Question on Carbon Monoxide

[spoolin01]

If you have a 5 ppm calibrator and 5 ppm is your minimum level of interest, then I think you're doing the best test. There's a saying - it's quite catchy - you validate your analytical methods to the user requirements. If you want to know about 2 or 3 ppm, you have to establish that your equipment can tell you about it. Extrapolating outside the field calibration - meaning 'as used' - testing can't be sure to mean anything, until you've shown it to be so. Digital readouts and marketing materials have a way of encouraging people to believe that if they see a number, it is accurate and precise.

From what I saw a few years ago, it was uncommon to find an entry level portable meter that was spec'd less than 5 or 10 ppm for minimum quantitation. That makes me want to see some data supporting the now-lower spec's of the new models. I'd like to know with confidence that I could measure to 1 or 2 ppm, since that provides a cushion for remark and response below where I'd like to set my personal tolerance limits, as you do.

 

[DandyDon]

I think sensor technology has improved a lot in recent years, at least in some models. I bet the manufacturers would supply additional info beyond the usual public releases on request.

My first Pocket CO did not read less than 5 ppm, but after ruining and replacing it - the one I have now starts at 2 or 3.

 

[spoolin01]

I think your approach of finding a calibrator for your tolerance limit gets right to the nub. Have you found a way to dilute down something from 5 or 10ppm, or can custom calibrators be ordered? What's their shelf life? I got an old inline unit with a compressor recently, and sensors are still available. I'd be interested in finding out what it can do.

 

[IyaDiver]

I use Toxi-Rae units, got bunch of them, they are great. Analox should be good too.
I calibrate every month with a 10PPM cal-gas
1 PPM accuracy for CO is not "special" these days.
Just don't calibrate with 50ppm cal-gas...too broad a range as we want to read as low as 3PPM.

Calgas for CO can be kept for 2 years.

When you have a calgas, what u need to do before and after calibration is to actually read the calgas CO content. This tells us how accurate is the CO meter before 7 after calibration.

How I do my calibration is :
01. Test at 10 PPM CO before calibration........what's the reading ?
02. Calibrate at 10PPM
03. Test again after calibration, can sensor read 10 PPM within at 20 seconds ?

If step 3 doesn't show 10 PPM in 20 second or say 30 seconds, the sensor is aging already.


Reading which stays 2 or 3 PPM in an "assumed" zero CO ambient air is usually the contamination of the filter paper on top of the sensor or the CO meter been exposed to big time contamination. Calibrate it and it will go away, unless the CO sensor is near or over 2 years old, it may have a slow response.

If I read a compressor's Honda exhaust output, it takes a long time for recovery on my Toxi Rae, sometime I need to calibrate it again......dig up sensor cross contamination in RAE technical library. SwampDiver been doing such test some years ago on cross contamination.

The safe way ( if you do not buy clean/zero air ) to calibrate a zero CO is to use a scuba tank with a known Zero value of CO. My tanks are all zero CO value, so it is easy for me to use it as zero air.

Our own breath is a good bump test, blow slow and if you just smoked, 3PPM is easy read. For me, if I blow hard and long after a smoke, I can get 10PPM easy.

Since I never have less than 2 Toxi Rae unit at hand, it is easy for me to detect if one my unit is out of tune, without even using to calgas.

Out of tune unit for me is, when it reads 8 or 9 PPM for a 10 PPM calgas.
Some units if battery is dead, do a calibration when it has new battery, the reading maybe thrown off.

Yes, you can order custom calgas.

Good luck boys.
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[spoolin01]

I
1 PPM accuracy for CO is not "special" these days.
.

OK, I'll bite. How do you know, do you have or make a 1ppm calibrator?

 

[IyaDiver]

No I don't have a 1 PPM calgas or calibrator. Using 10PPM calgas is already very good parameter for CO sensor to be more sensitive. Calibration tell the sensor that 10PPM is equal to "X" electrical value and X/10 is then 1 PPM. Hence do not calibrate with 50PPM calgas if we can............however, I like to test new meter which RAE calibrated using 50PPM calgas at production line and surprisingly they are damn accurate and can read 10 PPM calgas as 10 PPM out of the box.

1 PPM is nothing fancy today for modern sensors. For C0, there is no point to have accuracy better than 1 PPM, so 1 PPM accuracy is more than enough.

RAE or Analox are companies with gas detection background. RAE is big in mining and oil & gas and serving all sorts of industries where accuracy is paramount. Analox while doesn't do broad range of detectors, they are NATO approved for submarine and military diving use. These units are not garage built, that is if you are worried that 1-2 PPM accuracy seems too magical.

If you are also worried of accuracy overall, you should also not trust the Calgas being sold/approved to calibrate these detectors.

It was Swampdiver who tried a few big brands portable CO detector for diving use and fortunately today Analox responded with a portable diver's unit. The sensor technology have improved A LOT and price have became more affordable.


PID based sensor for VOC can read as low as 0.001 PPM , as long as you want to pay for it.
http://www.ionscience.com/assets/files/brochures/Cub brochure V1.3 UK.pdf

If it weren't for a bitch maintaining PID in my kind of tropical humidity ( SwampDiver has PID type instrument ) and its very expensive price, I would have bought a PID to detect VOC gassing off from the compressor oil additives and whatnot. The only other poisons source from our lubricated compressor or even dry one like RIX, is the oil itself, its additives and for oiless RIX, overheating will burn its teflon piston rings and also produce dangerous gas.
Canaries in the Kitchen: Teflon Toxicosis | Environmental Working Group

The same reason we prevent compressor overheating to reduce CO possibility from burnt oil, will in someway ( I hope ) also save us from other possible nasty gases or cocktails produced by the lubricant or teflon or whatever things which when a certain temperature is reached, starts to produce poisons....where our activated carbon ( AC ) may or maynot be able to remove them. We know we have hopcatile to remove CO. Again I am assuming the air fill operator has "common sense" to use a filter cartridge with hopcalite regardless compressor is an electric motor driven.

Since CO comes as the by-product of some combustion/burning and so will other poisons too (which we can't detect cheaply ), CO and C02 meter are the cheapest kind of portable detector one can buy today.

I attached for you a photo of a simple example. That is a fitting on a Bauer 2nd stage from Bauer Mariner using K120 II block and with electric motor. That 90 degrees banjo like fitting has an o-ring so that the bolt can spin when the fitting is being tightened. See the brown residue on that fitting, those are lubrication oil being burnt. The oil can escape out of the fitting because the o-ring which is supposed to have a approx 200 Celcius rating, were overheated beyond 200C and leak it did. Now, even more alarming, assuming the compressor is using Bauer approved oil, which either the synthetic or even the older mineral one, has approx 260C flash point....what does that mean ? It meant the compressor cylinder head temperature at that 2nd stage surely close to 260C.....otherwise the oil stain will be liquid oil like a minor leak and not "fried" oil......in other words we have witnessed a compressor which burned its own lubricating oil and it burnt the oil on the compressor exterior fitting.......can you imagine how hot it is inside the compression chamber itself and what kind of "cooking" have happened ?

That overheated compressor pumps out approx 30 PPM of CO , at least that is the reading I get testing 10 tanks pumped using this compressor before the overheating caused more mechanical problem which put the compressor out of service. What I do not know is, 30 PPM CO at what overheating level ? If 30PPM CO is within 30 minutes of compressor run, by the 2nd hour there will be more CO for sure as above 30 minutes the compressor will be in a more severe overheating state. If I were to have a PID type detector, I probably can read VOC levels.

So anyone refusing say even a 3-5PPM CO level from a tank is making a smart choice as our CO detector can only read CO and not other poisonous gasses , while a burning oil will produce more toxic gas than just CO.


Anyone who can't make their compressor produce zero CO is probably because :

1A - Lazy , lazy to aim the exhaust output of the Honda downwind as wind direction changes
1B - Lazy to shut down compressor while knowing a car has its engine running near the compressor's snorkle air intake

2A - Stingy, stingy to buy extra cooling fans and filter cartridge with hopcalite and a CO detector
2B - Stingy, for those in the tropics or with 30C ambient temperature or more and not owning an infra red thermo gun at least, ( let alone 4 channel data logging one ) to read cylinder heads temperatures
2C - Stingy on proper maintenance of compressor

3 - Not qualified to operate a compressor. How can one be a qualified as an air-fill operator when his/her compressor produced CO and still sell air-fill service ?
4 - Ignorant......this is the most dangerous one...profit above all else attitude

Worse if all 4.......yikes !!


What I to do if without a CO detector at hand is to inspect a dive operator compressor room ventilation system and take a look at their compressor fittings and overall condition and the color of the water condensate from water & oil separator no1 and no 2. I can decide there then to run away or use their service while being very careful.

However, I always carry a CO detector when I travel and I am ultra sensitive when detecting sort of bad air which has no CO reading...........example is a "wet/stale" air from a compressor with a cool operation but overdue filter change. Air without CO can sometime smell too, those smell actually comes from the VNMH so it seems.......:depressed: New Page 1

"After taste" in air is also detectable to some degree even when it does not smell much or has zero CO reading.

I am hoping the newer PID instruments can detect more gases while costing less. Prices are dropping already, some units of US$7000 is now under US$3000.

The sticky on top of this section called Compressed breathing air – the potential for evil from within has lots of information.


Be safe...........
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---------- Post Merged at 04:23 AM ---------- Previous Post was at 04:19 AM ----------

Sorry, I cant make my photos stick

Here we go............

 

[spoolin01]

You clearly know quite a bit about this issue, including how it relates to compressor design, use, and maintenance. I'm just making the more simple point that if you want to use an instrument at the absolute limit of it's nominal discrimination, it's smart to verify that the instrument will do that. The usual way to do that is by reference to analytical standards. That introduces other challenges, as you point out, but there's really no other way. Assuming that response is linear to one log below (or above) the only point you can verify often does not pan out. It's not the electronics, it's the transducer. Transducers produce linearizable electrical output only over limited range. How this plays out in the field of CO monitoring would be nice to know.

I googled PID and carbon monoxide and saw that PID is not a suitable method for CO, more for hydrocarbons.

 

[IyaDiver]

Spool, I know what you mean on the "linear", that is also a concern....agree a 100%.
While I cant get RAE's sensor data, here is one which showed for CO it is linear.
http://www.dsmith-inc.com/protech/specs/electrochemical.pdf

Testing brand new RAE Toxi RAE CO units many of them and consistently able to read 10 PPM on my 10 PPM calgas where at factory 50 PPM gas is the calgas used, I have a great hunch it is linear.


PID is not for CO, nope but it is good for a person/company who can afford one ( choose the suitable model ) to actually have a real time sort of Lab Report on-line from his/their compressor output to detect other bad gasses.

Using activated carbon is a time proven process of purifying the air, even though AC does not adsorb well all sorts of bad gasses , it has preference too and also will depend on manufacturer using what kind of AC. Coconut shell one or coal one and the kind of pore size suitable for gas phase and not liquid phase. When u come to Indonesia, you will be surprised at the kind of AC and Molecular Sieve SOME are using for self replaced/packed filter cartridge medias.
The mind set is the cheaper the better. Also air purification is not simple and they don't bother to learn. What can't be seen shouldn't scare them, that is another mind set.

For me personally, I rather pay 1 - 2 dollar extra per tank, if an air fill operator has :
- CO sensor
- Dewpoint Monitor, both electronic one and that chemical one
- CO2 sensor. This is more for monitoring the scavenging process more than monitoring air quality itself but served both.
- PID type detector for whatever other bad gasses we would want to avoid
- Huge tower with plenty of quality AC , Hopcalite , M-Sieve and double pass , not a single tower but two and air flow no faster than 65% of the filter tower air flow rating. This way better dwell time and better air purification efficiency overall.

As I grow older, I value my life more because my kids are still growing up and I have understood or witness the creature comfort and extra safety $$ can buy.

Coming from a P21 ( P Zero for USA ) filter size to a P41 and to a P2 ( P61 for European ) and then P5 ( P81 for European ), it is a world apart and $$ investment indeed can be tested/felt on my tounge. Minimum is a P41 size from a 200 liter/Minute compressor. The only Bauer filter I have not had experienced with is the P31. The deeper I go and the more I dove hard underwater, the air quality really matters.

However, as most experts will tell you, filters & compressors are only as good as how you maintain them. The "maintain" part is where many failed. The pressure to generate more profits for dive resorts or to be still in business, have made things worse. Even PADI the giant is now hands off for air quality check requirement, unlike some years ago where PADI insisted a 5 star center must do X,Y,Z. Today they simply said, follow local regulation for air quality where the dive center is located.

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[spoolin01]

LOL, the link to the sensor sheet is a good example of how hard it is to know what these things will do looking at sensor specs. What the user cares about is accuracy of readout. That the underlying sensor is linear (vs some curvature) in electrical output may make the circuit designers' job easier, but shouldn't be paramount, just that the sensor has a well-behaved response profile, and what range that profile spans.

The bottom calibration point looks to be around 15 ppm, and the baseline offset parameter appears to say the sensor has a tolerance of +/- 10 ppm uncertainty in the zero level output. If that's the right interpretation, this data doesn't seem to me to show what the sensor will do at or below that bottom 15ppm point. At some point as [CO] drops, the behavior of the electrical output WILL break down. That baseline offset, and the dearth of detail shown for response profile, don't clearly permit any conclusions about using the sensor to measure CO levels at or below even 15ppm.

 

[IyaDiver]

The RAE CO sensor is a 500PPM version, order one with 500 PPM. It is 5 times smaller than the link I showed u, which is a year 2007 model technology and that link one, reads to 10,000 PPM. It is just an example but not the kind of sensor we use for dive gas.

Analox uses 100PPM sensor.

I been able to read 2-3 PPM CO with accuracy on the RAE repeatedly and same result from two detectors ( both are calibrated often ) and use clean air from a "clean" scuba tank to zero it. I would not worry about false reading, as long as the unit is calibrated often with a 10PPM calgas and a regulated flow one and does read 10PPM. I don't like using those "spray can" type some people are using, I use regulated 1 liter per minute flow regulator as ambient pressure may effect reading to some degree.