POSEIDON SE7EN+ - Decompression Diving with the SE7 EN

Poseidon SE7EN+ User Manual Appendix 3 Page 130
WARNING:
Planned decompression diving requires additional training
and support equipment. DO NOT attempt to use a SE7EN+
rebreather for decompression diving without proper training and
equipment! In particular, when diving with a SE7EN+ enabled
for decompression diving, it is the DIVER’S RESPONSIBILITY
to ensure access to an adequate supply of breathing gas to
effect a safe and controlled bailout to the surface, including full
decompression requirements!
Setpoint
A SE7EN+ enabled for decompression diving uses a different PO
2
setpoint algorithm. The
intent of the algorithm is to keep the setpoint higher for longer when a decompression ceiling
has been encountered during a dive. This comes at the cost of making buoyancy control more
difcult in shallow water. The algorithm will always use the highest setpoint (typically 1.3 bar),
subject to the following limitations:
1. The FO
2
is limited to 75%. Thus at the surface the setpoint would be 0.75 bar. At 3m the
setpoint would be 0.98 bar, and at 6m and greater the setpoint would be 1.3 bar (for a rig
with a 1.3 high setpoint value).
2. The hyperoxic linearity test still applies. Thus a rig that fails the hyperoxic linearity test will
not be allowed to use a setpoint > 1 bar. (See chapter 3, hyperoxic linearity test in the
SE7EN+ manual).
Open-Circuit Bailout
On a SE7EN+ that is not enabled for decompression diving, the system monitors the amount
of gas remaining in the diluent cylinder, and warns the diver when the calculated amount of
6. Decompression Diving with the SE7EN+
A SE7EN+ enabled for decompression diving will behave differently compared to a SE7EN+
that is not congured for decompression diving. Important changes in the functionality when a
diver approaches and enters decompression are:
• The ceiling indicator will not ash. It will just be on and not ashing. When the ceiling indi-
cator is on, the alert triangle will not be on.
• The rig will not issue an alarm (HUD & Buddy lights, Audio Alarm) when decompression is
entered.” There is no audio alarm when decompression is entered on a non-decompres-
sion conguration.
• When the mouthpiece is found to be in an indeterminate state (neither in Open-Circuit nor
Closed-Circuit position) a different audio alarm signal will alert the diver to correct the
mouthpiece position. The reason for this is that when the mouthpiece is in an indetermi-
nate position, decompression is calculated as though the diver is breathing in open-circuit
mode. The alarm helps prevent the diver from being penalized from a decompression
point of view.
Controlling Resource Algorithm (CRA)
A SE7EN+ enabled for decompression diving has a different controlling resource algorithm
(CRA).
In a standard SE7EN+, the remaining dive time is the minimum of remaining no-decompres-
sion dive time (RNDT), Oxygen supply, Battery supply or OTU’s. What this means in practice
for most divers on most dives is that the remaining dive time is the RNDT.
For a decompression-enabled SE7EN+, an RNDT of zero is permissible and will not generate
an alarm. Thus, after the RNDT reaches zero (i.e., when a decompression ceiling exists), the
CRA instead only takes into account the Oxygen Supply, Battery Supply, and OTU value when
calculating the remaining dive time.
While a decompression ceiling exists, the RDT is not displayed, because this part of the screen
is used for the total decompression time (see chapter 3, dive procedures in the SE7EN+
manual). However, the CRA is still calculated (excluding the RNDT value) and used to generate
alarms, if needed. Also, whenever a decompression ceiling exists, if the TTS exceeds 80% of
the CRA time (for any of the CRA values other than RNDT), an alarm will alert the diver that the
dive must be terminated.
diluent is insufcient to safely reach the surface in OC bailout mode. When using a SE7EN+
enabled for decompression diving, the system assumes that the diver is carrying additional
gas supplies for open-circuit bailout, and therefore no warnings are given to the diver when the
standad diluent supply is insufcient to allow a safe open-circuit bailout to the surface.