Decompression

BY DR. JOHNNY E. BRIAN, JR.

Photo by David Rhea

The idea that decompression stops deeper in the water column can allow for more efficient inert gas removal seems very counter intuitive. Traditional Haldane-based decompression theory emphasizes the need to move as shallow as possible to maximize gas removal from tissue. Haldane-based models assume that all gas remains in dissolved phase, where the gradient for inert gas removal is the partial pressure of the inert gas in the tissue (determined by the breathing mix and the time/depth profile) and the partial pressure of inert gas in blood (determined by the breathing mix and the current depth). In a dissolved gas model, formation of bubbles is assumed to indicate a violation of allowed supersaturation ratios. Today we know that bubbles are very common, and that phase transition (gas moving from dissolved phase to free phase in bubbles) should be considered in decompression theory. The gradients for gas movement are very different once gas leaves the dissolved phase and enters the free phase, which leads to the need for stops much deeper than predicted based on dissolved gas theory.

Read more: Dissolved and Free Phase Gas Dynamics

BY DR. R.W. BILL HAMILTON

John S. Haldane

During the last 15 or so years the practice of decompression has changed dramatically, after a long period of what might be considered as steady evolution dating from the original work of Haldane. This is a brief review of that changing landscape. This is not to say that there have not been many creative developments on the way; but to me the thing that is new, the really unique change, is the do-it-yourself capability of divers to generate their own decompression tables. Let us look at a bit of the history.

Read more: The Changing Landscape of Decompression

BY GENE HOBBS

Decompression in the blue water of the Caribbean. Photo ©Dickie Walls

Discussions of decompression theory inevitably center on theories involved in creating different models and algorithms. In this day and age of diver-worn computers and portable laptop decompression schedules, many divers use this information to create personalized models for efficient decompression. As a result, many divers are starting to rely on this technology without understanding what has gone into making it possible. More attention should be placed on understanding the empirical data that is behind these easy-to-use technologies.

Read more: How Are You Feeling? New Horizons in the Study of Decompression

BY JARROD JABLONSKI

Jarrod Jablonski on the Halcyon Rebreather at Wakulla Springs.

Photo ©David Rhea

From the logistics of underwater exploration to the strange malady that became known as decompression illness, divers and scientists have been struggling for decades to successfully investigate the underwater world. As early as 1670 Boyle described, with detailed accuracy, bubbles in the blood and body fluids of small animals subjected to low pressures. These bubbles, first located in the eye of a snake, marked more than 300 years of debate about the meaning, repercussions, and logistics of exposure to elevated ambient pressure. The quest for procedures that allowed effective immersion and safe retreat from hyperbaric exposures is dotted with a medley of evolving theories, best-guess practices, and hopeful global conceptualizations.

Read more: Decompression Experimentation