We are indebted to Peter ‘Herb’ Herbert for taking the time to write this comment.
The properties of this gas mean you have no idea of its presence until symptoms such as dizziness, vertigo and the usual light headedness associated with being tired start to show. When combined with changes in pressures on the body while free diving, the results can be very frightening.
As a gas, carbon monoxide has a domineering effect on the blood’s haemoglobin. It is well known that under normal circumstances haemoglobin carries oxygen to the muscles and exchanges oxygen for carbon dioxide to be transported back to the lungs and expelled in the normal breathing process. This happens for every moment that every animal is alive.
What carbon monoxide does is aggressively occupy the haemoglobin carrying cells forcing oxygen and carbon dioxide to take a back step. The carbon monoxide does not exchange for any other gas and hence the value of that haemoglobin cell in your body is ‘stuffed.’ As haemoglobin cells only last a short time in your body we have to wait until thishaemoglobin cell is removed via the liver and replaced with a new one from our bone marrow.
These properties coupled with the changing partial pressures of gasses when diving up to four atmospheres (30 meters), create significant problems if your body has been subjected to the intake of carbon monoxide.
It is well recognized that exhaust fumes from combustion motors in confined spaces, will certainly lead to CO poisoning. Indeed many a suicide has been done with a vacuum hose into the car, the CO occupying so many haemoglobins that there are not enough freehaemoglobins to carry out the normal gas exchanges needed for life.
Here is Herb’s account of carbon monoxide effects while diving in Tahiti in the 2006 Inter Pacific Spearfishing Championships.
"As we always do in pre-competition days, individuals were scouting or looking at areas that were going to be used during the competition. On this particular day, the 7 team members had dispersed around Area 1 and were looking at various fish. Our boat had been moving between divers shifting them around. I noticed the boat was not being used and not likely to be used for the next half hour and as my partner Dwane and I had found it rather boring in the area we were looking at, I decided to grab a rope and get towed behind the boat. It was something we had previously done in the World Champs in Croatia 1998. I was towed for 20 to 25 minutes behind the diesel Volvo Penta stern drive, hanging at about 3 meters behind the boat. This proved great for surveying the area, but I didn't have any idea that the fumes containing carbon monoxide were present enough to be an issue. Eventually I stopped being towed and Dwane and I started diving in 25m again. Basically, we were looking for competition fish.
The first indication that something was a little bit amiss was my first dive to 22 meters: everything was fine and it was NOT an extended dive (70 seconds). Coming up to about 10m slight fuzz hit me, and I thought “Wow!” I continued surfacing while thinking that I must focus on getting to the surface and noticed at the last 3m that things started to fizz and spin as if I had done a 35m dive for 2 minutes. It seemed strange and my thoughts were that I didn't prep myself for that dive properly. On the surface after a bit of a fizz, everything returned to normal in 15 - 20 seconds. There was no laboured breathing, I didn't feel dizzy and my legs felt like they had their normal strength. Dwane did his dive which filled another 4-5 minutes as I watched him from the surface. I think I did a couple of shallow dives 5-6 meters for 30 seconds and thought, “Right ready for another 25 meter dive.” Having breathed up as I have done for thousands of 25 meter dives, I was relaxed and feeling good, focused, with absolutely no cause for concern. Deep breath, duck dive and down you go.
On this particular dive something happened which I have never experienced before in 30 years of diving. As I approached 16 - 18m on my way down, I had a huge head spin. Things went dizzy and it was extremely evident something was badly wrong. Instantly I aborted the dive and looked up to Dwane who was watching. I released my weight belt and held on to it in my hand, a universal indication for your buddy on the surface that something is not right! As I came up through the 3m mark from the surface the dizzy went super dizzy and a sense of anxiety hit me. I must admit I felt secure in knowing that Dwane was directly above me and aware of an issue. On the surface I took 2 or 3 deep breaths while experiencing tunnel vision, dizziness and a sense of losing control. After 15 seconds and more deep breaths things started to come back to normal. I said to Dwane "Shit Dwane I don't feel too good. Just give me 5". For the next 30 minutes I was very aware of any abnormal feelings in my body but nothing came to light. I put this down to missing Sandy and doing deep dives on a very hot day (30m - 35m 2 minute dives, 4 minute recovery times for 2 hours, in 29o water). I was thinking, “heat stroke.”
An hour and half later, with all the divers on board the boat we headed out to a deep spot to check on some Wiwa (silver drummer) in 35 plus metres. I was feeling fine and had no reason to think things were a problem. I breathed up again, aiming for a 25m dive and felt fine at that depth, but thought I would make it a short dive just to be sure. Everything was fine coming up until the 3m mark again. Things went dizzy and a slight head ache came with it. I kept thinking, “I'm losing my touch, and maybe I'm getting too old for this kind of thing.” The rest of the day I spent diving with extreme caution and making sure Dwane was aware of my every dive. But I continued to get the dizzy, and had fuzzy tunnel vision upon surfacing which you associate with dives twice as hard as the ones I was doing. Eventually I said, "That's it Dwane I'm getting out", even though more scouting for that day was required.
During the long ride back in the boat I was a little light headed but otherwise everything was fine. As we unloaded the boat and I was standing up, moving around, lifting gear, etc I nearly blacked out. I was losing consciousness, vision was blurred and speech was distant. It was then I said to Neville, our Team Manager "I'm not feeling well, I think I might be bent." Sitting down I came right. I did no more heavy work and as the hours passed, I wondered what on earth had happened to me.
I talked to an Australian guy, Tony Heugh, who has free dived to 55 metres, and quizzed him on the effects of being bent on free diving. For me, the most noticeable aspect was that apart from one dive, when I was at 20 - 25 metres I felt 100%. This was due to the increased partial pressure of oxygen which makes the body think there's plenty of oxygen there and you are OK. BUT, unbeknown to me, the partial pressure drops dangerously low when you go through the 3 metremark.
The next day we started diving again and I noticed things were fine, although a little sluggish. About 1 hour into the day’s diving, the boat went past as a normal practice to pick up divers and I smelt and breathed a lung full of diesel fumes. The penny dropped!!! Yesterday’s problems were caused by carbon monoxide poisoning. A colourless, odorless, tasteless gas, you have no idea of its presence in a pure form, but it's generally mixed with exhaust fumes. It was comforting to know with great certainty the cause of the problem, and put at rest the minds of the others in the team.
It is interesting to note that there was no urge to breathe at any time. This is explained by the body's physiology in that you want to breathe because of CO2 build up, rather than lack of oxygen.