Opinions on CO sensor or detectors

[Doc Harry]

The key to having a CO detector for travel is that it be small and lightweight, so that you aren't tempted to leave it behind. It should be robust enough that you can pack it in your suitcase between your thong and Speedo. You don't want to have to bring along another Pelican case.

Personally, I prefer to have a unit that I can calibrate so that I know that I can trust my readings. When I say that the gas is "good" then I want to be sure of that. Likewise, when I say the gas is "bad" then I want to be 100% sure of that, too.

The calibration process is a necessary evil of CO dectectors, at least at this point in time given the technology. Be sure to budget in extra $$$ for the calibration gas and accessories. Use the 10 ppm calgas, not the 100 ppm calgas.

In my opinion, you need a small, robust unit of value that can be calibrated, that gives you a reading in 5 to 15 seconds, and can detect down to 1-2 ppm with a resolution of 1 ppm.

This eliminates the Pocket CO (takes too long), DCO 1001 (takes too long), Analox EII CO (too expensive), Drager Pac CO (resolution unclear) and the CO-Cop (can't be calibrated). THE BW Technologies Gas Alert Extreme is also up there on the expense scale.

I ended up purchasing the BW Technologies Gas Alert Extreme single-gas detector and have been very happy with it. It has a round detector port that fits nicely on either a DIN or Yoke valve. You can also buy an optional sampling hose. It is also robust and water-resistant.

I have my own compressor and I solo with my Voodoo gas, so I got a CO detector many years ago to be sure that I could safely solo with my gas. I take the CO detector with me when I travel.

POCKET CO ($140)
Takes 90 seconds to get a reading (T90=90 sec), detection range only goes down to 5 ppm, spec sheet does not mention resolution/accuracy, needs to be calibrated at least annually ($40 per year extra for calibration gas).

Drager Pac CO ($190) Takes 15 seconds to get a reading, detection range down to 1 ppm with a resolution of 1 ppm, the exact details, cost and schedule of calibration are not clear.

DCO 1001 ($160)
Takes 60 seconds to get a reading, detectin range down to 0 ppm with 20% accuracy but no mention of true resolution, no mention of calibration needs

ToxiRae III ($190)
Takes 12 seconds to get a reading (T90=12 seconds), dectection down to 0 ppm with a resolution of 1 ppm, must be calibrated every 6 months

Analox EII CO ($350)
Takes 20 seconds to get a reading (T90=20seconds?), detection down to 1 ppm with a resoluton of 1 ppm, must be calibrated every 6 months

Co - Cop ($55)
Tests only for "gross contamination" of scuba cylinder air without qualitative measurement

Also consider:

BW Technology Gas Alert Extreme ($265)
Continuous monitoring, detection down to 2 ppm with a resolution of 1 ppm, must be calibrated every 6 months

 

[Scared Silly]

The Toxirae is designed to provide sampling of ambient air. I think that you would have a hard time testing the air in a scuba cylinder with it unless you bought some hoses and plastic bags and use it like the Pocket CO unit.

The above is true for the designed purpose. But the ToxiRae is simple to use via BCD hose and an adaptor. The ToxiRae comes with a small adaptor that attaches to input side of the monitor (it is normally used for bump testing). Just slip it in on a short piece of hose with the BCD adaptor (which is also flow regulator at 2 l/min) and you are set once hooked up to the scuba regulator.

Some said that Analox is great product too but I am never a fan of unregulated air supply when testing gas. At low reading of PPMs, you crank open the valve too much, excessive pressure will effect reading due to partial pressure.

The cap on the Analox EII CO and O2 is actually a flow regulator made from I believe precision delrin. It limits the flow to around 2 l/min which avoids the problem of excessive pressure on the sensor.

I have both a Toxi Rae and a Analox EII CO. Both are nice units. I bought the Analox because I wanted to support them for their efforts in bring the product to market after listening to divers.

Shameless plug because I have two units my ToxiRae is available. It was just calibrated last month.

 

[DandyDon]

Silly, thanks for the input. You should be able to sell that spare unit easily. I didn't think the sensor could be replaced, but I learned that it can. IyaDiver has the info on that.

I'm looking at buying a portable CO detector. I'm not a "hard core" diver by any means, but I usually go on 1 or two dive trips a year. As far as I know I've never had bad air. However, I was nervous about my air on our trip to indonesia two years ago. I'll be traveling to Mexico and the philipeans this year and would like to have a CO sensor.

As far as my personal needs: I don't care about knowing exact amounts, just whether it's going to kill me or not. Of course having an accurate reading is always a good thing. I'd like simple, accurate, and low maintenance. I'd also like it to be easily portable and small. I'd further prefer it be cheaper if possible.

Hehe, I could tell a few stories. Nice shopping. I couldn't find these when I first started looking 2 or 3 years ago.

I've searched and see some reviewes, but not all of these options are compared.

So these are what I've found:

Pocket CO (cheap, small, simple, but just looks kinda hokey, is it reliable?) $140
Order the Pocket CO - Carbon Monoxide Detector

It's a lot better than nothing and affordable for anyone. You can actually get it for less if you google shop the basic unit by name, but - go for the 300S unit. I prefer to give it 3 minutes in the test bag while I check my Nitrox or other gear needs and the timer helps, but more so - it comes with a nifty test bag designed just for scuba tank needs, plus a can of cal-gas. No, I don't like that they cal with 100 ppm, but it does seem to work ok.

Drager Pac CO (Haven't seen used for Scuba. Spec sheet looks great 1ppm resolution, 15 second test time, good up to 90% humidity, 2yr warranty) $190
General DCO1001 Carbon Monoxide Detector Digital General Tools & Instruments Formerly Mannix DCO1001 DCO 1001 DCO-1001

You gave a link to the wrong unit there. They make a number of units. Which one are you looking at?

DCO 1001 (electromechanical sensor = longer sensor life?, accurate to 99% humidity, larger 6" size, low cost) $ 160
General DCO1001 Carbon Monoxide Detector Digital General Tools & Instruments Formerly Mannix DCO1001 DCO 1001 DCO-1001

I don't know about that one, but 99% accurate is nothing. We need to know that the air is less than 10 ppm, in units of 0.0001%. How low does it measure?

ToxiRae III (higher sensitivity 0.1ppm in a 0-100ppm scale - seems best for diving air although not necessary- durable, relatively small, medium cost) $190
SALE - RAE Systems ToxiRAE 3 Single Gas Detector - $153.47 - PK Safety Supplies

Yeah, a friend has that one and we compared it on the boat my last trip. Worked nicely, especially nice after I dropped mine in the ocean. :silly: How did you get that price; your link says $185, which is as good as I see. And you want the additional accessories = total around $300.

Analox EII CO (Specially made for diving, ease of use, but new and high cost) $350.
Analox EII CO Carbon Monoxide Analyzer - Dive Right In Scuba - Plainfield, IL

I've seen it sold for $300 and free shipping, and the company is great. They recently changed cal-gas from 100 ppm to 50 and has otherwise been great about meeting our needs. You can cal at home, which really needs to be done twice a year with any unit, or at least bump tested on 10 ppm.

Co - Cop (small package, simple, low tech, idiot proof, but requires replaceable sensors which may be an issue if you run out on a trip) $55 plus $6 sensors
Carbon Monoxide tester for scuba and firefighting

Hasn't been made in years. I spoke with the inventor a few years back and he said he took a big loss getting rid of the last ones, would cost way too much to make today, and besides - weren't that accurate.

Any opinions or other suggestions. I'm leaning toward the Toxirae III at this point because it's about half the price of t Analox and is very sensitive. It also would work well for general use as a safety device for boating or live aboard trips.

Thanks,

jbtut

Well, but the time you add the other parts, the cost goes up a bit, but it's a good alternative. I waited on ordering an Analox until right as they closed for Xmas to be closer to a possible dive trip, but they were delayed, then mine shipped overnight but got caught in the blizzard - so it'll be here Monday. I know I can carry their O2 analyzer and CO analyzer in the same Pelican case. Looking forward to comparing it to my Pocket CO, which I did replace after my screwup.

There's very little 'need' for a CO unit. However, if it brings you peace of mind, then it's a good thing. Plus, it doesn't hurt the scuba industry to see customers turning up for diving with a CO monitor...keeps us on our toes

I've never used a CO monitor, but was very impressed with my Analox nitrox analyzer.

I amazed to see you say that, but then you haven't stood on a boat, seen a CO test read 17 ppm, huh? We turned the boat. Do your compressors have inline CO monitors with auto shut-down at 10 ppm? Did you know that even an electric compressor with clean air intake can produce CO when working hard but incomplete burning of its lubricating oil? A bigger risk in tropical climes, where many of us like to dive.

The dark truth is that while we did not have the technology to prevent CO hits for many years, we do now, and it's affordable - but so many are in their old habits that the right people are not acting on this. IF YOU DON'T TEST, YOU ARE DIVING ON FALSE HOPE.

I've been a bit on the fence of whether I should buy one or not.

You may be aware that there was an incident recently in Cozumel Mexico where a couple divers were in life threatening condition as a likely result of a few tanks of bad air from a reasonably reputable dive shop with its own compressor. I've seen no results of any test of the tanks that those two divers had.

Although I've never experienced an air issue I've also never had a regulator fail, but I still carry an Octo. And when I look at the $ I've put into diving and the cost of a dive trip, $200 is relatively inexpensive compared to the consequences of getting a single tank of bad air.

I'm also wondering how often a tanks with something like 15ppm are used where it's not life threatening, but will still make you a little sick. They might give you nausea or mild vomiting upon surfacing, but you'd never really know if that was the issue or something else.

Anyway maybe it's a waste? I don't know.

I guess it depends on how safe one wants his air to be. I also wonder how many cases of "travelers flu" were really near CO hits? We know of some other injuries and a few deaths, altho local governments do suppress such news as bad for business. Try to find info on the DM and the tourist who died in Roatan a few years ago. Can't! They even got that thread pulled off of Scubaboard. The Texas widow settled out of court agreeing to not talk so all of her family and friends are honoring that, altho I've talked to a few in confidence. That resort now has a great CO compressor monitor I understand, but they won't talk about it because they don't want to talk about why. The other resort across from it just installed an Analox Clear unit on their compressor, but - I don't know about the others on the island. The big station on Cozumel is still in the process of installing a Clear unit, but I don't know about any of the many other compressors on the island.

Hehe, my home buddy just went along with me and my testing but don't think he was impressed until he saw his first 5ppm reading, then next there 7 to 17 ppm readings.

I'm considering making a custom bag for the ambient air type monitors. It seems like it could be very simple. Just cut apart a cheap SMB and add/glue in a window. as well as shorten it to about 4" long and put some type of sealable opening in it. That way you can throw the tester in, and fill it up. Pull the dump valve to empty and it's quick and easy, plus you have a water tight cover that doubles as your test bag.

If I go that route I'll post a few pics.

I find the the one gallon zip lock bags with slider handles the easiest to use. They leak after a day or two, but they're cheap and lightweight - replace daily, carry a spare.

Here's a related thread: http://www.scubaboard.com/forums/ba...shopping-carbon-monoxide-co-tank-testers.html
You also might want to PM DandyDon and ask if he has updated info.

No, that is really out of date and beyond updating. I am thrilled to see this thread.

 

[spoolin01]

As far as my personal needs: I don't care about knowing exact amounts, just whether it's going to kill me or not. Of course having an accurate reading is always a good thing. I'd like simple, accurate, and low maintenance. I'd also like it to be easily portable and small. I'd further prefer it be cheaper if possible.

You can have it simple... or accurate... or cheap. Pick one or two, forget having all three.

I wouldn't place much stock in the marketing materials and specs, without verifying them, except as an initial screening tool. There are many ways those can be misunderstood. The best thing would be to decide what your tolerance limit is, and ask to speak with an engineer at the manufacturer to determine if their instrument meets your needs, and how to use it to that end. There may or may not be anyone like that available at a given outfit....

When I looked into this, it seemed that 5ppm was about the lowest anyone would claim (for these inexpensive units). Unless you think this has changed in 5 years, or that scuba-oriented companies have had their own sensors designed, or sourced better ones, so that they can position their high-performance unit at the bottom of the workaday price range, if you want accuracy and precision at 1 or 2 or 5 ppm, you'll have to do some sleuthing (and paying, probably) to find out how to get that.

I bought a 'cheap' industrial model when I first got my compressor. The 'meter in a baggie' approach works fine (and protects the unit). It probably also helps to provide some dwell time in contact with the air for good results. I never saw readings above '0'. That doesn't at all have to mean that it was truly '0', but it probably means it wasn't 50, or 20, or even (hopefully) 10.

I used one from these guys, that was probably a predecessor of this
UEi CO Detectors - CO71 Carbon Monoxide Detector

At the time, it seemed to be a good combination of price and lower limit of detection.

Finding a $200 unit that you just wave in front of the gas, and it gives you tenths of a ppm accuracy (or even within several ppm), for the stated life of the unit, just seems improbable. The sensors die after two or three years, meaning almost certainly that they drift to that point. That engineer could help with that understanding.

I'd say the manner in which you'd want to use this doesn't require accuracy, just sensitivity. Would you breathe a tank that has 20 ppm CO? 10? 5? I'd say if it was "not 0", I'd reject the tank. The lower the detection limit, the better (this presumes that reliable sub-1ppm, or thereabouts, sensitivity is not a technical capability of these instruments). Accuracy per se wouldn't matter. To that end, finding a stable and reasonably accurate calibrator gas, at the level of your tolerance limit, or the limit of detection capability, whichever is lower, is the best way to have confidence you can technically achieve your desired surveillance. The most important question the unit needs to answer is: If I have 'my-max' ppm CO in this gas, will I see notice in the display?

 

[divermike1011]

Never used a diver CO monitor, but the Navy was nice enough to send me to Gas Free Engineer training so I've played with a few different units for shipboard use. All I wanted to add is that Cal Gas can be pricey, hard to get in some areas, and IIRC your have to pay to dispose of the bottles as HAZ-MAT. I haven't gas-freed anything in a couple of years, so my information could be out of date. I do agree with getting a 10 ppm cal gas, you really, really want to make sure you have no CO in your air.

Great idea on getting a monitor though, I may get one myself after reading this thread!

Michael

 

[jbtut]

Thanks for all of the responses. I'm learning a lot. Dandy Don; I've read a few of your postings about this. Particularly on the Cozumel testing, which is really what put the issue on my radar as I'm heading there in a month or so. - the price of $153 on the ToxRae was if you buy 100 or more. I didn't put that in though, I just copied and pasted the link which shows up with that price.


Maybe I'm just being cheap, but it seems like these are very simple devices. I don't know if all sensors are created equal, and possibly the CO sensors in these units are more expensive than cheap basic ones like those found in a home CO alarm. It may also be that the programming is very complex to sort out the output of a co sensor and turn it into a reliable number. I'm also inclined to support those who put in the leg work to produce a retail product for this purpose. I've just been considering what it would cost for me to make one myself.

I have a basic background in physics, so I'm probably just knowledgeable enough to get into trouble, however it seems as though a basic sensor: maybe even sourced from a home CO detector along with a simple chip programed to convert the signal and send it to a basic display could all be done very inexpensively.

The Electronic Brick system is what got me started as they sell a CO monitor plus potentiometer (to adjust sensitivity) on a little board for $10. Seeedstudio Electronic Brick MQ7 Carbon Monoxide Detector - RobotShop Add a battery, simple chip, and display, and you're ready to check air. You could even do it with say, 4 LEDs and it would be even cheaper. Just test so that 1 LED = 5 PPM, 2 = 10 etc. There's no need to know anywhere above 20ppm anyway. Put it all in one of these : Amazon.com: Clear Waterproof ID Case-BAU55180 (sold individually): Toys & Games

Then calibrate and you could have in inexpensive co monitor.

I don't have time to do it between now and my trip, but I think it would be an interesting experiment. Maybe an EE or someone with more knowledge than I could explain why this is a bad idea.

Anyway I'm learning a lot, but will probably just buy an off the shelf unit anyway.


EDIT: In looking at the spec sheet on that sensor, it's only good to about 20ppm, so that'd be a no-go for this use. I'd have to find a different sensor. Maybe something like this http://www.made-in-china.com/showro.../China-Electrochemical-Co-Sensor-COS001-.html . Plus if you wanted to get cute, you could add a humidity and/or temp. sensor to adjust for effects of those. The cost addition would be minimal. And with a cheap off the shelf sensor you could set it up with a plug style connection and just put a new one in every two years and calibrate as necessary.

 

[RubberDucky]

The Toxirae is designed to provide sampling of ambient air. I think that you would have a hard time testing the air in a scuba cylinder with it unless you bought some hoses and plastic bags and use it like the Pocket CO unit. IMO that process is a pain in the ass and take way too long, but it's cheap.

It takes less than 30 seconds to test a tank with the ToxiRae 3. All that it requires is purchasing some plastic tubing and a BC connector. It's about as fast and simple as it gets.

There's very little 'need' for a CO unit.

Somehow I doubt that the double digit number of divers that were poisoned in Cozumel last year would agree with you (note: that was related to some random dive op doing their own fills - their tanks were not filled by the main filling station on the island (though they weren't doing CO detection at the time then either, but should be soon as I understand it)). The same goes for anyone who knows someone who has died as a result of getting bad air. We can only wonder how many have died because of it, but the facts were never known.

You don't "need" a CO unit when you have good air. How do you know you're using good air if you're not testing it? You don't. Your advice is surprising.

 

[IyaDiver]

Guys,

I been doing some testing, for knowledge and for fun.
I am trying to find excuse to buy Analox hand held CO detector, so I have to read everything properly before hand.

01. Convenience of not needing a BCD type flow regulator ?
Yes it is true that the Analox small half ball flow limiter is like a regulator but one must remember that a BCD clip type of flow regulator works with the assistance of a dive regulator which has intermediate pressure of between 125 to 140 psi at all times. So no matter how you crank open the scuba tank, there will be limited pressure of 140 psi at the most feeding the BCD clip and further regulated for 1.5L or so air flow ( not pressure ) at so little pressure.

Cranking open a tank valve can result in anything from 500 psi to whatever amount our hand will open up the high pressure seat opening, if direct reading from a tank is the method.
Read Analox page 12 Section 4. Erratic reading : Pressure on Sensor, reduced gas flow rate.
Read the warning on page 9 at bottom page:
WARNING
Very high flows may pressurise the sensor and
inaccurate readings or sensor damage will result.

http://www.analox.net/product-docs/manual-91.pdf

From my personal point of view :
Why would I need to have a weakness in my testing protocol when I can get a BDC clip and eliminate pressure spikes which may cause erratic reading ? We are talking of reading as low as 5-10PPM of CO. In Analox O2 meter, 20.9 % oxygen is a huge amount, 1 % is 10,000 ppm , so playing with pressure spike caused by that derlin half ball is not too bad. With enough practice one can probably set decent tank pressure all the time and that half ball will be much faster than a BCD clip flow regulator, if one does testing for many tanks in one go.

Analox responded to the market demand to make a simple to use CO meter/detector.
They did just that, but they did warn user there are proper procedures one must follow in regards to pressure spikes on the sensor. They listen to divers requirement and this is very good offering they have.


02. Aside from tank testing, can I read ambient CO level ?
I like to hang the ToxiRAE 3 near dive compressor with its calibration cup removed and it reads ambient CO ( same as in mining operation worn on a belt ). Set the loud alarm for preset CO value and listen for the alarm to trigger. I believe when one remove the Analox half ball plug, it will read ambient CO, probably not as fast as RAE because Analox sensor located a bit deeper, but I am sure it can sense ambient CO.
- Analox has no audio or light/LED alarm. This I can't live without. As ambient CO monitor I can't keep looking at it, I must hear it only when a set limit is exceeded.This is of no use to diver who do not monitor ambient CO.
- Analox is IP 65 and not IP67. If ever dropped in a camera basin, its going to be costly.
- Analox may not ( must check ) have that special filter paper to reduce cross contamination on the sensor. This may not be important for diver using the CO detector as dedicated tank checker. For me it is important because I measure ambient CO often.

But one thing for sure, Analox is a purposely built diver CO detector, not like T3 which is more for industrial application....but this is why I like the ToxiRAE 3 so much. Everyone has different preference but flexibility is a bonus.


03. Sensor Replacement
ToxiRAE 3 is not a disposable unit, the smaller brother is , the ToxiRAE 2.
I can change the battery myself on T3 and can send it to Singapore for sensor change and at the same time I would want my circuit drift to be measured or calibrated or whatever. Sensor is an analog data input device, the circuit and the processor is the one converting the signal to CO numbers on the LCD display. As with any measuring device, sensor has drift and the circuit will have drift too. So a bench test at a RAE full blown service center would be best to run complete calibration and sensor replacement for the T3.

RAE Singapore is a full blown RAE service center because of the oil and gas industries service Singapore is famous for. If I buy an Analox, I will probably need to go send it to UK because the local Analox dealer in my country is a dive center and not an exclusive RAE full blown service center like RAE Singapore. I don't know how support will be in USA or other countries outside UK.


04. Method of Calibration , its differences
Analox fresh air calibration uses a small calibration knob.
Page 10, section 3.2. That is probably a potentiometer to zero the sensor. If anyone has the Analox, tell me how much +- can that knob adjust ? That knob if it can do +- 5 PPM, make sure you keep your hand away from that knob after getting a zero. Best to design that knob with pull-out to activate and push-in to disable rotary movement.
What I love to know is how linear the Analox sensor output is ? If it is linear output from 1 to 50PPM, it will be so sweet because the calibration knob will serve proper function at lower and higher CO limits.

So I am asking the question to myself, why would Analox place a calibration knob on its CO meter ?

So looking at the User Manual, I think I found the answer.
Analox spec : ( Page 17 )
Accuracy : +-0.5PPM + 5% of reading
This means at 10PPM of CO, worse case it is 9 or 11 PPM shown....damn nice !!
Temperature Effect : <2ppm of CO per Celsius
This one I am guessing. Most standard "temperature" definition for sensor is 20C.
Assuming 20C. So at ambient 30C on a tropical dive, I may get maximum error of say 1PPM per Celsius, at 30Celsius = up to 10 PPM ??.. I bet that Analox calibration knob will handle this temperature drift. Can anyone confirm that the Analox fresh air calibration knob can go 10PPM off set ?

RAE did not state much, only Drift <2% signal/month. It is also using 20C as standard temperature.
Page 2 for CO sensor drift.
http://www.raesystems.com/sites/default/files/downloads/FeedsEnclosure-TN-114_Sensor_Specs.pdf


Now, knowing my RAE does not have fresh air calibration knob and it is used by miners world wide in 4 seasons countries, I must know what is the effect of temperature to its reading. Some high end gas detector will compensate humidity and ambient temperature but this cheapo RAE of mine is probably not this advance.
So test is what I must do. If I read Analox temperature drift info correctly, 10PPM error maybe expected from 20C to 30C ambient temperature.

My dive being in the tropic, I will not see lower than 24C ambient air and higher than 34C. Ambient air temp at test is 28C.

I have two of T3, one I call red unit and one is black unit, based on the color of the code I wrote on them. I then turned them on and the black unit read 2 PPM. I am not surprised, I been smoking in this room, even though both doors each on opposite sides are open. So I am looking at one of my T3 being more sensitive than the other. See photo a1.

I then test to make sure the sensor is not having error.
I use my scuba tank ( guaranteed clean air... ) as fresh air for the black unit, to see if it will read zero PPM. See photo a2. It did read zero.

I then tested the red unit with fresh air, sure enough the red unit read zero too. It ha been showing zero anyway....ha ha ha. See photo a2-1.

Now to bump test the two units with 10 PPM cal-gas, the black unit did read between 10 to 11 PPM. I took photo of it at 11 PPM. See photo A3.

I then bump test the red unit, it shakes between 9 to 10 PPM. At took photo at 10 PPM. See photo a4.

I blow breathing exhalation to the T3 usually as a bump test because I am a smoker.
So far so good and I do not need to buy bump gas.

If anyone asking why I have two gas cylinders, the other one is 400 PPM C02 for my CO2 meter. I do not calibrate my CO2 meter with fresh air because my fresh air shift from 430 PPM CO2 to 500 plus a bit depending on time of day....you know photosynthesis and etc etc.

I then cool down the two T3 in the freezer. For like 3 minutes. See photo a5.

I tried measuring the T3 with my infra red thermogun but it won't read cooler than 25C while I know it is cooler than that. Never mind, I expected to see at least some reading change when the T3 is at least cooler by 5 Celsius. See photo a6.
I did not get any reading change. If the T3 sensor were to be similar in properties like what Analox uses, I should see at least 4-5 PPM change, if not 8-10 PPM.

What I can't test yet is to blow cool or hot air to the T3, assuming a real life use in different temperatures of air blown to the sensor, not only temperature of the sensor being cool or hot. I could only cool the sensors and the unit. Maybe next time I will do extended test. As far as I know, this electromechanical sensor on CO detectors have some sort of heating element. This is why it need 60 seconds to stabilize upon powering up. I know my flammable gas detectors run very hot.

So, what is my conclusion ?
For my use, where I am within 24C to 34C at the extreme, ToxiRAE3 is better suited for me. For cold country guys, perhaps the fresh air adjustment knob of Analox will be a better tool once temperature caused sensor drifts. But I hope such knob that can change values of CO reading, must be made secure and not easily spin by accident.

My last and only worry for a unit like Analox is that very knob - fresh air adjustment knob.
When is a fresh air fresh ?
You are at the back of a dive boat, engine is running, where will one find a guaranteed zero PPM CO ? Even my bedroom has 1-2 PPM CO usually and when I first own a ToxiRAE 3, I had trouble looking for zero PPM because my home is in a busy area. 1 or 2 PPM is so easy to detect in a city.

3.2 Air Calibration
Air calibration is essential before every use and is performed as follows.
1. Expose the analyser (with sampling dome disconnected) to clean air for two minutes
and adjust the calibration knob until the display reads 0ppm.

Now, we want to read as low as 5 PPM ( some standards is 3 PPM ) to decide if the tank is use able or not. If you zero a 3 PPM ambient because you think that 3 PPM is sensor drift due to temperature, 5PPM becomes 2 PPM. How ??
Bring a "zero air" bottle on every dive ?

There is also ONE weakness of ToxiRAE 3.
Since I have used one unit testing at least 1,000 tanks of more, the calibration cup which clips on the sensor outer housing, will worn out the plastic of the sensor housing "claw". Later after 1000s of clicking the sensor cup in place, the calibration cup won't stick/click anymore. This is why if you see my red T3, the calibration cup is already power-glued to the unit. The black T3, I use small lines to secure it, so that no more un-plugging of the calibration cup. Just push a bigger diameter hose to the small diameter hose of the calibration cup when air testing is required.

Hope you guys find my test interesting.

 

[DandyDon]

Thanks Ila. Interesting. But for ambient CO, why don't you just get a dedicated home CO unit with digital readings?

 

[IyaDiver]

Don, what I mean by ambient CO is not home use. Its for when I am on live on board dive trips or compressor room inspection. Do you see my detectors has a string for neck placement or tie-anywhere purpose ?

Live On Board vessel here are slow ones, maximum 9 knots. Often when the wind is from behind, the wind is faster than the vessel. So exhaust fume can overtake the vessel. I usually will place the RAE near the snorkel intake of the compressor. This is why the alarm is so important for me, its 95dB and it is so high pitch, it can be heard over diesel engine rumble. I usually tell compressor operator to shut down air fill under such circumstances. Its best to prevent CO entry than to detect CO in tank only. This way we can isolate where the CO comes from. The RAE has lots of reading features, maximum level CO recorded and exposure over time and etc etc. This is useful to read what CO level was triggered when I could not hear the alarm.

This are the features :

TWA
Time Weighted Average. TWA is the amount of gas that a worker must not experience over the duration of a shift. TWA is normally measured over an eight hour shift.

STEL
Short Term Exposure Limit. Some gases and vapours have an allowable maximum STEL which is higher than the 8 hour TWA. STEL values are usually calculated as 15 minute intervals.

No doubt the TWA and STEL is more for a person exposure to CO, but it can be a useful low level data logging of total CO registered. So I will know that the CO level increase been for sometime and not just a spike. My QRAE2 can real data log, but must use serial cable not USB. I failed to get a suitable serial to USB converter.


Compressor room, can mean a permanent building or open air compressor area.
In some island where electricity is in shortage, many dive centers use Honda powered compressor and they bring the unit out in open air, some under some not. This is the most dangerous situation because wind direction may change and worse if no wind at all. A Honda at 1 meter away and if exhaust gas not properly blown away by wind, may read as high as 150+ PPM CO. This is already a diluted CO level and not a direct hit.

Some live on board vessel place their compressor in engine room or in a partition within the engine room. The compressor may have a snorkel hosed all the way to outside the engine room, but it will be nice to know if the engine room itself does not have much CO.

Modern diesel engine have closed crankcase system where the engine's crankcase air ( piston blow-by ) is channeled back to engine air filter/intake housing, but loose hose or other problem may occur where CO can be exhausted to engine room. I like being careful when one install a compressor in engine room or close by to engine room.

We don't have winter here, so no fire-place or heater fueled by burning gas.
My water heaters at home are gas ( LPG ) powered, but I placed it in open space, not only because of CO but more for fear of explosion.

My emergency generator is also placed outside my house, at the open air garage. So no CO worry. I have LPG gas leak detector in the kitchen, but no CO detector because the ventilation is very good.

Happy diving Don.

IYA