Tube Tied

An enlargeable satellite image of Grand Cayman...Image via Wikipedia In 2003, I was fortunate enough to go to the Cayman Islands to take an advanced course and have nice vacation with my family. In addition to the instructors, there were several other divers from Richmond joining us on the trip. One of the divers, whom I shall call "Martha", was a nurse and an apparently experienced diver. She was vacationing with her friend, "Brenda", and experienced firefighter EMT.

On day two of the trip, we were fortunate enough to dive the outer walls of the reef surrounding Grand Cayman Island. Grand Cayman is surrounded by deep ocean and a coral wall that stretches from approximate 70 feet below the surface to almost 6000 feet (or so I've heard). The coral formations are truly breathtaking and the government has done an excellent job of preserving the reef and marine life  through captive breeding programs, carefully managed anchor points, and limitations on the number of divers in the water in any given week. One of the exotic species of coral that many folks wish to see in Grand Cayman in is the black coral which, paradoxically, does not appear to be black. It's long branching arms reach out into the current rising from the depths against the reef wall like a Mesquite tree in a desert.

On this dive the bottom was set at 110 feet. We entered the coral canyons at 70 feet and proceeded through tubes of overreaching coral arches festooned with colorful corals and sponges.  In some cases, arches joined together to create tubes which completely surrounded divers in beautiful coral formations. One such tube began at about 75 feet with a diameter of about 15 feet. It angled down through the reef reaching a maximum ceiling depth of about 100 feet  and a maximum diameter of about 45 feet.  as we swam through the coral tube,  one diver, Martha, appeared to be following the bottom contours while most of the divers were suspended close to or at the ceiling. This placed Martha at a depth of almost 145 feet. Oblivious to her surroundings, she appeared completely unaware of the danger she was in diving to 145 feet, on-air, with only 80 ft.³ of gas. As the dive master moved to alert her, her bubbles suddenly stopped. She was out of gas.

Martha turned abruptly and wide-eyed for the rest the group.  When the dive master reached her, she snatched the regulator he offered and breathed greedily from his tank.  Having only 80 ft.³ of air himself, the dive master was forced to make a rapid ascent with Martha to ensure they were able to get back to the boats with any air left. This left the rest of us out on the reef without the necessary compass headings or local knowledge to return to the boat. Instead, we swam along the reef below the rescue pair and followed their shadows back to safety.

 Later I thought about what happened and how it could've been prevented. In retrospect several things could've been done to reduce the risk of this dive.
  1.  The pre-dive briefing did not include the description of the dangers of the coral tube.   It was easy once in the tube to lose track of the fact that we were descending at a fairly steep angle. Had this specific danger been raised, it is undoubtedly true that  Martha would have been much more aware of her surroundings as we traveled to the outer wall.
  2. Given the maximum depth, or rather the potential maximum depth of 145 feet, it is questionable whether air was the appropriate gas for most of the divers. At that depth, Martha made it clear, nitrogen narcosis was a serious risk. She had been completely unaware of either her depth, or her gas utilization during the dive. She  had also failed to see that she  had separated from the rest of the group.
  3. Again given the maximum depth, it is apparent that by diving and 80 ft.³ aluminum tank, the dive master had insufficient air to effect this kind of rescue without completing a somewhat more dangerous rapid ascent.  While all divers would've benefited from additional gas, as most of them returned with less than 500 psi remaining, it appears essential that the professional dive crew has sufficient gas to effect a rescue requiring them to provide gas in emergency such as this.
The other factor though that we didn't discuss, was Martha's level of fitness.  Although just  5'5" tall, she likely weighed in excess of 180 pounds.  While was unclear  how this additional weight affected her air consumption on the coral tube dive. But, two days later,  the weight became a serious liability on a shore dive at Eden's Rock.    More on that later.

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Nick said...

Wow, this actually sounds like it ended up in a very lucky situation. Whenever I take students/non-pro's on a dive near or beyond 100', I at least make sure I upgrade from my normal 63 ft^3 tank to an HP 80 ft^3 tank and will frequently be sure to bring a pony bottle along too.

Shawn said...

You know there are several bothersome points to this story... where was Martha's dive buddy? A dive buddy should ALWAYS be close at hand, the responsibility of monitoring each other's depth and remaining air come into play here as well. A buddy isn't someone to share photos with topside but a redundant safety precaution that is important to safe responsible diving. Last, the dive master should have been monitoring the group's PSI to avoid just this situation. Timely intervention could have sent Martha and her buddy back to the surface with reserves for a safe ascent, leaving the D/M to continue sharing a great experience for the rest of the group.