Touzil System

Started in 2007, the Touzil System Project is a continuous effort to better understand Oxygen Drop in pSCR diving and to develop better and safer pSCR diving.

Notice that when diving a pSCR rebreather a reduction in inspired FO₂, oxygen percentage in the Mix, occurs on each breath until just a portion of fresh gas is injected and partially raises the Mix FO₂. This is referred as "Oxygen drop", which ends up reducing the Minimum Operating Depth of a given Mix, when compare to Open Circuit.

Oxygen Drop is the main reason of accident in this unit type.

Oxygen Drop theory is paramount in the safety of pSCR diving, as the mechanics of rebreather diving affect gases properties. Furthermore the diver breathing efficiency and the real rebreather ratio plays key role in the true Oxygen Drop.

We developed the Touzil System, a proprietary software that can predict the Oxygen Drop and the consequent increase in the fraction of inert gases. The results provided by this software depend on the user and rebreather efficiency combinations. Both under workload and at rest. The density of the breathed mix is also calculated with an indication of whether the limits suggested by the Anthony and Mitchell studies have been exceeded.

Starting with version 2.2 (November 2024), the software estimates the scrubber life depending on the diver's consumption, brand and amount of absorbent used and whether it is a relaxing or strenuous dive.

Version 2.3 (July 2025) introduced the calculation of the rule of thirds for obstructed environments. The software suggests the maximum amount of bars or litres that can be consumed with the pSCR in order to be able to go out in two breathing in open circuit. Do not engage obstructed environment without appropriate training.

Version 2.4 (September 2025) introduces greater usability with smartphones.

We recommend the application of PO₂ / FO₂ monitoring devices at least until full understanding of Oxygen Drop.

Prediction is challenging especially if the gas is changing during the dive, both in bottom and decompression phase, as it does on pSCR diving. Furthermore your average Open Circuit decompression rules will not mirror your rebreather needs, and could end up becoming inefficient for proper decompression. In fact DCS in not well trained pSCR rebreather divers is quite common. As of today decompression theory in general is still not a full understood science.

Get proper rebreather training. Don't just get the c-card, get someone that actually dive extensively the unit in your conditions. Also dive within your training limitations, a No Decompression Limit rebreather course is not intended to cover rebreather Trimix diving.

This is the second version of the Touzil System; it is completely revamped and also adds the prediction of inert gas trends and scrubber life. We took great care in developing and writing the software, but mistakes are always possible. In fact, they are always lurking. Therefore, we cannot take responsibility for any accidents or incidents that may occur when using this software. However, we would be grateful if you would point out any errors, oversights, inaccuracies and anything else that might limit the use of the Touzil System.

Touzil System V. 2.4, September 2025