSummary PointsFormorein

formationabout...

Breathing Air at DepthSee the PADI Encyclopedia ofRecreational Diving and the PADIEncyclopedia Multimedia CD-ROM

Underline/highlight the answers to these ques-tions as you read:

17. What two primary gases make up air?

18. What are five possible symptoms of conta-minated air?

19. What should you do for a diver suspectedof breathing contaminated air?

20. How do you prevent problems with contam-inated air?

21. How do you prevent problems with oxygen?

MAINObjectives

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nitrogen and oxygen make up more than 99percent, so for practicalpurposes, we can con-sider air 79 percent nitrogen and 21 percentoxygen. When you breathe
your body uses the oxygen,and the nitrogen gas isphysiologically inert (your body doesn’t use it).
The compressed air inyour scuba tank is essen-tially the same as the air

Chapter Four 189

▲ Stay in good health.

▲ Have a physical examination at least every two years.

▲ Keep tetanus and typhoid immunizations current.

▲ Pregnant women shouldn’t dive.

▲ Review your dive skills and knowledge after a period of inactivity.

you’re breathing now. The filling process filters theair to remove chemical and particle impurities, and itremoves most of the moisture, which can damagescuba tanks and cause other problems.

Contaminated AirThe first possible problem involved with breathingair under pressure (underwater) involves contami-nates that aren’t supposed to be there. This problemis rare, but possible.

Compressors for filling scuba tanks (breathing air)use special filters and separators to keep contami-nates such as carbon monoxide or oil vapor out ofyour breathing air. This is important because pres-

sure proportionately increases the effects of a gas you breathe, sothat traces of contaminants that wouldbe harmless at the surface can be toxic underwater.

Contaminated air generally results froma problem with the compressor or its fil-tering system, and as a result oftentastes and smells bad — but it can also

190 Open Water Diver

Two gases.Air consists of many gases, but nitrogenand oxygen make up more than 99percent, so for practical purposes, wecan consider air 79 percent nitrogen and21 percent oxygen.

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be odorless and tasteless. A diver breath-ing contaminated air may experienceheadaches, nausea, dizziness and evenunconsciousness. A diver afflicted by con-taminated air may have cherry-red lipsand fingernail beds, though this may behard to see underwater.

Breathe easy.Contaminated air is rare as long as you buyyour air from reputable sources, such as

Give a person suspected of breathing con-taminated air fresh air, and administeroxygen if available. In severe cases, res-cue breathing may be necessary. Thediver should have medical attention inall cases.

Fortunately, as mentioned, contaminatedair is rare as long as you buy your air from reputable air sources,such as professional dive stores. These stores recognize the serious-ness of contaminated air and have their air checked frequently to be

Manual

professional dive stores.

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sure of its quality. Don’t fill your tank from a compressor or other airsource that isn’t intended specifically as a breathing air compressorsystem; for example, you wouldn’t use industrial air systems such asthose used for filling tires or powering sandblasters. To avoid conta-minated air, be certain you have your tanksfilled only with pure, dry, filtered com-pressed air from a reputable air station.

Even though you have a proper airsource fill your tank, if the air tastesor smells bad, don’t use it. If you feel

ill or get a headache during a dive, end thedive immediately. If you suspect you mayhave contaminated air in your tank for anyreason, save the air for analysis and don’tdive with it.

There’s another way to suffer contaminatedair poisoning, and that’s by breathingexhaust fumes aboard a boat. Try to stayout of a boat’s exhaust and in fresh air.

Too much of a good thing? To avoid oxygen toxicity problems, don’t haveyour cylinder filled with enriched air or use acylinder that’s marked as being an enriched aircylinder, unless you’re properly trained andcertified as an Enriched Air Diver.

OxygenBecause you need oxygen to live, it may seem strange thatoxygen can become toxic if you breathe it under pressure.But in fact, you can get “too much of a good thing” — if you

were to fill your scuba tank with pure oxygen instead of compressedair, you could suffer oxygen poisoning in water as shallow as 6metres/20 feet. This is why you should never have your tank filledwith pure oxygen.

The 21 percent oxygen in compressed air can also be toxic, but notuntil you descend well past the recommended maximum limits forrecreational diving. So when diving with air within recreationaldepth limits, oxygen toxicity isn’t an issue.

Recreational divers sometimes use enriched air (also known as“enriched air nitrox” or “nitrox”), which has more than 21 percentoxygen. Enriched air has some advantages regarding how long youcan stay underwater at a given depth, but you can have oxygenproblems using it within recreational depth limits. For this reason,enriched air diving requires special training and some special equip-ment requirements (to avoid combustion problems possible with

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1. The two primary gases that make up airare:a. hydrogen and oxygen.b. helium and nitrogen.c. carbon dioxide and hydrogen.d. oxygen and nitrogen.

2. Symptoms of contaminated air include(check all that apply):a. headache.b. nausea.c. cherry red lips/nail beds.d. limb and joint pain.

3. If a diver is suspected of breathing con-taminated air (check all that apply):a. give the diver fresh air.b. give the diver oxygen if available.c. the diver should get medical atten-tion.d. None of the above.

4. You avoid contaminated air problems byhaving your tank filled only by a rep-utable air source with a compressorsystem intended for breathing air.True False

5. To prevent problems with oxygen (checkall that apply):a. never have your tank filled with pureoxygen.b. don’t exceed the limits of recreationaldiving.c. don’t use enriched air (nitrox) unlesstrained and certified in its use.d. use air that has had all the oxygenremoved.

How’d you do?1. d. 2. a, b, c. 3. a, b, c. 4. True 5. a, b, c.


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high oxygen levels); reputable dive centers will notprovide enriched air without proof of enriched aircertification.

So, to avoid oxygen toxicity problems, don’t have(or try to have) your cylinder filled with enrichedair, unless you’re properly trained and certified.Don’t use a cylinder that’s marked as being anenriched air cylinder, (again, unless you’re properlytrained and certified).

Nitrogen NarcosisAlthough nitrogen has no direct influence at thesurface, that changes as you breathe it under pres-sure. Underwater, at depths approaching 30metres/100 feet, nitrogen has a noticeable intoxi-cating effect that intensifies as you go deeper.

A diver affected bynitrogen narcosisbehaves as you mightexpect someone tobehave if intoxicated.


22. What are five symptoms ofnitrogen narcosis?

23. What should you do if nitrogen narcosis becomesa problem?

24. How do you prevent nitrogen narcosis?

MAINObjectives

Narcosis impairs thediver’s judgment andcoordination, andmay create a falsesense of security,cause disregard forsafety and other fool-ish behavior.Nitrogen narcosis canmake a diver feelanxious or uncomfort-able, which can leadto panic or other poordecisions.

Nitrogen narcosis affects individuals differently,and affects the same individual differently fromday to day. Its effect can combine with some drugsor alcohol and impair a diver at shallower thanexpected depths (hence the warning not to

drink or use drugs before diving).

KKeeeepp aa cclleeaarrhheeaadd..UUnnddeerrwwaatteerr,, aatt ddeepptthhssaapppprrooaacchhiinngg 3300mmeettrreess//110000 ffeeeett,,nniittrrooggeenn hhaass aannoottiicceeaabbllee iinnttooxxiiccaattiinnggeeffffeecctt tthhaatt iinntteennssiififieessaass yyoouu ggoo ddeeeeppeerr.. TThhiissiiss ccaalllleedd nniittrrooggeennnnaarrccoossiiss..

1. Symptoms of nitrogen narcosis include(check all that apply):a. cherry red lips/nail beds.b. false sense of security.c. foolish behavior.d. anxiety.

2. If nitrogen narcosis becomes a problem(check all that apply):a. ascend to a shallower depth.b. descend slowly to a deeper depth.c. None of the above.

3. To prevent nitrogen narcosis (check allthat apply):a. avoid deep dives.b. make all your dives in the 30 - 40metre/100 -130 foot range

How’d you do?1. b, c, d. 2. a. 3. a.

QUICKQUIZ SSeellff AAsssseessssmmeenntt 77

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Nitrogen narcosis diminishes when you reach shal-low water, with no aftereffects. If you begin to feelintoxicated, uncoordinated or confused, immedi-ately ascend to shallower depths to relieve the nar-cosis. It usually goes away quickly. If your buddyacts impaired, assist your buddy to shallower water.

To prevent nitrogen narcosis, simply avoiddeep dives. Nitrogen narcosis is not dan-gerous or harmful in itself, but creates a

hazard by impairing the judgment and coordina-tion you need to prevent emergencies and respondto them if they occur.

DDeeccoommpprreessssiioonn SSiicckknneessssAs you’ve read a few times to this point, your timeunderwater has limits beyond your air supply, cold,fatigue and the like. The limits relate to how deepyou go, and result from nitrogen gas dissolving inyour body tissues during a dive. This is perhapsone of the most significant effects of breathing airunder pressure.

During a dive, the increased pressure causes nitro-gen from the air you breathe to dissolve into yourbody tissues. H

waydivedivenitr

Yougoesandthe andsolvout;thaascepres

ow much nitrogen you absorb this depends primarily on how deep you, and for how long. The deeper you and the longer you stay, the moreogen your body absorbs.

r body doesn’t use nitrogen, so what
into solution must come back out leave your body. When you ascend,pressure surrounding you decreases the excess nitrogen can’t stay dis-ed in your body, so it begins to cometherefore, making slow (no faster
n 18 metres/60 feet per minute), safents may reduce your risk of decom-sion sickness.

CChhaapptteerr FFoouurr 119933

As long as you keep excess nitrogen within reasonablelimits, your body eliminates it without complication. Tokeep within these limits, you use dive tables and divecomputers, which give you maximum times at a givendepth based on how much nitrogen your body theoreti-cally absorbs and releases.

If, however, you stay underwater beyond these limits,your body absorbs so much excess nitrogen that when youascend and surface, your body can’t eliminate the nitro-gen as fast as it comes out of solution. As it dissolves outof your body tissues, the excess nitrogen forms bubbles inyour blood vessels and tissues. The phenomenon is simi-lar to opening a bottle of soda; you release the pressureand the dissolved gas comes out of solution, giving your



25. What two primary factors influencethe absorption and elimination ofnitrogen in a diver?

26. What condition occurs when a diverexceeds established depth and timelimits, producing bubbles in thebody during and following ascent?

27. What nine secondary factors caninfluence the absorption and elimi-nation of nitrogen from the body?

28. What signs and symptoms areassociated with decompressionsickness?

29. What is meant by decompressionillness versus decompression sick-ness?

30. What is the necessary treatment fora diver suspected of having decom-pression illness?

31. What is the first aid procedure forassisting someone with decompres-sion illness?

32. How do you avoid decompressionsickness?

MAINObjectives

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soft drink its fizz. Bubbles forming in the body after adive cause a very serious medical condition called decom-pression sickness (DCS), sometimes called “the bends.”
(More about DCS in a moment.)
While your dive time and depth are the primary variablesinvolved with decompression sickness, other factors influ-ence how your body absorbs and eliminates excess nitro-
gen. When present, these secondary factors can con-tribute to developing DCS: fatigue, dehydration, vigorousexercise (before, during, or after the dive), cold, age, ill-ness, injuries, alcohol consumption before or after a dive,and being overweight. Also, diving at altitude without fol-lowing special procedures, or an increase in altitude afterdiving by flying or driving through mountains, can con-tribute to getting decompression sickness (more aboutthis in Section Five).
You want to dive well within the limits of divetables and computers, and use extra caution ifany of the secondary factors apply to you. To

reduce the risk of DCS, get in the habit of always divingwith a conservative margin between the time you actu-ally dive, and the maximum allowed by the dive table orcomputer you use.

Signs and symptoms of DCS. Because bubbles can formin different places in the body, DCS symptoms can vary.

Watch yourlimits.If you stay under-water beyondestablished limits,when you surfaceexcess nitrogendissolves out of yourbody tissues andforms bubbles in yourblood vessels and tissues.The phenomenon is similar towhen you open a bottle of sodaand the dissolved gas comesout of solution, giving it fizz.

Bubble trouble.The dive medical community lumps DCS andlung overexpansion injury under the clinicalterm decompression illness (DCI). They dothis because the first aid and treatment areidentical for both, and there’s no need todistinguish between them when assisting adiver.

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Signs and symptoms include paralysis, shock, weakness,dizziness, numbness, tingling, difficulty breathing, andvarying degrees of joint and limb pain. In the most severecases, unconsciousness and death can result.

Decompression sickness can also manifest subtly.Symptoms can include a mild to moderate dull ache,usually but not necessarily in the joints, mild to moderatetingling or numbness, usually, but not necessarily, in thelimbs. Weakness and prolonged fatigue may result fromDCS. Decompression sickness symptoms can occurtogether or individually, occur anywhere in the body,and may be accompanied by lightheadedness.

Symptoms usually occur anywhere from 15 minutes to 12hours after a dive, though they can occur later. They tendto come on gradually and persist, though they can beintermittent. Regardless of the severity of the symptoms,consider all cases of decompression sickness serious.

First aid and treatment. Lung over expansion injuries anddecompression sickness can produce very similar signsand symptoms, even though they result from two differentcauses (holding the breath versus exceeding time and
depth limits). The dive medical community lumps DCSand lung overexpansion injury under the clinical termdecompression illness (DCI). They do this because the firstaid and treatment are identical for both, and there’s noneed to distinguish between them when assisting a diver.
If a diver has symptoms of decompression illness, or isn’tsure, the diver should discontinue diving, seek medicalattention and consult a dive physician. As you learned inSection Three, some areas have special diver emergencyservices that provide consultation and coordinate withlocal medical services to assist the diver.

First aid for decompression illness includes having thediver lie down and breathe oxygen. Contact local emer-gency medical care, and the local diver emergency service(if available — or the closest recompression chamber).Your instructor will tell you the emergency contact infor-mation for your local diving areas.

Chapter Four 195

Don’t delay first aid and getting the diver to treat-ment. The faster treatment begins, the less riskthere is of permanent residual symptoms. Althoughdecompression illness is a serious medical condi-tion, with prompt, proper treatment it is rarelyfatal in recreational divers.

19

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Redissolution.Almost all cases of decompression illnessrequire treatment in a recompressionchamber, during which the diver is putback under pressure to help the bodyabsorb bubbles in the tissues.


Decompression illness is a rMedical services and recomered, or entirely covered, by

Fortunately, you can obtain vhave in the unlikely event yovary depending upon where ately priced mask. Having thcan reduce treatment delays

PADI Diver Protection Prograprograms. Chances are you you do, it’s likely you’ll have years coverage.

Remember, it’s your responsbeing prepared if somethingto have. Be prudent — see ying and maintaining coverag

A PrA Pr

Monitor the diver and prevent or treat shock asnecessary. A diver who isn’t breathing will needrescue breathing, and CPR if the diver has nopulse. If the diver is unresponsive and breathing,lay the diver level left side down, head supportedand breathing oxygen as described in SectionThree. Continuously monitor breathing and pulse.If the diver is responsive and breathing, the divermay lie on his back if lying on the left side is toouncomfortable.

are event among recreational divers, but it does happen.pression treatment can be costly, and may not be cov-your regular medical insurance.

ery inexpensive protection to fill coverage gaps you mightu suffer decompression illness. The costs and coveragesyou live, but the annual fee is typically less than a moder-is insurance can save you a tremendous expense, and it caused by concerns about how you’ll cover the costs.

m insurance is available worldwide, and there are otherwon’t need this insurance even in years of diving but ifsaved yourself more than 10 times what you spend for 10

ibility to manage your own risk by diving safely, and by happens. Diver accident insurance is just too cheap notour PADI Dive Center, Resort or Instructor about obtain-e. The least it buys you is peace of mind.

udent Measureudent Measure

Chapter Four 197

1. The two primary factors influencing howmuch nitrogen you absorb during a dive are:a. dive depth and amount of air used.b. dive time and dive depth.c. dive time and amount of air used.

2. The condition that occurs when a diverexceeds established depth and time limits,producing bubbles in the body followingascent, is called:a. decompression sickness.b. decompression illness.c. lung over expansion injuries.d. nitrogen narcosis.

3. Secondary factors that can influence nitro-gen absorption and elimination include(check all that apply):a. alcohol consumption before or immedi-ately after a dive.b. dehydration.c. aged. being overweight

4. Signs and symptoms of decompres-sion sickness include (check all that apply):a. limb and joint pain.b. mild tingling and fatigue.c. paralysis and unconsciousness.d. foolish behavior.

5. Decompression illness is a clinical term thatmeans:a. decompression sickness.b. lung over expansion injuries.c. both decompression sickness and lungover expansion injuries.d. any injury that happens underwater.

6. A diver with decompression illness requirestreatment:a. only in very few cases.b. in a recompression chamber.c. by being put back underwater.d. Both b and c.

7. First aid for decompression illness includes(check all that apply):a. emergency oxygen.b. lying on the left side if unresponsive andbreathing.c. contacting local emergency medical care.d. contacting a dive physician or local diveremergency service.

8. You reduce the risk of decompression sick-ness by (check all that apply):a. staying within the limits provided by yourdive table or computer.b. diving conservatively, well within estab-lished limits.c. making slow, safe ascents.

How’d you do?1. b. 2. a. 3. a, b, c, d. 4. a, b, c. 5. c. 6. b.7. a, b, c, d. 8. a, b, c.


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Almost all cases of decompression illness requiretreatment in a recompression chamber, duringwhich the diver is put back under pressure tohelp the body absorb bubbles in the tissues. Thistreatment usually takes several hours, requiresthe use of pure oxygen, and often drug therapies.Don’t allow a diver suspected of having decom-pression illness to go back underwater. Attemptsto treat a diver underwater typically end withworsened symptoms and disastrous results, andonly delay getting to proper treatment.

Although decompression sickness is a seriouscondition, both painful and potentially life-threatening, it is avoided by properly followingthe established safe time and depth limits ofdive tables and dive computers. Lung overexpansion injuries are also serious, painful andpotentially life-threatening, but avoided bybreathing continuously and never holding yourbreath. Additionally important in preventingdecompression illness (both DCS and lung overexpansion injuries) is a slow, safe ascent ratewith a stop for safety at 5 metres/15 feet. You’lllearn more about this stop in Section Five.

Your body absorbs nitrogen during a dive; afterthe dive, your body can tolerate a certain level ofexcess nitrogen without developing decompres-sion sickness. The question is, how do you knowwhat that level is, and then stay within it?

To answer this question, physiologists and otherscientists created mathematical decompressionmodels that track the theoretical nitrogen youhave in your body before, during and after div-


In this subsection on Breathing Air atDepth, you learned:

▲ Air is 79 percent nitrogen and 21percent oxygen.

▲ Contaminated air symptoms includeheadaches, nausea, dizziness,unconsciousness, and cherry red lips and nail beds.

▲ Don’t have your tank filled with oxy-gen, and don’t use enriched airunless certified in its use.

▲ To avoid nitrogen narcosis, avoiddeep dives.

▲ Decompression sickness is causedby excess nitrogen forming bubblesin the body after a dive.

▲ Stay well within dive table and divecomputer limits, especially if sec-ondary factors apply to you.

▲ Signs and symptoms of DCS includelimb and joint pain, tingling, numb-ness, paralysis, shock, weakness,dizziness, difficulty breathing, uncon-sciousness and death.

▲ Decompression illness (DCI) is aclinical term for both decompressionsickness and lung over expansioninjuries.

▲ A diver with DCI should receiveemergency oxygen, rescue breathingand CPR if necessary, and willrequire treatment in a recompressionchamber.

Summary PointsSummary Points

Dive Tables and DiveComputers (Introduction)

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ing. For practical field use, these models areexpressed by dive tables and in dive computers,which as you read earlier, you use primarily to

33. What is the primary use of dive tables anddive computers?

34. What are meant by no decompression/no-stopdiving and decompression diving?

35. What is a no decompression limit (NDL)?

36. Why should you avoid the maximum limits ofdive tables and dive computers?

37. How does the Recreational Dive Planner dis-tributed by PADI differ from other dive tables?

38. Why is your body nitrogen level higher after arepetitive dive than if you made the same diveas a nonrepetitive dive?

39. What is residual nitrogen?

40. What is a repetitive dive?

41. What are the general rules for using theRecreational Dive Planner, and how do youapply them?

42. What is bottom time?

43. What is the maximum depth limit for all recre-ational diving?

MAINObjectives

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determine your maximum allowable time atgiven depths.

especially true if any of the factors that con-tribute to decompression sickness (vigorous exer-cise, cold, age, etc.) apply to you or the dive situa-tion. You want to stay well within limits, andtake extra precautions to avoid the sec-ondary contributing factors that you can;that is, you can’t change your age, but youcan keep yourself from becoming dehydrated.

So, because people differ in their susceptibility todecompression sickness, no dive table or com-puter can guarantee that decompression sicknesswill never occur, even though you dive within thetable or computer limits. It is always wisest toplan dives well within table and computer limits,especially if any contributing factors apply.

No decompression (no stop) diving. As a recre-ational diver, you’ll be learning no decompression
diving. No decompression diving means thatyou’ll plan your dives and dive so that you canalways ascend directly to the surface withoutstopping, yet without significant risk of decom-pression sickness. This is also called (somewhatmore accurately) no-stop diving, because youdon’t have to make a stop (though you usuallywill — more about that in Section Five). As arecreational diver, you always plan your dives asno decompression dives.
The fact that you derive your dive time limitsbased on a model explains why you need to diveconservatively and avoid the maximum limitsyour table or computer provides. Theoretical mod-els can’t account for variations from one individ-ual to the next, so it’s prudent to stay well withinthe limits a table or computer predicts. This is

There are other types of diving besides recre-ational diving: military, commercial, research andtechnical diving often involve decompression div-

Chapter Four 199

ing. Decompression diving means that the divers absorb so muchnitrogen (or other gas) during a dive that it’s not possible to ascenddirectly to the surface without a substantial risk of DCS. Instead, thediver makes a series of stops, each progressively longer, to allow suffi-cient time for the body to release dissolved nitrogen. Decompressiondiving usually calls for using special synthetic breathing gases,requires a good deal of surface support, and even when done properly,compared to recreational diving the diver has more risk from DCS and

other hazards. Obviously, this type of div-ing is beyond the scope of the course andrecreational diving, though you’ll learn theprocedures for making emergency decom-pression stops in the unlikely event youaccidentally exceed a no decompressionlimit.

Dive tables. Although you’ll be diving witha dive computer, you’ll still want to under-stand basic table use. Dive tables havebeen around since 1907 and were the pri-mary method of planning dives until themodern dive computer debuted in the

1980s. Dive tables still have their place because they help you under-stand what your dive computer is telling you, and because they’re aneffective backup for your dive computer (though modern dive comput-ers are very reliable and rarely have problems).

Until 1988, the dive tables recreational divers used were really hand-me-downs from commercial and military diving. Although they wereadequate for planning recreational dives, they were tables for decom-pression diving and had to accommodate large amounts of theoreticalnitrogen, and consequently “penalized” recreational divers, who bymaking no decompression dives, had far less theoretical nitrogen.Further more, these tables were tested on predominantly young, malemilitary divers, which didn’t fully represent the population spectrumyou find in recreational diving.


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Commercial/military tables worked, but they weren’t ideal. In 1988,DSAT (Diving Science & Technology) introduced the Recreational DivePlanner (RDP),which were the first dive tables designed for planningand making no decompression recreational dives. They were the first(and at this writing, still the only) such tables validated by test divesby volunteer recreational divers — men, women, younger, older, etc.

This remains one of the largest and most extensive decompressiontests in recreational diving. Distributed by PADI, the RDP quicklybecame (and remains) the world’s most popular dive tables; quite afew popular dive computers even employ RDP test data in their elec-tronic decompression models.

It’s available in a Table (conventional) format, and inThe Wheel (circular slide rule) format, in both metricand imperial versions. For divers accustomed to conven-tional tables, DSAT developed the Table version. To sim-plify use and to make multilevel diving possible withouta dive computer (more about multilevel diving in amoment), DSAT developed The Wheel. The eRDP, intro-duced in 2005, is an electronic dive table that gives youthe same information that the RDP Table does. Manypeople find the eRDP’s calculator-type format morefamiliar than a table. You’ll be learning to use one ofthese three versions of the RDP as part of this course.

Dive computers. Dive computers do the same job as theRDP, which is to estimate how much dissolved nitrogenyou theoretically have in your body based on a decom-pression model. Dive computers are no more or lessvalid than a dive table, but take advantage of electronicsto apply the model to your exact dive depths and times,constantly updating you on your allowable dive timeremaining based on your depth. Dive computers are soversatile that today few people dive without them. Theiradvantages include:• They’re more convenient to use than tables because

they track your depth and time automatically. Thisreduces human error.

• They give you more no stop time on multilevel pro-files. As you ascend, you take up nitrogen more slowlyand your dive computer credits you for this by

increasing your available no decompression time. Tables must assumeyou spend the whole dive at the deepest depth you reach, giving youmuch shorter no stop times. The increased dive time offered by a com-puter is substantial and one of the primary reasons you’ll want one.(Note that The Wheel lets you plan multilevel dives with more no stopdive time, making it an excellent backup for your dive computer.However, a dive computer offers more dive time than even The Wheel.)

Chapter Four 201

Milestones.In 1988, Diving Science &Technology introduced theRecreational Dive Planner,which were the first dive tables designed for planningand making no decompressionrecreational dives. The eRDP,introduced in 2005, was thefirst electronic dive tableexclusively for recreationaldiving.

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• They track your theoretical nitrogen through-out the course of an entire dive dive (and oftenlonger). With tables, you have to calculate dif-ferent allowable no stop times for each succes-sive dive, which depends upon the depth andtime of prior dives and how long you’ve beenout of the water. Using the RDP this isn’t diffi-cult (you’ll learn how), but a computer is farmore convenient.

As mentioned, you’ll learn to use the RDP eventhough you’ll dive with a computer the vastmajority of the time. Knowing how your personaldive computer functions as well as being profi-cient with the RDP will allow you to better planand monitor all your diving activities. You’ll learnmore about dive computer procedures in SectionFive.

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OWDM_179_216.qxd 5/12/06 2:47 PM Page 202

Dive tables and computers tell you your nodecompression limit (NDL — the maximumallowable no-stop time at a given depth) based onthe theoretical amount of nitrogen you absorbduring a dive, and they also account for nitrogenyou absorb on previous dives. This is because it

AAllmmoosstt ssttaannddaarrdd..WWiitthh tthhee ccoonnvveenniieennccee aanndd aaddddeedd nnoo ssttoopp ddiivveettiimmee aa ddiivvee ccoommppuutteerr ggiivveess yyoouu,, ttooddaayy iitt’’ss mmoorreeuunnuussuuaall ttoo aa sseeee aa ddiivveerr wwiitthhoouutt oonnee tthhaann wwiitthh oonnee..

nitrogen left in your body after a dive is calledresidual nitrogen. A dive made before you lose allthe residual nitrogen from a previous dive iscalled a repetitive dive.

takes quite a few hours — in theory, sometimeslonger than a day — after surfacing for all theexcess nitrogen to dissolve out of your body. The

The illustration gives you an idea of how thisworks. Before your first dive, your body has itsnormal nitrogen level (A). Upon surfacing, yournitrogen level is higher, even though you’rewithin the safe limits established by your com-puter or table (B). After some time at the surface,your body has eliminated some of the residualnitrogen, but not all of it. You can also see thatyou’re still closer to the maximum limit than you

OOppeenn WWaatteerr DDiivveerr MMaannuuaall

were before your dive, so a repetitive dive will have ashorter no decompression limit (C). After the repetitive dive,you’re still within accepted limits, but your nitrogen levelhas risen and includes the extra nitrogen absorbed duringthis dive, plus the residual nitrogen left from your first dive(D). The RDP and/or your dive computer helps you deter-mine acceptable time and depth limits for your first andrepetitive dives, accounting for theo-retical changes in body nitrogen.

How long you have to wait before adive isn’t a repetitive dive dependson the computer or table. A com-puter tracks theoretical nitrogen forvarying intervals, but it isn’t reallyimportant to know how longbecause the computer accounts for itautomatically.

Using the RDP, if you don’t plan todive for at least six hours, the resid-ual nitrogen has little consequence.On the other hand, if you do plan to dive within six hours,you must account for the residual nitrogen when you planyour dive — and that’s part of what you’re about to learn todo with the Recreational Dive Planner.

General Rules for Using the Recreational Dive PlannerWhether you’re learning to use the Table or The Wheel ver-sion of the Recreational Dive Planner, there are some gen-eral rules to follow:

A

BC

DMAXIMUM NITROGEN LIMIT

SURFACE (NORMAL)

AFTER FIRST DIVE

AFTER SURFACE INTERVAL

AFTER SECOND

DIVE

Excess Nitrogen From Dive #2

Excess Nitrogen From Dive #1

Nitrogen loads.Before your first dive, your bodyhas its normal nitrogen level (A).Upon surfacing, your nitrogenlevel is higher, even though you’rewithin the safe limits establishedby your computer or table (B).After some time at the surface,your body has elimin-ated someof the residual nitrogen, but notall of it. You can also see thatyou’re still closer to the maximumlimit than you were before yourdive, so a repetitive dive will havea shorter no decompression limit(C). After the repetitive dive,you’re still within accepted limits,but your nitrogen level has risenand includes the extra nitrogenabsorbed during this dive, plusthe resi-dual nitrogen left fromyour first dive (D).

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1. Bottom time is the total time in minutes from the begin-ning of descent until the beginning of final ascent to thesurface or safety stop. (Note, for convenience, manydivers use the time they leave the surface until the timethey return to it as bottom time. This is more conserva-tive than the true definition of bottom time, and acceptable.)

2. Any dive planned to 10 metres/35 feet or less should becalculated as a dive to 10 metres/35 feet.

Chapter Four 203

204

• 18 m/60 ft Novice

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3. Use the exact or next greater depth shownfor the depths of all dives.

4. Use the exact or next greater time shownfor the times of all dives.

11.

5. Slowly ascend from all dives at a rate thatdoes not exceed 18 metres/60 feet perminute (.33 m/1 ft per second). Slower is fine.

6. Always be conservative and avoid using themaximum limits provided.

7. When planning a dive in cold water, orunder conditions that may be strenuous,plan the dive assuming the depth is 4metres/10 feet deeper than the actual depth.

8. Plan repetitive dives so each successivedive is to a shallower depth. The large bodyof existing test data primarily involves for-ward profiles, that is, the deepest dive firstand deep to shallow when multilevel div-ing. For this reason, forward profiles (deepdive first) is the recommendation.

9. Limit all repetitive dives to 30 metres/100feet or shallower.

10. Limit your maximum depth to your train-ing and experience level. Scuba Divers arelimited to 12 metres/40 feet. As an OpenWater Diver, limit your dives to a maxi-mum depth of 18 metres/60 feet. Diverswith greater training and experienceshould generally limit themselves to amaximum depth of 30 metres/100 feet.Divers with appropriate experience and/ortraining may dive as deep as 40 metres/130 feet. Plan all dives as no decompres-


• 30 m/100 ft Recommended• 40 m/130 ft Absolute

sion dives and no dive should ever exceedthe maximum depth limit for recreationalscuba diving, 40 metres/130 feet.
Decompression diving falls outside recre-ational diving, and the Recreational DivePlanner was not designed for planningdecompression dives.
Don’t exceed the RDP limits, and when-ever possible avoid diving to the limits ofthe planner. 42 metres/140 feet appearson the RDP solely for emergency purposes— don’t dive that deep.

Chapter Four 205

1. The primary use of dive tables and divecomputers is:a. to tell you the allowable dive time at agiven depth.b. to calculate your air use.

2. No decompression diving means:a. you can ascend directly to the surface atany time without significant risk of DCS.b. you cannot run out of air within the givenlimits.c. you’re within a depth range at which youcannot suffer nitrogen narcosis.

3. A no decompression limit is:a. the maximum time you can spend at agiven depth and still make a no decompres-sion dive.b. the maximum depth of a dive.

4. You should avoid the maximum limits of dive tables and dive computers because:a. people differ in their susceptibility todecompression sickness.b. a random number of tables and computersare inaccurate.

5. The RDP differs from other tables in that:a. it was designed specifically for recreational no decompression diving.b. it was designed to allow recreationaldivers to make decompression dives.

6. Your body nitrogen level is higher after arepetitive dive than if you made the samedive as a nonrepetitive dive because you stillhave nitrogen left from the previous dive.True False.

7. Residual nitrogen is:a. excess nitrogen in your tank left after youuse all the oxygen.b. nitrogen that remains in your body for sev-eral hours after a dive.

8. When using the RDP, if an exact depth ortime doesn’t appear, round to the closestdepth or time.True False

9. Bottom time is:a. the time from when you arrive at the bottom to the time when you leave for the surface.b. the time from when you leave the surfaceto the time when you leave the bottom foryour final ascent to the surface.

10. The maximum depth limit for all recreationaldiving is:a. 18 metres/60 feetb. 40 metres/130 feetc. 60 metres/200 feet

How’d you do?1. a. 2. a. 3. a. 4. a. 5. a. 6. True. 7. b. 8. False,always round up to the next deeper depth ortime. 9. b. 10. b.


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During ascent, your body needs time to adjustto changing pressure, and you need time toregulate your buoyancy, keep track of yourbuddy and watch for obstructions overhead.It’s important to ascend slowly — no fasterthan 18 metres/60 feet per minute, which isslower than you may realize.

As a new diver, you may find it a little difficultto judge your ascent rate at first. No worries.Start your ascent with plenty of air so you canmake a slow, leisurely trip to the surface.Preferably, ascend along a line or follow thebottom contours to give you a visual referenceand help you gauge your speed. Use yourdepth gauge as you ascend to help you knowhow fast you’re going up, particularly whenascending without a visual reference. It shouldtake you at least 10 seconds to ascend 3metres/10 feet — but don’t worry about beingexact, as long as you’re not exceeding this rate.In fact, it’s a good idea to come up slower –most computers and gauges warn you if youexceed 10 metres/30 feet per minute.

Whenever possible, stop your ascent when youreach 5 metres/15 feet and wait three minutes— more is fine — before continuing yourascent, particularly after deep dives or divesclose to the no stop time limit. This is called asafety stop (you’ll learn more about safetystops in Section Five), which gives you anextra margin of safety.

Think of the 18 metre/60 foot per minute rateof ascent as a speed limit. It’s fine to go slower,but don’t go faster. Be a S.A.F.E. diver: SlowlyAscend From Every dive.

In this subsection on Dive Tables and DiveComputers Introduction, you learned:

▲ Dive tables and dive computers usemathematical models to estimate thetheoretical nitrogen in your body before,during and after a dive.

▲ People vary in their susceptibility toDCS, so no computer or table can guar-antee you’ll never get DCS, even withinits limits. So, dive well within table/com-puter limits.

▲ A dive computer has some use advan-tages and disadvantages compared to tables, but it is neither more nor less valid.

▲ Recreational divers only make nodecompression (no stop) dives.

▲ The RDP is the most popular recre-ational dive table, and it is the first onedeveloped and tested exclusively forrecreational diving.

▲ The Wheel and dive computers offer youmore no decompression dive time whenmaking multilevel dives.

▲ You must account for nitrogen youabsorb on a dive if you make a repetitivedive before your nitrogen levels return tonormal.

▲ Stay within the depth limit of your train-ing and/or experience. Generally: ScubaDivers —12 m/40 ft; Open Water Divers— 18 m/60 ft; general recreational limit— 30 m/100 ft; maximum limit — 40 m/130 ft.

▲ Be a SAFE Diver: Slowly Ascend FromEvery Dive.

Summary PointsSummary PointsBe a S.A.F.E. Diver — Slowly Ascend From Every Dive

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Using the Recreational Dive PlannerTurn to the Instructions for Use booklet that comeswith your RDP. If you’re learning to use The Wheel,read the first five sections and work the sample prob-lems. If you’re learning to use the Table, read and com-plete the sample problems/exercises up to “Finding aMinimum Surface Interval.”

Then come back to this manual and pick up with theConfined Water Dive Preview.

Chapter Four 207

By the time you complete the assigned reading in theInstructions for Use booklet forthe RDP (Table or Wheel), youshould be able to answer thefollowing questions:

44. How do you find the NDL forany depth between 0 and 40metres/130 feet using theRecreational Dive Planner?

45. What is a pressure group?

46. How do you find the pres-sure group for a certain divedepth and time using theRecreational Dive Planner?

47. What is a surface interval(SI)?

48. How do you find the pressure group after a surface interval using theRecreational Dive Planner?

49. What is residual nitrogentime (RNT)? [Table versiononly]

50. How do you find residualnitrogen times on Table 3 ofthe Recreational DivePlanner for particular depthsand pressure groups? [Tableversion only]

51. What is an adjusted nodecompression limit?

52. How do you find an adjustedno decompression limit onTable 3 of the RecreationalDive Planner, for particulardepths and pressuregroups? [Table version only]

53. What is a dive profile?

54. In drawing a three-dive pro-file, where do you label:• surface intervals?• pressure groups?• depths?• bottom times?

55. What is actual bottom time(ABT)? — [Table versiononly]

56. What is total bottom time(TBT)? — [Table versiononly]

57. How do you calculate thetotal bottom time of a repeti-tive dive? [Table versiononly]

58. How do you find the finalpressure group after makingmultiple repetitive divesusing the Recreational DivePlanner?

59. What are the two specialrules for repetitive diving?

60. What are the minimum sur-face intervals that must bemade when planning threeor more dives when:• the ending pressure groupafter any dive is W or X?• the ending pressure groupafter any dive is Y or Z?

MAINObjectives

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Although this is a scuba class, you’ll start thisconfined water dive skin diving without scuba —but you’ll be into your scuba gear and back tobreathing underwater soon.

But what does skin diving have to do with learn-ing scuba diving? Actually, quite a bit, becausescuba diving often takes you into circumstanceswhere it might be better to snorkel or skin dive.For instance, you may find some very shallowsites where there’s no advantage to scuba. Or, youmay want to tour a bit with your buddy to see ifit’s worth scuba diving — you can swim muchmore quickly as a skin diver. Sometimes you maywant to dive a site, but the scuba weight and bulkget in the way, such as if diving from a small boatwith maximum passengers.

For skin diving, you’ll use all your equipmentexcept your scuba unit, and you’ll either use lessweight so you’re positively buoyant, or a snorkel-ing vest. Your instructor may have you set upyour scuba gear while you’re gearing up for skindiving so it’s ready to use later.

HyperventilationSince you don’t use scuba for skin diving, you holdyour breath to leave the surface (or not, but you’llbe back in a big hurry). Most people have troubleholding their breath for more than a minute,especially when they’re doing something thattakes lots of energy like swimming underwater.

To hold your breath longer, you can use hyperven-tilation, which temporarily suppresses your urgeto breathe. Intentional hyperventilation is noth-ing more than taking three or four deep, rapidbreaths before a breath-hold skin dive. Afterhyperventilating, it takes longer for you to feelthe urge to breathe, so you can stay down longer.

Confined Water Dive Preview


Here’s what you’ll be able to do whenyou successfully complete ConfinedWater Dive Four:

Note: Skin Diving Skills may be com-pleted on Confined Water Dives Two,Three, Four or Five.

Skin Diving Skills

1. Demonstrate the use of properhyperventilation when skin diving.

2. Dive vertically headfirst from thesurface in water too deep to standup in (without excessive splashingor arm movement).

3. Clear and breathe from a snorkelupon ascent.

Scuba Skills

4. Swim underwater without a mask fora distance of not less than 15metres/50 feet, and replace andclear the mask underwater.

5. Using buoyancy control only, hoverwithout kicking or sculling for atleast 30 seconds.

6. Buddy breathe sharing a single airsource for a distance of at least 15metres/50 feet underwater both as a donor and a receiver.(optional skill)

Skill RequirementsConfined Water

Dive Four

Skill Requirements

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Hyperventilation works because the urge tobreathe comes from rising carbon dioxide in yourbody, not from low oxygen. The three or fourbreaths drop your body carbon dioxide levelsbelow normal, so when you hold your breath ittakes longer for the levels to rise high enough totrigger breathing.

If you’ve never tried it, you may be amazed howwell hyperventilation works — but it’s importantthat you limit it to only three or four breaths.

Excessive hyperventilation — more thanthree or four breaths — can be dangerousbecause you can lower your carbon diox-

ide levels so far that your body runs out of oxy-gen before you get the urge to breathe. Thiswould lead to sudden unconsciousness — with-out warning — and drowning. Don’t hyperventi-late excessively.

Besides limiting hyperventilation to three orfour deep, rapid breaths, rest a minute or sobetween breath-hold dives so your body canrestore its normal oxygen level. If you feelfatigued, dizzy or light-headed, stop divingdown. Float, relax and rest.

You may be familiar with unintentional hyper-ventilation, which results from anxiety orstress, and causes someone to breathe rapidlyand shallowly. This leads to respiratory diffi-culty, and contributes to the overexertion andair starvation problems you learned about ear-lier. By using proper diving techniques, you’llnormally avoid this, but if you find yourselfreacting to stress and anxiety with rapid, shal-low breathing, force yourself to stop, breatheslowly and relax.

Skin Diving Surface DivesTo this point, you’ve made descents in a head-up,feet-down position using scuba equipment. Thisworks fine for scuba diving, but when skin diving

Chapter Four 209

Sans scuba.For skin diving, you’ll use all yourequipment except your scuba unit, andyou’ll either use less weight so you’repositively buoyant, or a snorkeling vest.

Shorter Dive Time LENGTH OF DIVE

Longer Dive Time

With excessive hyperventilation urge to breathe occurs here

With limited hyperventilation urge to breathe occurs here

Without hyperventilation urge to breathe occurs here

Normal

Low

LEVEL OF OXYGEN IN THE BODY

Danger Zone Oxygen Level Too Low to Sustain Consciousness

Avoid the extreme.Excessive hyperventilation — more than 3 or4 breaths — can be dangerous because youcan lower your carbon dioxide levels so farthat your body runs out of oxygen before youget the urge to breathe. This would lead tosudden unconsciousness — without warning— and drowning.

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it takes too long — in all but very shallow water,you’d have to surface to breathe before you everreached the bottom. Since you’re not wearing scuba equipment, you can use a faster headfirst surface dive.

A headfirst surface dive gets you underwater andheaded down quickly with minimal effort. Here’swhat to do: Deflate your BCD (if using one), andthen float face down breathing through yoursnorkel. Begin swimming forward and at the sametime, hyperventilate (not more than three or fourtimes), then hold the last breath. Bend forward atyour waist, thrust your head and arms downward,and simultaneously use your momentum to lift yourlegs above the surface. Get your legs as high andstraight as possible so their weight drives youtoward the bottom. Once your fins submerge, beginkicking, equalizing your ears and mask just like youdo to descend using scuba. You can use your armsfor leverage when you raise your legs for the dive,but once underwater use your fins to swim down. Ifyou’re not using a BCD, you should be somewhatpositively buoyant and need to swim to stay down.

While you’re down, your buddyremains at the surface watchingyou. You do the same when yourbuddy makes a dive. Use this one-up, one-down, buddy techniquewhile skin diving so that if youneed assistance, your buddy, whohas a fresh breath, can come toyour aid.

As you swim along underwater, move slowly to con-serve oxygen. By relaxing and becoming interestedin something, you’ll be surprised how long you cancomfortably stay underwater on a single breath.

When you come up, raise your hand over your head,look up and rotate so you get a complete view of thesurface as you come up. Get in the habit of looking


Head long.To make a head first surface dive,begin swimming forward. Bendforward at your waist, thrust yourhead and arms downward, andsimultaneously use your momentumto lift your legs above the surface.Get your legs as high and straightas possible so their weight drivesyou toward the bottom.

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for overhead obstacles such as boats and other divers.Before you reach the surface, you may be able to clearyour snorkel using a method called the displacementmethod.

Displacement Snorkel ClearingYou can clear your snorkel with the blast method likeyou’ve already learned, but when skin diving you mayfind the displacement method easier. However, it doesrequire a snorkel either without a self drain, or if ithas one, it needs to have a relatively small valve.

Displacement clearing works like this: As you ascendlooking at the surface, your head tilts back, so the topof your snorkel is lower than the mouthpiece. Keepyour head tilted back throughout the ascent by look-ing at the surface and exhale into your snorkel as yourise through the last one to one and a half metres/three to four feet of water. Your exhalation displacesthe water, pushing it out of the snorkel’s opening.

When you reach the surface, continue to exhale asyou roll your head forward into the surface swimmingposition. The snorkel will be clear of water, thoughyou’ll use airway control and take your first breathcautiously, in case a few drops of water remain.

The reason this may not work with a self drainsnorkel is that as you look up and exhale, your airmay exit through the drain valve instead of pushingout the water. It may work when exhaling steadilyusing a snorkel with a small valve because air can’tescape as fast as it comes in, so the snorkel clears. Ifyou can’t displacement clear your self drain snorkelbecause air escapes too easily, don’t worry about it.With the self drain it doesn’t take much effort to blastclear your snorkel anyway.

Sitting Back Roll EntryAfter you’ve practiced your skin diving skills a bit,your instructor will have you get into your scuba gear.You may practice new water entries appropriate todiving in your area, including the sitting back-roll

Chapter Four 211

Look up as you come up.As you ascend looking at the surface, yourhead tilts back so the top of your snorkel islower than the mouthpiece. Keep looking at thesurface and exhale into your snorkel throughthe last one to one and a half metres/ three tofour feet of water. Your exhalation pushes thewater out of the snorkel’s opening.

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entry. This is a good method when divingfrom a low, unstable platform such as asmall boat or raft.

To accomplish a sitting back roll entry, firstmake sure all your equipment is in placeand that your SPG or other hoses aren’tsnagged or hooked on something. Next,check the entry area to be sure it’s clear. Siton the edge of the platform with your BCDabout half inflated and your regulator inyour mouth. Hold your mask firmly in place,and lean back, so you roll gently into the

water. Keep your legs tucked close to you during the entire entryso they don’t strike the platform edge as you go. You may feelmomentary disorientation (it’s kind of exhilarating), then yourbuoyancy brings you to the surface. Let your buddy know you’reokay and clear the entry area.

No-Mask SwimmingIn the last confined water dive, you practiced breathing underwa-ter without your mask, which doesn’t do much for the view, but it’simportant to know in case your mask were to come off completelywhile diving. (Which, about half the time, results from swimmingtoo close to your buddy’s fin tips.) Since you might have to swim tothe surface without it, or to your buddy to get help finding it, inthis session you’ll practice by swimming at least 15 metres/50 feetunderwater without your mask.

Remember to concentrate on breathing through your mouth andnot your nose, and to exhale through your nose if you need to pushwater out. During your swim, open your eyes because even with-out your mask you can usually see well enough to tell whereyou’re going. With contact lenses, however, keep your eyes shutand have your buddy guide you. In a real mask-loss situation, youmight have to risk losing a lens, but there’s no reason to do so dur-ing this dive.

Buoyancy Control — HoveringYou’ve been learning to control your buoyancy in each confinedwater dive, which as you recall helps you avoid stirring up the bot-tom, damaging aquatic life and wasting energy. First you learnedthe basics— proper weighting and BCD use. Then you learned to


For low unstable platforms.When using a sitting backroll entry, keep your legstucked close to you duringthe entire entry so they don’tstrike the platform edge asyou go.

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fin pivot. Now you’ll demonstrate the nextmastery level by (drum roll please) hoveringmotionless in midwater.

To hover, first adjust for neutral buoyancy onthe bottom (you’ll probably use the fin pivot).Once you’re neutrally buoyant, push gently offthe bottom just about a metre/a couple of feet.Then, without holding your breath, use lungvolume to maintain a stationary position inmidwater. If you begin to rise a bit, decreaseyour buoyancy by breathing with your lungssomewhat less full. If you begin to sink a bit,

increase your buoyancy by breathing with your lungs a little fuller.It helps to have a stationary visual reference to judge whetheryou’re rising or sinking, so you may want to do this near a poolside, next to a line, or anything else that gives you this reference.You can fold your legs under you, stretch out, whatever works.

As you gain experience diving, you’ll subconsciously and automati-cally adjust your buoyancy so you remain off the bottom and canstop and hover without even thinking about it. It only takes a lit-tle practice, and you’ll find hovering easy.

Buddy BreathingIn Section Three, you learned about the options you have in theunlikely event you run out of air, and you’ve practiced your twoprimary options, using an alternate air source or making a con-trolled emergency swimming ascent. Another option you may prac-tice (at your instructor’s discretion) is buddy breathing, whichrequires you and your buddy to share a single second stage.

Buddy breathing is a less desirable option than the other optionsbecause it is a more complex skill, which increases the possibilityof error. By remaining close to your buddy and making certain you and your buddy always equip yourselves with alternate airsources, you shouldn’t ever need to buddy breathe. However, itremains a practice in a few areas, so your instructor may have youlearn it.

To initiate buddy breathing, swim to your buddy and signal “out ofair” and “share air.” Your buddy should respond by passing you thesecond stage and allowing you to take two breaths. Your buddy

Chapter Four 213

No strings or wires.To hover, adjust for neutralbuoyancy and push gentlyoff the bottom just about ametre/a couple of feet. Then,without holding your breath,use lung volume to maintaina stationary position inmidwater.

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will not let go, but will hold the second stage by the hose near themouthpiece without covering the purge button (so you can use it ifyou need to).

As you begin buddy breathing, you andyour buddy grasp each other face-to-facefor stability. Your buddy holds the secondstage with the right hand and grasps yourBCD or tank straps with the left. Yougrasp your buddy similarly with your righthand and guide the second stage to yourmouth with your left.

After your two breaths, your buddy takesthe second stage back. Remember not tohold your breath and to make an aaaahhhsound, blowing bubbles, when the regula-tor isn’t in your mouth. Your buddy takes

two breaths and returns it to you for two breaths. Continue theexchange back and forth until you and your buddy establish a nat-ural, relaxed rhythm.

Once you’ve got the rhythm set, you and your buddy would ascendto the surface, buddy breathing all the way. Your instructor mayhave you practice buddy breathing first in a stationary position,and then swimming along the bottom to simulate how long itwould take to ascend while buddy breathing.


Two, then two.When buddy breathing,remember not to hold yourbreath and to blow bubbles,when the regulator isn’t inyour mouth. Your buddytakes two breaths andreturns it to you for twobreaths.

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Chapter Four 215

Knowledge Review—Chapter 4

Knowledge Review—1. A detailed log book is the proof-of-experience documentation typically requested in

many dive situations. Check those listed here.

a. for additional diver trainingb. by dive stores when buying dive equipmentc. when diving at resorts or on boats

2. Explain how to prevent problems with contaminated air.

3. State the two ways divers prevent problems with oxygen.

a. ____________________________________________________________________________

b. ____________________________________________________________________________

4. Check each symptom related to nitrogen narcosis:

a. impaired coordinationb. foolish behaviorc. joint and limb pain

5. Check one. To prevent nitrogen narcosis:

a. skip breathe.b. equalize your air spaces early and often.c. avoid deep dives.

6. Check each symptom which may be related to decompression sickness:

a. foolish behaviorb. moderate tinglingc. cherry-red lipsd. weakness and prolonged fatigue

7. Outline the first aid procedure for assisting someone with decompression illness.

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8. True or False. When using either version of the Recreational Dive Planner, you mustascend at a rate that does not exceed 18 metres/60 feet per minute. ______________

9. Match the following by placing the correct letter in the blank.

____________ Maximum depth limit for Open Water Divers

____________ Maximum depth limit for divers with training and experiencebeyond the Open Water Diver level

____________ Maximum depth limit for divers with Deep Diver training

a. 18 m/60 ft b. 40 m/130 ft c. 30 m/100 ft

10. According to the Recreational Dive Planner, the no-decompression limit for 18 metres/60 feet is ________ minutes.

11. What is your pressure group after a dive to 12 metres/42 feet for 24 minutes?

__________ Pressure Group

12. After a dive, you are in pressure group K. What will your new pressure group be aftera 34-minute surface interval?

__________ Pressure Group

13. A diver in Pressure Group G plans a dive to 17 metres/56 feet. What is the maximumallowable bottom time according to the Recreational Dive Planner?

__________ Maximum Allowable Bottom Time

14. Indicate the final pressure group upon surfacing after the following series of dives.First dive: 16 metres/50 feet/23 min.; surface interval: 1:30.Second dive: 10 metres/35 feet/46 min.

Final Pressure Group = ____________

15. Indicate the final pressure group upon surfacing after the following series of dives.First dive: 18 metres/60 feet/15 min.; surface interval: 1:00.Second dive: 12 metres/40 feet/30 min.

Final Pressure Group = ____________

Student Diver Statement: I’ve completed this Knowledge Review to the best of my ability,and any questions I answered incorrectly or incompletely I’ve had explained to me, and Iunderstand what I missed.

Name ________________________________________________ Date ________________________

Knowledge Reviews may not be reproduced in any form without the written permission of the publisher.

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