Thanks for chiming in. This helps to know. Obviously understanding the sensor response up to 1000, rather than just 50, makes a big difference in what you should make of such a reading. Simply a terrifying set of facts if true. I've been reading Don's posts on this subject for a long time and I think this one has pushed me over the edge.
Ronda Cross Tank CO Test cause of Death
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Thanks for chiming in. This helps to know. Obviously understanding the sensor response up to 1000, rather than just 50, makes a big difference in what you should make of such a reading. Simply a terrifying set of facts if true. I've been reading Don's posts on this subject for a long time and I think this one has pushed me over the edge.
A couple of points. A tank can be filled in 5-7 minutes but it shiuldn't be. It gets way too hot and stresses the tank.
And many compressors only use vegetable oil. There is nothing inappropriate about that.
And many compressors only use vegetable oil. There is nothing inappropriate about that.
Ken T
Contributor
After watching the video I was struck by the lack of evidence continuity....I would be very surprised if this was any video from an official investigation.
It certainly would not be acceptable in any North American court - criminal or civil.
Don't know if it would be accepted in Mexico...rather doubt it.
It certainly would not be acceptable in any North American court - criminal or civil.
Don't know if it would be accepted in Mexico...rather doubt it.
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swamp diver
Contributor
Show me one compressor company which recommends a vegetable oil (i.e sunflower, canola, rapeseed oil) be used in a high pressure breathing air compressor.
In the past a mineral oil was the oil of choice, but today all the major manufacturers have switched to ester or polyalphaolefin (PAO) synthetics.
Bauer USA loads its compressors with Ultrachem Chemlube 800 a trimelliate ester, Bauer Germany loads its new compressors with a trimellitate ester from Shell. Coltri Europe uses a diester Alusynt CE750, and Nuvair (Coltri USA) uses either a diester from Ultrachem (Chemlube 751) or a PAO Omnilube 455 from Ultrachem.
The switch from mineral to synthetic oils was due to improved thermal and oxidative resistance, a very important improvement in flash point and auto-ignition point plus a decrease in the toxicity of the volatile vapors which come off the oil when heated which are adsorbed on the activated charcoal bed but present a risk to the diver if released back into the compressed breathing air.
There are no vegetable oils used in the industry and the only time I have come across a vegetable oil used in a compressor two divers died from CO poisoning at a Mexican fill station. Vegetable oils have poor flash points and thermal resistance.
I have seen automobile oils which consist of about 30 percent toxic additives used in scuba high pressure compressors on the island of Roatan.
If one sees a vegetable or automobile oil being used in a breathing air compressor please walk away.
---------- Post added December 13th, 2012 at 09:57 PM ----------
Take a trip to Mexico sometime and this would be par for the course. Often no chain of custody and tampering of evidence has happened with previous fatalities.
This one looks like they may have learned from previous mistakes such as not having a CO analyzer available.
swamp diver
Contributor
One can see the change in auto-ignition point (AIP) vs oil type in this diagram. The mineral oils have the lowest AIP, in particular an oil with iron oxide compressor wear products, which also lowers the oils oxidative resistance and explains why under harsh environmental conditions (high ambient heat, nitrox pumping, etc) the compressor oil needs to be changed out more frequently. If not your AIP starts to fall.
Also take note that with increased pressure the AIP is reduced. Those little Coltri 3 stage compressors run much hotter than a big well cooled 4-stage compressor such as Bauer K-14.
If given the choice it is better to use a synthetic ester over a PAO as the AIP is higher. The flash point of these oils follow similar patterns.
The figure is from the book "Synthetics, Mineral Oils and Bio-based Lubricants" by Leslie Rudnick
Also take note that with increased pressure the AIP is reduced. Those little Coltri 3 stage compressors run much hotter than a big well cooled 4-stage compressor such as Bauer K-14.
If given the choice it is better to use a synthetic ester over a PAO as the AIP is higher. The flash point of these oils follow similar patterns.
The figure is from the book "Synthetics, Mineral Oils and Bio-based Lubricants" by Leslie Rudnick
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You are absolutely correct. They shouldn't be. Personally, when I fill my tanks they usually don't rise in temperature by anymore than 10 degrees F. But I have the time to do slow fills. Unfortunately, most fill stations will fill even larger tanks very fast, and they will overfill them so that when they do cool down they cool to the desired pressure. That's just reality.
Bauer recommended (I no longer run a dive shop, so I can't say with certainty what they do now) that I run my 26cfm Super-Quiet compressor on vegetable oil. Throughout my ownership of that and my oxygen booster (used to produce air and a wide range of breathing gases) I only ever used vegetable oil. It was hardly a cheaper option, as it was more expensive than mineral oil and didn't last as long. But I never had any problems with air cleanliness, either from hydrocarbons or carbon monoxide.
---------- Post added December 13th, 2012 at 09:41 PM ----------
It may be reality, but so was the death here recently from an exploding tank. I forget the exact figures, but I remember that to fill an 80 cf tank here without overstressing the tank it had to be done in no less than around 20 mins. Any decent book on blending procedures will give the exact values. But it's normal here to fill such aluminum tanks in 5 or 6 minutes, and to fill a tank rated at 3000 psi to close to 4000 psi so that when it cools it drops to "a high but acceptable fill". Combine that with a dearth of tank testing and you have a recipe for disaster. That would be considered criminal activity in the USA and UK and probably most of Europe, as what they're producing is time bombs.
---------- Post added December 13th, 2012 at 09:41 PM ----------
It may be reality, but so was the death here recently from an exploding tank. I forget the exact figures, but I remember that to fill an 80 cf tank here without overstressing the tank it had to be done in no less than around 20 mins. Any decent book on blending procedures will give the exact values. But it's normal here to fill such aluminum tanks in 5 or 6 minutes, and to fill a tank rated at 3000 psi to close to 4000 psi so that when it cools it drops to "a high but acceptable fill". Combine that with a dearth of tank testing and you have a recipe for disaster. That would be considered criminal activity in the USA and UK and probably most of Europe, as what they're producing is time bombs.
swamp diver
Contributor
You must be confusing a vegetable oil with a synthetic such as an ester or possibly your local distributor was misinformed regarding the type of oil purchased. I have every Bauer USA and German oil recommendation going back 15 or so years and there never was a vegetable oil used.
Prior to the mineral oils with low additive content Bauer was using a Mobil Delvac series 1200 oil which was actually a diesel motor oil loaded with additives. From that Bauer USA went to the Shell Corena P150 a mineral oil with very little additive in it. When Shell USA put out a warning not to use this oil in breathing air applications Bauer USA switched to the Chemlube ester about 5 years ago.
See if you can pull up the name of the oil brand you were using in the compressor. If truly a vegetable the recommendation did not come from Bauer USA or Germany.
swamp diver
Contributor
There was a fatality in New Zealand in 2004 following which the 2006 coroner's inquest attributed the fatality to the production of CO from within the compressor either due to the combustion of the compressor oil or activated charcoal bed. The level of CO found in the diver's tank, confirmed by an independent laboratory, was 13,600 ppm.
The diver was solo diving and hit the water and never surfaced. The friend on the boat did not see any bubbles as he said he normally would while waiting on the boat for his friend to return. The following day the police located the body at the dive site where expected.
The compressor was examined by 3 mechanical and chemical engineering experts who felt there was sufficient evidence to implicate the compressor system. The coroner stated, "[FONT=&]that it is likely that the carbon monoxide which was found in the xxx tanks was produced by an idiosyncratic malfunction of the xxxx air compression equipment. [/FONT]"
The following safety recommendations were made by the coroner:
[FONT=&]The internal production of carbon monoxide by air compressors is preventable or at least the risks of it can be minimized. The evidence suggested that scrupulous maintenance regimes, the avoidance of modifications to manufacturers equipment, the correct choice of lubricating oils, the avoidance of overheating (and therefore combustion) in the process and scrupulous attention to the packing of filter materials and filters will all go some considerable way to reducing the risk. Furthermore, none of these disciplines is likely to be effective in the absence of proper training in relation to the risk to ensure that operators understand the purpose of these disciplines.
[/FONT] [FONT=&] These procedures and disciplines alone cannot completely eliminate the risk. Ultimately, there needs, wherever possible, to be certainty that the gaseous substance injected into scuba tanks by air compressors is free of carbon monoxide. Doctor xxx (Ph.D in mechanical engineering and university professor) in his evidence indicated that it is possible at relatively low cost to install a carbon monoxide monitoring device with an alarm in the outlet lines from air compressors. The presence of such a device here would have saved xxxx's life. [/FONT]
No doubt had there been a CO monitor on the compressor used to fill Rhonda Cross's tank her life would have been saved as well. Since so few compressors in the dive industry have a CO monitor installed it behooves the individual diver to carry a portable CO analyzer at all times.
The diver was solo diving and hit the water and never surfaced. The friend on the boat did not see any bubbles as he said he normally would while waiting on the boat for his friend to return. The following day the police located the body at the dive site where expected.
The compressor was examined by 3 mechanical and chemical engineering experts who felt there was sufficient evidence to implicate the compressor system. The coroner stated, "[FONT=&]that it is likely that the carbon monoxide which was found in the xxx tanks was produced by an idiosyncratic malfunction of the xxxx air compression equipment. [/FONT]"
The following safety recommendations were made by the coroner:
[FONT=&]The internal production of carbon monoxide by air compressors is preventable or at least the risks of it can be minimized. The evidence suggested that scrupulous maintenance regimes, the avoidance of modifications to manufacturers equipment, the correct choice of lubricating oils, the avoidance of overheating (and therefore combustion) in the process and scrupulous attention to the packing of filter materials and filters will all go some considerable way to reducing the risk. Furthermore, none of these disciplines is likely to be effective in the absence of proper training in relation to the risk to ensure that operators understand the purpose of these disciplines.
[/FONT] [FONT=&] These procedures and disciplines alone cannot completely eliminate the risk. Ultimately, there needs, wherever possible, to be certainty that the gaseous substance injected into scuba tanks by air compressors is free of carbon monoxide. Doctor xxx (Ph.D in mechanical engineering and university professor) in his evidence indicated that it is possible at relatively low cost to install a carbon monoxide monitoring device with an alarm in the outlet lines from air compressors. The presence of such a device here would have saved xxxx's life. [/FONT]
No doubt had there been a CO monitor on the compressor used to fill Rhonda Cross's tank her life would have been saved as well. Since so few compressors in the dive industry have a CO monitor installed it behooves the individual diver to carry a portable CO analyzer at all times.
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