Ask Jill: A number of us were discussing your book last night over conversation and things crossed into the whole O2 Toxicity thing. While we know it is bad, and in fact more likely fatal than Narcosis and such, much of it seems to be speculative outside of the rebreather community.
Are there cases being reported of O2 Tox on Open Circuit? It seems that there are two schools. Those who say “It’s a rebreather problem” and those, like myself, who just plan for it, just in case. I know that, while in Coco View, diving 5 times a day with EAN, my OTU’s clearly exceeded safe recommendations, enough so that I moved to Air diving by Wednesday.
My answer:
When people say "it's a rebreather problem" they are likely referring to Pulmonary Toxicity which is caused by long exposures of PO2's as low as .5. That is what you are counting with OTUs. When you count OTUs you are not walking close to the edge of a precipice that will result in a symptom that will result in drowning. Not at all. You are keeping track of a number of units that will leave room for you to have a chamber run if needed. Chamber runs give you a very high dose of oxygen. If you had already dived aggressively in Coco View for a week and not heeded the OTU count and then got bent, they could still treat you, but you might start to suffer symptoms of Pulmonary Toxicity. You might experience substernal irritation, difficulty getting a full breath and something that feels like the heaviness of a bad cough. If you needed further treatments, they could be delayed or canceled because of the potential lung damage and loss of vital capacity. This type of toxicity knows no equipment boundaries. It can occur from open or closed circuit diving that is lengthy, especially when long decompression is involved. More likely than not, individuals will not experience it unless they are diving aggressively for a week or more. Most people use the "Repex" Method to county Oxygen Toxicity Units (OTUs).
The other type of oxygen toxicity is CNS (Central Nervous System) Oxygen Toxicity. This is the one that can cause symptoms that result in drowning. It can and does happen to open circuit and closed circuit divers equally. Essentially, there are two ways to get CNS toxicity. You can breathe a mix too deep or stay too long at a high partial pressure. Anecdotally, some experts argue that there may be pre-disposing factors to an individual’s likelihood of having CNS toxicity. Specifically, they argue that some drugs heighten your chances of having an oxygen toxicity convulsion. One could argue that if your medication has side effects that are similar to the list of symptoms of CNS toxicity, then effects could be additive (I get to say this stuff, because I do NOT have a medical degree). An argument in support of this comes from many incidents of death where there seemed to be no reason for the underwater convulsion, yet the diver(s) had prescriptions or Sudafed in their systems and used marginal to hot mixes for their dives and were otherwise healthy and young.
So what are the symptoms of “oxtox?” Visuals disturbances (like seeing spots), hearing disturbances (like ringing), tingling, nausea, irritability, dizziness and convulsions are all symptoms, but may not occur before convulsions resulting in drowning and death.
You can keep track of your “CNS count” using a CNS clock. This is a 24-hour clock that tracks how much extra oxygen you are putting into your system. Think of your body like a campfire. If you keep putting a few logs on the fire, they get slowly consumed and then end result is just a little ash. If you throw a bunch of gasoline on the fire, everything burns super hot and creates a lot of ash, smoke and flame. Your body is similar. It can tolerate a little extra oxygen and will use it in normal metabolism. Eventually you hit a threshold of how much oxygen the body really needs and you start creating extra byproducts that we call free radicals. Our amazing body can tolerate and manage a certain amount of those, but if we throw gas on the fire, like extremes of partial pressures for a long period we reach a tipping point. The body cannot tolerate the additional free radicals and starts to have symptoms. Eventually the body is overwhelmed and convulsions may occur.
That is a much longer answer than you might have expected, but I hope it illustrates a good general picture of oxygen risks. I will finish this answer over the next several posts.
Are there cases being reported of O2 Tox on Open Circuit? It seems that there are two schools. Those who say “It’s a rebreather problem” and those, like myself, who just plan for it, just in case. I know that, while in Coco View, diving 5 times a day with EAN, my OTU’s clearly exceeded safe recommendations, enough so that I moved to Air diving by Wednesday.
My answer:
When people say "it's a rebreather problem" they are likely referring to Pulmonary Toxicity which is caused by long exposures of PO2's as low as .5. That is what you are counting with OTUs. When you count OTUs you are not walking close to the edge of a precipice that will result in a symptom that will result in drowning. Not at all. You are keeping track of a number of units that will leave room for you to have a chamber run if needed. Chamber runs give you a very high dose of oxygen. If you had already dived aggressively in Coco View for a week and not heeded the OTU count and then got bent, they could still treat you, but you might start to suffer symptoms of Pulmonary Toxicity. You might experience substernal irritation, difficulty getting a full breath and something that feels like the heaviness of a bad cough. If you needed further treatments, they could be delayed or canceled because of the potential lung damage and loss of vital capacity. This type of toxicity knows no equipment boundaries. It can occur from open or closed circuit diving that is lengthy, especially when long decompression is involved. More likely than not, individuals will not experience it unless they are diving aggressively for a week or more. Most people use the "Repex" Method to county Oxygen Toxicity Units (OTUs).
The other type of oxygen toxicity is CNS (Central Nervous System) Oxygen Toxicity. This is the one that can cause symptoms that result in drowning. It can and does happen to open circuit and closed circuit divers equally. Essentially, there are two ways to get CNS toxicity. You can breathe a mix too deep or stay too long at a high partial pressure. Anecdotally, some experts argue that there may be pre-disposing factors to an individual’s likelihood of having CNS toxicity. Specifically, they argue that some drugs heighten your chances of having an oxygen toxicity convulsion. One could argue that if your medication has side effects that are similar to the list of symptoms of CNS toxicity, then effects could be additive (I get to say this stuff, because I do NOT have a medical degree). An argument in support of this comes from many incidents of death where there seemed to be no reason for the underwater convulsion, yet the diver(s) had prescriptions or Sudafed in their systems and used marginal to hot mixes for their dives and were otherwise healthy and young.
So what are the symptoms of “oxtox?” Visuals disturbances (like seeing spots), hearing disturbances (like ringing), tingling, nausea, irritability, dizziness and convulsions are all symptoms, but may not occur before convulsions resulting in drowning and death.
You can keep track of your “CNS count” using a CNS clock. This is a 24-hour clock that tracks how much extra oxygen you are putting into your system. Think of your body like a campfire. If you keep putting a few logs on the fire, they get slowly consumed and then end result is just a little ash. If you throw a bunch of gasoline on the fire, everything burns super hot and creates a lot of ash, smoke and flame. Your body is similar. It can tolerate a little extra oxygen and will use it in normal metabolism. Eventually you hit a threshold of how much oxygen the body really needs and you start creating extra byproducts that we call free radicals. Our amazing body can tolerate and manage a certain amount of those, but if we throw gas on the fire, like extremes of partial pressures for a long period we reach a tipping point. The body cannot tolerate the additional free radicals and starts to have symptoms. Eventually the body is overwhelmed and convulsions may occur.
That is a much longer answer than you might have expected, but I hope it illustrates a good general picture of oxygen risks. I will finish this answer over the next several posts.
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