DIVE PLANNING TABLES vs. COMPUTERS
The fact that most cases of decompression illness occur following the ‘correct’ use of dive computers or tables prompts us to urge caution when planning any dive, even if the diver is well within the No-Stop Limits. There is no such thing as a completely safe dive computer or table, since no table or computer allows for the individual variation of divers. Because a diver’s predisposition to decompression illness varies with health, fitness, exertion, level of hydration, cold, the presence of a patent foramen ovale (PFO) and many other factors, what may have been a safe dive on one day could be hazardous on another.
The risk of decompression illness and nitrogen narcosis increases when making repetitive dives, or deeper dives (more than about 24 meters). Dives requiring mandatory decompression stop(s) may also be more hazardous, partly due to the difficulty of doing the stop(s) correctly. Accordingly, it is generally recommended that deeper and/or decompression stop dives should be avoided where possible and that repetitive dive schedules be calculated conservatively, especially multi-day repetitive diving using dive computers. Therefore, maximizing surface intervals may also reduce the likelihood of decompression illness.
Rapid or multiple ascents increase a diver’s chance of developing decompression illness. Consequently, divers are urged to train themselves in ascent techniques and to avoid ascending faster than about 18 meters per minute when ascending from depths of around 30 meters or shallower.
Divers are advised to go to the maximum depth early in the dive and then progressively and slowly move shallower, ending each dive with a safety stop of at least 3 – 5 minutes at 5 – 6 meters.
Where possible, repetitive dives should become progressively shallower and surface intervals should be at least two hours. When multi-day diving is conducted for several consecutive days (such as on diving holidays) reasonable precautions should be taken not to make more than three dives in one day and to refrain from diving on the third or fourth day.