Jay Harding
New Member
Okay, I'll start the Hypercapnia thread. I feel pretty strongly about this topic since a bad CO2 incident almost killed me in September 2009. So, I'm copying the text of my write up from that "other rebreather site" below:
Hi All,
I just wanted to share an incident that happened to me a couple of days ago.
I have been diving a pure O2 chest mount rebreather this summer in the shallows just as a fun rig and to shoot the occasional fish. It's an ex-Iraqi military Fenzy PO-68, undived until I got my hands on it. I had to modify the pneumatic system (ie-add a standard cylinder/reg and associated fittings to accept a BC quick disconnect) but it is otherwise stock in scrubber, counterlung, hoses, dsv, adv, etc.
My dives have been short sorties of 30 min or less. Typically I jump in for a 15 min swim after work (I work a 5 min walk from the beach). The US Navy has tested PO-68s and rate the scrubber for 95 min. So, I typically do 2-3 short dives on a single fill.
This particular day the scrubber was sitting at about 70 min and I wanted to take a 10 min swim to shoot a fish for dinner. I figure with more than 20 minutes remaining, it shouldn't be an issue So, I rock up to the beach, suit up and begin prebreathing as I walk from the parking lot down to the beach, across the sand and wade out into the water. I'm in 4-5 feet of water about 30 yards from the shoreline and start putting on my fins with one hand while holding my speargun with the other hand. I get one on and then start putting on the second. I notice I'm a bit winded but chalk it up to the exertion. While in the process of putting on the second fin, it hit.
Now, I've breathed a loop with no sorb in it while sitting on my couch just to test what hypercapnia feels like. IT DID NOTHING TO PREPARE ME FOR THE SPEED OF THIS HIT. The scrubber broke through so fast and I was overcome by hypercapnia so fast, that I literally couldn't react.
One second I'm putting on my second fin, the next I'm falling through space. I had the feeling that I was weightless in outer space tumbling head over heels with no way to stop my movement. The feeling was actually quite nice. It was a soft, flowing motion, not unlike diving in the warm waters of the tropics in an easy surge. I have no idea how long this lasted, but it felt like an hour. It was probably only a couple seconds.
Then, a tightness began to grow in my chest disrupting the calm, flowing feeling. I began to notice a kind of squeezing discomfort that flared exponentially until . . . . WHAM!!! It was like time had been stretched and then suddenly snapped back on itself. I had an immediate surge of uncontrollable panic. My body, which had sunk down onto the sandy bottom at about 5 feet of depth, jerked and went rigid driving my heels into the seabed. This propelled my head up and out of the water as if I was standing up. My face breaking the surface must have oriented me to the shoreline and initiated a blitz toward terra firma. I slipped, hit bottom again, this time on my face, and began clawing hand over hand toward my last sight of the shoreline some 30 yards away.
At this point my breathing rate is off the charts. My chest is heaving so hard that if it had not been for the PO-68's gag strap and lip seal I surely would have aspirated water and drowned. My inhalations are only receiving bad gas as a result of their efforts so panic continues to rise, if that's even possible. I'm sucking in so hard in an effort to get some beathable gas out of the rig (which, of course, isn't going to happen . . . the loop is completely hypercapnic) that I suck my mask down right onto the bridge of my nose. As it bottoms out the negative pressure breaks blood vessels in my eyes and the soft tissue around them and water gets pulled past the nose seal and floods my sinuses.
Finally my head breaks through the water/air interface and as I'm dragging my body across the threshold of the beach with one hand and pushing it with my finless right foot, my other hand is ripping off the mask and pulling down the gagged DSV. People enjoying the beach rush to pull me out of the water and onto the beachface. I'm still heaving like I've sprinted a marathon and I'm gagging and burping up foul breathing gas that I had swallowed in my ordeal. My head is swimming like I've got the 8 shots of tequila spins and I've got the kind of slamming headache that makes you try to swat away the hammer that you swear must be hitting you repeatedly between the eyes. Somewhere in all of this I get a vague realization that I've shit myself and slimy saltwater is running out of my sinuses.
At that point time restores its normal pace. But, how did I get here? What happened? How did I get out of the water? These are the questions that I had to mull over for two days until I could piece what happened together. The human mind is truly great at blocking out trauma, and I only remember the ordeal in snips and moments. The feelings, the pain, a few visual memories, and the aftermath are all that are clear. For instance, I know that I clawed my way along the bottom because the tips of my gloves are shredded. I know that I was pushing myself along with my right foot because I distinctly remember the feeling of the gravel gouging the top of my foot during my efforts (it's summer so I've been using full foot fins and bare feet). I also have the wounds on said foot to corroborate the memory.
The results of the incident have left me with bumps, bruises, scrapes, two black eyes with bloodshot whites, an incessant nagging ice cream headache, and sore, phelgmy lungs. Not to mention a general feeling of soreness and extreme fatigue. And, yes, more than a little trepidation when the thought of diving that beautiful, sleek, light, wonderful-to-dive little rig crosses my mind. So, I came within a hair's breadth of dying (I mean well and truly kicking the bucket, sayonara, good night sweetheart, my kids are orphans and my wife's a widow dying) in 4 ****ing feet of water, but I'm alive, I'm healing, and I'm smarter. Have I been scared out of the water? Much to the dismay of my wife, my family, and my friends the answer, for better or worse, is no. But, I now carry to my diving table a bulging bag of realizations, wisdom, and new personal rules.
So what did I learn:
1. Hypercapnia is an evil beast that is powerfully underestimated by those who have not experienced a hit. My couch test was sorely, foefully, inadequate to prepare me for recognization and mitigation of hypercapnia. The early symptoms are too easily blown off and the progression is far too fast to cut off the downward spiral after you have ignored the early symptoms.
2. My twenty years of diving (from age 13 to now) did not condition the weight belt drop response . . . and thank God it didn't. Dropping your weight, I now understand is a conscious decision, and in my fight to survive, the thought never crossed my mind. If it had, and I had dropped the belt, I would be dead. I would have floundered on the surface, thrashing with one fin instead of being on the bottom where I could use my hands to drag myself out. This is significant not because of the weight belt or dropping it (although in this case it might have contributed to my demise) but because thought processes break down. The confusion, euphoria, and then panic are sheer and bold and unrelenting. They do not let you make decisions. Instinct is what carries you through. Obviously it is not my instinct to drop my weight belt. But it seems it is my instinct to claw my way to shore.
3. Gag straps and lip seals work. Without them, I would have sucked water into my lungs and the Navy would be reporting a rebreather diving mishap. The lip seal prevented me from sucking water into my mouth even though I sucked water past my mask seal and into my sinuses. The gag strap prevented me from blowing the DSV out on my violent exhales. Thumbs up for those jewels of engineering.
4. Bailout would not have helped unless it had been in the form of a BOV or within a very few inches of my mouth. Even then, I'm not sure that I would have had the wherewithall to make the switch. A sling tank or sidemount tank with stowed regulator would have simply ended up as expensive decoration on a dead man. If it's not plumbed to your mouth in the form of a BOV, then your bailout had better be on a necklace within inches of your mouth and charged and ready to flow large, voluminous amounts of clean beathable gas . . . your body will demand it. Shitty unbalanced regs have no place in this job.
5. Lastly, but in this case most importantly, scrubber fills are not worth your life. I was trying to get my money's worth squeezing multiple dives (albeit very short dives) out of my fill. I see this now for the suicidal stupidity that it is. My new personal rule is to dive the scrubber duration with ultra conservativism. I will not dive that PO-68 beyond 60-65 mins. And I will do not more than two dives within that 60-65 mins duration. And even then, only if they are the same day or within a day or two.
Okay, this is the last bit. That heat at the base of your skull? The one that goes with that impulse to breathe in just a little bit deeper this time, and that extra hard heartbeat that you just felt in your ears? THEY WILL NOT BE IGNORED. They mean that you should bail and bail now because your loop is probably going hypercapnic.
Just my experience and my thoughts . . . actual mileage may vary. Feel free to flame me . . . there are a couple of decisions made that probably deserve it. Just rest assured that you'll be beating a dead horse . . . my kids won't be without a daddy and wife without a husband due to those same decisions, I can promise you.
Dive safe,
Jay
Hi All,
I just wanted to share an incident that happened to me a couple of days ago.
I have been diving a pure O2 chest mount rebreather this summer in the shallows just as a fun rig and to shoot the occasional fish. It's an ex-Iraqi military Fenzy PO-68, undived until I got my hands on it. I had to modify the pneumatic system (ie-add a standard cylinder/reg and associated fittings to accept a BC quick disconnect) but it is otherwise stock in scrubber, counterlung, hoses, dsv, adv, etc.
My dives have been short sorties of 30 min or less. Typically I jump in for a 15 min swim after work (I work a 5 min walk from the beach). The US Navy has tested PO-68s and rate the scrubber for 95 min. So, I typically do 2-3 short dives on a single fill.
This particular day the scrubber was sitting at about 70 min and I wanted to take a 10 min swim to shoot a fish for dinner. I figure with more than 20 minutes remaining, it shouldn't be an issue So, I rock up to the beach, suit up and begin prebreathing as I walk from the parking lot down to the beach, across the sand and wade out into the water. I'm in 4-5 feet of water about 30 yards from the shoreline and start putting on my fins with one hand while holding my speargun with the other hand. I get one on and then start putting on the second. I notice I'm a bit winded but chalk it up to the exertion. While in the process of putting on the second fin, it hit.
Now, I've breathed a loop with no sorb in it while sitting on my couch just to test what hypercapnia feels like. IT DID NOTHING TO PREPARE ME FOR THE SPEED OF THIS HIT. The scrubber broke through so fast and I was overcome by hypercapnia so fast, that I literally couldn't react.
One second I'm putting on my second fin, the next I'm falling through space. I had the feeling that I was weightless in outer space tumbling head over heels with no way to stop my movement. The feeling was actually quite nice. It was a soft, flowing motion, not unlike diving in the warm waters of the tropics in an easy surge. I have no idea how long this lasted, but it felt like an hour. It was probably only a couple seconds.
Then, a tightness began to grow in my chest disrupting the calm, flowing feeling. I began to notice a kind of squeezing discomfort that flared exponentially until . . . . WHAM!!! It was like time had been stretched and then suddenly snapped back on itself. I had an immediate surge of uncontrollable panic. My body, which had sunk down onto the sandy bottom at about 5 feet of depth, jerked and went rigid driving my heels into the seabed. This propelled my head up and out of the water as if I was standing up. My face breaking the surface must have oriented me to the shoreline and initiated a blitz toward terra firma. I slipped, hit bottom again, this time on my face, and began clawing hand over hand toward my last sight of the shoreline some 30 yards away.
At this point my breathing rate is off the charts. My chest is heaving so hard that if it had not been for the PO-68's gag strap and lip seal I surely would have aspirated water and drowned. My inhalations are only receiving bad gas as a result of their efforts so panic continues to rise, if that's even possible. I'm sucking in so hard in an effort to get some beathable gas out of the rig (which, of course, isn't going to happen . . . the loop is completely hypercapnic) that I suck my mask down right onto the bridge of my nose. As it bottoms out the negative pressure breaks blood vessels in my eyes and the soft tissue around them and water gets pulled past the nose seal and floods my sinuses.
Finally my head breaks through the water/air interface and as I'm dragging my body across the threshold of the beach with one hand and pushing it with my finless right foot, my other hand is ripping off the mask and pulling down the gagged DSV. People enjoying the beach rush to pull me out of the water and onto the beachface. I'm still heaving like I've sprinted a marathon and I'm gagging and burping up foul breathing gas that I had swallowed in my ordeal. My head is swimming like I've got the 8 shots of tequila spins and I've got the kind of slamming headache that makes you try to swat away the hammer that you swear must be hitting you repeatedly between the eyes. Somewhere in all of this I get a vague realization that I've shit myself and slimy saltwater is running out of my sinuses.
At that point time restores its normal pace. But, how did I get here? What happened? How did I get out of the water? These are the questions that I had to mull over for two days until I could piece what happened together. The human mind is truly great at blocking out trauma, and I only remember the ordeal in snips and moments. The feelings, the pain, a few visual memories, and the aftermath are all that are clear. For instance, I know that I clawed my way along the bottom because the tips of my gloves are shredded. I know that I was pushing myself along with my right foot because I distinctly remember the feeling of the gravel gouging the top of my foot during my efforts (it's summer so I've been using full foot fins and bare feet). I also have the wounds on said foot to corroborate the memory.
The results of the incident have left me with bumps, bruises, scrapes, two black eyes with bloodshot whites, an incessant nagging ice cream headache, and sore, phelgmy lungs. Not to mention a general feeling of soreness and extreme fatigue. And, yes, more than a little trepidation when the thought of diving that beautiful, sleek, light, wonderful-to-dive little rig crosses my mind. So, I came within a hair's breadth of dying (I mean well and truly kicking the bucket, sayonara, good night sweetheart, my kids are orphans and my wife's a widow dying) in 4 ****ing feet of water, but I'm alive, I'm healing, and I'm smarter. Have I been scared out of the water? Much to the dismay of my wife, my family, and my friends the answer, for better or worse, is no. But, I now carry to my diving table a bulging bag of realizations, wisdom, and new personal rules.
So what did I learn:
1. Hypercapnia is an evil beast that is powerfully underestimated by those who have not experienced a hit. My couch test was sorely, foefully, inadequate to prepare me for recognization and mitigation of hypercapnia. The early symptoms are too easily blown off and the progression is far too fast to cut off the downward spiral after you have ignored the early symptoms.
2. My twenty years of diving (from age 13 to now) did not condition the weight belt drop response . . . and thank God it didn't. Dropping your weight, I now understand is a conscious decision, and in my fight to survive, the thought never crossed my mind. If it had, and I had dropped the belt, I would be dead. I would have floundered on the surface, thrashing with one fin instead of being on the bottom where I could use my hands to drag myself out. This is significant not because of the weight belt or dropping it (although in this case it might have contributed to my demise) but because thought processes break down. The confusion, euphoria, and then panic are sheer and bold and unrelenting. They do not let you make decisions. Instinct is what carries you through. Obviously it is not my instinct to drop my weight belt. But it seems it is my instinct to claw my way to shore.
3. Gag straps and lip seals work. Without them, I would have sucked water into my lungs and the Navy would be reporting a rebreather diving mishap. The lip seal prevented me from sucking water into my mouth even though I sucked water past my mask seal and into my sinuses. The gag strap prevented me from blowing the DSV out on my violent exhales. Thumbs up for those jewels of engineering.
4. Bailout would not have helped unless it had been in the form of a BOV or within a very few inches of my mouth. Even then, I'm not sure that I would have had the wherewithall to make the switch. A sling tank or sidemount tank with stowed regulator would have simply ended up as expensive decoration on a dead man. If it's not plumbed to your mouth in the form of a BOV, then your bailout had better be on a necklace within inches of your mouth and charged and ready to flow large, voluminous amounts of clean beathable gas . . . your body will demand it. Shitty unbalanced regs have no place in this job.
5. Lastly, but in this case most importantly, scrubber fills are not worth your life. I was trying to get my money's worth squeezing multiple dives (albeit very short dives) out of my fill. I see this now for the suicidal stupidity that it is. My new personal rule is to dive the scrubber duration with ultra conservativism. I will not dive that PO-68 beyond 60-65 mins. And I will do not more than two dives within that 60-65 mins duration. And even then, only if they are the same day or within a day or two.
Okay, this is the last bit. That heat at the base of your skull? The one that goes with that impulse to breathe in just a little bit deeper this time, and that extra hard heartbeat that you just felt in your ears? THEY WILL NOT BE IGNORED. They mean that you should bail and bail now because your loop is probably going hypercapnic.
Just my experience and my thoughts . . . actual mileage may vary. Feel free to flame me . . . there are a couple of decisions made that probably deserve it. Just rest assured that you'll be beating a dead horse . . . my kids won't be without a daddy and wife without a husband due to those same decisions, I can promise you.
Dive safe,
Jay
