The Thalmann exponential-linear model is a dissolved-gas model that lets gas into your tissues the way Bühlmann does and refuses to let it out the same way. Once a compartment holds more inert gas than the depth you are at will support, its off-gassing is held to a fixed rate instead of accelerating with the size of the gradient. That asymmetry is the whole of the difference between the two models, and it is what “E-L” names.
What the assumption costs you
Bühlmann credits a large pressure difference with driving faster washout. Thalmann assumes it does not: beyond a point, a tissue clears at whatever rate it can and no faster.
A profile Bühlmann clears can therefore take longer under E-L, and the extra time does not fall evenly. E-L tends to produce brief stops deep and noticeably longer ones at 9 m, 6 m and 3 m. If you are used to reading a Bühlmann schedule, the shape is the first thing you will notice, before the runtime is.
Gradient factors do nothing under Thalmann
Selecting Thalmann E-L makes the GF Low and GF High fields inert. The model has no conservatism control of any kind: the ceiling it hands the planner is its own limit, taken raw. The planner passes your pair in and the Thalmann path discards it.
Conservatism under Thalmann means selecting a different parameter set. The Parameter set field appears next to the algorithm whenever Thalmann, either hybrid model, or GF Calibration is selected, and it is the only lever the model answers to. Which set is selected changes the schedule more than any other control on the page.
The parameter sets are not verified
The numbers behind every set in this build were transcribed from second-hand sources and have never been checked against the original research they cite. Treat every set as an unvalidated reconstruction, and do not plan a dive you intend to make on one. The default set has no sourced helium behaviour at all, so running it on trimix is a guess wearing a citation. Most of the others were fitted to constant-ppO₂ rebreather diving, so selecting one on an open-circuit plan asks it to schedule diving it was never fitted to.
What the model is good for is comparison: running the same dive under Bühlmann and under Thalmann, and reading the gap between the two runtimes, shows how much of your schedule is an assumption rather than a measurement. If you want that disagreement to inform a real plan rather than replace it, use Hybrid OC, which holds you at whichever model is deeper at every stop.
Like Bühlmann, E-L has no bubbles, no anatomy and no diver. The fixed off-gassing rate is an assumption about washout chosen because it fitted trial outcomes, not an observation of what tissues do.
Next
- Hybrid models run this model alongside Bühlmann.
- GF calibration expresses a Thalmann schedule as a gradient-factor pair.