AIM OF NOVICE DIVER TRAINING
NOVICE DIVER
To train a person to be competent in the safe and correct use of aqualung diving equipment in a sheltered water training area...
NOVICE DIVER II
and then to introduce the dtudent to open water diving with all appropriate equipment, in the company of a Dive Leader or more highly qualified diver / instructor.
| Code | Subject | Duration |
|---|---|---|
| NT1 | Introduction to Driver Training | 60 Minutes |
| NS1 | Diving Skills - Part1 | 60 Minutes |
| NT2 | Pressure and Buoyancy | 60 Minutes |
| NS2 | Diving Skills - Part 2 | 60 Minutes |
| NT3 | Diving Equipment | 60 Minutes |
| NS3 | Diving Skills - Part 3 | 60 Minutes |
| NS4 | Snorkelling Skills | 60 Minutes |
| NS5 | Diving Skills - Part 4 | 60 Minutes |
| NS6 | Water Confidence Test | 30 Minutes |
| NS7 | Diving Skills Assessment | 60 Minutes |
| NT4 | Safe Diving Practices and Diver Rescue Part 1 | 60 Minutes |
| NS8 | Diving Skills - Part 5 | 60 Minutes |
| NT5 | Introduction to Decompression Tables | 60 Minutes |
| NS9 | Diving Skills - Part 6 | 60 Minutes |
| NT6 | Novice Diver Theory Test | 30 Minutes |
| NS10 | Novice Diver II Open Water Dive No 1 | 90 Minutes |
| NS11 | Novice Diver II Open Water Dive No 2 | 90 Minutes |
Novice Diver qualification is issued on successful completion of all lessons up to and including NT 6 and NS 9.Novice Diver II qualification is awarded to holders of the Novice Diver qualification once they have successfully completed the two Open Water Dives NS 10 and NS 11.
The Novice Diver Course should follow this sequence, but so long as safety and logical progression are not compromised, BS-AC Branches and Schools are permitted to vary the order of presentation. Also, limitations on the availability of classroom or pool time may require some lessons to be sub-divided.
THE PURPOSE OF THIS WORKBOOK
This Workbook contains Study Notes for all Theory and Practical Lessons which make up the BS-AC Novice Diver Course. Theory Lessons appear first, followed by Practical Lessons. Lesson durations indicate the time spent actually under instruction and do not include time for assembly, preparation, changing for / after water sessions, and the like: nor do they include student study time.Please note that private study of this workbook, and the BS-AC Diving MAnual Sport Diving, is a necessary part of the Course.Failure to undertake private study means that your rate of learning will be slower, and this might hold up other students in your class.
Good luck.Enjoy the Course!
NOTES ON THEORY LESSONS
While diving is essentially a practical activity, knowledge of the underlying theory is necessary for your safety and greater enjoyment of the sport. Theory training tells you why: practical training teaches you how.The Achievement Target summarises what you will learn during the lesson.In the Novice Diver Course, theory lessons cover only the things you need to know. As you advance your BS-AC diving qualifications, you will be taught more about the same subjects, but in greater detail as befits the higher qualification.
If you study this Workbook, and appropriate referances in the BS-AC Sport Diving Manual, before each theory lesson, you go to the lesson with some knowledge of the subject. The lesson is then more of a 'review' and an oppertunity for the instructor to help you understand those points which confuse you. You should take this Workbook to all theory lessons.
Before and after lessons, try the test questions on the concluding page of each lesson. Answers are given in the back of the book. If you are successfull, you are learning well. If not, you can highlight those areas where help and further explanation from your instructor will put things right.
Towards the end of the Novice Diver Course, you will have to take a simple theory knowledge test, which uses questions of the same type and standard as those in this Workbook. Review lessons and repeat the end of lesson tests as you prepare for this test.
NOTES IN PRACTICAL LESSONS
The Achievement Targets summarise what you will learn during the lesson. The Objective explains why you need the skill.Advice gives you hints and tips aimed at helping you achieve success quickly. By studying these practical lesson notes and associated referances in Sport Diving beforehand, you will have better understanding of what you are about to learn and will be able to mentally visualise what you will have to do. This should speed up your learning process.
Safe diving depends on the ability to use a range of equipment eficiently. The Novice Diver Course concentrates on teaching the basic skills needed to go diving in open water with an experianced leader. Each skill will be demonstrated by the instructor; you then mimic the demonstration while the Instructor watches. Corrective instruction will be given if necessary and after further supervised repetitions, you will be able to perform the skill to a satisfactory standard. You then move on to learn the next new skill.
The contents of practical lessons may appear to be repetitive. There are a limited number of skills to be learned but for an activity which takes place in an environment which does nt support human life, they must be practiced until correct responses are instinctive. Regular repetition during lessons, and at any other opportunity, achieves this.
AQUALUNG EQUIPMENT
The modern aqualung system includes the buoyancy compensator (BC) and this training programme assumes use of one for all Practical Lessons. To avoid confusion in this Workbook between the words aqualung mouthpiece (regulator second stage) and BC mouthpiece, the term demand valve will refer to the aqualung mouthpiece and the initials BC will always preceed the word when referring to the BC mouthpiece. The abbreviation D/F will be used for Direct feed : AAS for Alternative Air Source.
Since procedures given in NS 1.1 - 3 and NS 1.12 - 13 for checking equipment, assembling, testing and putting on the aqualung and BC; for briefing and buddy checks: and for removing and dismantling and caring for equipment after the lesson, are common to all Practical Lessons, they will not be repeated in detail in subsequent lesson texts.
Underwater, an aqualung system is normally just a negatively buoyant. An aqualung diver without a diving suit should be able to reach neutral buoyancy (weightlessness) within the span of breathing, without a weightbelt: a little air may be needed in the BC to achieve it. Only when wearing some form of buoyant diving suit are you likely to need a weightbelt.
Yet, if no weightbelt is worn during training, how can you learn to dump one in an emergency? For some exercises in BC use and Buoyancy Control, the instructor may choose to require use of weightbelts, to make students negatively buoyant so that kills can be effectively learned.Remember: if in distress or if you require an immediate return to neutral / positive buoyancy, dump the weightbelt.
For safety and well-being during practical lessons and future diving, you are advised to follow these recommendations:
GENERAL NOTE
When transferring membership from one BS-AC Branch to another, or when joining a Branch after training with a BS-AC School, you may be asked to demonstrate your competence as a diver before you are allowed to take a full active part in diving activities according to your qualification. Branches are allowed to make such judgements in the interests of the safety of all members.
Achievement Targets
On completion of this lesson and subject study, you should know:
1.INTRODUCTION
The British Sub-Aqua Club. (Sport Diving 6, 244 - 246. New Member Welcome pack)
Formed in 1953 in order to promote underwater exploration, science and sport, BS-AC is the UK governing body for for underwater swimming, with membership of some 50,000 in about 1,000 Branches.It is the largest diving club in the world; about 15% of membership is in overseas Branches. BS-AC is a founder and leading member of the World Underwater Federation(CMAS).
As a national body, BS-AC is managed by an elected Council nominated from Branches and elected by membership. BS-AC has it's own headquarters in Cheshire, where full-time staff carry out day-to-day business of the club.
BS-AC Diver training is available from two sources:
About this Branch/School (Students: write your own notes / details here)
Our Title is .............................................................................................................................................................................................
Brief history of Branch/School ...........................................................................................................................................................
Branch run by elected committee [School by proprietor]. Branch [School} Officers are:
Chairman [Proprietor] ...........................................................................................................................................................
Diving Officer [Chief Instructor] ...........................................................................................................................................................
(Branch Training Officer) ...........................................................................................................................................................
Secretary .............................................................................................................................................................................................
Treasurer .............................................................................................................................................................................................
Branch Diving Officer [Chief Instructor] is responsible for organising and arranging training and open water diving. If you have any questions or matters concerning training or qualification, discuss them first with your Instructors, and subsequently with the D.O [C.I] if necessary.
Refer questions concerning Membership, Diver Magazine, etc., to Secretary or Treasurer. Other matters to appropriate committee members.
Branch [School] Meetings take place at (time / place)
Classroom Lessons ...............................................................................................................................................................................
Pool Training ........................................................................................................................................................................................
Social Meetings ....................................................................................................................................................................................
BS-AC Membership Services (a) from the Branch.
BS-AC Membership Services (b) from the national body.
2.NOVICE DIVER TRAINING
Aim of Novice Diver Training: to train a person to be competent in the safe and correct use of all appropriate open water aqualung diving equipment in a sheltered water training area, and then (Novice Diver II) to introduce the student to open water diving in the company of a Dive Leader or more highly qualified diver / instructor.Novice Diver Training involves some 5.5 hours of theory instruction and 8.5 hours of practical instruction.Novice Diver II open water dives involve a further 3 hours of practical activity. These times do not include time for changing, travelling between facilities, etc., nor for your own private study of Workbook and Manual, which is an important part of the learning process.
If training is to run smoothly and efficiently, your co-operation is required in the folowing matters of pool discipline, essential for safety during practical training sessions:
Medicals:You must undergo a full medical examination and chest X-ray, and hold a BS-AC 'Certificate of Fitness to Dive' signed by the doctor, before you are allowed to start Novice Diver Practical Lessons.
[Different arrangements apply to Novice Diver students at BS-AC Schools].What to bring.
To theory lessons:This Workbook, Sport Diving Manual,Notebook and pen.
To pool lessons:Swimwear and towel, pool suit (if you have one) or tee-shirt, your basic equipment, and any other personal diving equipment if approved by your instructor.
Bring Qualification Record Book to all lessons (not onto poolside!) so training can be signed up.
3.INTRODUCTION TO BASIC DIVING EQUIPMENT
Mask
Mask permits eye to work in natural medium of air, in which eyes can focus.
Mask should enclose the nose permitting: Balancing air pressure within mask. Equalising pressure on ears (ear clearing).Clearing water which may enter mask.
Look for these features
What to avoid and why
Testing for correct fit.
Snorkel
Snorkel allows diver to breathe while swimming on surface with face submerged. Vital piece of equipment for all divers.Look for these features.
Testing for correct fit.
What to avoid and why.
Fins
Fins provide propulsion, permitting diver to swim further and faster. Without fins and with encumbrance of all other equipment, diver is virtually immobilised.Features Of Fins
Testing For Correct Fit.
What to avoid and why.
Weightbelts.
Diving suits and some aqualung sets are buoyant: this is undesirable. Ballast weights carried to achieve neutral buoyancy, so diver slowly rises or sinks as he breathes in or out.Weights carried on a belt which has a quick-release buckle. If emergency buoyancy is needed, belt can be quickly jettisoned.Features of weightbelt and weights.
What to avoid and why.
The Aqualung(Sport Diving 36)
This lesson will introduce the aqualung. It will be looked at in more detail in Lesson NT3.5.DIVING SIGNALS.(Sport Diving 62 - 65)
Diving hand signals.
Speech is main means of communication among humans. Speech is not possiable under water, but there is a need for divers to communicate - during training and diving - so that instructions are understood; for safety; and so that dives may be conducted in accordance with agreed dive plan. Hand signals are simplest means of communication.Main series of hand signals apply to open water diving situations. You should learn them all. Additional 'training situation' signals will be introduced as your training progresses. Diving Signals largely standardised throughout world of sport diving.
All hand signals must be clearly and boldly given and equally clearly acknowledged by the diver receiving them. Divers should check between themselves before dive so that they know and understand all signals to be used. This check is part of normal pre-dive briefing.Diving hand signals fall into two categories:
Because they have to be seen over greater distance, both hand and arm are used to make signal.
Signals between divers are made at close range, so hand or hand and forearm only are used.
International diving flagWhen diving at sea, boat traffic could be dangerous to divers ascending or at the surface. Hence it is necessary to have a conspicuous signal to warn surface craft that divers are in the water.
International marine regulations requires vessels from which divers are operating to display International code Flag A to indicate that diving operations are taking place. This flag means I have a diver down: keep well clear at low speed.Code Flag A (Alpha) should be displayed only while diving is taking place, and not by boats moving to / from dive site. Sensible safeguard to use same flag on surface marker buoys or other floats used by divers. (In some places overseas, other flags may be used - check!).
6.THE IMPORTANCE OF BUDDY DIVING.(Sport Diving 120 - 121)Underwater swimming involves an element of risk: It is part of the challenge. Golden rule in world of sport diving is: Never dive alone.
Diving partner commonly knowen as your buddy: practice of diving in pairs as buddy diving. Object of buddy diving is for one diver to provide assistance to the other should help be needed at any time during the dive - whether in kitting up, entering or leaving the water, while underwater or in an emergency. An agreed Dive Plan and common interests increase the satisfication gained from the dive and from the sport.Buddy diving requires vigilance by both divers, who should regularly monitor each other to ensure all is well, and dive going according to plan. Buddy diving techniques are taught and encouraged throughout diver training so that you learn to work as a member of a team. As often as possible during your practical training, you will be 'buddied up' as a means of teaching / reinforcing the importance of buddy diving.
TESTOnce you have read this Lesson in Workbook, and the appropriate pages of Sport Diving, test yourself to see if you have understood the subject. You will find the answers on page 59.
You should get most questions right. If you do not, then read through both texts again and repeat the test. If you still have difficulty with the subject, discuss the problem areas with your instructor - then review the subject again.You should now study Lesson NT2 in this Workbook.
Achievement Targets
On completion of this lesson and subject study, you should know:
1. INTRODUCTION AND LESSON OBJECTIVES
You will have noticed effects of changes in pressure on your ears when in an aircraft, a lift, when a train enters a tunnel, or when diving to the bottom of a swimming pool. The discomfort you feel is one of the more noticeable effects of pressure change on the body.This lesson will give you a basic understanding of pressure and volume relationships and their effect on the diver. Ways of avoiding pressure injuries will be explained, as will the subject of buoyancy.
2.UNITSFollowing units are used in BS-AC Diver Training.
Composition
Air is a mixture of the gases Nitrogen (N2) 79% (say 80% = 4/5) and Oxygen (O2) 21% (say 20% = 1/5). Minute quantities of Carbon Dioxide (CO2) and other gasses may be ignored.Atmospheric Pressure
Earth surrounded by an atmosphere of air, which applies a downward pressure of approximately 1kg per square cm at sea level.Measurement of pressure : guage / absolute pressure
Pressure guages read zero at atmospheric pressure. Guage reading of 200 bar is 200 bar above atmospheric pressure (guage pressure). Since atmospheric pressure is 1 bar, absolute pressure is actually 201 bar.Compressibility
All gases are compressible, having neither shape or volume.
On the other hand, liquids have volume and mass and can be considered to be incompressible.
4. THE DIVING ENVIRONMENT - WATER(Sport Diving, 27)
Water is dense, incompressible medium, which exerts pressure on anything immersed in it.Water pressure increases with depth such that a 10m column of water, of 1cm cross - section (i.e volume of column is one litre), applies a downward pressure of 1 kg/cm2.Water pressure increases by 1 bar for every extra 10m depth.
| Depth | Water Pressure | Absolute Pressure |
|---|---|---|
| Surface | Water Pressure = 0 | Absolute Pressure = 1 bar. |
| 10m | Water Pressure = 1 bar | Absolute Pressure = 2 bar. |
| 20m | Water Pressure = 2 bar | Absolute Pressure = 3 bar. |
| 30m | Water Pressure = 3 bar | Absolute Pressure = 4 bar. |
5.GASES UNDER PRESSURE(Sport Diving, 28 - 29)
Pressure/volume change.Since gases compressible, volume they occupy will diminish / expand in direct proportion to increase/decrease in pressure. (This assumes no significant temperature change - as is usual in diving.)
Thus, inverted bucket full of air at surface (1 bar), if taken underwater, will be half full of air at 10m (2 bar): one third full at 20m (3 bar): and so on.On returning to surface, air will expand in volume as pressure falls, so that bucket once again full of air on reaching the surface. Note that greatest pressure / volume change occurs between 10m (2 bar) and surface (1 bar).
What will happen to the buoyancy of the bucket during its travels? Air will give an upthrust. As volume of air is compressed in direct proportion to increase in pressure on descent, buoyancy will diminish by same proportion. On ascent, buoyancy will be regained as volume increases and pressure falls.Thus, any flexiable airspace will lose buoyancy if allowed to compress on descent, and gain buoyancy as it expands on ascent.
What happens if the bucket is pumped full of air at 10m (2 bar) and brought to surface? Air will expand two-fold and surplus will escape. Buoyancy will be constant during ascent.
A closed, rigid air container is likely to be collapsed by increasing pressure (compression) when taken underwater, unless structure strong enough to withstand it.If filled with air at bepth, it will try to expand (or explode!) on ascent, unless structure strong enough to contain the increasing air pressure within. Danger of sudden release of pressure when opened.To prevent damage to rigid air space, whether by compression or expansion, pressure within must remain equal to surrounding water pressure at all times.
Human body contains both flexible and rigid air-filled spaces. Failure to equalise pressure within rigid spaces - and flexiable ones to lesser degree - will cause damage to tissues forming / surrounding such spaces. Discomfort / increasing pain, will be felt. Unless pressures are reduced / equalised, injury will result. Injuryin or underwater obviously puts the diver in danger.Pressures are easily equalised by allowing air into air spaces on descent (deliberate effort sometimes required); and by allowing air to release / escape on ascent. Process knowen by various names - equalising / compensating / clearing.
Effects of pressure / volume change on diving equipment will explained in other lessons.6. BODY AIR SPACES(Sport Diving 31)
Body air spaces include : Middle ear cavities, sinus cavities within skull: breathing system comprising nasal passages, throat, windpipe, lungs; stomach and intestines. An additional air space is created by wearing facemask, which becomes an extension of nasal passages.7. EFFECTS OF AIR SPACE COMPRESSION
Parts of the body most affected by compression are the ears and sinuses; and lungs of the breath-holding snorkel diver.The air space within diver's mask is also affected.Ears and sinuses are most sensitive to increases in pressure, so effects on them disscussed first.
The EarsThree main parts: Outer ear and ear passage, Middle ear cavity and tube connecting it to nasal passage. Inner ear containing organs of hearing and balance. We are concerned with the first two.
Ear drum seperates outer ear passage from middle ear cavity. Middle ear cavity connected to nasal passage in nose by narrow airway called Eustachian tube. This can be opened and air admitted to middle ear cavity by yawning or pinching nose and blowing against closed nose.Try it!Ear Drum is flexiable and sensitive to changes in pressure. In day-to-day life, vibrations recieved by ear drum transmitted to inner ear, interpreted as sound.
Ears and diving As diver descends, water pressure pushes ear drum inwards. Pain is felt. If pressure continues to increase , drum is likely to rupture. Water enters middle ear cavity, will upset balance organs and lead to deafness, vertigo, risk of infection.Water pressure on ear drum is equalised by allowing air up Eustachian Tubes into middle ear cavity. you did this a moment ago.This process of ear clearing, and is why divers mask has pockets for pinching nose - and one reason why mask encloses nose. If ear clearing difficult, ascend a meter or so; try again. DO not force an ear which will not clear. Abandon dive.
Ear plugs or tight hoods may seal outer ear passages, preventing normal compression of ear drum. Increasing air pressure in middle ear cavity can cause drum to bulge outward and suffer damage (reversed ear). Allow water to get to outer ear when diving.Sinuses
These are cavities in the bone structure of the head with fine connecting airways to nasal passage which ensure equal pressure.If airways are blocked, any imbalance of pressure causes acute pain. Normally sinuses will clear as ears are cleared. If they do not, and pressure increases - if you can bear it - linings of cavities will bleed, flooding cavity to balance pressure.
Diving With A Cold or Nasal InfectionA cold, heavy catarrh or hayfever causes inflammation and secreation of mucus in nasal tract, Eustachian Tubes, sinus cavities and airways; which can lead to blockage of airways and inability to clear ears and sinuses.
Do not dive - even in a pool - with such an infection.Ear drums may be damaged; infrection forced into middle ear and sinus cavities.
Decongestant medication should only be used under medical guidance. Seek medical advice if you suffer persistent difficulty with ears and sinuses.Lungs and airways
Lungs are flexiable airspaces; airways to them (nasal passages, throat, windpipe, etc) are rigid.In breath-holding diving, lung volume will reduce a ambient pressure increases, so that air pressure in lungs and airways remains equal to water presure. Effects on lungs is same as breathing out (when lung volume is reduced). Diver does not feel anything - but may notice loss of buoyancy.However, there are limits. If breath-holding diver went to depth where pressure has compressed lung volume beyond that achieved in normal full exhalation, there must be risk of lung injury.Condition is knowen as thoratic squeeze.
Thoratic squeeze can also occur if attempting to breathe through long tube to surface. Air within lungs at atmospheric pressure: water pressure acting on chest is at higher pressure: Muscles cannot bring about normal inhalation due to imbalance of pressure.Mask Squeeze
Mask is extension of nasal airways. Air space in mask will compress on sescent, causing injury to eyes / eye sockets, if not relieved. Condition knowen as mask squeeeze.Air should be exhaled through nose into mask on ddescent, to equalise air pressure and prevent squeeze (second reason why nose enclosed in mask).
8. EFFECTS OF AIR SPACE EXPANSION(Sport Diving 82 - 83)Lungs
Breath-holding diver will not notice that lung volume is increasing when returning to surface, except by increase in buoyancy.However, aqualung diving, breathing air and keeping lungs full while underwater, over-expansion of lungs (flexible air spaces) on ascent is major hazard.
Normal breathing from aqualung means that lung volume does not compress on descent, as it does with breath-holding diver. On ascent, volume of air in lungs expands and must be released through normal exhalation.So long as diver breathes normally, or exhales steadily during ascent, risk of injury to lungs is minimal.
Remember bursting balloon analogy. If diver were to hold breath on aascent - in panic perhaps - falling ambient pressure will cause lungs to expand to maximum volume (as full inhalation) Since expanding air not escaping, pressure within lungs will become higher than ambient pressure.this will cause lung tissue to stretch beyond normal limits, forcing air into bloodstream or tearing lung tissue and possiably allowing air to escape from lung sacs to be trapped within chest cage where it creates a variety of problems. The condition is knowen as Burst Lung, and is avoided by following this golden rule:
Understanding subject, and knowing how to avoid it, makes Burst Lung a rare condition, despite being perhaps most serious risk to diver.
Note that greatest volume / pressure changes (greatest rate of expansion) occurs close to the surface.hence diver is at greatest risk during final stages of ascent. Burst Lung can occur even in a training pool!Other air spaces.
Rare to encounter ear / sinus problems on ascent. Body generally copes better with falling pressure than increasing pressure.Gas in stomach / intestine causes no trouble on descent, but may on ascent, especially if air has been swallowed during dive. Feeling of fullness relieved by natural methods. !:) Avoid gaseous food and drinks before diving.
Teeth - air under pressure may enter cavites, causing pain on ascent. Have filling replaced.9.BUOYANCY
Object immersed in liquid recieves upthrust equal to mass of liquid displaced, i.e. whose volume it occupies.If mass of object exceeds mass of water displaced, it will sink. If less, it will float. For example, a jam jar filled with lead will sink: one filled with air has much less mass, so will float.
What we can do with our own buoyancy spaces - our lungs? Breathing in increases lung volume, so swimmer / diver with full lungs will displace greater volume of water and will float (positively buoyant).On emptying lungs, body displaces less water so diver will sink (negatively buoyant).Within the span of normal breathing, between positive and negative buoancy, is the desired state of neutral buoyancy, when a diver becomes weightless. A diver can change buoyancy simply by breathing! To start a descent, breathe out. To start an ascent, breathe in.
Diving equipment adds both positive and negative buoyancy to body, usually more positive than negative. Weights are worn to restore neutral buoyancy to within span of normal breathing. Weightbelt can be dumped in emergency to give positive buoyancy.Differing densities of sea and fresh water (seawater is slightly more dense) mean that diver who has achieved neutral buoyancy in fresh water will find himself positively buoyant in sea (and vice-versa). Will have to carry out buoyancy check and adjust weights.
Buoyancy reduces with depth, due to compression of lungs in snorkel diver, and other equipment-related reasons which will be explained in other lessons. On ascent, buoyancy regained as pressure decreases.Diver uses Buoyancy Compensator to maintain neutral buoyancy throughout dive.More of this in other theory and practical lessons.TEST
Once you have read this Lesson in this Workbook, and the appropriate pages of Sport Diving, test yourself to see if you have understood the subject. You will find the answers on page 59.You should get most questions right with any aspect of the subject, discuss the problem areas with your instructor - then review the subject again.
Achievement Targets
On completion of this lesson and subject study, you should understand:To stay underwater for more than a few seconds, diver must have air supply. The aqualung developed in 1940's by French pioneer Jacques Cousteau, opened up underwater world for recreation. In colder waters, a diving suit provides thermal protection. Instruments and accessories allow monitoring of depth, time and position, add to safety of dive. This lesson will explain the purpose and function of aqualung breathing apparatus, diving suits and associated open water diving equipment.
2.THE AQUALUNG(Sport Diving 36 - 37)Aqualung comprises three main parts :
AIR CYLINDERS
Diver's breathe air (Not oxygen, which can be harmful if breathed under pressure) cylinder contains enough air for a dive, after which must be refilled from high pressure air compressor.Strict controls apply to design, manufacture and maintenance of aqualung cylinders. Diving cylinders used in UK must comply with British Standard (BS) specification BS 5045. Cylinders are made from steel (BS 5045/1) or aluminium alloy (BS 5045/3)
Another Standard (BS 5430) applies to inspection / testing of cylinders, and requires aqualung cylinders to be visually inspected every 2 years, and hydraulically pressure tested every 4 years.Cylinder Markings and Capacities
All cylinders carry series of markings, stamped on sholder or neck of cylinder. Markings must include : Manufacture's mark and serial number. Specification (e.g BS 5045/3) Dates of manufacture's pressure test and of subsequent tests. Water capacity (WC) and Tare (not always showen on older aluminium cylinders) Working pressure (WP) and Test Pressure (TP)Note serial number of your cylinder in case it goes missing - it is it's identity number, unique to that cylinder.Do not alter or deface cylinder markings.
Diving cylinders available in range of capacities / sizes, usual ones being 10, 12 and 15 litre.Capacities usually measured in terms of it's empty volume (Water Capacity - WC), multiplied by Working Pressure (WP) in bar: e.g. 12 litres x 230 bar = 2760 litres.4.Buoyancy Compensators(Sport Diving 46 - 47)
Diving suits are compressed and lose buoyancy as diver does deeper. Variations in depth of breathing not enough to compensate for such losses. Divers need device which can be inflated / deflated at will to maintain neutral buoyancy while resting at the surface, escape to surface from depth in an emergency, and act as lifejacket if diver in distress at surface, so much the better. The Buoyancy Compensator (BC) does all of these. Two styles available:Waistcoat pattern BC:
This type of BC is now the preferred pattern and all future references to BC's in this course will refer to this type. It incorporates a backpack and cylinder clamping band and thereby dispenses with need for a separate cylinder support harness. Adjustable Buoyancy Lifejacket (ABLJ):Traditional lifejacket (horse collar) shape. Forerunner of the stabiliser jacket BC - embodies similar features and still does the job! However, does not incorporate an aqualung cylinder harness.Inflation Systems
Inflation may be by mouth; by direct feed inflator from regulation first stage; by emergency air cylinder or carbon dioxide (CO2) cylinder.Mouth Inflator: Flexiable tube attached to top of bag with mouth inflator / breathing valve. Usually necessary to depress mouthpiece valve to open it when inflating.
Direct feed inflator:Best system for routine inflation at surface or underwater. Simple and safe, offering fine control. However, direct feed inflation time is slow - 15 to 20 seconds. Use of direct feed during dive does not significantly reduce air supply for breathing.
Emergency air cylinder:Inflation by high pressure air takes 2 to 3 seconds, so beter for emergency use.Emergency cylinder, filled from diver's aqualung cylinder before each dive, has own shut-off valve allowing diver to admit air to BC at will. Inflation equally rapid with CO2 emergency cylinders, but CO2 cylinders not refillable.An emergency inflation system is a very desirable feature on a BC. Venting systems Since BC inflatable at depth, must have means of venting, and ressure relief valve to prevent bursting on ascent.Dump valve provided to release air rapidly: often doubles as relief valve. For fine control, air may be released by holding mouth inflation hose at / above shoulder level and mouthpiece valve 'tweaked' open.Venting systems
BC emergency air cylinder has empty capacity of about 0.4 litre. When charged from full aqualung at 230 bar, cylinder will contain about 90 litres of air - enough to fill BC four times at surface or once at 4 bar absolute pressure (30m). Even at 50m, full emergency cylinder will give 12 - 14 kg buoyancy - enough to lift diver : and air will expand to give maximum buoyancy during ascent.However, if emergency air cylinder only partly charged to say 100 bar, or if used for routine buoyancy compensation, surface buoyancy, etc., less air available for emergency use, and effective operating depth reduced. Keep air in emergency cylinder for emergency use only. Use direct feed inflation for buoyancy compensation underwater, mouth inflator for surface use.
Warning:If BC fully inflated at depth, its buoyancy will bring diver to surface at dangerous rate of ascent.Future lessons will explain dangers and will give advice on correct procedure for buoyant ascent if the only means of escape.Practical training will teach you how to control rapid ascent.
5.THE REGULATOR.(Sport Diving 37 - 39)
Since it is the unit the diver breathes from, the regulator is perhaps the most important part of the aqualung system. It is a two-stage pressure reducing valve which reduces the high cylinder air pressure to ambient water pressure at which the diver breathes. The first stage is also sensitive to changes in water pressure, so intermediate pressure remains constant in relation to water pressure. An intermediate pressure hose links first stage to the mouth-held second stage demand valve, through which the diver breathes.As the diver inhales from the mouth-held demand valve unit, a spring loaded valve opens, allowing intermediate pressure air to flow into the mouthpiece chamber, its pressure falling to ambient as it does so. The breath is taken : exhaled air exhausts into the water through a simple flap valve. As intermediate pressure falls, the first stage immediately operates to maintain it at the pre-set level.
The regulator first stage should be fitted with high pressure cylinder contents gauge which records air pressure in the cylinder at any time. By monitoring this guage regularly, the diver can see what air remains and when it is time to surface. Other direct feed hoses from the regulator first stage suply intermediate pressure air for BC and drysuit inflation.6.ALTERNATIVE AIR SOURCE.(Sport Diving 130)
A diver normally relies on a single source of air - their own regulator. It rarely lets him down, but if it does, he is in great danger. Wise diver's provide an alternative air source. These are the options currently available:'Octopus Rig': Fit another intermediate pressure hose and a demand valve unit attached to your buddy's regulator. If you return the compliment by fitting one to your regulator, you are both much safer! Every diver should have one. A long intermediate pressure hose makes it easier to use.
Twin Regulators: Its possiable to fit twin take-off cylinder valve to your aqualung cylinder, when two seperate regulators can be fitted, one used as an emergency system.BC Breathing device (e.g. Air 2): A special breathing mouthpiece on the BC inflator hose allows diver to breathe air via the BC direct feed hose: and / or the air in the BC emergency air cylinder.
Pony cylinder and regulator: A small air cylinder with its own regulator is clamped onto your main cylinder.An AAS should be conspicuous and accessible, so out-of-air buddy can take it without warning if needed - or you can find it immediately if easier to give buddy your own regulator.
7.DIVING SUITS.(Sports Diving. 48 - 51)There are few places in the world where divers can remain in water for long without thermal protection. In UK waters, diving suits are essential because body loses heat faster than it generates it. The primary function of diving suits is to provide thermal protection; secondary benefits are protection against abrasion.
Wetsuits.Widely used for all watersports. Durable, readily obtainable, relatively inexpensive, and provide sufficient insulation for recreational purposes. Suit is not waterproof but retains layer of water warmed by body temperature, between body and inside of suit.
Wetsuits made from 'closed cell foamed neoprene', which has millions of minute gas-filled bubbles, making it light in weight, flexible, stretchy - and buoyant. Heat penetration through material is very low, providing bulk of insulation. The thicker the suit material the more insulation - butalso more restrictive and buoyant. Bonded nylon linings / facings give strength, abrasion resistance, simplifies dressing and adds colour to suit for safety and fashionable apperance. Thicknesses are 4mm for warm water use, 6.5 mm or 8mm for cold waters. Available as one-piece; jacket and trousers; long-john trousers and hood-attached jacket, according to use. Seperate hoods, bootees and gloves also available.
Increasingly popular with those who dive in colder waters. Waterproof drysuits are a one-piece garmet made from either closed cell foamed neoprene (neoprene drysuit) or rubber / plastic impregnated fabrics (membrane drysuit).
Foamed neoprene drysuits use the same material as wetsuits, so excellent insulatiors. Even more insulation is possiable if undergarments are worn inside the suit. Membrane suits offer no natural insulation. A diver would need to wear thick wooly undergarments ('Wolly Bears') to provide insulation. All drysuits have waterproof entry zip, usually from elbow to elbow across the sholders with built in boots and seals at neck and cuffs.
Both wesuits and srysuits are buoyant, so weights must be worn to regain neutral buoyancy at the waters surface. Compression of suit (or airspace within) ,as depth increases, means loss of buoyancy so air is admitted by direct feed into drysuit (or BC) to maintain neutral bouyancy throughout dive.
Drysuits and drysuit diving is the subject of the BS-AC Drysuit Training Course, which may be undertaken once you have completed BS-AC Novice Practical Lesson NS 9.
Protection in tropical waters.Thermal protection may not be necessary except for long exposures, where a thin wetsuit would be adequate. Protection is necessary however from coral abrasion, stings, skin chafing from equipment and sunburn while snorkeling. A Tee-Shirt and jeans would normally be sufficient. Gloves are strongly recommended to minimise the risk from coral abrasion. Protect bare feet against abrasion in shallow tropical waters.
8. INSTRUMENTS Depth guage and watch / Dive Timer.In order to avoid decompression sickness, accurate recording of depth / and time is vital.
Your Depth guage should be of a sealed / enclosed bourdon tube type, or diaphram type. It should be robust, with a clear face calibration. Inaccuracies can develop if a guage is knocked or droped resulting in errors which can mislead and prove dangerous. Therefore take extra care of your depth guage as you would with your wrist watch.
Diving watches have a rotatable bezel which is used as a timing device. The zero mark on the bezel should be set against the minute hand at the start of the dive as this will show the elapsed time at a glance when reading from the bezel. The watch should have a clear uncluttered face with luminous hands and marks at 5 minute intervals. Digital displays allow more accurate monitoring of dive time but may be difficult to read in some conditions.
A Dive Timer or Bottom Timer is a pressure operated stopwatch for diving use. It starts automatically on descent and stops upon resurfacing. Records elapsed time untill zeroed.
Computerised instrumentsModern electronic diving instruments combine functions of a depth guage and timer as well as indicating the decompression requirements for the current dive and possiable dive options for the next or future dives within a series as well as other useful functions. An ascent rate indicator is especially valuable.
Even though decompression information given by most dive computers is not based on BS-AC '88 Decompression Tables, the club permits their use. However, they are not infallible and must be used with care and common sense. Back-up instrumentation is a wise safeguard. You will be taught more about Dive Computers during the BS-AC Sports Diver Course.
CompassIts easy to loose your sense of direction underwater. A compass is a simple, reliable guide to direction, requireing little practice to use correctly. A favoured type is worn on the wrist which is oil filled and incorporates a clear luminous 'direction of travel' line, needle and rotatable bezel. Another subject for Sports Diver Training.
9. ANCILLARY EQUIPMENTKnife: An essential piece of kit for cutting possiable entangling nets or lines. The knife must be of a robust construction, and is usually supplied with a leg-sheath enabling the diver to wear on the calf of the leg. It should be worn in such a position to enable it to be drawn with either hand. Ensure your knife is sharp and kept lightly greased.
Surface Marker Bouy : A valuable aid on all sea dives other than fixed sites such as wrecks. An S.M.B marks a divers position so boat cover remains close to the divers position. It can be used as a signal line to the diver, act as a warning to other craft of divers within their proximity and can provide bouyancy if required when on the surface. In its simplest form a S.M.B consists of a large float (15kg bouyancy) and a 50m light nylon line. A hand reel helps to keep the line at optimum length and rewinds the line when the diver asscends while acting as a Small Flag 'A' warning surface craft that there are divers below.
Torch / Lamp : In dark water or whilst night diving, a torch is necessary to see and to signal. Also usefull for looking into dark holes on bright days. Ranges from small 2 cell models to large 8 cell / 6 volt lantern batteries; or rechargeable units. Should have a wrist lanyard and slight positive bouyancy.
Slate and Pencil:Usefull for notes; and conversations that go beyond the scope of hand signals; and good for recording dive times etc. Ordinary pencil attached to thin cord to corner of slate.
Instrument console : Console on end of pressure guage hose can carry depth guage or dive computer and compass. Permits display of air, depth, time, decompression requirements and compass direction in one array.
Gear Bag / Holdall:Capacious bag to carry all your kit (except cylinder and weightbelt, carried seperately). Most equipment manufacturers have one in their range.
A wide range of minor accessories are available - see Sport Diving Manual, Diver Magazine advertisements and your local dive shop.
10. EQUIPMENT CAREWash all equipment in fresh water after use, dry thoroughly before storing in a well ventilated area and out of direct sunlight. Hang suits on hangers, store BC inflated. Keep electronics away from magnetic fields / electrical appliances. Attend to any repairs before storage.
Cylinders are required by law to be visually inspected, inside and out, every two years, and hydraulically tested every four years. Use a reputable IDEST test house. Your regulator is your life-support system ! have it serviced annually by a manufacturer's approved service agent.
Prepare a check list to make sure you take everything you need for the dive. Carry a small tool-kit with spare parts - O Rings, spare mouthpiece and tie-wraps, spare fin straps, etc to allow you to rectify minor faults on site.
Diving equipment is expensive - look after it and it will look after you! And get it insured!
TEST
Once you have read this Lesson and the appropriate pages of Sports Diving, test yourself to see if you have understood the subject. You will find the answers on page 59.
You should get all questions right. If you do not, then read through both texts again and repeat the test. If you still have difficulty with any aspect of the subject, discuss the problem areas with your instructor - then review the subject again.
You should now study Lesson NT4 in this workbook.
Achievement Targets
On compleation of this lesson and subject study, you should:1. INTRODUCTION AND LESSON OBJECTIVES.
Few dangers associated with diving and good diver training prepares you to cope with them. Even so, it is safer to dive with someone else rather than alone. It also makes sense to follow practices which ensure safe conduct of dive.This lesson will introduce diving practices which ensure your diving is safe and enjoyable.
BUDDY DIVING.(Sport Diving 120 - 121, 126 - 127)
Lesson NT1 introduced this subject. You have been using buddy system during practical training so far. Accident statistics prove that diving is safest and that the lone diver is a diver at risk.Abide by the rule : Never dive alone.Buddy diving involves:
Buddy diving does not mean total dependance on buddy, or taking risks because buddy is there to help. Be self-sufficient, but buddy dive to share the enjoyment and increase the level of safety.
Diving in a larger group.May be times and reasons for not diving as buddy pair, but in larger group. Reasons should be good - it is not so safe. Group of three is awkward size. Larger group can be split into pairs.
Experiance shows that thee, diving together, tend to end up as pair plus one - who can easily become lone diver. Dive leader has to work extra hard to keep larger group together, has little chance of enjoying dive while seeing that others do. Strict discipline necessary for group diving.Dive Plans : Dive Leadership
Dives should be planned: plans should be followed. Overall command of BS-AC Branch dive lies with Dive Marshal, who selects experianced dive leaders for each pair wishing to dive. Each dive leader will plan dive he is to lead, within overall plan dor the day. Most BSAC Diver qualifying dives likely to be made on Branch dives using this chain of command.Your future diving will include dives made privately with friends; at dive centres; while on holiday. Whatever the circumstances, someone must be in charge, and their leadership accepted by other diver(s). Dive leader and diver(s) should work out and agree dive plan together. Agree / accept dive plan only if you are happy with it. If not, say so; explain why; change plan.
Be satisfied with following aspects of dive plan:
Not necessarily reasons not to go diving, but rather to alter dive plan or conduct dive so worries / inexperiance are taken into account / overcome. Do not be persuaded to dive beyond limits of your ability / experiance / equipment - it's your life!
3. PREPARING TO DIVE.(Sport Diving 122 - 123)Kit Up.
Novice Diver training will give you experiance in putting on all items of open-water diving equipment ready for dive. Seek help from buddy if necessary. The following sequence of kitting up is advised :Briefing.
Same procedure / briefing sequence used in practical lessons applies to open water diving. Aide memory is SEEDS. Check / agree on as much as possiable, while you can talk about it.Buddy Check.
Buddy check ensures : (a)Both divers know how to operate each others equipment, so able to assist / rescue if needed. (b) Ensures nothing missing or incorrectly fitted. Check that:Buoyancy Check.(Sport Diving 76 - 77)
Untill diver knows he is correctly weighted for dive, buoyancy check should be carried out:Correct weighting is important : diver must be able to achieve neutral buoyancy at any point during dive and especially in final 6m of ascent where slower ascent rate applies. Sea and fresh water have different densities : weighting will be a little less in fresh for same set of equipment.
Concurrently / after buoyancy check, ensure all equipment fits comfortably, is working correctly.4.THE DIVE.(Sport Diving 124 - 133) Entry Methods Entry method depends on dive site.Berfore entering, make sure a good exit is available. Following procedure generally applicable / advised for entry from shore:
Approach water in full kit, 'portables' in hand / place. Rinse and fit mask and fins at water's edge (buddy help?). At this point, if buoyancy has to be checked, enter water. Breathe from demand valve until clear of shallows, then conduct in wayter checks. Give OK signal to leader; change to snorkel for surface swim, or prepare to descend.
Surface Swims.Keep together, swim side-by-side at steady pace. Look up / around at intervals to check direction, surface dangers. Partial inflation of BC adds to safety / comfort during a surface swim.
Snorkel DivingWhen diving, divers should remain close together and only one should dive at a time. Observe safe practice of 'one up - one down'. Have adequate SMB or float to provide added buoyancy for resting between breath-holding dives. Other recommendations for safe aqualung diving in this lesson also apply to snorkeling. (Those interested in Snorkelling are advised to read the BS-AC manual Snorkelling For All.
Descent.General order of descent as follows:
Close up at surface, exchange 'OK' signals. Fit demand valve, stow snorkel, set watch / instruments. Leader gives ' OK' signal to shore / boat cover, 'go down' signal to partner, who acknowledges. Descend only when both are ready: vent air from BC to drysuit, exhale to shed buoyancy and make feet first or head first descent as agreed.Equalise pressure on ears and mask continuously during descent. Use datum for descent if available - anchor line / shot line / rock face. Keep close together. Give 'stop' or 'something wrong' signal if necessary to stop descent. Use buoyancy compensation to control rate of descent / maintain neutral buoyancy. On bottom, exchange 'OK' signals, achieve neutral buoyancy, get comfortable and in control, and proceed with dive.
Staying togetherPosition yourself as agreed relative to leader : side-by-side best. Concentrate on staying together. Distance apart should equal limit of visibility, or 5m maximum, whichever is least.
Enjoying the dive.DOn't allow leader / buddy to rush you. get close to marine life. pay attention to detail. few things or creatures harm you. Enjoy !!
Buddy monitoring'OK' and other relevant signals to be exchanged at intervals. Regularly check depth, time, direction and air. Divers using dive computers should follow 'worst case' readings of either instrument, especially if they have made previous dives with other buddies.
Ascent and surfacing.Start ascent after time or when air falls to agreed (normally 50 bar) reserve level. First diver to notice dwindling air supply should give 'I am on reserve' signal to indicate air supply low.
Normal aqualung surfacing drill carried out thus : Dive leader dives 'Go up' signal : other diver acknowledgs with 'OK' signal or 'go up' signal.Facing partner (in bad visibility, hold onto each other), fin upwards. Crect rate of ascent is 15m per minute (conveniently, small exhaust bubbles ascend at approximately this rate) up to 6m, then 6m/mn to surface.
Controlled venting of BC / drysuit to remain buoyant. Breathe normally. Look up / around to ensure water unobstructed.Hold one arm above head in final 2m of ascent. Immediately on surfacing, scan complete circe in case boat or other danger threatens.Be ready to descend if necessary.
Inflate BC, exchange 'OK' signal with partner. Change over to snorkel breathing. Signal 'OK at surface' to boatcover or shore party - or no signal, which will be interpreted as distress.Leaving the water.
Exit generally reverse of entry. Swim in to waist-dep water, slip fins off, walk ashore. On ladders / steps, pass fins ashore if possiable. clear landing area quickly if others wish to use it.After the dive
Dive debriefing will be carried out by dive leader while things fresh in mind. Creature comforts welcomed after debrief. Food, hot drinks. Protective clothing over wetsuit if to dive again soon, otherwise change. Stow own equipment, assist other members with Branch equipment, boats, etc. Record dive details in own Dive Record Logbook.5.ABANDONING THE DIVE : SEPARATION.
Sometimes expedient to abandon dive : deteriorating surface weather conditions; deteriorating underwater conditions; equipment difficulties; onset of illness or extreme apprehension in members of diving party; or dive getting beyond diver's abilities. An accident at surface or underwater should lead to abandonment of dive. Stop before things get out of control. Nothing 'chicken' about abandoning a dive : if dive no longer enjoyable, it is time to stop.In event of separation from partner, do not 'press on' alone. Stop: look up and around through full circle for a few seconds only. If no sign of partner, begin normal ascent, look around while surfacing. If buddy in dificulty / in need of help, underwater or at surface, best means of locating him (and acquainting surface party) is to ascend.
At surface, locate partners bubbles or SMB. Seek help from surface / boatboat cover. Partner should be taken same actions to find you. Re-unite at surface. Check dive time, surfacing code and resume dive if practical.6.DIVER RESCUE.(Sport Diving 156 - 157, 152 - 154)
The prospects of being involved in a diving accident are remote - but occasionally, it happens. An accident is usually the end-result of a chain of events. Poor planning, preparation and conduct of dives; lack of skill or fitness; failure to stop in time or adhere to established safe diving practices, usually evident when diving accident is analysed.Accidents are avoided by:
‘Press on regardless’ attitudes lead to trouble. lf things not going to plan; if you feel ill-at—ease, Stop - regain control. The time difference between ‘in control’ and ‘in distress’ is just a few seconds. Signal to leader / buddy nature of problem. Regain composure, resolve the problem. After regaining control and if happy to do so, proceed with dive. lf not, abandon it. Do not worry about spoiling dive for leader / buddy - safety first.
Minor problem noticed and put right can be major problem averted. Remember: stop - regain control. First, try self help: sort out your own problem; second, seek help from buddy to sort it.
For example:
7. EMERGENCY ASCENTS (Sport Diving 130 - 131)
What is ultimate problem for diver? Answer: anything which interrupts air supply. Other problems are minor compared to it. If able to breathe, diver who is disorientated, lost, suffering cramp, minor injury, is not yet in great distress, should be able to remedy situation through self help. Diver who has suffered interruption / loss of air is immediately in serious trouble.
Divers usually run out of alr because they do not monitor their air supply regularly. Occasionally, there is a rare equipment failure. Diver discovers the problem when inhaling. Has low lung volume and is faced with need for instant decision.
Escape options are:
Because of risk of lung damage, BS-AC does not permit practical training in Free Ascent or Buoyant Ascent techniques. Know what to do, but do not practice.
Diver(s) faced with need to make any type of emergency ascent should dump anything held in hands. Less risk of entanglement; hands will be needed to operate equipment during emergency ascent.
Loss of air supply undenrvater, followed by failure to successfully share air / use AAS, quickly leads to drowning. Subject needs rescue. Diver Rescue requires a wide range of skills, which you will start to learn in Lesson NS 8 and will expand as you advance your diving qualifications.
8. EXPIRED AIR RESUSCITATION(Sport Diving 152 - 153)
When giving Expired Air Resuscitation (EAR), rescuer exhales own breath into lungs of casualty. Sufficient oxygen in exhaled air to revive casualty if blood circulation taking place. EAR is undoubtedly the most effective method and is easy to learn.
When to apply EAR
If air is unable to reach the lungs, casualty will quickly collapse (hypoxia). Heart failure will follow as body starved of oxygen. If casualty can be resuscitated before heart fails, greater chance of recovery.
EAR should be applied when casualty is not breathing because of asphyxia due to drowning or airway obstruction; or gas poisoning. EAR with External Cardiac Compression (ECC) necessary in cases of heart attack, electrocution, or after heart failure. ECC will be taught in Sports Diver Training.
Non-breathing casualties will be recognised by the following:
How to apply EAR
There should be improvement in casualty’s skin colour (less blueness) after 5 to 6 breaths if oxygen is getting in and circulating. Continue EAR at normal breathing rate of 12-16 breaths / minute - effectiveness more important than rate.
Cease EAR only when casualty resumes breathing (or when qualified medical personnel take over). Put casualty into recovery position. Monitor continuously until hospitalised.
9. IN-WATER RESCUE (Sport Diving 156 - 152 154)
Rescue techniques
Casualty can be brought to surface using Controlled Buoyant Lift; by dumping casualty’s weightbelts and swimming up; or by rescuer making himself buoyant and lifting casualty to surface. Once at surface, make casualty bouyant before commencing EAR.
EAR in the water
EAR can be given to casualty floating in partly inflated BC, using mouth to nose method. You will learn this in Novice Diver Practical Lesson NS 8. Note imponance of using your forearm as lever against casualty’s shoulder in order to extend neck / open airway; and need to roll casualty towards you to seal your mouth over nose for EAR.
Give full effective breaths at rate of about 10 breaths per minute. Fewer effective breaths better than many ineffective ones.
Summonfng help
Summon help immediately on bringing casualty to surface, then begin EAR. Shout for help, use whistle, give ‘Distress at surface’ signal. Continue to summon help between breaths of EAR until evident that assistance is approaching, then concentrate on EAR.
As well as studying the subject in the Manual Sport Diving, study of the specialist BS-AC Manual Safety and Rescue for Divers is also recommended.
TEST
Once you have read this Lesson, and the appropriate pages of Sport Diving, test yourself to see if you have understood the subject. You will find the answers on page 59.
You should get all questions right. lf you do not, then read through both texts again and repeat the test. If you still have difficulty in understanding any aspect of the subject, discuss the problem areas with your instructor - then review the subject again.
You should now study Lesson NT 5 in this Workbook.
Achievement Targets
On compleation of this lesson and subject study, you should:1. INTRODUCTION AND LESSON OBJECTIVES
Anyone who dives is subject to the effects of nitrogen absorption and release. This lesson will explain the part played by nitrogen in causing Decompression Sickness and how the condition can be avoided by use of Decompression Tables. It will then introduce the BS-AC '88 Decompression Tables and will show you how to use them to make no-stop dives.
2. NITROGEN ABSORPTION AND RELEASE: DECOMPRESSION SICKNESS
From Lesson NT 3 you know that air is 80% nitrogen / 20% oxygen, and that these gases enter the bloodstream through the lungs. While oxygen is used in body metabolism, nitrogen serves no useful purpose in the body. However, because it forms so much of the air breathed, our bodies are saturated with nitrogen at its atmospheric pressure. When diving, increasing ambient pressure is matched by an increase in the pressure of air breathed, so more nitrogen is absorbed into tissues. On ascent, pressure falls (decompression) and tissues release nitrogen. After a long dive during which lots of nitrogen has been absorbed, sudden drop in pressure (i.e. fast ascent) may not give time for normal safe release of nitrogen. Nitrogen bubbles can form in body tissues, where they cause disorders known as Decompression Sickness (DCS), or coloquially, ‘the bends’.
DCS can lead to permanent disability. Risk of DCS faces every diver, but it is easily avoided by limiting time spent underwater and / or taking time over ascent.
Safe release of nitrogen
It takes time for body to absorb (and release) nitrogen. Possible to dive and return to surface before body has absorbed enough nitrogen to cause problem. Back on surface, excess nitrogen taken up during dive will continue to release from body. Another dive soon after first means that diver starts second dive with excess nitrogen in body tissues.
Research has shown that amount of nitrogen absorbed if diver goes no deeper than 6m will not cause DCS on surfacing, however long the dive. It has also established a safe time limit (no-stop time) for any given depth, after which diver faces risk of DCS. By keeping dive times within no-stop times, risk of DCS is minimised. Rate at which diver ascends also important, even on no-stop dive. Ascent is decompression.
lf no-stop times exceeded, pauses are made during final stages of ascent to allow nitrogen to be released. This process of making decompression stops will be explained in Sports Diver training.
Research by navies / diving research institutes has resulted in schedules which state longest time you can stay at given depth and still make direct ascent (No-stop dive); depth l duration of pauses on ascent if no—stop times exceeded (decompression stop dive) ; and the rates at which you should descend and ascend. Such schedules are called Decompression Tables.
3. BS-AC ‘88 DECOMPRESSION TABLES
BSAC ‘88 Decompression Tables are designed to meet the requirements of sports diving. However, using them or any other table will not guarantee freedom from risk of DCS. A decompression table - whatever its origin - represents nothing more than best available advice for avoiding DCS. Divers who ignore such advice put themselves at risk of serious disability.
You should have a copy of the BS-AC *88 Decompression Tables beside you as you read on. The Tables reproduced on pages 112 — 113 of Sport Diving will do: far better is the complete set of BS-AC ‘88 Decompression Tables Levels 1 - 4 available from the BS-AC Shop. Acquaint yourself with general layout of Tables and associated instructions.
During Novice Diver Training, you will learn to use the ‘88 Decompression Tables for no-stop dives only, for which you must know the following definitions:
Definitions (Sport Diving 110 - 111, or Tables 2)
DEPTH: The deepest depth reached during the dive, measured in metres ...however briefly you were there. lf in doubt, use next deeper increment of depth.
Plan dives so that maximum depth reached early in dive. Avoid any redescent, significant 'ups and downs' during dive. They invite decompression problems.
ASCENT CHECK DEPTH: A point reached during ascent where dive time is checked against dive plan and surfacing arrangements finalised. For No-stop dives, this is at 6m.
DIVE TIME: The time elapsed from leaving the surface to reaching Sm on the return to the surface.
ASCENT TIME: The time elapsed from leaving the bottom (assumed to be at the dive’s maximum depth) to arriving at the 6m level.
lt is calculated at an ascent rate (q.v.) of 15m l minute and rounded up to the next full minute.
SURFACING CODE: A code describing the diver's tissue (nitrogen) saturation state on surfacing from a dive.
Surfacing Code A indicates no excess nitrogen (normal atmospheric saturation): G represents maximum permissible excess nitrogen saturation.
SURFACE INTERVAL: The time elapsed from surfacing at the end of one dive to the time of leaving the surface at the beginning of the following dive ('Head up to head down')
CURRENT TISSUE CODE: A code determined by applying a SURFACE INTERVAL to the LAST DIVE CODE or SURFACING CODE. lt indicates the Table on which the diver can now make another dive.
Remember that diver's body continues to release nitrogen (decompress) during the Surface Interval. A Surface interval of 16 hours or more returns diver to normal atmospheric saturation level - all extra absorbed nitrogen from previous dive has been released. The longer the interval, the less excess nitrogen remains and therefore the Surfacing Code ‘decays’ back towards code A.
NO-STOP DIVE: A dive for which the table indicates no need for Decompression Stops during the ascent. (A dive with a SURFACING CODE between A and F inclusive).
A no-stop dive is one where insufficient nitrogen has been absorbed to give rise to problems on normal ascent.
DESCENT RATE: The speed at which the diver descends. The maximum Descent Rate allowed for is 30m per minute.
ASCENT RATE: The speed at which the diver ascends through the water. The maximum permissible rate is 15m per minute, and this is the rate at which all ascents up to a depth of 6m are calculated. On all dives, one minute should be taken to reach the surface from 6m.
Descent Rate may be slower but not faster. Ascent rate is critical and should not be exceeded. Ascent is decompression: too fast an ascent means missed decompression, which provokes DCS.
Dive Times shown in Tables include time taken to make ascent to 6m . Ascent column indicates time required to make this ascent. Ascents to 6m may be slower than 15m / minute, provided you reach 6m within the planned Dive Time.
lt is important that divers control buoyancy so they can slow up / stop at 6m, for final part of ascent at 6m / minute.
(By all means learn the other definitions listed in Sport Diving and the Tables, even though you do not need them for the Novice Diver Course)
Important points to remember:-
Table Layout
To begin with, you need only concern yourself with Table A (Level 1). For time being, ignore Surface Interval Table at top (omitted in combined Levels 1 - 4 Tables). Main body of Table has tour vertical columns, headed: