2.1 Pre-Dive Checklist, H.A.P.P.Y
While the mechanics of a checklist can vary slightly from system to system, the following simple mnemonic provides for a streamlined pre-dive sequence.
Quite simply, if you can answer the question ‘Are you H.A.P.P.Y.?’ at the water’s edge, then you are good to go. This pre-dive was adopted from Mr. Dan Wible, one of the early authorities on rebreather development with his work on the CCR2000. The checklist was incorporated by IANTD for numerous years, though drifted away for unknown reasons. I've revitalized the H.A.P.P.Y. mnemonic to reflect contemporary rebreather understanding by modifying the items to be more readily applicable to a variety of systems. We now offer the H.A.P.P.Y. checklist as a sticker which may be affixed to any rebreather or a slate to provide a fresh reminder to the diver.
Each section of the mnemonic H.A.P.P.Y is described below.
Predive Checklist Sticker (5 pack) | Lombardi Undersea
H - Hydrophobic Loop
A hydrophobic loop is critical to rebreather diving. This ensures that no water is leaking in causing a flood, and no gas is leaking out, which is a waste, and could also cause fluctuations in your ppO2. Both inward and outward leaks may or may not go hand in hand, and so to check for a hydrophobic loop, both positive and negative leak tests should be performed. With all cylinders off, exhale into the rig to fill the counterlungs until the OPV purges slightly. Close the mouthpiece and let the unit stand for a minimum of two minutes. Providing the counterlungs remain inflated, the system has passed a positive pressure test. Next, inhale from the unit and exhale through your nose to remove all gas from the system. Do this until the bags are collapsed entirely and a slight vacuum is drawn, then close the mouthpiece. Let the rig stand for another minimum of two minutes. Open the mouthpiece. A ‘whoosh’ sound indicates that the breathing loop was holding a vacuum, and the system has now passed the negative pressure test. Passing both the positive and negative pressure tests indicates that you have a hydrophobic loop.
A - Active Oxygen & Diluent Addition. Activate Display.
Active additions are those required to be actively made by the diver; something the diver has to ‘actively’ do. In this case, we want to confirm that the diver has the ability to manually add both oxygen and diluent gasses to the breathing loop. During the course of a dive, this ability ensures that the diver can maintain a breathable volume of gas within the counterlung(s) and is able to manually adjust the gas contents should any passive oxygen addition methods fail. To check for active oxygen and diluent addition capabilities, verify that all gasses are on and plugged into the unit and that there is adequate gas to complete the dive. Manually inflate the counterlung with oxygen and then circulate the gas to ensure that you have 100% oxygen in the loop. This is an opportune time to calibrate your electronics if needed, so activate your display. After the calibration procedure specified by the manufacturer, actively add a few short bursts of your diluent gas to test for active diluent addition. This will also verify that your sensors are responsive to the change in gas contents.
P - Passive Oxygen and Diluent Addition
Passive additions refer to oxygen and diluent added without diver input, i.e. they occur passively. Rebreathers may have one of several passive oxygen addition mechanisms. This includes a computer or electronically controlled solenoid valve, a needle valve, or an orifice or ‘leaky valve’, sometimes referred to as the ‘KISS’ valve. In our preferred case described throughout, we utilize a needle valve. Ensure that this has oxygen flowing through it using a flowmeter and adjust the needle valve to just below the diver’s metabolic consumption rate. Most often, this is approximately 1.0 LPM. The diver should note how many turns open or closed are required to achieve this flow rate, and then slightly adjust to/from the 1.0 LPM flow rate as needed. To verify passive diluent addition, the breathing loop can be breathed down until a slight vacuum actuates the automatic diluent valve (ADV). The ADV should be reasonably responsive to reduction in breathing loop volume at the surface, and if so, then it will most certainly be responsive with increasing water pressure during the descent.
P – Prebreathe
Prebreathing the unit at the surface prior to the dive serves several functions. First, it ensures that the entire system is performing and maintaining an adequate loop volume and target pO2 for a brief period of time. Second, it is the time necessary to catalyze the scrubber’s reaction and allow the breathing loop volume to equilibrate. A good pre-breathe of 2-5 minutes is recommended. This time may be used to program your computer for the pO2 and gasses you have on board and review decompression schedules for the dive. Prebreathe time should also be used to confirm that all systems are double and triple checked on your unit and any mechanical components are within physical reach for manual actuation of valves and auxiliary devices. As a matter of habitat, which will be expanded upon in subsequent sections, I use this time to establish a pO2 of 1.0 bar (100% oxygen at the surface). This reference point measurably aids in loop management throughout the dive and is a good target to start and finish a dive...to be continued.
Y - Yourself
Lastly, check yourself. Make a final check head to toe of you, your equipment, and the environment. Check your dive partner, and simply very that all is OK for YOU. Before entering the water, the ppO2 should be stabilized.
So, H.A.P.P.Y. get you off the boat or beach and into the water. Then the dive starts. While a mouthful to articulate here, this full process can be completed in less than a minute in practice (less the pre-breathe) and should become a habitat. Routinely asking yourself 'Am I H.A.P.P.Y.?' during the dive helps to verify system integrity and builds confidence.