Oxygen Cylinder Empty
Cause
Tut, tut, Who forgot to fill that cylinder! Or diving with not enough O2 for the dive. Maybe a leak somewhere, but you notice bubbles on a rebreather
Symptoms
Surface
Failure to calibrate. Failure to hold set point during pre-breathe. Low O2 Alarm Sounding. Oxygen contents gauge showing empty
Dive
Failure to hold set point. Low O2 Alarm sounding. Oxygen contents gauge showing empty
Recovery action during Dive
Urgent. Bail out to open circuit or diluent flush and fly unit in semi closed mode
Preventative action
Check the cylinders contents during the pre-dive checks
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Oxygen Cylinder Switched Off
Cause
Lack of brain power and failure to do pre-dive checks. This should not happen, but it has claimed lives
Symptoms
Surface
Failure to calibrate. Failure to hold set point during pre-breathe. Low O2 Alarm Sounding. Oxygen contents gauge showing empty
Dive
Failure to hold set point. Low O2 Alarm sounding. Oxygen contents gauge showing empty
Recovery action during Dive
Urgent. Open O2 valve, ready to bail out to open circuit or diluent flush and fly unit in semi closed mode
Preventative action
Check the cylinders contents during the pre-dive checks
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Oxygen First Stage Failure
Cause
Wear or structural failure. Overpressure valve fitted may blow or unit may jam
Symptoms
Surface
Failure to calibrate. Failure to hold set point during pre-breathe. Low or high O2 Alarm Sounding. Oxygen contents gauge showing empty or audible air loss from cylinder
Dive
Failure to hold set point. Low or high O2 Alarm sounding. Oxygen contents gauge may show empty. Bubbles in water
Recovery action during Dive
Urgent. Bail out to open circuit or diluent flush and fly unit in semi closed mode
Preventative action
Pre-dive checks. Oxygen Interstage pressure checks when servicing
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Oxygen First Stage Over Pressure
Cause
Bad servicing, or wear of first stage
Symptoms
Surface
Only if battery low. Solenoid can fail to fire before low battery warning given. Hence Failure to calibrate. Failure to hold set point during pre-breathe. Low O2 Alarm Sounding
Dive
Only if battery low. Solenoid can fail to fire before low battery warning given. Hence Failure to hold set point during pre-breathe. Low O2 Alarm Sounding
Recovery action during Dive
Urgent. Bail out to open circuit or diluent flush and fly unit in semi closed mode
Preventative action
Check interstage pressure during servicing and use fresh batteries
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Oxygen Hose Leaks
Cause
Wear, bad servicing
Symptoms
Surface
Failure to calibrate. Failure to hold set point during pre-breathe. Low O2 Alarm Sounding. Oxygen contents gauge showing low or audible air loss from cylinder
Dive
Failure to hold set point. Low O2 Alarm sounding. Oxygen contents gauge may show empty. Bubbles in water
Recovery action during Dive
Urgent. Bail out to open circuit or diluent flush and fly unit in semi closed mode
Preventative action
Pre-dive checks
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Oxygen Solenoid Stuck Open
Cause
Corrosion, Bad servicing, salt crystals or contaminates in unit. High Interstage pressure. Low Battery
Symptoms
Surface
Failure to calibrate. Failure to hold set point during pre-breathe. High O2 Alarm Sounding. Counter lungs full
Dive
Failure to hold set point. High O2 Alarm sounding. Excessive buoyancy. Can hear solenoid injecting at all times
Recovery action during Dive
Urgent. Close O2 valve. Bail out, or diluent flush. Option to fly manually using O2 valve or to go semi closed
Preventative action
Regular service. Lube and ensure solenoid clean, Check mesh filter above solenoid. Fresh Batteries
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Oxygen Solenoid Stuck Closed
Cause
Corrosion, Bad servicing, salt crystals or contaminates in unit. Low battery. High interstage pressure
Symptoms
Surface
Failure to calibrate. Failure to hold set point during pre-breathe. Low O2 Alarm Sounding.
Dive
Failure to hold set point. Low O2 Alarm sounding
Recovery action during Dive
Urgent. Fly unit manually using manual O2 injector. Consider bail out
Preventative action
Regular service. Lube and ensure solenoid clean, Check mesh filter above solenoid. Fresh batteries
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Oxygen Manual Injector Failure
Cause
Bad maintenance. Failure to plug hose on properly
Symptoms
Surface
Failure of pre dive checks
Dive
Loss of gas from loop, flooding of loop.
Recovery action during Dive
Urgent. Reconnect Hose or rescrew injector down. Bail out if loop flooded
Preventative action
Pre-Dive checks
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Wrong Gas in Oxygen cylinder
Cause
Nitrox fill or gas other than 100% oxygen
Symptoms
Surface
Failure to calibrate (maybe). failure to hold set point. Lungs full
Dive
Failure to hold set point (maybe), Excessive buoyancy and injector function
Recovery action during Dive
Bail out (you don't know what you are breathing)
Preventative action
ALWAYS analyse your gasses after a fill. You'd be amazed how many places don't give a 100% fill, or nowadays, how many air fills aren't
On these two fills one is 96% and the other 99.8%. I always analyse and label my gases myself. Never trust a shop
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Diluent Cylinder Empty
Cause
Someone forgot to fill it, or a bad leak
Symptoms
Surface
Failure of pre-dive checks, Diluent contents gauge reads zero
Dive
Lung squeeze on descent, unable to inject diluent. Auto Air out not functional. Dry suit inflate not functional
Recovery action during Dive
Plug in a reserve gas supply. Inflate lungs with manual O2 inject if above 6m
Preventative action
Pre-dive checks
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Diluent Cylinder Switched Off
Cause
Silly mistake
Symptoms
Surface
Failure of pre-dive checks, Diluent contents gauge reads zero
Dive
Lung squeeze on descent, unable to inject diluent. Auto Air out not functional. Dry suit inflate not functional
Recovery action during Dive
Open valve
Preventative action
Pre-dive checks
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Diluent First Stage Failure
Cause
Wear or structural failure
Symptoms
Surface
Failure of pre-dive checks, Diluent contents gauge reads zero
Dive
Lung squeeze on descent, unable to inject diluent. Auto Air out not functional. Dry suit inflate not functional
Recovery action during Dive
Plug in a reserve gas supply. Inflate lungs with manual O2 inject if above 6m
Preventative action
Service correctly and Pre-dive checks
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Diluent First Stage Over Pressure
Cause
Wear or structural failure. Bad adjustment
Symptoms
Surface
Auto air free flow, BC inflation
Dive
Auto air free flow, Excessive buoyancy in BC
Recovery action during Dive
Shut down diluent valve. Manually operate when needed (Shouldn't need to surface). Consider bailout if alternate supply
Preventative action
Service correctly and pre-dive checks
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Diluent Hose Leaks
Cause
Wear. Bad servicing
Symptoms
Surface
Failure of pre-dive checks. Audible gas escape. Diluent contents decreasing
Dive
Audible gas escape. Diluent contents decreasing
Recovery action during Dive
Abort dive
Preventative action
Pre-dive checks and servicing
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Diluent Manual Injector Failure
Cause
Bad maintenance. Failure to plug hose on properly
Symptoms
Surface
Failure of pre dive checks
Dive
Loss of gas from loop, flooding of loop.
Recovery action during Dive
Urgent. Reconnect Hose or rescrew injector down. Bail out if loop flooded
Preventative action
Pre-Dive checks
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Wrong Gas In Diluent Cylinder
Cause
Cylinder filled wrongly
Symptoms
Surface
None with normal pre-dive checks
Dive
Problems maintaining Setpoint during descent
Recovery action during Dive
Abandon dive, of connect alternate diluent source (Not likely to notice during dive)
Preventative action
Analyse ALL gasses prior to use. Once unit is calibrated you can check the diluent O2 content by doing a diluent flush. This should be added as part of the pre-dive tests
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Alternate Air Source Free Flow
Cause
Dirt or high diluent interstage pressure
Symptoms
Surface
Failure of pre-dive checks. Audible gas loss
Dive
Audible gas loss and bubbles
Recovery action during Dive
Disconnect Auto air, or try shaking to reseat things. Consider aborting dive
Preventative action
Service equipment and pre-dive checks
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