My Portable CO Monitor/Tester Field Experiences….

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Super! Very interesting testing. I'd noticed the CO Expert model on sites, wondered how accurate it may be. The 6"x3.75"x1.75" dimensions were not discouraging so much as the unit starting to read at 10 ppm, but it looks like it performed well and gave readings below 10 ppm? Seems to be a good alternative unit for divers to consider. And the BCD restrictor looks like a good idea, bleeding air at the lowered rate. :thumb:

Certainly appreciate the work you put into this, along with your well informed information you add to these threads.
 
All electrochemical sensors will have certain volatile compounds they react to other than the target gas (CO). These interfering gases will result in false positive readings which will result in the end user assuming that carbon monoxide is present when in fact it is not. These false positives readings can not only confuse the end-user, but create costly and embarrassing situations where a work place is shut down for a contaminant positive reading which later turns out to be a false positive. At a fill station if you are going to announce that a tank is potentially contaminated with CO one had better be sure it is a true positive and not from an interfering gas.

The sensor manufacturers try to minimize these cross-reacting compounds by placing an adsorptive filter such as activated charcoal over the sensor which will remove many of the interfering compounds in question but still allow the CO to pass through. Activated charcoal does not adsorb CO.

Common interfering gases with CO electrochemical sensors include the alcohols (methanol, ethanol, isopropyl alcohol), hydrogen, hydrogen sulfide, nitric oxide, nitrogen dioxide, ethylene, and other hydrocarbon solvents such as toluene.

Have a look at Table 3 in this paper and one can see the large variation between different detectors, and what interfering gases the sensors react to. The BW Gas Alert is one of the best sensors and only reacts to the alcohols whereas the Drager Datalogger reacts to just about everything under the sun making it a poor choice for trying to detect solely CO. There would be so many cross-sensitivities one would never know whether a positive reading was CO or something else.
Cross-sensitivities of electrochemical detectors used to monitor worker exposur..... (DOI: 10.1039/b510084d)

In this document sensors CO-B1 and CO-BF are identical except that CO-BF has an adsorptive filter on it to remove many of the interfering gases. While the filter is not perfect it does reduce many of the interfering gases to zero or close to zero.
http://www.alphasense.com/pdf/AAN_109.pdf

Probably the biggest disadvantage of the Pocket CO is the large number of interfering gases since the sensor is not filtered while the BW Tech Gas Alert and the CO Experts sensors are.

All three detectors will react to the alcohols (commonly found in permanent and non-permanent marker pens) with the Pocket CO showing very high false positive CO readings. When an Avery-Dennison Dryboard marker (ethanol/isopropanol) was held a the gas inlet of the three detectors for one minute the Pocket CO read 80 ppm and then took close to an hour to recover to 5 ppm. The BW Tech unit which has an alcohol filter read 7 ppm and also took an hour to recover. The CO Experts unit with its very large filter was not affected by the marker pen challenge.

For a two week period all three units were tested in my vehicle to see if they could discern CO in traffic from many of the other interfering gases such as NO and NO2. Nitric oxide (NO) is from vehicle exhaust but is a very unstable molecule and with ground level ozone formed on hot sunny days quickly becomes nitrogen dioxide (NO2). The Pocket CO unit particularly on hot sunny days (temp 80 to 85 F) would show 5 to 20 ppm while driving on an 8 lane highway which was full of traffic. The other two units would remain at 0 ppm indicating that the Pocket CO is likely reacting to the NO and NO2 in the air and not the CO. I suspect when you were walking around PDC or Tulum and reported CO at the 10 ppm level this was in fact NO or NO2.

On many occasions such as pulling up behind a truck or stopped in traffic all three units would register a CO hit and when this did occur they all read within a couple ppm of each other. Once away from the true CO source the reading would quickly decay back to zero.

One of the best ways to tell if one has a true CO reading with the Pocket CO or false positive from an interfering gas is to examine the recovery time. With a true CO reading if the detector is removed from the CO point source it will recover to zero within two minutes, whereas if it is sensing something like NO/NO2 the recovery time is prolonged often in the 10 to 15 minute range. If one removes the apparent CO point source and the Pocket CO does not quickly return to zero it is likely not CO, but an interfering gas.

One interesting very reproducible interfering gas occurred when I would wash my truck's windshield with methanol (used up here for cold weather) while driving. The Pocket CO would pick the methanol vapors up each time and read 5 to 10 ppm and then take 10 to 15 minutes to return to zero. Even the BW Tech unit would read a few ppm and then take 15 minutes for the interfering methanol to clear. The CO Experts unit did not react to the methanol vapors at this low concentration.

The multiple cross-sensitivities with the unfiltered Pocket CO sensor is a real problem if you can't measure your tanks in a nice cool clean room. From my experience to date if the unit is "stuck" and shows a reading which won't decay back to zero within a minute or two one is not dealing with CO but some other interfering gas. If I was to approach a fill station owner about CO in the tank I would want to see the display rise from zero to a positive reading and then return to zero within two minutes after removing the potentially contaminated gas. If the CO Pocket does not recover to zero I'd assume you are measuring something other than CO likely not in the tank but in the ambient air.

I think the Pocket CO is a great unit for what the manufacturer originally designed it for which was to detect potential lethal levels of CO in planes, vehicles, hotel rooms, etc. at one atmosphere. Without a filter on the sensor I would be hesitant to attribute low tank air/gas readings to carbon monoxide unless I was in an air conditioned room away from traffic NO/NO2, and solvents which could interfere with the sensor. It does make a reasonable portable "go/no-go" detector though for detecting potentially heavily CO contaminated tank air.

Peter
 
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Super! Very interesting testing. I'd noticed the CO Expert model on sites, wondered how accurate it may be. The 6"x3.75"x1.75" dimensions were not discouraging so much as the unit starting to read at 10 ppm, but it looks like it performed well and gave readings below 10 ppm? Seems to be a good alternative unit for divers to consider. And the BCD restrictor looks like a good idea, bleeding air at the lowered rate. :thumb:

Certainly appreciate the work you put into this, along with your well informed information you add to these threads.

The only place I have seen the CO Experts unit available is on the Aeromedix.com site. Be careful as that white housing is used for about a dozen other OEM CO detectors most of them the home models which are not low-reading.

I can appreciate the attractiveness of the Pocket CO's small size, however if I had to purchase one inexpensive CO detector in order to test tank air in the 0 to 10 ppm range while sitting on the back of a dive boat with gasoline vapors, or in a dive shop with lots of volatiles around (wet suit off gassing, glues, lubes, compressor oils, etc.) I'd choose the CO Experts unit with its very robust sensor filter. The detector is large and bulky, but if you really want to challenge a fill station owner over potential CO contamination in the tank air the risk of a false positive would close to zero with the CO Expert unit, and it also has excellent stability in the high temp and humidity environment of the tropics although the baseline will drift up a few ppm once the temp is sustained at 35 C. One just subtracts this reading off any positive reading from an identified CO point source.

The CO Expert's sensor is actually rated by the manufacturer Monox to last 7 years (very large sensor so lots of electrolyte) although I think CO Experts says 5 years under their label.

Another disadvantage with the Pocket CO is that there is no sensor self-check circuit so that when it does stop working the only way the end user will know is to apply some calibration gas. The BWT and CO Expert units both have self-check circuits which will tell the end user the sensor is no longer working.

That being said my Pocket CO last week alarmed at 400 ppm at the back of the dive boat where there was a strong station wagon effect which was pulled the transom discharged exhaust back into the cabin while underway at full speed. In effect it probably saved the group from the proverbial "sea sickness" we see so often on dive boats which is more likely in many cases mild to moderate CO poisoning. I think keeping the Pocket CO for this type of dive boat application is what it was designed to do. When traveling I will take my BWT detector for identifying low-level tank CO contamination, and keep the Pocket CO on my key chain for all the other potential CO sources especially those on rear-exhausted inboard engine dive boats.
 
The only place I have seen the CO Experts unit available is on the Aeromedix.com site. Be careful as that white housing is used for about a dozen other OEM CO detectors most of them the home models which are not low-reading.

I'm looking at a new CO-EXPERTS MODEL 2002 a guy has for sell. Would this be an eight year old model? Would the sensor still be good? Do you have an opinion of how long their sensor will last?

Since you seem to know more about all this than anyone else I know, what do you think about old household CO detectors? How long is one trustworthy in use? What about a new unit from old stock?

thanks!
 
I'm looking at a new CO-EXPERTS MODEL 2002 a guy has for sell. Would this be an eight year old model? Would the sensor still be good? Do you have an opinion of how long their sensor will last?

Since you seem to know more about all this than anyone else I know, what do you think about old household CO detectors? How long is one trustworthy in use? What about a new unit from old stock?

thanks!

Those 2002 units came with a battery fully functional so I'd take the term "new" with a grain of salt since the electronics have likely been powered up for six years or so, and the sensor exposed to the air for the same period of time. That being said Monox guaranteed the sensor for 7 years, but said a life expectancy of 10 years was expected. I'd give the guy ten or twenty dollars at most for the unit as they were originally $120 from Aeromedix.

If the 9 volt battery is not in it install one and wait for the unit to go through its self-checks. If the electronics have failed the display will show "Err" for 5 seconds each minute and it will beep. If the sensor is dead the display will say "SenSOr End" every minute for 5 seconds and beep.

That 2002 model will visually display the CO concentration from 5 ppm and up but if you push the Reset button it will recall the concentration down to 1 ppm. I have a hunch the current 1070 model still does display at 5 ppm, but they don't advertise the fact. I will try and find out for you next week. In any case if you can get the old 2002 model for a fair price, and at least put some 50 ppm calibration gas on the sensor to ensure it is still accurate I'd use that until it fails. Any safety shop should be able to put some 50 ppm gas across the sensor.

As far as the old house detectors if they are of the metal oxide sensor type from the late ninties those had very high failure rates and likely would not pass the current UL standard. I think the standard changed in 1998 and again in 2003 after those massive CO detector recalls in those years. Since then things seemed to have improved considerably and many home detectors in Canada and the USA have electrochemical sensors with expiry dates (usually 7 years), and electronic and sensor self-check circuits. I'd get one with battery and AC power, and a digital display.

Here is a report showing how extensively these home CO monitors should be tested. Notice the section on interfering gases and the comment in the conclusion which states the unit with multiple cross-sensitivities did not have a charcoal filter.
http://media.godashboard.com//gti/4ReportsPubs/TechReports/020112.pdf

I had a look at Consumer Reports from Feb. 2008 and the home stand-alone CO detectors they recommended were the Kiddie NightHawk and American Sensor shown here:
http://www.kiddeus.com/utcfs/ws-384/Assets/900-0146 Sheet.pdf
http://www.kiddeus.com/utcfs/ws-384/Assets/900-0076 Sheet.pdf
co920.htm

Remember just like an oxygen sensor most CO sensors if electrochemical are consumable so even though the unit might be new in the box the sensor could be past its best before date. I see the Kiddie units above are good for 7 years.
 
Don I thought this might interest you as the list has been recently updated. From 1981 to 2008 there have been 810 boat-related CO poisonings in the USA including 149 fatalities. Having a Pocket CO or CO Experts detector while on the dive boat even if underway is likely just as important if not more important than checking one's dive air for carbon monoxide.
http://www.doubleangel.org/documents/NatlCaseListingBoat-RelatedCOPoisoningsMay2007April2008.pdf
http://www.nps.gov/glca/planyourvisit/upload/BSC86.pdf
http://www.aiha.org/TheAcademy/documents/pcih06-mccammon.pdf
 
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Don I thought this might interest you as the list has been recently updated. From 1981 to 2008 there have been 810 boat-related CO poisonings in the USA including 149 fatalities. Having a Pocket CO or CO Experts detector while on the dive boat even if underway is likely just as important if not more important than checking one's dive air for carbon monoxide.
http://www.doubleangel.org/documents/NatlCaseListingBoat-RelatedCOPoisoningsMay2007April2008.pdf
:shocked2: I've never owned a boat with a cabin, but have been on a few with inside dry rooms as well as slept on a few. It never occurred to me that I might be at risk; we like to think our charter hosts take care of our basic safety needs. No one ever warned me before. I've been amazed that hurricane survivors often own $500+ electric generators and rationalizations & mistakes happen, but from what I've heard recently - they don't own $30 battery powered Kidde CO Monitors.

But this article lists more dangers than I would have thot of. Damn!
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Boats are not required to have CO Monitors, huh? Damn!

The CO Experts detector I was watching on Ebay went for $37 including shipping, so I passed. If I could have had it for $20, even tho older, it would have been interesting. I'm sure even new ones on Ebay will be older, but I found a new Fireboy-Xintex CO Detector With Generator Shut Off for $10 including shipping. :D Gave it to my LDS that just lost their truck, trailer, compressor, etc in a horrible wreck. From looking over the manual, I think I'd want one of those on any boat with a generator, and the partner units in every room hooked up to the main unit.

My next liveaboard Skipper is certainly going to remember me, after I ask to see his air test results, compressor, CO monitors & scrubbers, smoke alarms, etc. I've been asking about some of these for over a year now, so far in brief, dead-end discussions - hence my campaign here on SB. Greatly appreciate your input and help..!! :medal:
 
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I checked on a few of the specifications for the CO Experts 1070 model today. It will only display when a CO concentration of 10 ppm is reached and below this the display will show zeros. The older 2002 model will display at 5 ppm CO, however given that these units were manufactured close to 6 years ago the sensors will likely start to fail after the 7 year mark. Unfortunately these older sensors are no longer made so they cannot be replaced.

The sensor on all the CO Experts detectors is protected by a filter with 8 layers in order to shield it from alcohols, NOx, and other hydrocarbon solvents. It is probably the best protected sensor on the market today. The biggest disadvantage with the Pocket CO model is the sensor is not filtered and will cross-react with numerous other volatiles giving false positive readings. The Pocket CO manufacturer should really produce a list, as all the other sensor manufacturers do, revealing what are the sensor's exact cross-sensitivities. These appear to be numerous and problematic when away from a clean room.

Here is a very good deal I came across today for a handheld unit from RAE Systems. Normally the manufacturer sells these ToxiRAE II CO detectors for $US205 and they are available here for $140, the same price as the Pocket CO.
EMS Sales :: CLEARANCE - ToxiRAE II


This unit requires the purchase of calibration gas at $50 for 17 liters and a 0.5 lpm regulator (one time purchase) for $115. One can change the concentration of calibration gas used down to 10 ppm for diving applications, but it comes set at 50 ppm.

Here are the specifications and manual:
ToxiRAE II | RAE Systems

Cross-sensitivities are posted here:
http://www.raesystems.com/~raedocs/App_Tech_Notes/Tech_Notes/TN-114_Sensor_Specs.pdf
http://www.raesystems.com/~raedocs/App_Tech_Notes/Tech_Notes/TN-121_CO_Sensor.pdf

If anyone in your area has an Analox CO Clear detector one could calibrate using the calibration gas (20 ppm) and regulator required for operation of the Analox detector. Probably might cost $10 to $20 for a calibration.
 
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Yeah, I have learned a lot here, and more fully appreciate the limitations and false positives available with the Pocket model. On future trips, I expect I'll...
  • Wear it face down on my shirt collar on the planes, as I understand many of them don't have any CO monitors - and I would like to know even if the $300,000 year pilot isn't bothering to check;
  • Hanging from something in the hotel room - I have never noticed a CO monitor in one;
  • In an airtight cigarette box until I get to the tanks to test, then quickly inside the over bag to fill with tank air - minimizing exposure to humidity and other vapors;
  • Maybe hanging from my collar on boats, even tho that will expose it to humidity.
The CO Experts, even starting at 10 ppm might not give the lower readings we'd prefer, but would protect divers from the more serious threats of higher concentrations. Using one chart's listing of "100 PPM: Slight headache after 1-2 hours" at sea level, then I guess it would take around 20 ppm in a tank to cause the same problems at 130 ft - or around that - with increased exposures building up worse reactions? I think the Maldives tragedy involved much worse concentrations. I see that it also tops out at 70 ppm max reading, so while one would know for certain not to breathe the tank, it wouldn't read the more serious contaminations like they had in the Maldives. The Pocket CO monitor claims to read up to 500 ppm.

Still, since the CO Experts model will protect in the 10-70 ppm range, I'd say that it gets the job done well, and the Dimensions: 6"x3.75"x1.75" (HWD) - Weight: 10 ozs are not that much bigger than my Analox Nitrox analyzer. Better choice or second choice, depending on the traveling divers views on size, they both seem to be worthwhile products with important benefits. Someday soon I guess I need to take the best information from this thread in quotes and start a new one summarizing as not many who might find this thread today would read all the way thru it; they want to know what to do earlier I think.

If anyone in your area has an Analox CO Clear detector one could calibrate using the calibration gas (20 ppm) and regulator required for operation of the Analox detector. Probably might cost $10 to $20 for a calibration.
I wonder if my local fire departments could help me with testing and calibrations? My home village is served by a volunteer department, but well equipped. They might have materials and training, or might be interested in expanding. Plainview with a population around 25,000 might be better equipped. My dive bud lives there and has had close calls at his shop and nice, modern home both with his Kidde alarms sounding, and knows of other close calls in the town. Lubbock fire department is probly keeping up to date, as I think I recall them loosing some department divers to CO poisoning years ago - unless my memory is wrong there.
 
I fill my Tanks at my local Vol Fire Dept of which I am a member of.
We have a really great system with a CO monitor set at 0ppm.
You should join your towns FD, I am sure they are a great bunch of folks.
 
https://www.shearwater.com/products/swift/

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