Disclaimer
DecoDive computes theoretical plans with the Bühlmann ZHL-16C algorithm and gradient factors, for training and comparison purposes. No algorithm guarantees freedom from decompression sickness: individual response depends on factors the model does not consider (age, hydration, cold, exertion, patent foramen ovale, multi-day diving, flying after diving). The plan does not replace specific training, the training agency's procedures or the dive computer, which remains the reference during the dive. Decompression diving requires appropriate certification. These results are used at the user's own risk.
How it calculates
- ZHL-16C model with 16 compartments for nitrogen and helium (OSTC parameter table), Schreiner equation for descents and ascents.
- As on dive computers, the no-decompression limit uses GF high: if a direct ascent is allowed at the end of the bottom phase, there are no mandatory stops.
- When decompression is required, the first stop is found with GF low; from there GF increases linearly up to GF high at the surface. Stops every 3 m, in whole minutes, at least one minute each.
- Up to four deco gases, trimix included: each is switched to at the 3 m stop nearest to its MOD computed with 1 bar every 10 m (or at the depth entered, if shallower), must be richer in oxygen than the gas it replaces and, if two fall at the same depth, the richer is used. With ppO₂ 1.6: oxygen at 6 m, EAN50 at 21 m, Tx 35/30 at 36 m; with 1.4: Tx 21/35 at 57 m.
- CCR: constant ppO₂ equal to the setpoint, but not above ambient pressure and not below the diluent ppO₂; inert gases keep the diluent ratio. Tissue loading follows the mix in steps of at most one minute.
- Bailout plan (CCR): loop failure at the end of the bottom phase, 2 minutes at the bottom depth on open circuit, then the ascent on the bailouts with recalculated stops and a SAC of 20 l/min, for one diver.
- END with oxygen considered narcotic. Gas density with values at 0 °C; above 5.2 g/l a warning is given, above 6.2 g/l it should be avoided (Anthony and Mitchell).
- Ascent at the given rate up to 6 m; from 6 m to the surface in the given time (5 minutes, i.e. 1.2 m/min).
- The first dive starts with tissues saturated with air at the given altitude. Repetitive dives (up to four, each with its own gases and circuit): each starts from the tissue loading left by the previous one, after the interval spent breathing air at the surface at the altitude of the following dive; CNS decays with a 90-minute half-time, OTU is added up over the whole series.
- Salt water 1.03 kg/l, fresh water 1.00 kg/l. CNS with NOAA limits, OTU with the Lambertsen formula. Gas consumption uses the SAC at the mean pressure of each segment.
- Bottom time from rock bottom (open circuit only): the bottom time is the longest, in whole minutes, that still leaves the rock bottom in the bottom gas cylinder at the end of the bottom phase (2-minute emergency at the bottom and ascent for two up to the first gas switch or the surface, with recalculated stops and a SAC of 20 l/min per diver), rounded up to the next bar.
- Open-circuit plans, trimix and multiple deco gases included, have been checked against decotengu, an independent implementation of the same model. The CCR is tested on known cases (with the setpoint below the diluent the plan matches open circuit).