PADI theory

What is the pressure change for each 10m/33 feet of depth change?

* increases by 1 bar/ata every 10 m/33 feet when descending in water
* opposite is true for ascending in water

What is the relationship between pressure, and the volume and density of air?

* as you go deeper and pressure increases, the gas volume decreases because the molecules become compressed and this causes the density to increases → the same amount of molecules but in a smaller space
* air volume and density change proportionately with pressure

If I take a volume of air from one depth to another depth, how much will the volume and density change?

e.g.

* 0m to 10m → the pressure increases (1 bar to 2 bar), the volume of gas halves (1 to 1/2) and the density increases (1 to 2).
* 10m to 20m → pressure increases (2 bar to 3 bar), volume of gas decreases (1/2 to 1/3) and density increases (2 to 3)

How is pressure measured in metric?

bar

How is pressure measured in imperial?

atmosphere

What is the total pressure at 0m/ feet (sea level)?

1 bar/ata

What is the total pressure at 10, 20, 30 and 40m?

* 10m → 2 bar/ata
* 20m → 3 bar/ata
* 30m → 4 bar/ata
* 40m → 5 bar/ata

Why doesn’t the volume and density of water change with pressure changes?

because water can’t be compressed

Why don’t we feel pressure changes on most of our body when diving?

because our body tissues are mostly made of water

What 3 major air spaces does increasing pressure affect as I descend?

* ears
* sinuses
* mask

What is a ‘squeeze’?

* causes discomfort and injury by pressure imbalance (pushes tissues into an air space)
* happens because pressure outside air space is greater than inside
* e.g. discomfort in ears is from an ear squeeze

What is ‘equalization’ and how do I equalize as I descend?

* equalization is the act of adding air to the air spaces as you descend
* to equalize ears and sinuses, block nose and blow gently against it → could also swallow (all these send air from throat into sinuses and ears)
* to equalize mask, blow air into mask from nose

How often should I equalize?

* every metre before you feel discomfort → prevents discomfort and pain if done as often as you should
* if you equalize as or after you feel discomfort equalization may be impossible

What should I do if I can’t equalize? What could happen if I don’t or can’t equalize and keep descending?

* stop descent immediately and signal buddy/instructor → signal problem and point to ear
* ascend slightly until discomfort passes and try again → after you equalize, descend more slowly and equalize more frequently
* if still can’t equalize, stop dive

Why should I equalize gently?

* never attempt forceful or prolonged equalization
* these can cause serious damage to your ears and hearing
* use short, frequent equalizations

Why does congestion from a cold or allergy temporarily keep me from diving? Why should I never dive with earplugs?

* congestion can block normal air flow and make equalization difficult/impossible → cold medicines will wear off mid dive
* earplugs create an airspace that you can’t equalize

What other body spaces are affected by increasing pressure? How do I equalize them?

* air space under filled tooth → stop descent and dive. see dentist to get it fixed

Why does increasing pressure affect air spaces in and in contact with your body?

it compresses the air in the space

What is the most important rule in scuba diving?

breathe continuously and and **never** hold your breath → otherwise lung overexpansion (paralysis and death)

What can happen if you don’t follow the most important rule in scuba diving?

* if breath held while ascending, decrease in pressure would cause air in lungs to expand and cause a lung rupture → this is because air breathed in from scuba gear matches depth diving to
* even small pressure changes can cause these injuries (e.g. 10m ascent)

What is a ‘reverse block’?

* AKA reverse squeeze
* when expanding air becomes trapped in a body air space

What should I do if I feel discomfort in my ears, sinuses, stomach, intestines or teeth while ascending?

* immediately slow and stop you ascent
* descend a metre to reduce discomfort and give trapped air a chance to work its way out
* Ascend more slowly

What should you do if you don’t have your regulator in under water?

breathe a long, slow breath out so you’re not holding your breath

What should you do if you have lung congestion?

* don’t dive
* cause overexpansion injuries in lungs

What causes buoyancy?

caused by the water displaced by the object and is equal to the weight of the water displaced

What is positive, negative and neutral buoyancy?

* positive → when an object weighs less than the water is displaces = floats
* negative → when an object weighs more than the water it displaces = sinks
* neutral → when an object weighs the same as the water it displaces = neither sinks nor floats

Why does salt water cause more buoyancy than fresh water?

* salt water has dissolved minerals (salt) in it so a given volume of salt water weighs more than fresh water
* therefore, because salt water weighs more, more buoyancy

What 2 pieces of equipment are used to control buoyancy?

* weight system → holds just enough lead weight to offset your +ve buoyancy
* Buoyancy Control Device (BCD)

How does breathing affect buoyancy?

* inhale → chest expands, volume increases, increased water displacement = increased buoyancy
* exhale → chest contracts, volume decreases, decreased water displacement = decreased buoyancy

Why is it important to master buoyancy control?

it affects everything divers do, in and underwater

What is the buddy system?

diving with another diver/s in a team that provides shared assistance and safety benefits

What are 3 overall benefits of the buddy system?

* practicality → assist each other before, during and after dive
* safety → help each other prevent problems and assist each other if there’s an emergency
* fun → diving is social so rewarding to have someone to share underwater adventures with

What are the 3 most important considerations in choosing scuba equipment?

* suitability → appropriate for you and the dive
* fit → equipment sized and adjusted for you
* comfort → you can wear the item for an hour or more without a significant distraction due to its feel or configuration

What are 4 secondary considerations when choosing scuba equipment?

* cost and features
* serviceability
* colour and style
* accessories

How do I generally care for scuba equipment?

Different pieces of scuba gear have specific care requirements, but all items have the following steps in common:

* inspect equipment for proper wear, operation and damage before use
* rinse everything thoroughly with fresh water after being in salt water, chlorinated or fresh water with dirt or silt → allow to dry out of sun
* avoid leaving kit exposed to direct sunlight for extended periods and cover up between dives
* some items require periodic professional inspection → these items should be serviced regularly
* follow maintenance specified by manufacturer

Why do you need a mask?

to see clearly underwater → eyes only focus properly in air space which is created by mask

Why does a mask need to enclose the nose?

* mask creates air space that needs to be equalised
* nose enclosed so air can be blown into mask to equalise

What features should be considered when choosing a mask?

* low profile → sits as close to face as possible but still fits (wider vision field and requires less air for clearing of water and equalising
* wide vision field → special shapes to accommodate wider field view
* silicone colour → clear silicone rubber (‘open’ feel) or reduced glare black
* frame colour → can match to rest of kit

How do you check the fit of a mask?

* place mask gently against face and inhale slightly through nose
* should stay in place with light suction without pushing to make seal

How is a new mask prepared for diving?

* scrub interior glass with mask cleaner → removes protective chemicals that increase fogging (not true of all masks)
* adjust strap → fit over crown of head, above ears and tighten for snug but not overly tight fit

Why do you need a snorkel?

conserve your air supply when at surface and you need to breathe with your face in the water

What features should you consider when buying a snorkel?

* flexible lower portion → mouthpiece drops out of way when not in use


* self-drain valve → easier to blow water out of snorkel
* splash guard → reduces water that splashes in during use
* colour → match to other gear

How do you prepare a snorkel for diving?

Adjust it to fit comfortably in your mouth with the top at the crown of your head

Which side of the mask does the snorkel go on?

left

Why do you need fins?

provide large surface area for leg muscles to push against so can move efficiently through water

What are the 2 basic fin styles?

* adjustable-strap → open at heel with straps (used with wet suit boots)
* full foot → enclose heels. best for warm water swimming

What features should I consider when buying fins?

* fit
* blade size

What four equipment systems combine to make scuba kit (scuba unit), and what is the purpose of each?

1. BCD (buoyancy control device) → holds kit together and controls buoyancy
2. regulator → delivers breathing air at surrounding pressure when you inhale and directs exhaled air into the water
3. cylinder → holds high-pressure breathing air supplied by regulator during the dive
4. weight system → holds lead weight to counteract positive buoyancy of body and equipment with mechanism for dropping some/all of weight in emergency

\n What should I consider when choosing my scuba kit?

* size
* preferences
* type of dive adventures and how it fits in with equipment you have/will have
* get integrated kit (all sold put together as although equipment interchangeable, easier to have professional advice)

What are the 2 cylinder positions and what are they?

* on back → 1 cylinder on your back
* sidemount → 1 - 2 cylinders on your side

What five components make up a BCD, and what does each do?

* **inflatable bladder** → durable bag that inflates/deflates to control buoyancy
* **cylinder band and harness/jacket** → bladder integrates with harness that holds cylinder on back
* **LPI (low pressure inflator) mechanism** → usually at end of wide-diameter hose. Inflates bladder with air from cylinder via regulator, when you press a button. Another button allows you to deflate bladder/inflate orally
* **overpressure/quick exhaust valves** → automatically vent BCD if too full to prevent rupture
* **weight system** → weight pockets that can be released and dropped in emergency

What considerations and options do I have when choosing a BCD?

* buoyancy capacity → enough buoyancy to easily float you and your equipment at surface
* pockets and d-rings
* shoulder quick release → easier to get out of kit
* colours and styles

How do I prepare my BCD for use?

* adjust to fit snug while wearing suit
* fully inflate to make sure doesn’t restrict breathing
* attach whistle near LPI
* attach hose retainers for regulators (as necessary)

What two special maintenance considerations do BCDs have?

* rinse inside of bladder with fresh water → 1/3 water, 2/3 air, slosh and then drain through LPI exhaust
* store partially inflated → keeps bladder from sticking together

What five components make up a regulator, and what does each do?

1. hub → supplies air to components. connects to cylinder valve. reduces air pressure to intermediate pressure (above surrounding pressure)
2. second stage → part breathe from → lowers pressure from first stage (hub) and provides air on demand
3. alternate air source → extra second stage for sharing air w/ buddy
4. LPI hose → supplies air to BCD inflator
5. The SPG (submersible pressure gauge) /computer → indicates air pressure remaining in cylinder in bar or psi

What is the most important consideration in choosing a regulator? What considerations and options do I have when choosing a regulator?

* most important → **ease of breathing**
* yoke or DIN → yoke system holds 1st stage to cylinder with clamp; DIN system regulator threads into valve (higher pressure rating) → can choose DIN regulator with yoke adapter so can use on either valve type
* Adjustable second stage → knob allows small air flow adjustments (keeps regulator breathing best)
* Dive/predive switch → reduces freeflow ( air released w/out control) when 2nd stage not in mouth
* cold-water 1st stage → 1st stage can freeze = freeflow. cold-water regulators reduce this likelihood by surrounding 1st stage with special liquid

What are my considerations and options when choosing an alternate air source?

* simplicity → extra 2nd stage and/or alternate inflator regulator as part of regulator
* independence → self-contained ascent bottle or pony bottle. can manage air supply without buddy assistance

What are my considerations and options when choosing an SPG?

* dive computer → if not air-integrated, standard mechanical SPG used; if part of air-integrated computer on hose it will attach similarly to non air-integrated, unless it is wireless in which case SPG on wrist
* SPG may be independent or combined with other instruments in a console
* secures to left side of BCD in hip/torso area

How do I prepare my regulator for use?

* have scuba professional attach components to their ports
* \

Where do I place or secure each regulator component when diving? Why is this important?

* primary 2nd stage comes over right shoulder and isn’t secured bc normally in mouth
* alternate air source attaches with quick release → don’t let dangle bc could fill with mud or sand and cause damage → placement, marking and quick release important so buddy can locate it quickly if needed
* SPG w/ hose under left arm and secures with a clip/hose retainer or route through BCD jacket sleeve → don’t let dangle bc cause damage and creates drag

What three special maintenance considerations do regulators have?

* rinse w/ gentle fresh water flow with first stage dust cap firmly in place → stops water entering air inlet
* run water through second stages but don’t press purge button → could cause water to flow up hose to first stage
* require professional overhauls every 1-2 years

When should you have your submersible pressure gauge’s accuracy checked?

when it doesn’t read zero while unpressurised

What two components make up a scuba cylinder? What does the burst disk do?

* the cylinder
* the valve → controls air flow to and from cylinder
* burst disk → relieves accidental overpressure by rupturing and releasing air

What considerations and options do I have when choosing cylinders and valves?

* **material** → ^^aluminium^^ (resists corrosion in wet climates) and ^^steel^^ (holds same amount of air w/ smaller size + pressure)
* **size and capacity** → metric refer to size by ^^internal liquid capacity^^ (e.g. 8 litres). imperial refer to amount of ^^air held when full^^ (e.g. 50 cubic feet)
* **yoke or DIN** → good option is cylinder with DIN valve that accepts yoke insert so can be used for both types of first stage valves
* **reserve or non-reserve valve** → reserve valves restrict air when only 20- 40 bar remains (not common as used to alert diver of air level before use of SPG)

What do the markings on a cylinder tell me?

* cylinder alloy → code number
* serial number → record in case cylinder lost/stolen
* working pressure → max. fill pressure
* manufacturer’s identification
* manufacture date
* test pressure → pressure used for hydrostatic tests
* hydrostatic test date → at least one with added dates over time

What three safety precautions for handling scuba cylinders should I follow?

* lay unattended cylinder down with BCD facing up
* secure cylinders when transporting → don’t let slide
* keep cylinders secured on boats w/ restraining cord

What six special maintenance considerations do cylinders have?

* test cylinder pressure at required intervals
* visually inspected annually
* close and open valve gently
* never completely empty cylinder (prevents moisture) → draining air quickly can also create condensation
* store in standing position in safe place where won’t get knocked over
* keep out of high heat → raises pressure and could blow burst disk

Where do I get scuba cylinders filled? Why?

* reputable scuba air station
* scuba air must be specially filtered and filled by compressors specifically designed for breathing air → without filtering may be thing in air that are toxic at high pressure

What is the most important feature in my weight system?

quick release → enables you to drop weight in an emergency

In an emergency, is it necessary to drop all my weight?

* when wearing full wet suit or dry suit, only dropping some of weight should be enough
* when wearing no exposure suit or partial wet suit, drop all weight

What is trim? Why is it important?

* trim is orientation and balance in the water → desired trim is natural horizontal swimming position
* helps to maintain optimum body position in water, save energy and reduce accidental damage to fragile organisms

Why might I use more than one weight system?

* help distribute weight
* when wearing buoyant exposure suit (dry suit) easier to handle 2-3 weight systems than 1 heavy one

What are my considerations and options when choosing one or more weight systems?

* preferences
* weight required
* trim requirements
* weight-integrated BCDs most common so will mostly likely choose weight when buying BCD

→ popular bc simplify kitting up, eliminate separate piece of equipment, provide more comfort and include trim pockets

How does being underwater affect the apparent size or distance \n of things?

magnifies things by about a third

How does water affect light intensity and colour?

* water absorbs some wavelengths of light before others
* the deeper you go red is lost, then orange, yellow, green and blue
* colour loss also occurs when looking at far away objects

How does hearing differ underwater?

* transmits sound more efficiently than air so
* underwater sounds travel longer distances as travels faster than in air
* sounds sound like they’re coming from all around

How do I move efficiently as a diver?

* move slowly and steadily
* avoid rapid/jerky moves

How does streamlining benefit me as a diver?

* reduces drag → use less energy
* helps save air

Why is trim important to streamlining, moving efficiently and protecting the underwater environment?

* if not enough weight, will use more energy kicking down to stay at depth with feet above head
* if too much weight, will inflate BCD which will cause head to go up and feet to point down and increase drag

What skill allows me to use water’s density to make moving in water more efficient?

* neutral buoyancy

How does water’s density affect moving in water?

* water more dense than air so movement takes more effort
* tire faster because have to use more energy to move

Why do I chill faster in water than in air at the same temperature?

water absorbs more heat than air of the same temperature and at 20 times the rate air does

What do I do to stay comfortably warm while diving?

* choose an appropriate exposure suit to insulate you
* this depends on the temperature of the water and how long you plan to dive for

What should I do if I’m not warm enough while diving?

end the dive and use more exposure protection next time

What should I do if I start shivering uncontrollably?

* exit water
* dry off
* seek warmth

What is the most effective way to breathe while diving? Why is it important?

* slowly and deeply → more dense air takes more effort to breathe
* important for effective gas exchange
* if breathe rapidly and shallowly, will inhale more dead air as diving creates dead air space

What is “airway control”? What are two techniques for it?

* airway control is skill of breathing past residual water in regulator without drawing it into your throat
* 2 techniques → inhale slowly and hold tongue to roof of mouth (helps to look down with both these methods and can use both at the same time)

What are eight symptoms of overexertion while diving?

* panic
* fatigue
* muscle cramping
* headaches
* anxiety
* laboured breathing
* weakness
* a feeling of suffocation or air starvation

What causes overexertion while diving? How do I prevent it?

* prolonged elevated effort (e.g. fighting a current)
* caused by trying to breathe air rapidly, faster than the equipment can provide it
* prevent by avoiding lengthy, strenuous activity while diving

What should I do if I think I’m becoming overexerted at the surface and underwater?

* surface → inflate BCD and/or drop weights. signal boat to pick you up
* underwater → hold onto something or rest at bottom here you won’t damage marine life. after restoring normal breathing, resume activity at lower pace

How do my buddy(ies) and I plan dives together? What nine points should a dive plan normally include?

* discuss what you want to accomplish, best techniques, hazards and what to do if problems occur


1. discuss which entrance and exit techniques are best for the environment
2. decide what course you’ll follow
3. agree on maximum time and depth
4. review underwater signals and other communications
5. Determine when you will turn the dive and head back based on your remaining air, time and/or other factors
6. Agree on how you’ll stay together during the dive
7. Establish what you will do if you become separated
8. Discuss emergency procedures
9. Agree on an objective

How do my buddy(ies) and I kit up together?

* gear up at same time
* assist with zipping exposure suits, adjustments, holding scuba kits for each other, etc.

How and when do we conduct the predive safety check?

* when kitted up (except for mask, snorkel, fins)
* ‘Begin With Review And Friend’ (BWRAF)


1. Begin -B- BCD → check adjustment, LPI attachment, how to operate and that cylinder is firmly in band → Confirm that your visual and audible surface signalling devices, which are usually attached to your BCD or in a BCD pocket, are in place
2. With - W - Weight → check that you have right amount of weight, that it’s correctly distributed for trim and that the quick release is clear
3. Review - R - Releases → confirm everyone’s releases are secure and that all buddies know how to work each others releases in case of emergency
4. And - A - Air → test breathe regulator (2 - 3 breaths). check air pressure to be sure cylinder full. All buddies make sure they know how to find each others AAS
5. Friend - F - Final Check → check each other over for anything out of place, missing or not adjusted properly

What do I do if I get separated from my buddy(ies) during a dive?

* look for each other for no more than a minute and if unable to locate each other, ascend and reunite on the surface
* may not be possible in some circumstances so important to plan what to do before dive

Whose responsibility is the buddy system?

mine/ours

What’s the rule of thumb for buddy distance?

to be able to reach each other in 2 seconds

How do my buddy(ies) and I manage our air supply together while diving?

* share air supply information and turn and end the dive depending on who’s using air quickest

Why is it a good habit to keep my mask on and a snorkel or regulator in my mouth while at the surface in water too deep in which to stand?

* under stress you do what yo usually do by habit
* therefore the habit of having your regulator in and mask on helps you to see and breathe effectively underwater if you need to without wasting time trying to put your equipment on
* also protects vision and airway from unexpected waves

What are three reasons why I may swim on the surface while scuba diving?

1. to save air when entering the water some distance from where you want to ascend/descend → snorkel on surface so don’t lose air
2. save air while looking for where you want to descend → snorkel on surface so don’t lose air looking for particular spot
3. may surface away from exit point and swim to it on the surface

What are two methods for surface swimming while scuba diving?

* swimming face down breathing through snorkel → good for when you want to see the bottom
* swim on back with head out of water and breathe through snorkel