During the open water course, dive students are taught about the limits of their certification. Most entry level certifications limit divers to a maximum depth of 60 feet when accompanied by another open water certified diver. Unfortunately, many entry level divers exceed the limits of their certification, not understanding the dangers that they face by doing so. My opinion is that this is a weakness of the open water course. Students are told not the exceed the limits of their training, but they are not always told why they shouldn't. Here are some of the reasons for the limits placed upon open water certified divers.
Nitrogen narcosis, also known as the rapture of the deep, is the narcotic, inhibitive effect of nitrogen breathed on deep dives. Nitrogen narcosis affects divers in different ways. Some divers experience a sensation of euphoria, almost like a pleasant drunkenness, while other divers experience a feeling of dread and fear. Either way, nitrogen narcosis is dangerous because it inhibits a diver's ability to think and problem solve underwater. All divers are susceptible to nitrogen narcosis, some at more shallow depths than others. Some divers experience nitrogen narcosis at depths as shallow as 80 feet. Because it is impossible to predict at what depth a diver will feel the effects of nitrogen narcosis and what his reaction will be, it is essential that divers make their first dive deeper than 60 feet under the watchful eye of a certified scuba instructor.
At extreme depths, the concentration of oxygen in a diver's tank becomes toxic, a physiological reaction known as oxygen toxicity. A diver experiencing oxygen toxicity will twitch, convulse, and may even become unconscious. While unconsciousness is frightening enough, the seizures caused by oxygen toxicity are even more dangerous. Divers experiencing oxygen toxicity usually lose their regulators and may drown. If you are are interested in deep diving, take a deep diving course in order to learn how to avoid the risk of oxygen toxicity.
Air Consumption Rate:
The deeper a diver descends, the more rapidly he uses his air. A diver who descends to 90 feet will use his air about twice as rapidly as he will use it at 30 feet. This gives him a shorter amount of time to enjoy the underwater world and less time to deal with problems. Divers who dive deeper than 60 feet may need to adjust their air reserve (the tank pressure at which they begin ascent) in order to have enough air to ascend at a safe ascent rate and deal with any problems that occur. Of course, learning to manage gas at deeper depths requires additional training beyond the open water certification level.
Divers absorb nitrogen underwater. If a diver absorbs too much nitrogen, he can not ascend directly to the surface without running the risk of decompression sickness. Instead, he must make a series of stops known as decompression stops during his ascent to allow the excess nitrogen to escape from his body tissues. The amount of nitrogen a diver absorbs is proportional to both his depth and the amount of time he spends underwater. While all divers must track the amount of nitrogen their body absorbs on a dive, a diver who stays above 60 feet is unlikely to absorb so much nitrogen on a single dive that he must make decompression stops during ascent. Divers who descend deeper than 60 feet run the definite risk of entering into decompression, and must be very careful to ascend before exceeding their no decompression time limit. This is yet another reason that divers who wish to descend past the 60 foot open water certification limit should seek additional training before doing so.
Diving With a Certified Buddy:
Divers who have completed their open water certification have practiced basic emergency skills such as air sharing. Familiarity with safety protocols and emergency skills is essential for safe diving, and most emergency management taught in the open water certification course depends on team work. Open water certified divers who wish to solo dive or those who wish to dive with non-certified divers must seek training above the open water certification level both for their own safety and for the safety of the divers who accompany them. An open water certified diver should never take non-certified friends or family diving, not even in a pool. This is the job of a trained scuba instructor, who is proficient in emergency management and knows what essential information must be conveyed to a new diver before taking him in the water.
Diving in Conditions Similar to Those in Your Certification Course:
Open water certification guidelines explicitly state that divers are certified to dive in conditions similar to those in which they were trained. A diver who has trained in warm, tropical waters is unfamiliar with the additional risks of diving in a cold, murky lake. Similarly, a diver who has trained in a cold, murky lake may be unfamiliar with the special procedures used when drift diving over warm, tropical reefs. Divers who are interested in exploring a new environment definitely should! However, they should make their first dives in the new environment with an instructor or a dive master who can give them pointers on local protocol and procedures. Never enter a wreck, cave, or other overhead environment without proper training. Such dive sites limit a diver's ability to ascend directly to the surface and are beyond the scope of the open water course.
The Take-Home Message About the Open Water Certification Limits:
Open water certification limits are in place for your safety. Many open water certified divers do not understand the risks they take when making dives that exceed their certification limits. If you wish to dive deep, dive in a new environment, or to take non-certified friends and family diving, seek the appropriate training.