Repetitive Dive
Introduction
A repetitive dive refers to a dive that is performed before the complete off-gassing of residual nitrogen or other inert gases from the previous dive. This is generally within a time frame of at least 10 minutes, but no more than 12 hours after a previous dive. Off-gassing, the process by which these inert gases are eliminated from the body’s tissues, is critical to ensure diver safety and prevent decompression sickness.
Understanding Repetitive Diving
In scuba diving, gas absorption and elimination in the body is driven by pressure differences. When a diver descends, the increased pressure causes inert gases like nitrogen to dissolve in the body’s tissues. Upon ascent, these gases are slowly released or “off-gassed.” If a diver makes a repetitive dive before this off-gassing is complete, the inert gases from the previous dive are added to those of the subsequent dive, potentially increasing the risk of decompression sickness (DCS).
Risks and Safety Measures
Repetitive dives can present increased risks due to the potential for elevated inert gas levels in the body. Divers should be aware of the dangers, including decompression sickness, nitrogen narcosis, and oxygen toxicity. To manage these risks, it’s essential to follow proper diving procedures and use dive tables or dive computers, which account for residual nitrogen time (RNT). This time is added to the actual bottom time of the subsequent dive to calculate a new, total theoretical dive time.
Decompression Considerations
Decompression stops are crucial during ascent from a repetitive dive, especially when no surface interval or a short surface interval is involved. These stops allow extra time for off-gassing. The duration and depth of these decompression stops depend on various factors, such as the depth and duration of both the previous and the repetitive dives, as well as the surface interval length.
Dive Planning for Repetitive Dives
Planning repetitive dives requires considering the cumulative effect of multiple dives on the body’s inert gas load. Divers should incorporate surface interval times, which help facilitate off-gassing. Furthermore, diving best practices often suggest performing the deepest dive first when planning multiple dives in a day, to minimize the accumulation of inert gases.
Dive Tables and Computers
Dive tables and dive computers are essential tools for managing repetitive dives. Dive tables provide pre-calculated information on no-decompression limits and necessary surface intervals for repetitive dives. Dive computers, on the other hand, offer real-time tracking of nitrogen absorption and elimination, adjusting the diver’s profile based on actual depth and time.
Training and Certification
Specialized training and certification for repetitive diving are available from recognized dive organizations. These programs cover topics such as dive planning, managing residual nitrogen, using dive tables and computers, and handling potential emergencies.
Advanced Techniques and Considerations
As divers gain experience and venture into more complex dives, such as deep diving, cave diving, or technical diving, managing repetitive dives becomes even more critical. Advanced divers often utilize various gas mixes, such as Nitrox or Trimix, which can alter the off-gassing process and thus impact the management of repetitive dives.
Special Gas Mixes
The use of enriched air Nitrox (EANx) or Trimix in repetitive diving offers certain benefits. EANx has a higher oxygen content and a lower nitrogen content than regular air, which reduces nitrogen absorption and accelerates off-gassing, thus extending no-decompression limits (NDLs). Trimix, a mixture of oxygen, nitrogen, and helium, is primarily used in deep and technical diving. Helium off-gasses faster than nitrogen, which can be advantageous in repetitive diving scenarios.
Rebreather Diving
Rebreather diving is another advanced technique that impacts repetitive diving considerations. Rebreathers recycle exhaled gas, remove carbon dioxide, and add fresh oxygen, maintaining an optimal breathing mix. This technology reduces nitrogen absorption and helps divers extend their bottom time and shorten decompression stops, making them particularly useful for repetitive diving.
Hyperbaric Medicine and Repetitive Dives
The field of hyperbaric medicine, which studies the health effects of high atmospheric pressure, has significant implications for repetitive diving. Hyperbaric chambers are used for therapeutic recompression and treatment of decompression sickness, a risk associated with repetitive diving.
Effects of Altitude and Flying
Divers must also consider the effects of altitude and flying on off-gassing after repetitive dives. Diving at altitude or flying soon after diving exposes the body to lower atmospheric pressure, which can expedite the formation of gas bubbles, leading to DCS. Divers are generally advised to wait at least 12 to 24 hours after their last dive before flying or ascending to a significantly higher altitude.
Final Thoughts
The practice of repetitive diving showcases the intricate relationship between physics, physiology, and underwater exploration. Through understanding and respecting these elements, divers can safely engage in repetitive dives, maximizing their underwater adventures. Each dive offers a unique experience, and with proper planning and caution, scuba enthusiasts can safely continue to explore and appreciate the marine world’s wonders.
Conclusion
Repetitive diving is a common practice among recreational and professional divers. However, it requires careful planning, understanding of decompression theory, and adherence to safety protocols to manage the risks associated with residual inert gases. With the right knowledge and tools, divers can safely enjoy the underwater world multiple times within a single day or over consecutive days.
