Carbon monoxide

[azure]

So I sprung for the Aeromedix PocketCO detector because I had noticed some exhaust smell inside the cabin of my Cardinal during maneuvers in the pattern with the gear down. I've used it for my last three flights and confirmed that there is a small amount of exhaust getting in -- indicated levels on takeoff are nonzero but never higher than 5 ppm, and drop quickly to zero once the gear come up. Then again in the pattern they come up again to the 10-15 ppm range. Oddly this does not happen when flying a straight-in approach, so I suspect it is banking, and probably banking to the left, that allows a trace of exhaust in through the cracked door seal in my right side door. Anyway there is definitely something going on that is not an immediate health threat but still requires investigation.

But... the reason for this post isn't fumes in the airplane. I've also been carrying it with me to see what my exposure is like during my other waking hours. What I've learned is very disquieting. The only place I've detected measurable CO is inside my car in traffic -- and there it can get quite high. I had a brief reading of 45 ppm once last week. Then this morning as I exited the freeway on my way to work, I heard three beeps coming from my pocket. As soon as it was safe I took it out and was shocked to see a reading of 124 ppm (the dosimetry function later confirmed a maximum of 127). Immediately I lowered the windows to get some fresh air and the detector indication went down gradually into the single digits. I parked soon after and haven't driven since then so I still don't know whether the source was my own exhaust or something ambient drawn into the cabin. What concerns me though is that although CO itself is odorless, if the source was auto exhaust shouldn't there have been a strong exhaust smell? What other sources could there be in traffic (or produced inside the car) of high enough CO concentrations to give a >100 ppm reading yet no smell of exhaust? Any ideas?

 

[dmccormack]

The be sure you're not getting gassed, have the A&P strip the heater cuff off and thoroughly inspect the exhaust manifold for leaks.

You'll rest and fly easier knowing it ain't leakin'

 

[azure]

The be sure you're not getting gassed, have the A&P strip the heater cuff off and thoroughly inspect the exhaust manifold for leaks.

You'll rest and fly easier knowing it ain't leakin'

It's already been inspected. He found no leak in the exhaust manifold -- in fact he did a pretty thorough inspection and couldn't find any way exhaust could get in, until I suggested the door seal. He couldn't detect any smell when taxiing, and decided it was my imagination. That's why I bought the Aeromedix detector.

The other Cardinal I flew also had a trace of exhaust smell in the pattern with the gear down, so it seems to be endemic to the breed. I suspect mine's a little worse because of the door seal, and I'll be having it resealed soon. In any case I'll be carrying the detector with me whenever I fly and will know PDQ if it gets any worse.

At this point I'm a lot more worried about my car.

 

[dmccormack]

Exhaust odor <> CO poisoning

It may seem like you're getting blasted with CO, but it's highly unlikely if you've had a complete inspection and it's sealed tight.

Some folks are extra-sensitive to the odor.

 

[azure]

No, no. I'm NOT getting blasted with CO in the plane. The readings on the detector are low, all they indicate is that the exhaust is not my imagination. Maybe I'm extra sensitive to the smell. But there is SOMETHING getting in there, wouldn't you say? Worth watching? That's what I plan to do anyway, and get the door resealed to hopefully reduce it (plus help to reduce engine noise )...

Again though, what I really posted about is the 127 ppm reading in my car this morning. No detectable exhaust smell at all. Could my air filter have removed the larger, heavier particles that contribute to the smell? I thought a lot of that was NO2 and aerosolized solids that would be too small to get filtered out. If it wasn't from exhaust, then what?

 

[Chip Sylverne]

A quick google search showed levels of ambient CO in heavy traffic ca reach 160 ppm. How heavy was the traffic, and how stiil was the air?

 

[gismo]

5 PPM is hardly cause for concern, I'd say what you found in your airplane is perfectly normal and likely due to exhaust finding it's way into the cabin via other routes than a heater leak. CO detectors for home use are federally mandated to show "0" when the levels are below 35 PPM to eliminate false alarms. The advantage of a more sensitive detector in an airplane is twofold. One issue is the fact that you are more susceptible to CO at altitude and therefore lower limits apply. The other is that being able to measure low levels allows you to detect a pending problem before it becomes critical, but to do that you need to know what's "normal" for your airplane. If you were seeing 15 PPM in cruise flight I'd look into the cause but I'd still fly the plane as long as it didn't get worse. 5-15 PPM on the ground and/or in slow flight wouldn't bother me at all.

As to what you get in traffic, I've heard that under certain conditions (high traffic, low wind, confined freeway, etc) the levels can become significant, e.g. in excess of 100 PPM. I believe there's a pretty high limit in tunnels but the expectation is that the exposure time there is low for automobile passengers. And if you want to see scary levels, look at the published numbers for CO in the lungs of smokers who just took a long drag! BTW do not attempt to test this with your own CO meter, the other contaminants in cigarette smoke can damage the sensor.

 

[azure]

The drive home today told the story. The CO isn't coming from my own car's exhaust. My detector read zero (or close to zero) everywhere except around the intersection where I had the high reading this morning. Driving through that area, it shot up to the mid 40s and then gradually went back down. That intersection is very busy and was also downwind (today) from a major downtown freeway junction a couple of blocks away. So it all makes sense. The things you learn about your environment with a sensitive instrument!

 

[Maxmosbey]

The drive home today told the story. The CO isn't coming from my own car's exhaust. My detector read zero (or close to zero) everywhere except around the intersection where I had the high reading this morning. Driving through that area, it shot up to the mid 40s and then gradually went back down. That intersection is very busy and was also downwind (today) from a major downtown freeway junction a couple of blocks away. So it all makes sense. The things you learn about your environment with a sensitive instrument!

That is very interesting. I would not have thought that in the open there would be that much carbon monoxide. I bought a propane heater. It is called the heater buddy, and if the oxygen level gets below a certain point the heater will turn off. The directions say that if it is used in a confined space to make sure to ventilate it. That is all they say, ventilate it. I wondered what they meant by ventilate it? So I contacted them. They said to open a space at least 9 square inches to allow ventilation. So I wrote them back and asked what to do then? Should I put the heater close to the ventilation? Should I some how direct the ventilation to some area of the heater? The answer came back to simply open a vent at least 9 square inches to allow oxygen to enter the enclosure. For some reason that just doesn't seem to be safe. I keep thinking that the carbon monoxide has to be forced out, and the oxygen needs to be forced in, but evidently I'm over thinking it.

 

[azure]

I thought it was surprising too, but the CO was clearly coming from the area I was driving through. I suppose it's possible the source was something other than auto exhaust, but I don't know what else it could be. Also, considering how windy it was yesterday, there would have to be quite a bit leaking out of somewhere to give readings as high as that.

On the heater buddy, I would think that if you had a fan to create circulation it wouldn't really matter whether the heater was right up against the opening or not. As long as it has a plentiful oxygen supply, burning propane will produce negligible CO. Does the heater come with a fan or blower?