Long way to go down, long time coming up

Everyone who has been certified as a recreational scuba diver knows about ascending slowly from a dive and calculating bottom time — the amount of time you can spend at the deepest part of a dive — and the need to decompress, or allow nitrogen gas to leave your bloodstream.

The deeper the dive, the shorter the bottom time and the more time needed to decompress.

At Pulley Ridge, a reef 275 feet down, tech divers averaged about 20 minutes of bottom time, and nearly 90 minutes of decompression time. They followed staged decompression, in which the divers ascend to different levels and stop, allowing gas to purge from their systems.

If the gas does not leave a diver's system, they could suffer from decompression sickness, a debilitating syndrome also known as "the bends."

Divers on the Pulley Ridge project would start their ascent and stop for the first decompression stop when they reached between 160 to 140 feet, staying for about two minutes. They would stop again at 106 feet for a few minutes, followed by stops at 80, 60, 50, 40, 30, 20 and finally 15 feet underwater. They could not make their next dive for six to seven hours.

As a beginning sport diver you are taught to ascend slow. This is to allow gas to come out of your system. The extended range divers at Pulley Ridge have much more gas absorbed in their systems and must make short stops at different depths in order to accomplish the same thing. This allows them to make a controlled ascent to the surface without substantial risk of DCS. Decompression time allows divers to release nitrogen and helium that cause decompression sickness.