A
Little Knowledge
by
Larry
"Harris" Taylor, Ph.D.
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After several hundred dives in the Port Huron region of the St. Clair River (one of North America's most intense navigable waterways ... current under the Blue Water Bridge can exceed 10 knots), we were looking for something a bit more challenging (thrilling). Since we had already dived under the Blue Water Bridge on the less intense current Canadian Shore (from southeast shore of Lake Huron to the now shore non-accessible wreck of the Monarch), we decided to do a "fly" (never touch the bottom) under the Blue Water Bridge from the American side starting from the mouth of the St Clair river to our favorite exit spot, the (now non-accessible) Bramble dock. Since we knew the current would be extreme and this dive would require major physical exertion, we chose to do the dive using an oxygen enriched air breathing gas (NOAA I or 32 % oxygen). Our thinking was the added oxygen would facilitate the anticipated tremendous aerobic exertion of the dive.
Our plan was to enter above the mouth of the St. Clair River, drop down into the main channel (~60 ffw) and then to be rapidly hurled downstream. After 12 minutes, we would move to a posture at right angles to the current and vigorously swim until we reached a bottom contour. Then, we would use our "river sticks" (see River diving lecture slides 32 and 33) to facilitate moving towards the exit point.
During the dive we flew over a white object that looked like a Blazer automobile, but we were moving too fast (in ~ 10 foot (3 Meter) visibility) for a positive identification. After 12 minutes, we went to right angles to the current and started swimming towards shore. Shortly after doing this, I felt enormously tired ... more tired than I have ever been underwater. This surprised (and concerned) me 'cause I considered myself to be in excellent physical condition (At this time, I was doing an hour a day of high-impact aerobics from national champion aerobic instructors at a studio known for its intense workouts. I was even a token male on their early morning aerobics exercise TV program). The experienced fatigue was extreme. Once reaching the river bottom, we stopped several times with our "river sticks" embedded in the river bottom to hold position while we caught our breath. We reached our exit point (after covering a total of ~1.5 miles (2.4 km) ) in 14 minutes. Traveling 1.5 miles in 26 minutes means our average downstream speed was ~ 3.5 miles/hour ( 5.6 km/hr, 3.03 knots) which is impressive considering our multiple stops to "catch our breath."
After the dive, we wondered about the white object we saw and decided after a 2 hour surface interval (and lunch), to repeat the dive and confirm that what we saw was a Blazer. Turns out we had found a Blazer sitting upright and facing upstream that had apparently been used as a suicide vehicle the previous winter. (Someone had intentionally driven out on the ice. The ice could not support the vehicle and so the Blazer fell through the ice). We were able to give law enforcement an approximate location of the Blazer based on the depth and time from the automobile to the stern of the Tremble.
Once again, the profound fatigue (voluminous perspiration, shortness of breath (feeling air-starved), and an overwhelming sense of tiredness) was present.
I did not understand why we both had felt so fatigued (air starved) on the dive.**
A few years later, I ran across an article in Undersea Biomed Research where the Israeli military reported that the slightly increased density of oxygen enriched air exacerbated CO2 retention. We then repeated this dive on compressed air and did not experience the sensation of massive air starvation associated with our earlier dives. So, I now believe that the extreme fatigue we both experienced was a result of unanticipated CO2 retention.
We thought we were being clever in using an oxygen enriched air mix, but it turns out that our cleverness worked against us on that particular dive.
The points are:
1. A little (insufficient) knowledge can be a dangerous thing.
2. In diving, as in life, it is the unknown that can pose a significant risk
3. Divers doing physical tasks on oxygen enriched air (Nitrox) should pay particular attention to symptoms of CO2 build-up.
4. No matter how much is known, there is always more to learn.
Disclaimer:
The dive described above is not for the feint of heart, the physically unfit, improperly equipped, or limited swift water experienced diver. (Suggested experience is ~200 dives in extremely intense swift water). We labeled this dive the "push the envelope dive."
**Things we considered to not be
the proximate cause of the oxygen enriched breathing gas air starvation
experience:
1. Gas contamination: Divers
obtained their oxygen enriched air from different dive shops. All cylinders were
on-site analyzed with two different brand oxygen analyzers to be 32.0 % oxygen.
No CO was detected. Similar contamination from different sources is unlikely.
2. Pre-dive anxiety: No observed
signs / symptoms of CO2 buildup prior to dive was observed by either
diver. Divers had more than 200 dives in this region of the river. The
predominant emotion was eager anticipation of an awesome (later confirmed) thrill.
3. Anxiety about using EANx: Both divers were experienced oxygen enriched air divers. Neither had experienced symptoms of carbon dioxide buildup on any previous (or later) recreational dives using EANx.
4. During dive separation
anxiety: Divers were experienced as a river diving buddy pair; there was no "lost
contact" during the dive.
5. Different paths: While no two
river dives are exactly the same, our "under the bridge dives" had a
similar trajectory based on recognition of bottom objects (like the white blazer
and the stern of the
Tremble wreck) which allowed a mental image of our location relative to surface
landscape.
6. Different current flow: The St
Clair river is one of North America's most intense navigable waterways (current
velocity
in excess of 10 knots) and even in
the presence of some slightly altered current velocity, the current speed would have been
extreme.
7. Different work loads: Swimming
for greater than 10 minutes at right
angles in extreme current would generate massive amounts of metabolic CO2. So,
lots of CO2 was present in our system as we moved from main
channel to the shore.
8. Poor Equipment: The regulators were top of the line (but each diver had a different brand) tuned for maximum performance. No air starvation issues were noticed by either diver on any other river dives.
Bottom line: No matter what was considered, the most relevant observation was the air starvation sensation (and other typical CO2 buildup symptoms) for both divers occurred on two separate dives (4 total cylinders of EAN32) only while breathing the oxygen enriched air while engaged in the intense aerobic work of sustained swimming across an intense current. Although the difference in density between air and NOAA I is extremely small, apparently this difference becomes significant when ventilating enormous amounts of metabolic CO2 (Note that CO2 has a density 1.96 g / L at STP which is much greater than dry air (1.29 g/L), oxygen (1.43 g/L), nitrogen (1.25 g/L), or EAN32 (1.31 g/L)).
Since
this was a dive in extreme current requiring continuous vigorous aerobic
activity, this dive should not be compared to typical recreational diving.
More stuff:
My slide set (126 slides in PDF) on river diving is at River Diving Lecture Slides
My slide set ( 248 slides in PDF) on EANx is at EANx Lecture Slides
My slide set (128 slides in PDF) on diving physiology is at Dive Physiology Lecture Slides
Sources 1989 Article: Reading Rivers
Sources 1990 Article: River Diving Equipment
Sources 1990 Article: River Diving Techniques
Aerial View of the Dive
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About
The Author:
Larry "Harris" Taylor, Ph.D. is a biochemist and Diving Safety Coordinator at the University of Michigan. He has authored more than 200 scuba related articles. His personal dive library (See Alert Diver, Mar/Apr, 1997, p. 54) is considered one of the best recreational sources of information In North America.
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