Dick and Jane are new but enthusiastic divers. They have dived every weekend since their OW class a month ago. Dick and Jane surmise from their reading of scubaboard threads that PADI was only after their money and the only place to receive good training was from GUE. Therefore they declined their lds invitation to join them for an AOW class. Instead, they plan to wait for a DIRF, which is scheduled in the spring in a neighboring state. In the meantime they endeavored to learn all they can. Last weekend, after reading this thread they decide it would be wise to incorporate rock bottom combined with minimum deco into their gas planning. Confident in their newfound knowledge they begin to plan a 100 ft wreck dive. Their deepest to date has been a 75 ft dive with a dive master in the Caribbean. They carefully calculate the gas needed for both to ascend based on a surface consumption rate of 1 cu ft/min, an ascent rate of 30 ft /min and stops at 40, 30 and 20.
Dick and Jane descend on the wreck. All is going well. They are comfortable in their surroundings and confident in their plan. Even though the dive has been planned within the no decompression limit, as the dive progresses, it becomes clear that gas supply will be the limiting factor. Jane being small and of slight build is diving with a AL 63 cu ft tank while Dick being rather large has chose a HP 100 cu ft tank. They know from previous dives that their tank pressures are similar at the end of most dives. With Jane nearing rock bottom they stay near the down line. As they approach the ascent line Dicks rented regulator free-flows violently. He handles this as taught and breaths from it up to the line. Jill stays very close and is prepared to offer gas to Dick. As Dicks air is depleted and the flow diminishes he switches to the regulator that Jill offers.
They begin their ascent. They are careful to ascend slowly and not exceed the planned ascent rate of thirty ft/minute. They have difficulty matching and controlling their ascent speed. As Dick begins to ascend more rapidly he vents his bc as Jane inhales more deeply to speed her ascent to keep up. As Dick slows after dumping and Jane speeds up they continue working to control their rate of ascent. The ascent and the events leading to it are somewhat stressful and both are kept busy by the task at hand. Though they do manage to check depth on occasion neither is able to check the change in depth against the elapsed time to gauge ascent rate. In reality, with all the speeding up and slowing down and swinging from positively buoyant to negatively buoyant they ascend at a rate much slower than 30 ft/ min. On all previous dives they ascended very slowly and feel that they may be ascending too quickly. Neither has a free hand to check Janes gas supply. As they approach 40 ft they struggle to get neutral and hold their depth. After a time, neither is sure how long they communicate the need to head for their 30 ft stop. After a couple false starts they resume their ascent. Suddenly both notice that it is becoming difficult to draw a breath.
What Dick and Jane didnt know is that Dick has a normal surface consumption rate of 1.2 cu ft/min and it varies drastically with activity and comfort. During this ascent he may have been as high as 1.6 cu ft/min. They also never gave thought to how far off their gas plan could be with an ascent rate other than the planned 30 ft/min. They also had never measured their air consumption rates under different conditions and used the recommended 1 cu ft /min rate assuming it would be adequate. Even though they were aware of how to convert surface consumption rate to that of a given depth, they used an intermediate depth for their calculation. They never considered that their calculations were only valid for a constant ascent rate. Due to the difficulties in the beginning of the ascent they actually ascended more slowly early on and were behind their gas plan from the start.
I hope this story is fiction and born only of my own imagination.
Dick and Jane descend on the wreck. All is going well. They are comfortable in their surroundings and confident in their plan. Even though the dive has been planned within the no decompression limit, as the dive progresses, it becomes clear that gas supply will be the limiting factor. Jane being small and of slight build is diving with a AL 63 cu ft tank while Dick being rather large has chose a HP 100 cu ft tank. They know from previous dives that their tank pressures are similar at the end of most dives. With Jane nearing rock bottom they stay near the down line. As they approach the ascent line Dicks rented regulator free-flows violently. He handles this as taught and breaths from it up to the line. Jill stays very close and is prepared to offer gas to Dick. As Dicks air is depleted and the flow diminishes he switches to the regulator that Jill offers.
They begin their ascent. They are careful to ascend slowly and not exceed the planned ascent rate of thirty ft/minute. They have difficulty matching and controlling their ascent speed. As Dick begins to ascend more rapidly he vents his bc as Jane inhales more deeply to speed her ascent to keep up. As Dick slows after dumping and Jane speeds up they continue working to control their rate of ascent. The ascent and the events leading to it are somewhat stressful and both are kept busy by the task at hand. Though they do manage to check depth on occasion neither is able to check the change in depth against the elapsed time to gauge ascent rate. In reality, with all the speeding up and slowing down and swinging from positively buoyant to negatively buoyant they ascend at a rate much slower than 30 ft/ min. On all previous dives they ascended very slowly and feel that they may be ascending too quickly. Neither has a free hand to check Janes gas supply. As they approach 40 ft they struggle to get neutral and hold their depth. After a time, neither is sure how long they communicate the need to head for their 30 ft stop. After a couple false starts they resume their ascent. Suddenly both notice that it is becoming difficult to draw a breath.
What Dick and Jane didnt know is that Dick has a normal surface consumption rate of 1.2 cu ft/min and it varies drastically with activity and comfort. During this ascent he may have been as high as 1.6 cu ft/min. They also never gave thought to how far off their gas plan could be with an ascent rate other than the planned 30 ft/min. They also had never measured their air consumption rates under different conditions and used the recommended 1 cu ft /min rate assuming it would be adequate. Even though they were aware of how to convert surface consumption rate to that of a given depth, they used an intermediate depth for their calculation. They never considered that their calculations were only valid for a constant ascent rate. Due to the difficulties in the beginning of the ascent they actually ascended more slowly early on and were behind their gas plan from the start.
I hope this story is fiction and born only of my own imagination.
