Prism 2 CCR Checklist

A systematic pre-dive workflow for the Hollis Prism 2 eCCR

Warning: This checklist is a reference aid, not a substitute for proper CCR training. Never dive a rebreather without manufacturer-approved training and certification. Failure to properly assemble and check your unit can result in serious injury or death. Always follow the procedures taught by your instructor and outlined in the Hollis Prism 2 owner's manual.

Hollis Prism 2 Owner's Manual Shearwater Support Docs

Overall Progress

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Analyze everything. Trust nothing.

Your cells are your lifeline.

If the computers disagree, the dive is over.

Pause. Review your work.

Everything from here forward depends on what you just built. Before moving to leak checks, take 30 seconds. Look at your loop. Trace every hose. Check every connection with your hands, not your memory. If something feels off, now is the time to find it. Not at 100 feet.

The next 5 minutes could save your life.

The pre-breathe is not a formality. It is your last chance to catch a bad scrubber pack, a failing cell, or a CO2 leak before you submerge. Breathe normally. Do not rush. Do not multitask. If you feel even a hint of headache, increased breathing rate, or air hunger, STOP. Do not dive. Remove from loop, breathe fresh air, and diagnose.

If you are rushing, you are not ready.

The dive is not over until the gear is clean.

Scrubber Duration Log

Track cumulative scrubber usage. Consult your manual for rated limits based on water temperature and workload.

CCR Cheat Sheet

In-water refresher

Three reflexes you should be able to recite, hood-on, with one regulator in your hand. Reference only — your training is the source of truth.

Skill 01

Diluent Flush

Replace loop gas with a known mix — your fastest way to reset a misbehaving PPO2 or suspect scrubber.

Do it when

  1. PPO2 too high — solenoid stuck open, runaway
  2. PPO2 too low — solenoid failed, sensor lying, hypoxia symptoms
  3. CO2 buildup — scrubber breakthrough, hyperventilating, headache
  4. Unknown gas — verify after a gas switch or maintenance
  5. Sensor calibration — cross-check cells against a known gas

Steps

  1. 1Check PPO2 of the diluent — must be breathable at depth
  2. 2Open the OPV (overpressure valve)
  3. 3Tightly squeeze the inhale counterlung
  4. 4Exhale forcefully into the exhale counterlung while pressing the ADV / manual diluent add
  5. 5Re-check the three O2 sensors — they should agree near your dil's PPO2
Skill 02

Bailout to OC

When in doubt — bail out. The loop will be there to fix on the surface. Your life is not.

Switch to open circuit when

  1. CCR malfunction — electronics, solenoid, MAV, or supply failure
  2. CO2 breakthrough — heavy breathing, confusion, headache
  3. PPO2 out of band — sensor failure, hypoxia / hyperoxia risk
  4. Loop flood — can't clear it back to a dry, breathable mix
  5. Multiple alarms / lost confidence — erratic sensors, conflicting reads
  6. Gas supply low — running out of O2 or dil
  7. Can't manage gas manually — controller down, hands full, task-loaded

Rule: open-circuit bailout, then sort it out — never the other way around. SCR is not a bailout for most CCR divers.

Skill 03

ID10T Test

The last sanity sweep at the giant-stride. Read it as "idiot" — because that's who skips it.

Before you step off the boat

  1. 1Mouthpiece — DSV / BOV closed against water, opens to loop on demand
  2. 2Cylinders open — O2 + diluent (and stage / bailout)
  3. 3Computer on, gas set — PPO2 set point correct, dive mode armed
  4. 4Bailout routed — reg accessible, clipped on weak side, breathable
  5. 5Wing & drysuit — inflators connected, both vent
  6. 6Mask & weights — clear, defogged, weight on and trimmed
  7. 7Buddy check — they did yours; you did theirs
  8. 8Loop in, hand on BOV — breathe before you step. Then go.

Why This Checklist Exists

Rebreathers don't forgive complacency. An open-circuit diver who skips a check might have a bad dive. A CCR diver who skips a check might not surface. The Hollis Prism 2 is a capable unit, but every CCR demands the same discipline: a methodical, unhurried pre-dive ritual performed every single time.

This checklist follows the general flow taught in most CCR courses: unit assembly, gas verification, electronics and sensor calibration, leak checks, pre-breathe, and final buddy checks. It is not a replacement for your training or your instructor's specific procedures. Adapt it to your workflow, but never skip steps.

The three most dangerous words in rebreather diving: "I already checked."

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