176. The thought process behind
GUE’s CCR configuration
GUE is known for taking its own holistic approach
to gear configuration. Here GUE board member and Instructor
Trainer Richard Lundgren explains the reasoning behind its
unique closed-circuit rebreather configuration. It’s all about
By Richard Lundgren -
January 2, 2020
incidents over the years have resulted in tragic and
fatal outcomes due to inefficient and insufficient
bailout procedures and systems. At the present time,
there are no community standards that detail:
How much bailout gas volume should be
How to store and access the bailout
How to chose bailout gas properties
Accordingly, Global Underwater Explorers
(GUE) created a standardized bailout system consistent
with GUE’s holistic gear configuration, Standard
Operating Procedures (SOP), and diver training system.
The system was designed holistically; consequently, the
value and usefulness of the system are jeopardized if
any of its components are removed.
Bailout Gas Reserve volumes (BGR)
of gas needed to sustain a diver while bailing from a
rebreather is difficult to assess, as many different
factors impacts the result— including respiratory rate,
depth and time, CO2 levels, and stress
levels. These are but a few of the variables. All
reserve gas calculations may be appropriate under ideal
conditions and circumstances, but they should be
regarded as estimates or predictions at best.
volume needed for two divers to safely ascend to the
first gas switch is referred to as Minimum Gas (MG) for
scuba divers. The gas volume needed for one rebreather
diver to ascend on open-circuit during duress is
referred to as Bailout Gas Reserve (BGR).
is calculated using the following variables:
GUE recommends using a surface consumption rate (SCR) of
20 liters per minute, or 0.75 f3 if imperial
Average Pressure (AvP or average ATA):
The average pressure between the target depth (max
depth) to the first available gas source or the surface
The ascent rate should be according to the decompression
profile (variable ascent rate). However, in order to
simplify and increase conservatism, the ascent rate used
in the BMG formula is set to 3 meters/10 ft per minute.
Any decompression time required before the gas switch
(first available gas source) must be added to the total
time. One minute should be added for the adverse event
(the bailout) and one minute additionally for performing
the gas switch.
BGR = C x AvP x T
Note that Bailout Minimum Gas reserves
are estimations and may not be sufficient! Even though
catastrophic failures are unlikely, other factors like
hypercapnia (CO2 poisoning) and stress
warrants a cautious approach.
Decompression bailout gas volumes are
calculated based on the diver’s actual need (based on
their decompression table/algorithm), and no additional
reserve is added.
It should be noted that GUE does not
endorse the use of “team bailout,” i.e. when one diver
carries bottom gas bailout and another diver carries
decompression gas based on only one diver’s need. A
separation or an equipment failure would quickly render
a system like this useless.
Common tech community rebreather
Backmount rebreather (note side mount
rebreathers are gaining in popularity)
Typically, three-liter oxygen and a
three-liter diluent cylinder on board (each hold 712
Bailout gas in one or more stage
bottles which could be connected to an integrated
Bailout Valve (BOV).
Containment and access
carry bailout gas reserve (BGR) in a stage bottle, which
is typical in the rebreather diving community, GUE has
designed its bailout system as a redundant open-circuit
system consisting of two 7-liter, 232 bar cylinders (57
f3 each) that are integrated into the
rebreather frame, and called the “D7” system, i.e. D for
doubles, 7 for seven liter. Note that GUE has
standardized the JJ-CCR closed-circuit rebreather for
training and operations.
cylinders, each with individual valves, are linked
together using a flexible manifold. This system holds up
to 3250 liters of gas (114 f3), of which only
about 10% is used by the rebreather as diluent. Hence,
close to 3000 liters (106 f3) is reserved for
a bailout situation. This gives a tremendous capacity
and flexibility in a relatively small form factor for
dives requiring additional gas reserves (when direct
ascent is not possible or desirable).
following advantages were considered when designing the
The D7 system is consistent with
existing open-circuit systems utilized by GUE
divers. A bailout system that is familiar to the
user will not increase stress levels, which is
important. A GUE diver will rely on previous
experience and procedures when most needed.
The system contains the gas volumes
needed according to the GUE BGR calculations as well
as the diluent needed for a wide range of dive
The system is fully redundant and has
the capacity to isolate failing components, like a
set of open-circuit doubles and still allowing full
access to the gas.
The overall weight of the system is
less, compared to a standard system with an AL11
liter (aluminum 80 f3) bailout
cylinder. In addition, it contains 800-900
liters/20-32 f3 more gas available for a
bailout situation compared to the AL11 liter system.
Weight has been traded for gas.
The system does not occupy the
position of a stage bottle which allows for
additional stages or decompression bottles to be
If the ISO valves on each side were
closed, the flex manifold can be removed and the
cylinders transported individually while still full.
can be accessed quickly by a bailout valve (BOV), which
is typically configured as a separate open-circuit
regulator worn on a necklace, consistent with GUE’s
open-circuit configuration. However, some GUE divers use
an integrated BOV. After evaluation of the situation,
while breathing open-circuit from the BOV, the user can
transition to a high-performance regulator worn on a
long hose if the situation calls for it.
The long hose is carried under the loop
when diving the rebreather. The chances of having to
donate to another GUE rebreather diver is low, as both
carry redundant bailout. Still, GUE maintains that the
capacity to donate gas must be present. The process is
more likely to involve a handover of the long hose
rather than a donation.
Still, if needed, such a donation is made
possible by either removing the loop temporarily or by
simply donating the long hose from under the loop.
decompression gasses are carried in decompression stage
bottles. If more than three bottles are needed, the
bottles that are to be used at the shallowest depths are
carried on a
(i.e. a short lease that clips to your side D-ring to
carry multiple stage bottles). Maintaining
bottle-rotation techniques and capacity through regular
practice is important and challenging, as this skill is
rarely used with the rebreather.
of bailout gas is extremely important, as survival may
well depend on it. It is not only the volume that is
important, the individual gas properties will decide if
the bailout gas will be optimal or not. As the D7 system
contains both the diluent and bailout gas, both gasses
share the same characteristic. The following gas
characteristics must be considered when choosing gas:
equivalent (air) gas density depth should not exceed 30
meters/100 ft or 5.1 grams/liter. This is consistent
with the latest research by Gavin Anthony and Simon
Mitchell that recommends that divers maintain maximum
gas density ideally below 5.2 g/l, equivalent to air at
31 m/102 ft, and a hard maximum of 6.2 g/l, the
equivalent to air at 39 m/128 ft. You can find a simple
gas density calculator here.
Ventilation is impaired when diving, due
to several factors which increase the work of breathing
(WOB); when diving rebreathers, the impairment is even
more so. High gas density, for example, when diving gas
containing no or low fractions of helium, significantly
decreases a diver’s ventilation capacity and increases
the risk of dynamic airway compression. CO2
washout from blood depends on ventilation capacity and
can be hindered if a high-density gas is used. The
impact of density is very important, and the risk of
using dense gases is not to be neglected. Note that this
effect is not limited to deep diving. Using a dense gas
as shallow as 30 meters/100 ft reduces a diver’s
ventilation capacity by a staggering 50%.
equivalent narcotic depth should also not exceed 30
m/100 ft, or PN2=3.16.
Rebreathers and emergency situations are complex enough
without further being aided by narcosis.
should be limited to allow for long exposures. GUE
operating standards call for a maximum PO2
for bottom gases of 1.2 atm, a PO2 of 1.4 for
deep decompression gases, and a PO2 of 1.6 for shallow
decompression gases. GUE recommends using the next
deeper GUE standard bottom gas for diluent/bailout when
diving a rebreather in combination with GUE standard
Bailout gasses are not chosen in order to
give the shortest possible decompression obligation.
They are chosen in order to give the best odds of
surviving a potentially life-threatening situation.
GUE’s D7 bailout system is flexible and
contains the rebreather’s diluent as well as bailout gas
reserves needed for a range of different missions. The
familiarity the system, along with the knowledge that
they are carrying ample gas reserves, gives GUE divers
peace of mind. Choosing gases with properties that will
aid a diver in duress while dealing with an emergency
completes the system.
GUE did not prioritize the ease of
climbing boat ladders or reducing decompression by a few
minutes. These are more appropriately addressed with
sessions at the gym, combined with finding aquatic
comfort. Nothing prevents a complete removal of the
entire system at the surface if an easy exit is needed.
Torna su all'inizio della pagina