CO levels

[fastj22]

I've never had a CO monitor in my plane, but during my B conversion I installed a hand held unit. So I don't know if this was always an issue.


I get very high CO levels while taxiing, run up, climb, but it goes down during cruise. The peak was 65 PPM at runup. taxi it goes down to 45 PPM. climb I'm seeing 22 PPM. The low during level flight was 15PPM.
I had all fresh air vents open. The monitor is mounted to the panel. The firewall is sealed with fire stop caulk. The exhaust exits directly down from the firewall. I don't have cabin heat installed. The wing fairings are sealed. The flap pushrod is about as sealed as I can. The really only entry point is the fresh air intakes and the tail cone push rod exits.
Where is all this CO getting in?

[Rynoth]

My best guess would be the wing root in most planes (though you said yours are sealed.) Also, pulled rivets are not necessarily air/water tight (fuselage floor.) I have a typical cheap CO patch in the cockpit and have yet to see the color change on it.

I don't have any idea what PPM of CO is safe so I went to the internet. Seems like the levels you are seeing aren't too alarming? Runup is a very short phase of flight.

"The health effects of CO depend on the CO concentration and length of exposure, as well as each individual's health condition. CO concentration is measured in parts per million (ppm). Most people will not experience any symptoms from prolonged exposure to CO levels of approximately 1 to 70 ppm but some heart patients might experience an increase in chest pain. As CO levels increase and remain above 70 ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained CO concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible."

Source: https://www.cpsc.gov/Safety-Education/S ... nd-Answers

[WaiexN143NM]

hi john ,
Thanks for the post. there are a few back posts on this . put co levels in the search window.
i think it comes thru the back of the plane. air draft creeps up the fuselage with the co.
i have the factory leather upholstery with the leather half circle with constant velcro perimeter to seal off the aft top baggage area. then i made a panel for the lower sq box bulkhead. with constant velcro around perimeter. there is a baggage sling with constant perimeter velcro. but the sling doesnt seal on the bottom.
This set up seals up good. i too have the walmart yellow co monitor. i always have low co levels.
i also crawled underneath one day with the creeper and white caulk(our plane is painted white) i sealed up all the pop rivets with white caulk from the firewall to the fuselage bulkhead where the aft fuse starts to taper.
i will do the rest of the aft bottom fuselage someday. a little may come thru the wing roots, flap drive openings. we have our wing roots sealed up good.


WaiexN143NM
Michael

[GraemeSmith]

I "flew" the FAA PROTE chamber at KFRG - Republic two years back. A chamber where O2 is reduced to higher than 29,900ft equivalent - pressure is not reduced - that would make things worse but in the short training time available would also give you the bends. So they stick with just reducing the oxygen. It's a convincing enough demonstration. During the training I was invincibly and absolutely AOK - carrying out the required tasks - till the trainer slapped the O2 mask on me. I was extremely annoyed with him. I was doing fine. However the video showed that actually after 150 secs - I was barely functioning. At 165 seconds despite a trainer standing over me and yelling at me to put on the Oxygen mask - I never heard him or could do so. He had to assist me. While in the environment - we were given tasks. My math skills made complete sense to me and were a garbage doodle on the page. I solved a simple maze perfectly - another scrawl on the paper. Hand flying bank angles as requested - I was awesome - but actually was doing someone else's task and I wasn't awesome either! Color vision - forget it. The world was grey and white.

The fit young CFI who arrived hung over - he didn't last 15 seconds.

--

The acceptable standard in certificated aircraft is a maximum of 50ppm.

More modern medical thinking puts that in a danger range when some people have an O2 saturation level down at 80% as low as 5,000ft Pressure Altitude. An added risk being if they are smokers. You could suffer nagging slight headache and impaired judgement at 5,000ft or so with 50ppm.

So after the training - my personal standard for the aircraft is ZERO.

And you are not going to find that out with one of those "orange dots" stuck to the panel. A home CO alarm though it offers PPM readings will not tell you sufficient as most are tuned to 80-135ppm before they will alarm - to allow for cooking and smokers in the house. You need something like one of these:

https://smile.amazon.com/Carbon-Monoxid ... ref=sr_1_3

A recent alarm on the Sonex - I traced back to a pinhole in the recently changed No 3 exhaust gasket on the AeroVee. I left it leaking while I ran down how it was getting into the cabin.

Number 1 - holes in the firewall. Where cabling and control cables penetrated the firewall. And in the bottom corners where despite nice tight build tolerances - the corners of the gear leg support webs go through the firewall. Neat application of heatproof RTV to seal all these holes made a dramatic difference.

Number 2 - Front bottom corners of the canopy. Small gaps here were leaking CO. Which would seem unlikely - the exhaust pipes are below the wing and slightly after of those corners. So I'll put it down to some kind of propeller swirling - especially on the ground. Sealed with carefully trimmed window seal gasket.

And that basically solved the problem.

My upholstery does not seal the wings and the air coming in from the wings was not a source of CO.

Similarly the pilot side fresh air scoop was not a problem.

With CO down to zero - I repaired the exhaust gasket.

--

Another source on many aircraft is air entering from the tail of the aircraft and travelling forward inside the empennage. But this was not a source for me.

--

I don't have any idea what PPM of CO is safe so I went to the internet. Seems like the levels you are seeing aren't too alarming? Runup is a very short phase of flight.

"The health effects of CO depend on the CO concentration and length of exposure, as well as each individual's health condition. CO concentration is measured in parts per million (ppm). Most people will not experience any symptoms from prolonged exposure to CO levels of approximately 1 to 70 ppm but some heart patients might experience an increase in chest pain. As CO levels increase and remain above 70 ppm, symptoms become more noticeable and can include headache, fatigue and nausea. At sustained CO concentrations above 150 to 200 ppm, disorientation, unconsciousness, and death are possible."

That might be true at sea level. But even a little altitude makes a huge difference. At night I have a personal minimum of wearing an O2 mask above 5000ft pressure altitude. I can attest to the DRAMATIC improvement in color vision and acuity that takes place as you take just a couple of breaths of O2. The same point is made in the training video below.

YMMV

Sources:

FAA Outline
https://www.faa.gov/pilots/training/air ... t/hypoxia/

PROTE training session recorded at Sun N Fun
https://www.youtube.com/watch?v=saq8u-APDPU

[Rynoth]

One other location that just came to mind is the hole where the piano hinge for the gear leg fairings (in a conventional gear at least) comes through. I never thought to seal that hole, but may add a dab of RTV since they are not removed very often.

[WaiexN143NM]

Hi graeme, ryan, all,
Thanks for good thoughts. Yes to seal the firewall also at each rivet and the motor mount corners. jab 3300’s always leak at the slip joint3 into one. hi temp black is good for us since we painted the glareshield area black. the type of rivets we use are not air or water proof. Good idea with the gear fairings pins. i’ll look for some small rubber grommets for that. also some seal for the canopy front and rear.

WaiexN143NM
Michael

[tx_swordguy]

You might try putting a gasket on the egt sensor to seal it. I have a jab 3300 with two piece exhaust on each side. I placed fiberglass exhaust wrap on and over the attachment points of the two pieces that helps to keep exhaust moving through, instead of pushing outside of the pipes. You might as a last resort add 3” to the pipes. Perhaps the aerodynamics of the plane and the length of pipe is allowing it to swirl and be pulled into the plane somewhere. I also have a vent in the tail that sucks air out of the inside . If you cannot stop it getting in, perhaps you could get it out through the tail and replace the CO with fresh air from your cabin vents, if that made sense.
Mark

[fastj22]

You might try putting a gasket on the egt sensor to seal it. I have a jab 3300 with two piece exhaust on each side. I placed fiberglass exhaust wrap on and over the attachment points of the two pieces that helps to keep exhaust moving through, instead of pushing outside of the pipes. You might as a last resort add 3” to the pipes. Perhaps the aerodynamics of the plane and the length of pipe is allowing it to swirl and be pulled into the plane somewhere. I also have a vent in the tail that sucks air out of the inside . If you cannot stop it getting in, perhaps you could get it out through the tail and replace the CO with fresh air from your cabin vents, if that made sense.
Mark

I would think the shape of the push rod exits of the waiex at the tail would create a suction that would extract all gasses from the cockpit.
My plane is vinyl wrapped so all the rivets are sealed by the wrap. The firewall rivets have a dab of RTV to seal them. The edges of the firewall have that fire seal caulk. I have fresh air vents forward of the canopy in the windshield. They are opened. Even if my exhaust is leaking at the junctions of the manifold or at the heads, the flow through the cowl should extract them overboard.

[Rynoth]

I also have a vent in the tail that sucks air out of the inside .
Mark

I would think the shape of the push rod exits of the waiex at the tail would create a suction that would extract all gasses from the cockpit.

The inside of the airframe will be negative pressure to the outside. The pushrod exits or added vents may enhance this effect, but the fact that the fuselage is displacing airflow and higher-speed air is flowing around it, it WILL be negative pressure all of the time. The only way to reduce/prevent CO from coming into the cabin is to seal the areas where CO is present outside of the cabin (and/or the sources from which it is being emitted.) In other words, you can't really "purge" an unpressurized cabin of unwanted gasses if the gasses still have a way to seep in. In fact, adding vents that further reduce the negative relative pressure inside the cabin would invite more inflow.

Fresh air (intake) vents would/should certainly help reduce the PPM in the cabin. The solution to pollution is dilution.