pSCR

Best known by the acronym pSCR, Passive Semi Closed Rebreather, this rebreather is also identified by the CMR acronym, Constant Mass Ratio rebreather and CVR, Constant Volume Ratio rebreather.

 A distinctive feature of the pSCR is its completely mechanical operation controlled by the diver's breathing. In a nutshell, at every inhalation a percentage of exhaust gas is eliminated. The cycle is repeated until the reduction in the volume occupied by the gas triggers the injectors which refill it. This occurs on average every 3 or 4 breaths when remaining at a constant depth.

The pSCR is a simple and intuitive rebreather as it is the diver's breath that controls the expulsion of the exhaust gas and its refilling. By its nature, it is a particularly solid piece of equipment, also due to the absence of any electrical or electronic part; it is intended for cave diving or particularly long dives.

 The pSCR is a rebreather because it recycles a portion of the exhaled gas; it is semi-closed because it does not recycle all the exhaled gas and it is passive since it expels and supplies gas only according to the diver's breathing.

The pSCR Diver Level 2 course introduces students to diving with the use of Trimix and decompression; therefore, students are required to have previous experience in open circuit decompression dives. The scope of use is the normoxic trimix limited to 60 meter depth. Hypoxic gases are excluded. This course provides further knowledge on the use and management of the equipment and the Oxygen Drop highlighting the effects on decompression. Special attention will be paid on the differences in decompression using a pSCR compared to the open circuit, emphasizing the selection and management of the gas. Brief description of changes in equipment performance in relation to changes in Actual Efficiency. 

The idea that use of pSCR is suitable for longer dives than those normally carried out in open circuit mode shall also be conveyed. In this respect, two dives are scheduled of a minimum length of 90 and 120 minutes, respectively, subject to the T-value limit of 100.

Use of the UPV is mandatory.

Ratio greater than or equal to 1:10

Maximum depth 60 meters

Tt-Value 100

Up to 3 decompression stages

1 bottom stage

The pSCR Diver Level 3 course introduces students to the typical pSCR diving. The scope of use consists in long bottom dives breathing hypoxic mixtures; therefore, students should have previous experience in similar diving in open circuit mode. Please note that use of the UPV is compulsory in order to avoid fatigue and the consequent presence of dangerous CO₂ levels. In this respect, particular attention will be paid to gas switches, the flow check and, in general, management of stage cylinders using the handle and UPV. The course will also focus on pSCR Volume Ratios and changes in pSCR performance in relation to changes in Actual Efficiency. During the course students will acquire further knowledge of the equipment, the physical principles that govern its operation and the basic mathematical representation of those principles. Of particular importance is the selection and management of the gas in order to maintain the PO₂ within suitable limits for long dives. In addition, the concept already introduced in Level 2 that use of pSCR is suitable for longer dives than those normally carried out in open circuit mode shall be further expanded. In this respect, two dives are scheduled of a minimum length of 120 and 150 minutes, respectively, subject to the T-value limit of 110. The oxygen decompression section shall be entirely carried out using the pSCR. It will be shown that during the decompression phase it is possible to perceive the expulsion of inert gases from the body using the oxygen sensor and possibly adjusting depth to maintain an adequate PO₂ in accordance with planned CNS.

Use of the UPV is mandatory.

Ratio greater than or equal to 1:10

Maximum depth 80 meters

Tt-Value 120

Up to 4 decompression stages

1 bottom stage

The pSCR Unlimited award is intended to empower students to recognise and respect their own limits and those of the team. In this sense, the certification does not place limitations on the depth and use of mixes, limits that, once successfully completed learning, will be totally left to the student himself. Specifically designed to go beyond the confines of the Open Circuit, the course explores in detail the functioning of the passive rebreather, the physical principles and the mathematics underlying them. Knowledge of the effects of changing Volume Ratios and Effective Efficiency will be developed. Particular attention will be paid to the development of judgmental skills as well as to the planning of deep, long and complex dives.

The use of the UPV is mandatory. 

Limits during the course:

• Ratio greater than or equal to 1:10
• Maximum depth 100 meters
• Tt-Value 120
• Up to 5 decompression stages
• 1 bottom stage