Ceiling-controlled versus staged decompression: comparison between decompression duration and tissue tensions

Introduction: In dissolved gas decompression algorithms, the ceiling is the depth at which the dissolved gas pressure in at least one tissue equals the maximum tolerated value defined by the algorithm. Staged decompression prescribes stationary stops in three-metre intervals so as to never exceed this maximum tolerated value. This keeps the diver deeper than the ceiling until the ceiling itself decreases to coincide with the next, three-metre shallower stage. Ceiling-controlled decompression follows the ceiling in a continuous ascent. Methods: Mathematical simulations using the ZH-L16C decompression algorithm and gradient factors were carried out for several dive profiles to compare patterns of tissue gas supersaturation and overall decompression times for decompressions based on these approaches. Results: During a stationary staged decompression stop the available pressure gradient for inert gas washout diminished as inert gas is washed out while inhaled inert gas partial pressure remained unchanged. Ceiling-controlled decompression, on the other hand, maintained the available pressure gradient for inert gas washout at its maximum tolerated level. Decompressions were 4-12% shorter using ceiling-controlled approaches but at the cost of exposing tissues with faster half times to higher levels of supersaturation than they would experience during staged decompression. Conclusions: Ceiling controlled approaches accelerate decompression but the effect of this on the risk of decompression sickness is unknown.