top of page

The five sacred rules

Accident Analysis

Any accident with a high risk of injury or death can benefit from a procedure to investigate an accident.  Some people believe that accidents are inevitable and will always happen.  Sadly, accidents do occur and typically much too often.  The truth is that all accidents are preventable.  There is no reason for any accidents to occur, but our carelessness allows them to be part of our existence.


How did accident analysis evolve within our cave diving community and the scuba-diving industry? During the 1960's the sport of scuba diving began to grow as courses were developed that offered information,knowledge and certifications. This training was a major step toward making diving safe and fun. At the same time, diving equipment manufacturers grew hand-in-hand with scuba diving's growth and popularity. Equipment slowly became easier and more comfortable to use for recreational diving to move forward came very close to outlawing access for scuba diving and develop into the industry we see today. As more scuba divers emerged, they started to discover the springs of North Florida. That was the beginning of many years of multiple-drowning accidents. The worst year of fatalities was 1974 when 24 divers perished diving the springs and sinkholes of Florida. The Florida legislature came very close to outlawing access for scuba diving the springs and sinkholes of North Florida.


Though there was a serious legal threat to scuba diving in the springs during the 1960's, there were many divers who were diving the caves safely and successfully. The realized it was not the caves killing the divers, but people unwittingly placing themselves into a very dangerous environment and situation. The information and training needed was not available.


During the 1990's, there was a remarkable drop in the number of open water divers dying in underwater caves. This was the result of a spectacular improvement in education and awareness initiated and maintained by the cave diving community. Rarely do accidents in Florida occur now due to many of the popular dive sites being controlled as recreation areas, or private campground and dive sites. Owners or managers help enforce the rules and qualifications for diving in the underwater caverns or caves.


The first cave diving certifications in the United States were awarded in 1970 by the NAM Today there are at least six training agencies in the United States and countless others in countries all around the world that offer cave diving certifications. This has resulted in boom periods during the mid-1980's and the second half of the 1990's. This has increased the number of accidents in the cave diving sector it's worthy to note that the increase is small compared to the increase in the number of cave divers.

Evolution of Safe Cave Diving Principles


Credit should go to Sheck Exley, who was known for his exploration achievements, contributions to cave diving safety, and his founding of the Cave Diving Section of the National Speleological Society. In 1977, Sheck published an outstanding booklet titled Basic Cave Diving: A Blueprint for Survival.


This book briefly described and listed the reasons for known accidents that had occurred in the late 1960's and the early 1970's. He concluded theanalysis with a summary of the principle causes of cave diving accidents. The book is a "classic" and still available through the NSS-CDS and the NACD. The first cavern course organized and introduced to the public was in 1976 by NACD cave instructor Rory Dickens for the PADI Specialty Training Program. It was in 1979 when the Cave Diving Section initiated its training program and introduced their version of a cavern diving course. As the years went by, the CDS Training Committee began to see a consistent, emerging pattern in accidents and incidents. It was becoming quite obvious that a formal evaluation of these accidents was needed to make cavern and cave diving safer and more enjoyable.


Lessons of Accident Analysis



The most alarming factor contributing to these accidents was a "lack of training" for this specialized diving activity in an overhead environment. This was the key reason why open water divers were getting killed in underwater caves. Without training and education, how could anyone understand the fundamentals of safely diving this specialized environment? Knowledge makes a big difference in avoiding a dangerous situation when participating in a high-risk endeavor.


The second critical factor that stood out in many of the fatalities was the lack of a guideline to the underwater cave's entrance. Too many times divers swam in and could not find their way out. The way out was usually through bad or zero visibility. Without a guideline to follow by feel, how could anyone find the way out? Yes, there have been close calls where divers were able to stumble their way out and survive. They were the lucky ones. Without the aid of a line, the odds are highly against you.


The third factor that consistently appeared in accidents was a lack of proper gas management. Anytime a diver places himself in an area with a ceiling, he automatically eliminates one of his escape routes in case of a problem or emergency, the surface. Common sense should tell you that once the surface is no longer a choice, you must manage your gas supply in a manner of having a reserve supply in case of an emergency. If you swim so far in, you better have plenty of gas to get out. Delays due to silt, buddy out-of-air, or other issues must be accounted for.

Sheck Exley helped devise and make known to the tiny cave diving community of the early 1970's one of our most sacred rules, the rule of thirds. Always plan ahead for your exit or return with your remaining 2/3rd's gas supply. Whatever amount of gas allotted to going in can be used for any suitable purpose. Once you reach your planned turn-around gas supply, it is time to start out, without question. For example, you begin your dive with 3000 psi (210 bar). Your planned 2/3rd's out is 2000 psi (140 bar). The thirds rule was developed on the buddy concept. Once any member of the in exiting an overhead environment dive team reaches their first third, either diver should have enough gas left that both can reach the entrance sharing gas from one source. At least in theory, this gas plan should work for any "out of gas emergency'. Of course, it does not factor in stress and increased gas consumption rates. Perhaps the best reason to use the rule of thirds is that any problem in exiting an overhead environment must be solved underwater. The extra gas buys you the time to work with the delay and solve the problem.



The fourth factor was not usually a problem with untrained, open water divers, but was a frequent factor with trained and certified or experienced cave divers. This problem is diving too deep. Statistically, the biggest killer of certified cave divers is diving too deep for their training or experience or beyond the physiological safe limit. Fortunately, 98 percent of cavern areas are shallow and safe. With the 100 feet (30 meter) depth limit to cavern diving, there should be few problems with narcosis. Divers must recognize their personal depth limits and stay within their personal comfort zones.



The fifth factor is associated with light failure. By always diving with a minimum of three lights, the statistical probability of a complete lighting failure is drastically reduced.  In cavern diving, sunlight represents the primary light source or beacon used as a navigational tool. The second and third lights are battery powered and carried by each cavern diver. Be sure the lights have sufficient power and burn time and the batteries fully charged. Open water divers frequently try to dive in a cave with one light. The failure of a single light has often been the cause of an accident leading to a fatality.

In recent years there have been several fatalities involving cave divers drowning while diving solo. The NACD standards clearly emphasize the importance of the buddy-team concept in terms of increasing dive safety. In addition to violations of the five accident analysis rules, there are other factors that have contributed to the diving fatalities of the past. Alcohol intoxication, the improper use of drugs, and the improper use of equipment have played a part in some of these tragic events. However, the primary cause, with any doubt, is a lack of training. Completion of training to become a certified cavern or cave diver dramatically improves one's chances of safely enjoying this unique and beautiful environment.

cave diving mexico_edited.jpg




1.  Be trained in cavern or cave diving and dive within the limits of your training.
2.  Always run a single continuous guideline from the open water.
3.  Always reserve at least two-thirds of your beginning gas supply for the exit.
4.  Do not dive too deep. Stay within your training, experience level and ability.
5.  Always use a minimum three lights per diver.

These rules form the fundamental basics of safety for all divers who choose to dive in the overhead environment. These rules do not guarantee a diver's safety.

Say "Yes" to your next amazing adventure!

Join Advanced Diver Mexico for a dive!

bottom of page