Carbon Monoxide PPM?

[AlexLev]

I've had a Sensorcon for about two years and had 0PPM during cruise flight, but lately it's 5-10PPM with the heat on. Usually, if I turn the heat off, I can get it down to 0PPM and then if I turn it on again later in flight and mix it with cabin air, it's only 1-2PPM or even back down to 0.

Is this indicative of a developing leak? Or is the number so small it's negligible? What would be the next steps? For those with a digital carbon monoxide reader, what do you see in cruise?

Edited March 2, 2019 by AlexLev

[DXB]

Physiologically, exposure to 5-10ppm CO  in ambient air seems pretty negligible, but I can't speak to whether it is informative regarding your exhaust system and heater ducts or not.  

I decided that being informed of readings down to 1ppm would be distracting and TMI and went with the Guardian 12V outlet monitor that gives different alarms at 50ppm and 100ppm.  If you find a serious exhaust issue, I may have to change my opinion.

I also wonder if the change might reflect aging of the sensor, which has a very finite lifespan. 

[Marauder]

I've had a Sensorcon for about two years and had 0PPM during cruise flight, but lately it's 5-10PPM with the heat on. Usually, if I turn the heat off, I can get it down to 0PPM and then if I turn it on again later in flight and mix it with cabin air, it's only 1-2PPM or even back down to 0.
Is this indicative of a developing leak? Or is the number so small it's negligible? What would be the next steps? For those with a digital carbon monoxide reader, what do you see in cruise?

Alex - mine sometimes will show a low value if I use more heat than when it is mixed with more fresh air. Store bought units have alert levels set to trigger as low as 30 PPM.

The OSHA standard is 50 PPM for an 8 hour period. I think if it stays below 10, you’re in the safe zone. I would however keep monitoring it and if you see it increase, I would begin suspecting a leak.


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[carusoam]

Something has changed....

There should be no CO coming through a healthy heater...

Sometimes, you might smell the exhaust... or see moisture on the inside of the windows... (signs of a strong leak)

 

So if you turn the heat on... and CO goes up.... it is telling you something...  CO is coming in with the heat...

If you turn the heat off... and CO goes down.... it is confirming the same thing...  CO was coming in with the heat...

 

The actual readings you are reporting are not very high... but....  how long will they stay that low?

When a crack propagates in a muffler...

It has been proven to go from barely noticeable on one flight to nearly deadly on the next flight later that same day...

Inspecting the muffler probably takes removing the heater muff to get a good look....

PP thoughts only, not a mechanic...

Best regards,

-a-

[Dialed In]

I agree with what Anthony has said I have had my sensorcon for a year and see 0 in cruise with full heat.  We have been real cold lately 10-20 below, the detector will rise to  2-5 while on the ground taxing and warming things up. 

-Chase

[jaylw314]

If it's an heater leak, the number might also change with opening the cowl flaps, but yes, I pretty much see absolute zilch during cruise with the heater on.

[jackn]

That’s the thing with airplanes (and ourselves), rarely do they just fail outright. There are warnings that something is changing. In both cases it’s critical to your health to listen. 

[skydvrboy]

The problem is not that you have 5-10 ppm of CO.  That is harmless. The problem is that you have an exhaust leak into your heater system. How long will that small hole stay small? What are you willing to gamble on that?

[Rick Junkin]

We love stability and consistency in aviation. When something that is normally stable and consistent changes, its telling you something.

Has your Sensorcon been recalibrated? If not, that could be what is changing.

Have you had any exhaust work done? Check manifold torques, etc. lately?

Those are the two questions I would ask myself as a starting point. And then I'd do something and see of there is another change. That "something" depends on the answer to the questions.

My 2 cents.

BTW, I have a Sensorcon and I've had the same thing happen (changes in PPM indications) and found mechanical issues both times - once a loose clamp, the other exhaust manifold flange bolts had not been re-torqued after running some hours on the engine after exhaust flange gasket changes. Granted, they were much larger PPM changes than what you're seeing before I followed my own advice, but they creeped up to those levels over a short period of time.

Cheers,
Rick

Just realized I didn't answer your question - I see 0 in flight with the cowl flaps closed, and single digits with the cowl flaps open. I am currently searching for a possible leak along the belly of the airplane.

[DXB]

Paying close attention to a very sensitive monitor that reads down to 1ppm and was designed for industrial but not aviation use has its own liabilities.  The very low readouts were not meant to have useful positive predictive value of a muffler leak or other threatening problem in the context they are being used. What percent of us fly around with levels in the 5-10ppm range without any imminent issue that requires action (and without a monitor that reads down to 1ppm to tell us about it)? I don't know, but I did note that none the none of the purpose-built certified monitors from Guardian Avionics will even display a reading below 10ppm, which led me to select a less sensitive monitor.  Could the intermittent 5-10ppm reading in cruise with heat on be the earliest indication of a deteriorating muffler?  Certainly, but I suspect a high false positive rate for predicting that, and inspecting the muffler meticulously now may not be worth the hassle and risk of new maintenance-induced issues.  I would take a quick look at the exhaust, heating ducts, and firewall now but  probably wait until annual to pull the muffler shroud, unless the monitor develops progressively higher readings over time.  

[DanM20C]

8 hours ago, AlexLev said:

I've had a Sensorcon for about two years and had 0PPM during cruise flight, but lately it's 5-10PPM with the heat on. Usually, if I turn the heat off, I can get it down to 0PPM and then if I turn it on again later in flight and mix it with cabin air, it's only 1-2PPM or even back down to 0.

Is this indicative of a developing leak? Or is the number so small it's negligible? What would be the next steps? For those with a digital carbon monoxide reader, what do you see in cruise?

If you can get a repeatable rise when turning the heat on vs off you can be confident of an exhaust leak someplace. I have had many reports of similar small rises (less than 10ppm) that proved to catch issues early.  

That has been the great part of these high resolution monitors. They have found many problems well before they were dangerous. 

5-10ppm is not dangerous from a CO poisoning perspective but it may be an early sign of exhaust trouble.  Like I said, if it is repeatable I would take a close look at the exhaust/heating system at your earliest convenience.

cheers,

Dan

[AlexLev]

All good points. My Sensorcon unit does need calibration, but I still feel it may be a sign of a small leak since if I take the unit and hold it up to the heating duct after pulling full heat, I'll get a small readout. I don't think I had that before--I'll take a look during the next oil change with an A&P and inspect for trouble.

[Jim Peace]

These detectors are great....they always are within a few numbers of each other......I have one to check the checker...anyone have a carbon dioxide detector?  is it needed?

[Austintatious]

that's smart.   Im going to get some blood 02 sensors and probably a pair of CO detectors like you have as well.  I have experienced Hypoxia but never due to CO

 

As far as Co2, I have never heard of that being an issue... but if it is I would certainly like to know!

[Bob_Belville]

Mine is zero in flight, with or without heat on. depending upon the wind I might see a positive reading up into the low double digits on the ramp.

FWIW, we did a 500 hour pressure check of the PFS "collector" Saturday. No leaks. I don't know what schedule A&Ps might use for conventional mufflers.

[Hank]

24 minutes ago, Austintatious said:

that's smart.   Im going to get some blood 02 sensors and probably a pair of CO detectors like you have as well.  I have experienced Hypoxia but never due to CO

 

As far as Co2, I have never heard of that being an issue... but if it is I would certainly like to know!

 

Blood oxygen sensors won't pick up CO, as it bonds to your hemoglobin instead of O2 (and much tighter), so is misread as oxygen. Find Dan's story here of passing out in flight; even at the hospital, they didn't detect CO poisoning for several hours, until he mentioned it to them as a possibility.

[Austintatious]

6 hours ago, Hank said:

 

Blood oxygen sensors won't pick up CO, as it bonds to your hemoglobin instead of O2 (and much tighter), so is misread as oxygen. Find Dan's story here of passing out in flight; even at the hospital, they didn't detect CO poisoning for several hours, until he mentioned it to them as a possibility.

yea, sorry I didnt mean to suggest in any way that blood sat monitors were to be used to detect CO.

[EricJ]

15 hours ago, Jim Peace said:

...anyone have a carbon dioxide detector?  is it needed?

If the cabin CO2 levels start to get too high, just stop exhaling.

 

[Jim Peace]

1 hour ago, EricJ said:

If the cabin CO2 levels start to get too high, just stop exhaling.

 

Co2 does come from our engine....just wonder how much is too much and if it is ever a player......

[jaylw314]

Carbon dioxide fairly non-toxic.  Toxic effects become noticeable at around 5% (50,000 ppm), with concentrations above 30-50% being potentially lethal.  Either way, it's pretty hard to get that much CO2 with any kind of airflow

[EricJ]

43 minutes ago, Jim Peace said:

Co2 does come from our engine....just wonder how much is too much and if it is ever a player......

Yes, the primary by-products of combustion are CO2 and water.   Neither are toxic. 

 

[chriscalandro]

I just got one of these and flew with it for the first time the other day. 

 https://www.amazon.com/dp/B076S6KBP2/ref=cm_sw_r_cp_awdb_t1_PgZHCb74M0TT0

I saw I think mid 30s on run up. Level flight once in a while it went to around 10. It did not seem to be affected by any combination of heat or air. 

Edited March 12, 2019 by chriscalandro

[Jim Peace]

10 hours ago, chriscalandro said:

I just got one of these and flew with it for the first time the other day. 

 https://www.amazon.com/dp/B076S6KBP2/ref=cm_sw_r_cp_awdb_t1_PgZHCb74M0TT0

I like how you can change the battery on that one yourself....good price,,,good find

[MikeOH]

20 hours ago, chriscalandro said:

I just got one of these and flew with it for the first time the other day. 

 https://www.amazon.com/dp/B076S6KBP2/ref=cm_sw_r_cp_awdb_t1_PgZHCb74M0TT0

I saw I think mid 30s on run up. Level flight once in a while it went to around 10. It did not seem to be affected by any combination of heat or air. 

That's the one I have, too.

Happy, so far.

[DanM20C]

14 hours ago, Jim Peace said:

I like how you can change the battery on that one yourself....good price,,,good find

Jim, you can change the battery of the Sensorcon also.  Remove the 4 screws holding the case together, it uses a cr123a.  

Cheers,

Dan