DAN Medical Frequently Asked Questions
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Steel Tank Causes Diver to Become Inverted While Descending
>Unused to the heavy tank, a diver gets inverted during descent
>This diver is an experienced diver who knows he has a higher than normal air consumption rate. He is aware this may be inconvenient for other divers in the group who have the air supply to dive longer, but must cut their dive short when diving with him. His instructor advised the diver that if he could dive with a steel tank he could carry more air for his dives, but it would reduce the amount of weight needed to stay negatively buoyant. The instructor explained the larger steel tank was negatively buoyant and therefore has a tendency to flip an unaware diver upside down. The diver was instructed on how to handle the steel tank underwater and was advised to remove 2kg (approximately 4lbs) from his 5kg (approximately 11lbs) weight belt.
>The diver began a normal descent and started to equalize. While he was descending, the extra weight of the steel tank on the diver's back started turning him upside down. This caused the diver's descent rate to increase and equalizing a challenge. Being inverted, his regulator was also causing problems by allowing water to enter through the exhaust valve as the diver exhaled. He consequently inhaled sea water and gagged water back through his regulator. The diver inflated his BCD to halt his descent, stabilize himself, and then ascended until he could equalize his ears and stop gagging. He signaled to his instructor that he needed to surface so he could calm down and adjust his weight. By the end of the dive trip, the diver was able to trim his weight down to nothing and had the best control just using the steel tank with no additional weight.
>Suggesting the diver migrate to a steel tank from an aluminum tank was a good idea to address his concern regarding his air consumption rate by allowing him a larger reserve of air supply. The instructor was correct in giving the diver tips on this new configuration and pointing out some of the drawbacks for this configuration for the diver.
>One of the lessons normally taught during training is to test out new gear configurations in controlled environments; such as a pool or confined open-water. This allows divers to have better control. Divers can adjust buoyancy and weight distribution in shallow water enough to stand up in if they have difficulties. It may have been more beneficial to the diver if the instructor had allowed the diver to try the new configuration first in a pool before actually diving in an open-water environment with the steel tank. This way, the diver would have discovered the difficulties in a more controlled environment. The instructor would have been able to assist the diver and practice with the new diving configuration allowing him to be more confident and comfortable diving in open water. If this had been a less experienced and trained diver, this incident may have been more serious as he might have panicked and ascended quickly to the surface.
- Diving with an instructor to work through gear configurations is an excellent idea.
- Do not dive without formal training when trying new specialized gear for the first time.
- Spending time in a pool or confined open-water environment is recommended for familiarizing a diver with new equipment.
— Brian Wake
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