Karlīs Rebreather Page

A wise man speaks about solved problems, to help others preventing similar problems.

Many thanks to Steve Millard for his story.

From:          Steve Millard <ec96@liverpool.ac.uk>

Reply-to:      Steve Millard <ec96@liverpool.ac.uk>

To:            Rebreather mail-list <rebreather@nwdesigns.com>

Subject:       Low ppO2 incident

Date:          Mon, 16 Mar 1998 15:09:40 +0000 (GMT)

Priority:      NORMAL

I had a minor problem with low ppO2 a couple of weeks back that is probably worth sharing. I learned from it..but it would be even better if I was not the only one.

The event began when I started a dive (for a number of reasons) with only 50 bar of oxygen in my Inspiration rb. The depth was around 20 metres & the water was cold (around 5 or 6 degrees C). Apart from the cold, the dive conditions were good.

A pertinent point was that I am using a very small oxygen gauge made by Apeks with a diameter of about 15 or 20mm. This is pretty neat solution & as the oxygen & diluent pressures don't vary very much on any dive, a large, bulky accurate guage seems pointless. However, the downside of these tiny guages is that it is hard to discriminate between an empty oxygen tank & one containing 25 bar. 25 bar of O2 is good for 1/2 hour - 1 hour of diving. An empty O2 tank isn't.

On this particular dive I spent about 1 hour at 20 metres & was starting to get pretty cold & was thinking of coming up anyway when I noticed that my ppO2 had dropped from the set point of 1.3 to around 1.0. I figured that the O2 cylinder was now completely empty & so surfacing was an even better idea.

By 10 metres the ppO2 had dropped to 0.4 & the audible alarm kicked in.

At around 6 metres I was doing a safety stop & made the mistake of adding some air...which only dropped the ppO2 even lower, to around 0.3. This prompted me to think that hitting the diluent button wasn't such a smart idea as it made my low ppO2 situation even worse.

By the time I was on the surface the ppO2 was down to 0.2. 'No problem' I think...this is the same as air anyway.

However, my problem started to increase when the dive boat was slow in coming to get me & the ppO2 dropped down to 0.15. I struggled hard to close off the mouthpiece to prevent water entering the loop, but my hands were too cold. Eventually to avoid passing out, I held the open mouthpiece out of the water so that I could breath some fresh air.

Finally I succeeded in closing off the mouthpiece & put the open circuit bailout reg into my mouth & relaxed & waited for ther boat pickup.

Lessons learned :

Don't start with so little oxygen.

Get a larger O2 guage if I am going to run the O2 so low.

If the ppO2 runs low on the surface & the O2 is empty, simply hit the diluent button the get the ppO2 back to 0.2. All that sturggle to get the mouthpiece closed so that I could access the same diluent source with an open circuit reg was pretty pointless on the surface.

It's easy to get too focussed on one task to the exclusion of others in a stressful situation. Letting water into the loop when on the surface isn't a life threatening problem....passing out through hypoxia is !

When I hit the diluent button at 5 metres & the ppO2 dropped from 0.4 to 0.3, this made me think it was a bad idea. On the surface, it wasn't such a bad idea at all but I was getting too focussed on other solutions to my problem & I forgot about the most obvious one.

Hope that this story might help someone else too.

Regards, Steve M.


*    Dr. S. G. Millard,            *    E-Mail : ec96@liv.ac.uk          *

*    Senior Lecturer,              *	                                 *

*    Dept of Civil Engineering     * Tel :    0151 794 5224 (UK)   	 *

*    University of Liverpool,      *        44 151 794 5224              *

*    PO Box 147,                   *             (International)         *

*    Liverpool L69 3BX,            *                                     *

*    UK.                           * Fax :    0151 794 5218 (UK)         *

*                                  *        44 151 794 5218              *

*                                  *             (International)         *


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http://Rebreather.de/rebreather/CCR_low_O2_incident.htm © Karl Kramer, 28.8.1998