■ Decompression Stops and Decompression Time

Each tissue compartment has a maximum allowable level of inert gas pressure that can be tolerated without forming harmful bubbles. This limit is known as the M-value (maximum allowable supersaturation) and varies according to ambient pressure.

If, during ascent, the inert gas pressure in a tissue exceeds the allowable M-value for the current depth, a decompression stop is required.

Decompression time is the period needed to allow sufficient nitrogen elimination so that tissue gas pressure falls below the M-value before ascending to a shallower depth.

Because M-values differ among tissue compartments, decompression stops are performed to protect the most critical or “leading” tissue at that moment.

In recreational diving, where bottom times are relatively limited, decompression sickness most commonly involves faster tissues with half-times of approximately 80 minutes or less. This explains why many cases of recreational DCS present as joint pain (especially shoulders, elbows, and knees), muscle pain, or neurological symptoms.

■ Dive Computer Algorithm

Dive computers calculate nitrogen absorption and elimination every second using mathematical models based on inert gas saturation theory.

The concept of M-values was originally developed by Dr. Robert D. Workman at the U.S. Navy Experimental Diving Unit. Modern dive computer algorithms build upon this work and incorporate multiple tissue compartments and safety factors to reduce the risk of decompression sickness.

Although different manufacturers use slightly different mathematical models (such as Bühlmann-based algorithms or modified versions), the fundamental principle remains the same: controlling supersaturation to prevent bubble formation.