SCUBA 101 – The Terminologies

Introduction

This excerpt is the opening chapter of the book Diver Down: Real World SCUBA Accidents and How You Can Avoid Them, written by Seaduction.com's Editorial Director, Mike Ange and Published by McGraw Hill Publishing.  It is placed here as a reference for our readers as an introduction to SCUBA Diving's myriad of terms and terminologies.  If you would like to purchase the book it is available in major bookstores and on Amazon.com. 

SCUBA 101 – The Terminologies

One of the most daunting tasks encountered by the uninitiated entering the world of diving is understanding the sport’s acronyms, terms and procedural minutia.  This introduction cannot come close to addressing all of those issues; in fact, entire books have been written that do nothing but define diving’s terminologies.  However, we have included some of the most common and frequently used terms and descriptions.  For the active certified diver this section may seem to hold little interest, but we have included many advanced terms, a list of diving’s “rules” and even a brief description of the various training programs up to and including Instructor Trainers that may be informative.  For readers who lack a full command of the terms used in all levels of diving, this brief overview of the most common terminologies will be helpful in understanding the text that follows.

• Training Terms:  The first step in understanding training is understanding training agencies.  Contrary to the mysticism that you will find in the marketing from many agencies, training agencies are merely vendors.  They vend the books, core support materials and a registration process.  They also provide a set of minimum standards for each level of training that each diving professional must agree to comply with in order to maintain membership with a particular training agency.  Perhaps in diving’s early days, these standards varied greatly from agency to agency.  But a cooperative spirit and inter-agency organizations such as the Recreational SCUBA Training Council (RSTC) have forced the agencies to evolve and produce minimum standards that are now fairly consistent from agency to agency.  Travel to any dive destination around the world, pull up a stool at one of the local diver’s bars and eventually you will hear a discussion about which agency produces the best instructors and which produces the worse.  The reality is, of course, that every agency has both good and bad instructors and different agencies simply choose to focus their marketing efforts in different areas.  In spite of these differences, around the world, nearly every diver is trained with the same basic procedures.  While each agency strives to set itself apart with different marketing campaigns and business models, they are all fairly scrupulous in one commitment, the commitment to safety.  The reason they choose to use generally the same dive training procedures even where there is no governmental regulation or mandate is because those procedures work and they are proven safe.  Some of the more commonly encountered agencies include:  the British Sub Aqua Club (BSAC); The World Underwater Federation, commonly called CMAS; National Association of Underwater Instructors (NAUI); Professional Association of Diving Instructors (PADI); SCUBA Diving International (SDI); Scuba Schools International (SSI); and the Young Men’s Christian Association (YMCA) SCUBA Program.  These agencies compose a partial listing of the agencies providing training predominantly for traditional recreational divers.  However, at least two of those agencies now also have smaller divisions focusing on more advanced forms of diving as well.

Sport diving, like many activities, has evolved a number of limits over the decades.  These limits invariably are based upon safety considerations and in some cases liability concerns for the commercial entities that vend services to diving instructors and the instructors themselves.  However, as technology evolves, and our understanding of diving physics and physiology expands, it has become safer and safer to push these traditional limits.  As a result, the sport of diving has divided itself since the 1960’s into two separate braches:  recreational and technical.  The terms are somewhat confusing since both branches are recreational in nature and are clearly distinguishable from professional diving activities like commercial diving, military diving and public safety diving.  The recreational diver, sometimes referred to as the traditional sport diver, includes probably well in excess of 85% of all sport divers.  These divers are basically identified as those divers who adhere to the traditional and long-standing recreational limits.  Those limits are best described by defining technical diving.

Technical divers are typically identified as divers that complete dives that include the following activities, which exceed traditional sport diving’s rules:  (1) Completing dives that require staged decompression stops.  (2) Completing dives that exceed a maximum depth limit of 5 atmospheres of pressure or 40 meters/132 feet of depth (in some countries this limit is 165 ft/50 m or 6 atmospheres of pressure).  (3) Diving into overhead environments that deny the diver a direct access to the surface such as underwater caves and extended penetrations into underwater wrecks.  (4) Completing dives with gas mixtures other than normal atmospheric air (as recreational agencies have moved into the basic levels of mixed gas diving, this line is becoming blurred).  (5) The latest addition to this list are divers using equipment other than traditional open circuit SCUBA gear.

In addition to a couple of small off shoots from the agencies listed above, there are several agencies which specialize in developing standards and vending materials catering to technical or more advanced forms of diving.  An incomplete list of these agencies includes:  Professional SCUBA Association International (PSAI); International Association of Technical and Nitrox Divers (IANTD); and Technical Divers International (TDI).  By definition, traditional recreational diving includes all those things not listed above.

• Levels of Training:  Even within these subdivisions, there are numerous levels of training.  A small number of recreational divers begin with what is known as a Discover SCUBA class, which is a very brief orientation allowing divers to dive in very shallow water under the direct supervision of a diving professional.  But most divers begin their diving careers in an open water class; the first course providing an independent certification which authorizes the diver to purchase life support equipment, fill tanks with air, and gain access to dive charter boats or protected inland dive sites.  The open water diver has very basic knowledge and is only qualified to dive in very limited circumstances at depths that generally do not exceed 3 atmospheres of pressure (66 feet or 20 meters of sea water).  In the industry, this card is really treated as a sort of learner’s permit for diving and open water courses are focused on minimizing the knowledge provided and the skills required to the lowest possible safe level, allowing access to as many people as possible. 


• Traditionally, the next level in recreational diving is the advanced open water diver.  The term is somewhat of a misnomer and in fact many agencies have pulled away from using the term advanced in this second level of certification.  These courses are generally oriented to expand the experience level of the diver to elective areas of the diver’s choice.  These areas include most of the specialties listed below but in many cases they require a core of certain courses like deeper diving and underwater navigation.  Until very recently advanced divers were considered qualified for activities such as night diving and dives approaching the recreational depth limit of 5 atmospheres of pressure (40 meters or 132 feet of water).  However, as some of the larger agencies have moved away from the core requirements, individual specialty cards are rapidly becoming more important in assessing a diver’s qualifications than the traditional advanced open water card.


• Beyond the advanced course, the track for divers becomes very diffuse; divers can complete specialty training in everything from diving at altitudes above 1000 feet to underwater zoology.  Some of these courses merely provide an experience, while others provide real training that develops valuable skills like underwater navigation and deep diving.  See the side bar for a more comprehensive listing of specialty courses.  Some of these specialty courses require advanced certification as a prerequisite to enrollment, while others are open to certified divers of any experience level.  In fact, in the case of some training agencies, it is the accumulation of these specialty certifications that allows the divers to obtain advanced certification.





Altitude Diver – for dives over 300 meters or 1,000 feet Boat Diver Computer Diver – formerly referred to as multi-level diver focuses on diving at multiple stages with set depths Deep Diver – for diving beyond 4 atmospheres of pressure or 20 meters or 60 fsw up to 5 atmospheres or 40 meters (132 fsw) Diver Propulsion Vehicle Operator Drift Diver Dry Suit Diver Equipment Specialist Diver – Covers the operational methods and user maintenance procedures for diving equipment Ice Diver – An overhead environment course for diving beneath frozen bodies of water Marine Ecosystems Awareness Diver – Build an awareness of marine ecology and teaches the principles of identification for marine life Night Diver Recreational Nitrox – Use of air enriched with additional oxygen to a percentage less than 40% oxygen Research Diver – A catch all dealing with a number of programs ranging from ecology to archeology Semi-closed Rebreather Diver – Replacing traditional SCUBA with a breath recirculating system more fully described in the book Search and Recovery Diver – Methods for conducting fairly precise searches for small objects and methods for recovering heavier objects Shore/Beach Diver – Special procedures for diving through surf Underwater Hunter  - Methods for spearfishing, collecting shell fish preferably for food Underwater Collector – Methods of collecting marine life, non lethally for later display in aquariums, etc. Underwater Navigator – Use of a compass and natural terrain association to navigate underwater Underwater Photographer Underwater Videographer Wreck Diver – no penetration – Techniques for identifying the risk factors in wreck diving outside the wreck structure Wreck Diver – limited penetration – Expands the wreck diver to simple linear penetrations through relatively open portions of the shipwreck Solo Diver – Builds self sufficiency to limit or eliminate reliance on a dive buddy CPR Oxygen Administration First Aid

Beyond the dive specialties, most agencies require a separate certification for so called “rescue divers”.  These courses are really self-rescue courses designed to qualify the diver to deal with common emergencies independently and to provide some minimal level of assistance to a dive buddy.  Unfortunately, these courses are frequently confused with more intense programs designed for rescue professionals like police officers, etc.  Divers using these recreational courses as qualifications for professional diving activities are frequently involved in accidents because the environmental and operational concerns for so-called “public safety” or “emergency response” divers are extremely different from those encountered by recreational divers.

A few recreational agencies also offer a certification called Master Diver.  This certification is the highest recreational level certification and it is usually achieved through the accumulation of a number of subordinate courses and the attainment of certain levels of experience.  This certification should not be confused with the Divemaster certification which is actually the first professional level certification because the Master Diver has no qualification or certification to provide instruction or supervision for divers.

• Turning Pro:  The first professional level certification in recreational diving is the Divemaster.  When properly conducted, Divemaster courses are intense training programs requiring a fairly extensive commitment on the part of the student to attain instructor level knowledge in areas such as diving physics, physiology, first aid, life support equipment, recreational diving accident management, and in water rescue skills for use in the recreational environment.  Divemasters are logistics experts and although they work independently with dive charter vessels, etc. they are most frequently used as instructional assistants.  They handle equipment concerns, site logistics and some other issues allowing the Instructor he is working under to focus more of his attention on instructing the students.  For certified divers, and in very limited circumstances, divers in training, Divemasters may also provide direct in water supervision acting as a dive guide and safety.  Divemasters begin their certification courses with fairly significant experience (generally around 60 dives or more), open water, advanced and rescue diver certifications, and a demonstration of good physical fitness and swimming abilities.

Generally, Assistant Instructors are qualified by completing a teaching internship after being certified as Divemasters.  For most agencies, this level of certification is not required and Divemasters may skip directly to an Instructor Development Course.  However, for individuals not desiring the responsibilities of an Instructor, but still desiring to offer some levels of instruction with less direct supervision, the Assistant Instructor course is an asset.  Note that in some agencies, the Divemaster and Assistant Instructor terms may be reversed and in still some other agencies different terminology, such as Dive Control Specialist, may replace these more common terms.

Surprisingly, to become qualified as a diving Instructor, the Divemaster will receive very little additional instruction in anything related to diving.  Instructor candidates are expected to enter their Instructor Development Course with expert knowledge of all the required areas except for instructional methodology.  Instructor qualification is typically divided into two phases, the instructor development course (IDC) and the instructor exam (IE).  IDCs range from four to seven days (40 to 70 hours) and they are designed to give the candidate a commanding grasp of standards and procedures, liability management and instructional methodologies like lesson plan development, methods for increasing student retention of material, etc.  They will also refine their supervision skills and learn methods for controlling groups of inexperienced beginning divers so that they are maintained within safe response times of the Instructor or Divemaster.  Once these skills are mastered to the satisfaction of the Instructor Trainer and the candidate can demonstrate every diver skill to a level called demonstration quality, the candidate is cleared to attend an Instructor Exam.  Depending upon the agency, Instructor Exams vary in length from one to three days but they all share one thing in common, the only teaching or instruction conducted during an IE is that provided by the candidates for their evaluators.  Candidates are evaluated on their ability to develop complete lesson plans, to deliver lectures and in water presentations, to provide proper supervision for beginning divers in both pool and open water environments, to properly evaluate skills, to rescue students in distress, and they also must complete a reasonably extensive swim test to prove good endurance and physical fitness.

Beyond the basic Instructor level, there are numerous Instructor certifications that denote either additional training or the attainment of certain experience benchmarks by the Instructor.  Generally speaking, Instructors can teach most recreational courses providing they are experienced in those areas.  In some cases, more advanced Instructor ratings are required to qualify Master Divers and Divemasters, for example.

The Instructor Trainer, sometimes referred to as a Course Director, is an Instructor who has obtained sufficient experience in the qualifications necessary to teach the Instructor Development course.  In some cases, advanced Instructors may be allowed to assist in the training of an Instructor, but all courses must be conducted under the supervision of an Instructor Trainer.  Generally, the Instructor Trainer conducting the IDC must be different from the IT conducting the Instructor Exam.  Some agencies use a separate qualification for Instructor Examiners while others allow any IT to conduct an exam providing that none of his or her IDC students are taking the exam.

Technical or Extended Range Diving Courses

As previously mentioned, these courses generally exceed the recreational standards including any qualification of traditional recreational instructors.  Technical courses are generally divided into four specific areas.

1. Basic and Advanced Nitrox courses encompass the first area and the only area where the line between traditional recreational and technical are blurred.  Most recreational agencies now offer courses for very limited use of oxygen enriched mixtures.  Because of the limitations of the certification, these courses can be kept very short and contain cursory knowledge limiting divers to the use of diving computers or dive tables to calculate the limitations of the gases.  At the technical level, math is required and all Basic Nitrox divers will learn five formulas and obtain the ability to apply those formulas to specific diving situations.  Advanced Nitrox Divers will expand their capabilities to use gases up to and including 100% oxygen and, in some cases, use two different gas mixes on the same dive.

2. Decompression Courses - One of the key limitations on recreational diving, especially in the US, is the “no decompression limit”.  Due to the physiological implications of breathing gases at pressure, divers have to ascend at a set rate to avoid certain diving illnesses like decompression sickness (this is more fully discussed later in this book).  Recreational divers and Instructors are typically limited to dive durations and depths that allow them to ascend directly to the surface in the event of an emergency with a minimal risk of decompression sickness.  This limitation is called a no decompression limit.  Divers staying for longer periods of time or at deeper depths may be required to ascend to a certain level called a ceiling and stop for so many minutes before ascending to the next ceiling.  These stops, called stages or staged stops, allows the gas dissolved in the diver’s body to escape in a controlled fashion preventing diving illnesses.  Staged decompression courses teach divers to carry adequate equipment and use the proper procedures for planning and completing these stops due to the fact that surfacing for any reason – even dire emergencies – creates an unacceptably high risk of decompression sickness.  These divers must learn a whole new level of self sufficiency and carry adequate equipment to address most emergency contingencies without surfacing.

3. TRIMIX Courses - Divers completing the Nitrox and Staged Deco Courses may desire to move to depth limits which exceed the safe capabilities of normal breathing air and far exceed the safety limits of Nitrox.  These divers, called TRIMIX divers, will use a mixture of oxygen, nitrogen, and helium, called TRIMIX to: reduce the narcotic effect of nitrogen breathed at deeper depths; the toxicity of higher pressures of oxygen when breathed at deeper depths; and reduce the density of the gases moving through the diver’s breathing system so that these systems will continue to work at much deeper depths.  Because of the complex physiological ramifications of using alternate gas mixtures, TRIMIX divers will typically use three or more different gas mixtures during the course of a single dive and they must also be highly disciplined in the maintenance of their dive plan during the course of the dive.

An offshoot of the Nitrox and TRIMIX courses is the mix gas closed circuit rebreather and semi-closed circuit rebreather courses.  These divers use the technologies discussed above in a device the re-circulates the breathing gas to allow far greater efficiency.  Rebrathers are discussed in greater detail later in this text

4. Cave and Advanced Wreck Divers - The final category of technical divers are the extended overhead environment divers, specifically advanced wreck and cave divers.  Although these are very different disciplines, there is much overlap in the procedural methods used by both the wreck and cave diver.  The threat for both divers is the same – before they can move toward the surface in any situation, the divers must first reach an area where they have an unobstructed ability to swim to the surface, commonly called open water.    The chief difference between cave divers and wreck divers is that cave divers generally have swims of extended linear distances, thousands of feet in some cases, before reaching open water; however, they are generally swimming through stable structures with minimal entanglement hazards.  Cave divers can generally anticipate any restricted passages they will swim through on the way back out of the cave since they passed it on the way into the cave.  The primary hazard during a cave penetration is the confusion of the maze like passages and the constant threat of lost visibility due to either silting or light failures.  Wreck divers will never encounter swims with the distances involved in cave diving and they generally have access to multiple exits during their dive.  However, they will encounter a host of man made obstacles, decaying and unstable structures that can collapse or shift while they are inside; entanglement hazards that include everything from monofilament fishing line to electrical wiring, sharp objects that can cut navigation lines and numerous other hazards.  In most cases, cave divers will also surface in very controlled environments, typically in inland springs, whereas the wreck diver may also have to deal with the variables of the ocean at the end of his dive.

The Technical or Extended Range Instructor & Divemaster

Unlike recreational diving there is no instructor level that encompasses all levels of technical diving.  In fact, each area is considered a separate discipline and dive masters, instructors and even instructor trainers will typically qualify individually for every type of course they intend to teach or supervise.  To become a technical instructor or technical divemaster typically involves three steps:  first, they have to qualify as a diver at the particular level they plan to supervise or teach; second, they must become a recreational divemaster or instructor (although in the technical community it is not necessary for a recreational instructor to become a technical divemaster before enrolling in a technical instructor course); and third, they have to complete the technical instructor course.  With most agencies, it is also necessary to become an instructor or divemaster at any subordinate level before moving to the next higher level.  As a result, the course work completed by an advanced technical instructor can form quite an impressive resume in and of itself.  For example, a TRIMIX instructor would have a progression similar to that in the sidebar.  At the technical level, the instructor courses are more streamlined and less complex, however, the evaluation is far more stringent.  Since the instructor already has completed a thorough instructional methodology course and has been evaluated in those areas prior to becoming a recreational instructor there is no need to repeat that training and an evaluation of those skills will be repeated in any event during the instructor’s exam.  The instructor will typically complete a two or three day evaluation including: diving in the maximum range of the certification he or she is seeking; completing a comprehensive written examination evaluating all the physics, physiology, dive planning and dive safety issues pertaining to the course work; and presenting two or more randomly selected lectures from the diver course level for evaluation.  In most cases, the candidate will also be evaluated on their ability to supervise all of the water skills required in the class in real world conditions.  Ideally, each of the evaluated areas would be examined more critically than the average recreational instructor would anticipate.

Technical instructor trainers (TIT) go through a similar process for each level.  The only difference being that the TIT must also certify a number of instructor candidates at each level before becoming a trainer at the next higher level.

Throughout the following pages, you will see references to the rules of diving.  The reality is that these rules are somewhat ubiquitous and not nearly as cohesive as the illusion would indicate.  Throughout a number of different texts, there have been a number of different rules printed, yet, there exists no complete or comprehensive listing of diving’s rules.  Only two rules for traditional recreational divers permeate virtually all references.

The so called “number one rule of diving” is:  never hold your breath.  The reason for this rule will be fully explained in one of the following chapters but, for now, suffice it to say that this rule is necessary to prevent the diver from over pressurizing his lungs causing catastrophic injuries.

The second rule of diving appears in a number of variable forms but is most commonly stated as “plan your dive and dive your plan”.  Although frequently quoted, this rule has been interpreted to mean a number of different things in a multitude of different types of diving references.  The best interpretation is the literal one:  take the time to plan your dive SAFELY from start to finish and then stick to the plan no matter what happens.

More advanced or technical divers also use a short list of five inviolable rules initially developed by cave divers, but two of these rules are applicable to every advanced or technical diver:

1.  Be Trained – No matter what activity you plan to do underwater the first step in surviving it is to get proper training.

2.  Properly manage your air (gas) supply.  Usually this means using the rule of thirds, that is one third into the dive, one third back to the exit point and one third reserved for ascent and emergencies.

For tech divers we would add:

3.  Narcosis kills.  Originally written as no deep cave on air, this rule references the narcotic like effect of the nitrogen in air and its impairment on judgment, especially for inadequately prepared and inadequately trained divers diving beyond the traditional recreational limit of 130 feet.  (It is important to note here that this text in no way condemns dives deeper than 130 on air and, in fact, the author dives deep air routinely but only with proper preparation, training and an ability to recognize and manage his own narcosis levels.)

4.  Always use three light sources.  This rule predominantly applies to very deep divers or divers in overhead environments.  By carrying three sources of light the probability of being left with no light source is extremely minute.  This is important in environments where loss of light means complete loss of vision and a subsequent inability to find the exit.

5.  Always maintain a continuous guide-line to the surface.  Again, this rule applies predominantly to overhead environment divers, but every diver should have a reliable capability to return to the exit point at the end of the dive.  For open water divers, this could mean maintaining a reliable ability to navigate; but, the concept is the same.

From this point, the variety of rules is so scattered and broad reaching and so lacking of any coherent source that I am invoking a bit of editorial license and printing my own list of rules.  This list is by no means complete, nor are all the rules my own, as diving professionals frequently borrow from one another evolving the best techniques from the experiences of our peers as well as our own.

1. Murphy is alive and well (of Murphy’s law fame) and he resides in the unsuspecting diver’s gear bag where he patiently waits to kill him or her.  This rule is my own and it simply relates to the fact that of the hundreds of accidents that I have reviewed, a significant number have resulted from poor maintenance of equipment, the use of improper equipment, or the total lack of the equipment required for a certain dive.  I suppose it would also include the failure of rule two below.


2. No one plans to die in their dive planning.  Many divers pop happily from dive to dive thinking that a dive accident will never happen to them so they never plan for contingencies.  This rule simply means that every diver should consider every conceivable mishap, mistake or accident that could occur on every dive and at least consider some potential responses to those situations.


3. The dive never gets better.  Also known widely in technical circles as Odom’s rule - a reference to my friend and colleague, Joe Odom, the rule’s apparent originator or at least the person who appropriated it earlier than everyone else.  This simply means that any dive or any portion of a dive that begins badly will never improve until the problem is addressed and fully resolved.  Violations of this rule frequently start the cascade effect referenced in the next rule.


4. No one thing kills you.  This rule is borrowed from the aviation industry and it references the fact that there is rarely one specific cause for an injury producing accident or fatality.  Generally, one problem gets bigger leading to another problem and creating a chain reaction of events leading to panic.


5. Panic is the primary thing that kills divers.  It is amazing the situations and conditions from which the healthy human can recover providing he remains in control of the situation.  It is when the diver losses rational thought processes and control that most accidents occur.


6. Briefings are for everyone.  It is unbelievable the number of divers that will pay a professional for services and then totally ignore the information that professional with vast experience and local knowledge provides in a dive briefing.  It is even more amazing the number of statistics that begin with this failure.


7. Redundant not ridiculous.  It is important to have adequate equipment and adequate backups for your equipment on every dive.  It is just as important to be able to actually swim through the water with what you carry.  The mark of the true experienced diver is the one that can evaluate the equipment required for safe dive completion without waddling off the boat wearing an entire dive store.


8. It is good to be seen and heard, especially when you are twenty miles off shore drifting like flotsam on the surface of the ocean.  Every diver diving in any large body of open water should carry at least one highly visible visual device like a surface marker bag or safety sausage (international orange or fluorescent rescue yellow are the best colors).  You should also have a light source with significant duration and a sonic or sound signaling device; the best of these devices are connected to the compressed gas cylinder and deliver a piercing signal that can be heard for miles like the “Dive Alert”.


9. Bad days are predictable.  Experienced instructors are notorious for watching divers assemble their gear and identifying who to watch simply from this observation.  Do not fool yourself.  If you have a skill deficit or equipment problem, correct it before the dive and before you become a statistic.


10. You are responsible for you.  When it comes down to it, only you can swim for you, think for you, and save your own life.  Whether you are with an experienced buddy, a dive pro, or a novice, there is a very finite amount of assistance that can be provided to you underwater.  Never trust anyone else to keep you safe.  Take responsibility for your own safety.

As stated, this list is by no means comprehensive or complete and no doubt, you will note other “rules” of diving as you go through this book.  Although stated in other ways, most of them can be related back to the framework described above.

The final terminologies that may be somewhat baffling for the uninitiated are the various pieces of equipment divers use to survive and function and underwater.  Some of these items like the dive knife and the dive flag are easily recognized by most people in the general public and their uses are obvious.  Other items are more esoteric and the uses of still others may seem obvious but in reality be deceptive.  This entire text does not provide enough pages to do service to a comprehensive list of a diver’s equipment.  However, to understand some sections of this text, it is important to be able to identify a certain number of core pieces of equipment used by most divers on most dives.  So, the following list is a very generic overview of some important items of equipment that you may see referenced within.

• Exposure protection; wetsuits or drysuits - Water cools the human body as much as 25 times faster than air.  As a result, even when the water temperatures approach 80° F (27° C) or more, divers must protect themselves to slow the cooling process.  On the average dive, this is a comfort issue and on some dives where long exposures are unexpected but occur anyway, it may be vital for survival.  Wetsuits come in a variety of thicknesses and are made of various types of flexible neoprene rubber.  Although there are many real features and even more sales gimmicks, the important aspects of a wetsuit are proper fit, adequate thickness for the dive, and enough flexibility to allow reasonably free movement underwater.  As you would guess, wetsuits allow the diver to get wet.  Drysuits, on the other hand, keep the diver dry and allow the use of undergarments to further slow the cooling process.  In very cold water  (60 F / 15 C or less), or on dives of extended duration, this added protection may become vital to survival.   The core suit, whether wet or dry, may be combined with a number of different options as required to keep the diver warm.  Hoods, gloves and boots are but a few of the items that may be used.


• Buoyancy Compensating Device or BCD - Modern BCDs come in a number of styles and configurations; but they basically perform two vital functions.  One, they provide a harness system which attaches the diver’s SCUBA tank firmly to his body so that he does not become separated from his breathing gas supply during the course of the dive.  Two, they provide a bladder that can be inflated with either compressed gas from the SCUBA tank or air exhaled orally by the diver to increase the diver’s displacement in the water.  Divers have to be weighted to sink and the BCD’s primary function is to offset that weight or negative buoyancy when the diver reaches the desired depth so that he can hover and move freely without expending energy to maintain a constant depth (this state is called neutral buoyancy).  The other function of the bladder is to provide limited duration positive buoyancy to keep the diver afloat on the surface.  The BCD should never be confused with a life jacket.  It does not provide face up floatation nor is it designed for sustained surface floatation.


• SCUBA tank - In most places in the world today, it is more politically correct to use the term cylinder.  SCUBA Cylinders are containers made typically of either steel or aluminum that hold air or other breathing gases in a highly compressed state for use by the diver.  These cylinders are typically compressed to between 2400 psi / 160 bar and 3500 psi / or 230 bar.  In some more advanced forms of diving, divers may wear two cylinders connected together with a hard pipe manifold called twins or doubles.


• Regulators - In the diver’s lexicon, “regulator” has come to mean the entire gas delivery system consisting of a second stage mouth piece, an alternate second stage or safe second, a hose for connection to the BCD inflator, and a submersible pressure gauge, all connected at one central point to a brass pressure reducing valve which is properly the real regulator.  Regulators and their functions are discussed more fully in one of the following chapters.


• Dive masks.  This piece of equipment is easily recognizable but is a frequently misunderstood piece of equipment.  The mask has one purpose – to place an air space in front of the diver’s eyes so that he can see underwater.  It is not designed nor does it adequately perform the function of keeping water out of the nose.  The nose is merely enclosed to allow the air space in the mask to be equalized.  Ironically, this enclosure which traps water next to the nostrils when the mask partially floods is frequently the cause of panic episodes.


• Dive tables.  In one of the following chapters, there will be a discussion of diving illnesses to include decompression sickness (DCS).  We prevent DCS by estimating the amount of Nitrogen or other gases that can be absorbed into the body and predicting the proper rate of ascent to safely eliminate those gases.  This is accomplished by the use of a dive table.  However, even in the profession, decompression methodologies are referred to as theories, not as science.  Therefore, in some cases, even divers following the tables to the letter will have DCS incidents.


• Dive computers.  In the past two decades, digital technology has made automatic devices for calculating the information on the dive table safe and affordable.  Statistics show that computers generally provide a safer alternative to tables simply because the computers are fool proof.  They require no user interface to function in most cases, other than, perhaps, turning them on.  Thus, diver error is virtually eliminated.  Computers date back to the late 1950’s (mechanical spring or gas driven devices) but early designs were unreliable, at best, earning them nicknames like the “bend-o-matic”.  Electronic technology has improved these designs to the point that any serious diver would be foolish to dive without one.


• The only two remaining pieces of equipment that are standard for even the most basic diver are the fins and the snorkel.  Fins simply expand the surface area of the foot allowing the diver to push his body and ample amounts of equipment through the water with relative efficiency.  Snorkels are simple plastic tubes that allow the diver to breathe while his face is submerged.  This allows the diver to conserve air on surface swims and in the event that the diver finds himself on the surface in rough seas, it provides a more secure method of breathing while limiting the inhalation of water.

Finally, any discussion of equipment would be incomplete without defining the identifying term of our sport itself.  SCUBA has become a word in a number of languages including English.  However, the word began as an acronym for – Self Contained Underwater Breathing Apparatus.  SCUBA differs from technologies that have been used for hundreds of years because it allowed the diver to truly swim free beneath the surface carrying his air supply with him.  There are a number of claims, but it is generally accepted that the first successful SCUBA unit was created by a French Canadian, Emil Gagnon, and a former French Naval Captain, Jaques Cousteau.  Neither of them could probably have imagined the revolutionary discoveries or the awe inspiring thrills that millions would experience as a result of Captain Cousteau’s first experimental foray below the surface of the water.