One other thing I forgot to add regarding Dil flushes is loss of bouyancy. Improper technique could cause you to become negative or positive very quickly if you dont control the addition adequately and expel the gas.
Overbreathing the scrubber
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Randy,
You asked these questions in another post, I moved them here because I felt the answer would be more relevant in a thread about rebreathers. I am at work currently and won't likely have time to go in depth with an answer, but will try to get one posted tonight when I get home.
You asked these questions in another post, I moved them here because I felt the answer would be more relevant in a thread about rebreathers. I am at work currently and won't likely have time to go in depth with an answer, but will try to get one posted tonight when I get home.
Nice one Cave Diver, I think you answered it all.
OP
Thanks. I had a feeling that it would have to be possible to draw gas through the scrubber too fast to allow the reaction that removes the CO2. One would think the result would be high anxiety, but I remember watching a video of someone getting CO2 toxic on a RB, and he didn't go to bailout or even signal a buddy. I wonder if it just creeps up too slowly for the air hunger to register.
I have this awful feeling that CO2 is the culprit in a number of otherwise inexplicable scuba deaths, on rebreathers and otherwise.
I have this awful feeling that CO2 is the culprit in a number of otherwise inexplicable scuba deaths, on rebreathers and otherwise.
jimdiverman
Contributor
Cave Diver,
I am not trained on any rebreather yet, but if I understand your explanation correctly, and I understand what you are saying, the flow rate that gas is moving through the loop affects the dwell time within which the absorption reaction has to remove CO2 from the loop. What does that equation look like? That is, CO2 + Sorb + time -> what gas/liquid result, chemically? Based on your explanation, as time interacting with the scrubber for a molecule of CO2 decreases due to increased flow rate, the reaction slows to a point that may adversely impact the CO2 level in the loop.
Would a flow rate sensor in the loop be sufficient to notify the diver through an alarm that they need to slow their heart rate/ breathing and control their breathing because the loop flow rate exceeds the limit for the required gas exchange in the scrubber (exceeds dwell time)? Does this sensor or output exist in today's rebreathers? Obviously the flow rate would be an average generated over a periodic interval in order to prevent false alarms on instantaneous or spike readings.
Dive safe!
I am not trained on any rebreather yet, but if I understand your explanation correctly, and I understand what you are saying, the flow rate that gas is moving through the loop affects the dwell time within which the absorption reaction has to remove CO2 from the loop. What does that equation look like? That is, CO2 + Sorb + time -> what gas/liquid result, chemically? Based on your explanation, as time interacting with the scrubber for a molecule of CO2 decreases due to increased flow rate, the reaction slows to a point that may adversely impact the CO2 level in the loop.
Would a flow rate sensor in the loop be sufficient to notify the diver through an alarm that they need to slow their heart rate/ breathing and control their breathing because the loop flow rate exceeds the limit for the required gas exchange in the scrubber (exceeds dwell time)? Does this sensor or output exist in today's rebreathers? Obviously the flow rate would be an average generated over a periodic interval in order to prevent false alarms on instantaneous or spike readings.
Dive safe!
ianr33
Contributor
Ca(OH)2 (s) +CO2(g) -> CaCO3(s) + H2O(l)
Presumably if the CO2 passes through the scrubber too quickly some of this gas will not actually come into contact with the Calcium Hydroxide so will have no chance to react.
Ok, to take a stab at some of the other questions that have been posed:
DISCLAIMER: I am NOT an instructor or medical professional, nor do I claim to be. Nor am I attempting to "guess" as to the suitability of any equipment or person for the type of diving they do, or the cause of any accidents resulting thereof. I am relating MY understanding of how things work in the best way I know and cannot guarantee the accuracy of any statement. Most importantly, I did not stay in a Holiday Inn last night!
The full face mask is almost as hotly debated amongst some rebreather divers as Mask on Forehead/No Mask on Forehead. The proponents feel that if a diver did pass out while wearing a full fask mask, the chances of survival are better because the diver wouldn't "spit" the regulator out and drown.
CCR dive buddies should be made aware of fundamental things regarding the unit, things to look for that may be out of the norm and how to respond to such an emergency. These should include how to open/close the CCR mouthpiece
how to recognize signs of the 3 H's (Hypoxia, Hyperoxia and Hypercapnia) as well as when and how to add Diluent and O2.
There is a wide range of CCR units. Some are mCCR some are eCCR. mCCR are mechanical, which means they don't rely on electronics to monitor or control the injection of oxygen. eCCR are use electronic controls to monitor, inject and mix the breathing gas. The eCCR's vary wildly in their abilities. Some simply report and maintain PO2, others have advanced monitoring and decompression algorithms. While I'm not familiar with the specifics on every brand out there, I'm sure there are a couple that have "black box" like abilities to download dive data.
However, some of us chose our particular units because we DONT want all those fancy electronics on them.
There are three things a CCR diver has to contend with. Hypoxia, Hyperoxia and Hypercapnia.
Hypoxia is low oxygen. This can result from failure to turn O2 on, a problem with O2 delivery, incorrect mix, rapid ascent or several other failures. Hypoxia can cause euphoria, loss of coordination, clouded judgement and reduce a divers ability to take needed action. Unchecked, it can lead to unconciousness or even to Anoxia, where the lack of oxygen is sufficient to cause death. CCR divers are most at risk for Hypoxia during ascents or under high workloads, as the PO2 drops.
Hyperoxia is high oxygen. Many nitrox divers will be familiar with the effects of this from their class (I hope). Oxygen toxicity can occur and lead to the following symptoms:
Convulsions or loss of conciousness
Euphoria
Nausea
Twitche or spasms
Anxiety
Dizziness
Irritability
Vision problems
Ear ringing
Unchecked, it can lead to seizures, which may result in death by drowning if the mouthpiece is not kept in place.
Hypercapnia is excessive CO2 levels. This is usually caused by scrubber problems. Failure to pack properly, overbreathing the scrubber, using a scrubber past it's duration, wet/flooded scrubber, failure to properly pre-breathe scrubber.
Symptoms include mental confusion, hyperventilation, drowsiness, lethargy and even unconciousness.
There are ways of dealing with these issues, but a diver that is unable to resolve them is often advised to go "off the loop" and bail out to their open circuit stage bottle and turn the dive.
Hope this helps some.
DISCLAIMER: I am NOT an instructor or medical professional, nor do I claim to be. Nor am I attempting to "guess" as to the suitability of any equipment or person for the type of diving they do, or the cause of any accidents resulting thereof. I am relating MY understanding of how things work in the best way I know and cannot guarantee the accuracy of any statement. Most importantly, I did not stay in a Holiday Inn last night!
The full face mask is almost as hotly debated amongst some rebreather divers as Mask on Forehead/No Mask on Forehead. The proponents feel that if a diver did pass out while wearing a full fask mask, the chances of survival are better because the diver wouldn't "spit" the regulator out and drown.
CCR dive buddies should be made aware of fundamental things regarding the unit, things to look for that may be out of the norm and how to respond to such an emergency. These should include how to open/close the CCR mouthpiece
how to recognize signs of the 3 H's (Hypoxia, Hyperoxia and Hypercapnia) as well as when and how to add Diluent and O2.
There is a wide range of CCR units. Some are mCCR some are eCCR. mCCR are mechanical, which means they don't rely on electronics to monitor or control the injection of oxygen. eCCR are use electronic controls to monitor, inject and mix the breathing gas. The eCCR's vary wildly in their abilities. Some simply report and maintain PO2, others have advanced monitoring and decompression algorithms. While I'm not familiar with the specifics on every brand out there, I'm sure there are a couple that have "black box" like abilities to download dive data.
However, some of us chose our particular units because we DONT want all those fancy electronics on them.
There are three things a CCR diver has to contend with. Hypoxia, Hyperoxia and Hypercapnia.
Hypoxia is low oxygen. This can result from failure to turn O2 on, a problem with O2 delivery, incorrect mix, rapid ascent or several other failures. Hypoxia can cause euphoria, loss of coordination, clouded judgement and reduce a divers ability to take needed action. Unchecked, it can lead to unconciousness or even to Anoxia, where the lack of oxygen is sufficient to cause death. CCR divers are most at risk for Hypoxia during ascents or under high workloads, as the PO2 drops.
Hyperoxia is high oxygen. Many nitrox divers will be familiar with the effects of this from their class (I hope). Oxygen toxicity can occur and lead to the following symptoms:
Convulsions or loss of conciousness
Euphoria
Nausea
Twitche or spasms
Anxiety
Dizziness
Irritability
Vision problems
Ear ringing
Unchecked, it can lead to seizures, which may result in death by drowning if the mouthpiece is not kept in place.
Hypercapnia is excessive CO2 levels. This is usually caused by scrubber problems. Failure to pack properly, overbreathing the scrubber, using a scrubber past it's duration, wet/flooded scrubber, failure to properly pre-breathe scrubber.
Symptoms include mental confusion, hyperventilation, drowsiness, lethargy and even unconciousness.
There are ways of dealing with these issues, but a diver that is unable to resolve them is often advised to go "off the loop" and bail out to their open circuit stage bottle and turn the dive.
Hope this helps some.
I'm skipping the first part, because it was previously answered, but yes, flow (breathing) rate will adversely affect CO2 levels in the loop.
A flow rate sensor by itself would not likely do much good. Breathing rate is just one variable. Time on the scrubber, temp of water, how well the cannister is packed and a host of other things also impact it. Breathing hard on the start of a dive in warm water with a new scrubber would be much less likely to breakthrough than the same level of exertion on a cannister with 4 hours on it in cold water.
To my knowledge, CO2 sensors are in development, but no one currently has an accurate sensor on the market yet. Many of them use a temp probe to determine how much of the scrubber bed is currently active or used up to guesstimate duration.
I'm new to the rebreather stuff just beginning to learn about it now. Isn't the amount of CO2 you are exhaling proportional to the amount of O2 you are metabolizing. Theoretically couldn't you calculate the amount of CO2 being exhaled from the rate of O2 being injected back into the loop?
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