Hollis Prism 2 Rebreather

Technically Focused
The PRISM 2 is an electronically or manually controlled, constant PO2, modular, closed circuit diving system.

As open circuit (SCUBA) divers, we rely upon filling our lungs with air from a pressurized gas tank with every inhalation and then exhausting that volume of air into the surrounding water with every exhalation. As we descend deeper, the water pressure around us increases, and the volume required to fill our lungs increases; in other words, our air supply depletes more quickly the deeper we dive.

A rebreather recycles rather than vents the exhaled breath. The exhaled breath passes into a closed loop, where it is pushed through a chemical absorbent (scrubber) to remove the carbon dioxide and returns through the other side of the loop for the diver to re-breathe, hence the name “closed circuit rebreather” or CCR.

Breathing Loop
Its breathing loop, which is a keyed one-way assembly, consists of a closable mouthpiece assembly with mushroom/check valves on either side, ensuring uni-directional flow.

Independent 3rd party testing has also rated the Prism 2 the lowest work of breathing of any mixed gas rebreather available today.

Status Check
With the electronics switched on, the secondary also provides a status check for the battery and displays the set point selected for the dive along with other critical information. The electronics vote between the three proprietary galvanic sensors and control the operation of a low wattage solenoid valve on the oxygen supply.

Scrubber Design
A radial flow scrubber canister is mounted vertically on a backplate attached to the integrated BC, between twin supply cylinders (one each, oxygen and diluent).

Electronics
The electronics, sensors, and batteries are mounted in the electronics head assembly at the top of the scrubber, with supply hoses feeding over the diver’s shoulders into the top of the counterlungs. An analog LED primary display offers a quick reference of unit performance with status and alarm indicators, while an independent digital OLED secondary display verifies the unit’s performance.

Counter Lungs
Dual, front-mounted counterlungs provide the diver with a flexible reservoir equivalent to the maximum displacement of the diver’s own lung volume and ensure the lowest possible hydrostatic loading.

Secondary Display (COMPUTER)
• The Shearwater Petrel 3 is the computer display on the Prism 2 and was chosen for this application as it is one of the most advanced mixed gas CCR computers available today. The Petrel 3 is designed to control the Prism 2 setpoint and uses a basic decompression algorithm known as Buhlmann ZHL-16C which has been modified by the use of gradient factors.
• Depth, time and oxygen sensor display
• Wireless HP monitoring of Diluent and Oxygen gases with optional wireless transmitters
• Bühlmann decompression model with gradient factors conservatism
• Optional VPM-B decompression model
• Imperial and metric displays
• DiveCAN communications for robust connections to rebreathers
• A menu system that adapts to diving status
• Automatic turn off after 15 minutes on the surface
• Depth sensor rated to 450 feet/140 meters of seawater
• Dive Planner
• Any combination of oxygen, nitrogen, and helium (Air, Nitrox, Trimix)
• Open and closed circuit, switchable during a dive
• 5 CC and 5 OC gases
• Gases can be changed and added during a dive
• CNS tracking
• No lockout from violating deco stops
• Automatic PPO2 set-point switching (configurable)
• Two PPO2 set-points, each of which can be set between .5 and 1.5
• Flexible user replaceable battery. Almost any ‘AA’ type
• Tilt compensated digital compass (Petrel 2 only)
• 1000 hour dive log memory
• Log downloads and firmware upgrades using Bluetooth
HUD
• The Primary Display (HUD) is a Shearwater DiveCAN Heads-Up Display mounted on either the right or left side of the DSV/BOV mouthpiece just below eye level. Each HUD provides a status indicator for its corresponding O2 sensor by using a “Smithers Code” flashing the status on a cycling 5-second loop during the dive.
• PPO2 display from 3 oxygen sensors.
• Modified Smither’s code blink pattern.
• Bright light emitting diodes with vibrant colors.
• Color-blind blink pattern (optional setting).
• Wet contacts for automatic turn-on.
• Option to flip orientation – can be positioned on either side of the rebreather mouthpiece.
• DiveCAN® communications interface for robust data transmission and easy upgrades, disassembly and repairs.
• Bright red end-cap LED for buddy warnings.
• Automatic brightness control optimizes viewing in all conditions.
• Red color only used for unsafe PPO2 warnings.