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Myths & Misconceptions
Disclaimer & Invitation
Brief History of Diving
The Respiratory System
Explanation of Pressure
Water & Physical Laws
Unequal Air Pressures
Gas Pressure at Depth
Dive Tables & Computers
Stress & Diving
Non-air Gas Mixtures
Women & Diving
Medical Fitness for Diving
Asthma & Diving
The Great Debate
All About DAN
Scuba Training Agencies
Magazines & Newsletters
Books & Videos
Diving Odds N' Ends
Unless you score 80% or better on the short scuba quiz, you can
probably benefit from reading this book. Knowledge of basic underwater physiology is
critical to diving safety, of course, and the subject is taught in every certification
class. For example, the first rule of diving -- don't hold your breath -- is based on
Boyle's law of gas pressures, which predicts that a scuba diver's lungs will expand if
breath is held on ascent. The consequence can be a serious and even fatal over-expansion
Although all certification manuals and general scuba books review underwater physiology,
the coverage is necessarily limited. Typically, one chapter is devoted to the subject.
Important effects of altered physiology, such as decompression sickness and arterial gas
embolism, are covered only briefly.
As a recreational diver and pulmonary physician, I believe there is need for a book that
more fully explains this material. Not a textbook for the doctor, engineer or scientist,
but a book any recreational diver can understand. A book that answers questions frequently
pondered by the recreational diver. After searching and finding no such book, I decided to
write one! Scuba Diving Explained is intended for all sport divers because the material is
important for all of us, from beginner to people with years of experience.
Subjects include: the concept of pressure, the four major gas laws as they apply to
diving, composition of air, changes in gas pressures with depth, ear and sinus squeeze,
lung barotrauma, air embolism, decompression sickness, nitrogen narcosis, oxygen toxicity,
carbon monoxide and carbon dioxide toxicity, stress, hypothermia, hyperventilation, and
I also answer some questions on "deep diving" (below 130 feet), and diving with
non-air mixtures such as Nitrox. Both activities are outside the realm of recreational
diving (as defined by the scuba training agencies), but their physiology is fascinating
and germane to all diving. If you understand, for example, what Nitrox is and why it does
not allow one to dive deeper than with ordinary air, you can better appreciate the effects
of water pressure on nitrogen and oxygen in any gas mixture, including ordinary air.
A separate section answers some commonly-asked questions about women and diving, e.g.,
"Do women have an increased risk of the bends?" and, "Is diving safe during
pregnancy?" A section on medical fitness for diving explains the rationale of some
published guidelines, most of which are based on theory rather than hard data. Another
section reviews perhaps the most controversial of all conditions for scuba diving, asthma.
Scuba Diving Explained is designed to increase your understanding and enjoyment of the
sport. However, the book is not an instruction manual; it contains relatively little
information about scuba equipment (better taught with hands-on instruction in a scuba
course), diving skills or marine life. Instead, emphasis is on the physiology vital to all
sport divers. I go to great length to explain changes in gas pressures with depth because,
quite simply, that singular feature most affects the diver's safety.
In sections B through L are brief questions to 'test your understanding' of the material.
Placement of some questions within the text is preferable to putting all of them at the
end of a section or in an appendix. Each question is germane to the proceeding paragraphs;
answers are at the end of the section. For diversion, you will find paragraphs of 'Diving
Odds N' Ends' at the end of each section, in gray boxes. Some of this information is
gleaned from various popular periodicals and non-technical books. Because scuba magazines
are a prime source of information for the sport diver, I have prepared a list of
nationally-circulated periodicals published in the U.S., along with addresses, circulation
figures and phone/fax numbers (Section T). For U.S.
distributors of scuba books and dive videos, as well as a list of some comprehensive
internet scuba sites, go to Section U. Also included for most
sections is an extensive bibliography, covering both quoted sources and other books and
articles that may be of interest to recreational divers.
Although you will probably get more out of Scuba Diving Explained if you have some scuba
experience, it should also be useful to anyone interested in diving who has yet to don
scuba gear. There seem to be as many "wannabe" divers as there are the certified
kind. If you don't dive but plan to learn, it is not too soon to begin your exposure to
underwater physiology. There is no substitute for basic training from one of the national
scuba certification agencies. These agencies, listed in Section S,
teach the basic scuba skills and provide a general introduction to underwater physiology.
Scuba Diving Explained should help you better understand this physiology and the effects
of breathing compressed air underwater.
Happy and safe diving!
Lawrence Martin, M.D.
Several scuba divers reviewed the draft of this manuscript. They made many useful
suggestions, most of which I readily incorporated, and caught some errors, for which I am
grateful. For their efforts I thank (in alphabetical order): Pam Alderman, Anne Cath,
M.D., Jolie Bookspan, Ph.D., John Comley, Bernard Martin, Robert Martin, M.D., Ruth S.
Martin, M.D., and Lorain Rimko. I would also like to thank Debra Shirley for her many
excellent line drawings; and Diver's Alert Network and the Diving Historical Society for
permission to use some of their photos.
To Ruth, my wife and dive buddy.