Tissue Compartment — What It Is and Why It Matters
A tissue compartment is a mathematical construct in decompression algorithms that represents a group of body tissues with similar rates of gas absorption and elimination. The Bühlmann ZHL-16C model uses 16 compartments with half-times ranging from 4 minutes (fast tissues like blood) to 635 minutes (slow tissues like cartilage and bone).
Fast compartments absorb and release nitrogen quickly and drive the limits on short, deep dives. Slow compartments accumulate nitrogen gradually and become the limiting factor on long or repetitive dives. Your dive computer tracks all compartments simultaneously and bases its calculations on whichever compartment is closest to its safe limit at any given moment.
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Frequently Asked Questions
Do the 16 compartments correspond to specific body parts?
Not exactly. They are mathematical abstractions representing ranges of tissue types grouped by gas absorption speed. Fast compartments roughly correspond to blood and well-perfused organs; slow compartments roughly correspond to joints, cartilage, and fat. But they are models, not anatomical maps.
Why does my computer show different NDLs at the same depth on different dives?
Because residual nitrogen from previous dives remains in your slower tissue compartments. Even after a surface interval, some compartments retain nitrogen from earlier dives, reducing your available NDL. Your computer tracks this loading continuously.
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