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Carbon monoxide

bob888

Well Known Member
I am consistently getting low CO readings in flight, generally in range of 20 - 30 on the monitor (default alarm set at 50). This is not related to heater because unchanged whether heat is on or off. The question is whether this is typical for the -10, and acceptable. If not, any suggestions as to where exhaust may be getting into the cabin?
 
I have a CO detector in the 10 and always see O ppm. This is the 2nd 10 I've had one in, and have installed them in a few others and have not seen any readings.

Vic
 
Same as Vic - always 0. Kinda want to light up a cigar or something just to see what it would look like if there was CO...

==dave==
N102FM
 
I have an RV-14A with a dash-mounted Guardian CO detector. I am experiencing similar periodic low CO readings (10-20) on my EFIS - no alarms (set at 50).

No cause yet determined, so following this thread with interest.
 
I am consistently getting low CO readings in flight, generally in range of 20 - 30 on the monitor (default alarm set at 50). This is not related to heater because unchanged whether heat is on or off. The question is whether this is typical for the -10, and acceptable. If not, any suggestions as to where exhaust may be getting into the cabin?

I suggest starting with a light penetration test of the firewall.

At night in a darkened hangar with the cowl removed, have a helper pan a bright light across the entire firewall and watch for any light penetration on the aft side.
 
Beware: CO could be sign of exhaust crack

My CO detector started chirping intermittently on a long trip. Due to my ignorance I just carried on figuring I'd investigate when I got home, instead of pulling the cowling right away. After all, it was only chirping once in a while, never steady on, and only for a few seconds at a time. I could fly for an hour with no chirps at all. When I got home I found the number 2 exhaust pipe cracked almost all the way around at the bottom edge of the flange weld. My firewall is very tight but I suspect every firewall has little leaks that would allow CO to trickle into the cabin. So I would treat this as a valid indication and investigate.

I pulled the pipe (Vetterman system from Vans) and Vetterman's welded on a patch and had it back to me in short order where it has been fine for many hours ever since. I now inspect my exhaust system more carefully and very regularly. These cracks can start out as a hairline that can be hard to see. The area is in shadow and you need a good light.

Despite blazing hot exhaust gases coming out of the crack, the direction of it was such that no damage was done to any adjacent hoses, wires or cowling. I was very fortunate.

An exhaust crack can obviously lead to a fire and is not something to take any chances on.

LeRoy Johnston RV-6A Esperanza 1200 hours.
 
could be background

Does the level change from start up/Taxi to flight?

If not, it could be a bad baseline on the meter or a background level if you are in an urban area.

For Reference:

Recommended 8 hour exposure limit (REL) is 35 ppm. Permissible Exposure Limit is 50 ppm. These are from NIOSH and are for continuous exposure.

Short Term Exposure Limit (STEL) of 400 ppm. STEL is typically 20 min time weighted average (TWA).
 
My 14 had intermittent alarm sound on my Co Gaurdian early on (20 hrs. or so ). No heat on and I would open the air vent or turn on the heat to supply more air in the cabin and the alarm would go out. I looked for the cause but before finding it, problem went away. If I recall it usually occurred on decent . I tried plugging off the water drain holes in the bottom of the fuselage (temporary tape) , I sealed the rear bulkhead thinking fumes might be back drafting, no change. I looked for firewall leakage, nothing found and no sealant added. Then it stopped. I thought it might be my monitor but somehow I drained my battery and did not know it, then tried to start the engine. My Co unit would not work after that. A new one was installed and it has not sounded off either, so it should not be the unit. I have no idea what it was, unless it was a defect with the first unit and that had something for it going bust and not trying to start the engine with a low battery. Prop never made a turn and I gave up and put a charger on it. CO unit never worked after, power spike?
 
I have a CO detector and it, too, sometimes alarms. It seems to occur at low speeds, ie., nose up flight as in a climb or slow flight maneuvering, but only infrequently. Sitting in the queue waiting for takeoff at OSH has alarmed it due to the idling plane in front of me. I have tried several things to isolate the cabin, including the baggage compartment bulkhead, but have not found a fix.

Increasing speed usually makes it go away pretty quickly. I do not get anything above 0 in cruise.

The cabin has a very low pressure relative to the outside and is impossible to seal completely. I suspect inflow from the wing root fairing and into the cabin via the large hole where the aileron push-pull tube passes. I cannot prove that. Temporary extensions on the exhaust pipes had no effect.

I will try the light trick and look for a firewall path.
 
I have an RV-14A with a dash-mounted Guardian CO detector. I am experiencing similar periodic low CO readings (10-20) on my EFIS - no alarms (set at 50).

No cause yet determined, so following this thread with interest.
Keith,
Tell Chris she's just gonna have to lay off the weed inflight...
 
CO update

Upon careful inspection of the firewall, I noticed there are numerous small gaps around the perimeter of the firewall between the flanges. I did not seal these during construction but plan to do so now as I could find no other way for the CO to get into the cockpit. What have others done about these small gaps and does this sound like a reasonable explanation for the low level CO that I am detecting? I expect just putting a bead of red silicone around the perimeter may solve this....any better or alternative ideas?
 
On my RV-7 during test flights I measured around 20 ppm CO during climb with mixture enriched. I got 0 ppm during cruise mixture leaned. The CO almost certainly came in through openings in the empennage.
I believe the exhaust gases out of the exhaust pipes only can get inside the cabin somewhere behind them. Of course there can be leaks somewhere in the engine bay allowing fumes to penetrate the cabin through the firewall.
 
More or less CO?

Interesting fact for your consideration.

ROP operations such as takeoff and climb will produce the highest % of CO, compared to LOP in the cruise which produces hardly any.

So it is likely that you will see radically different CO levels depending on phase of flight if you have any exhaust gases finding their way in. And they may not be coming in the firewall points. Air flow is a funny thing.
 
CO inside the cowl

It seems like with any kind of airflow over the engine that there should not be any CO under the cowl at all, so even leaks in the firewall would not cause CO in the cabin, unless you have a cracked exhaust. Do I have this right?
 
It seems like with any kind of airflow over the engine that there should not be any CO under the cowl at all, so even leaks in the firewall would not cause CO in the cabin, unless you have a cracked exhaust. Do I have this right?

There can be slip joints in the exhaust system that are not 100% sealed (depending on what manufacturers system is installed).
 
Does the level change from start up/Taxi to flight?

Recommended 8 hour exposure limit (REL) is 35 ppm. Permissible Exposure Limit is 50 ppm. These are from NIOSH and are for continuous exposure.

Short Term Exposure Limit (STEL) of 400 ppm. STEL is typically 20 min time weighted average (TWA).

I would recommend adhering to MUCH lower limits for flight. EPA outdoor ambient air limits are 35 ppm for ONE hour, and 9 PPM for 8 hours.
Your body is much more sensitive to CO at altitude, and first effects will be slower thinking and impaired judgement.
NIOSH is for healthy workers that are not exposed during none work hours, and a lot of other caveats.
If you suspect any exposure while in flight (as opposed to taxi) I would recommend going on O2 mask and landing at nearest reasonable airport to check it out. It is nothing to fool around with.
JMHO from over 25 yrs of monitoring, forecasting and modeling air pollution.
 
CO persists

I am continuing to pursue the low level CO in my cockpit. At this point, I suspect it may be coming in from the open areas at the rear of the empennage. There is some exhaust staining on the lower edge of the rudder and if there is somewhat lower pressure inside the fuselage then the exhaust may be moving forward in the fuselage. Anyone have thoughts about this theory? Solutions?
 
I am continuing to pursue the low level CO in my cockpit. At this point, I suspect it may be coming in from the open areas at the rear of the empennage. There is some exhaust staining on the lower edge of the rudder and if there is somewhat lower pressure inside the fuselage then the exhaust may be moving forward in the fuselage. Anyone have thoughts about this theory? Solutions?

In terms of identifying the smoking gun, my first step would be to see the difference made when you turn on the cockpit vents. If you think it is coming through the tail then pressurizing the cockpit should stop it. Are there leaks in the cockpit, like around the canopy, that are creating suction? Do you have boots on the aileron pushrods? In order to have exhaust gases in the cockpit the pressure there has to be lower than where ever it is coming in. So either stop the suction in the cockpit so that it stays at ambient, or boost the cockpit pressure with positive ventilation that has to exit through the tail (nowhere else). I think the ey here is to stop any leaks so that you can start to control the direction of flow. If you have leaks everywhere then you have chaos.
 
I am continuing to pursue the low level CO in my cockpit. At this point, I suspect it may be coming in from the open areas at the rear of the empennage. There is some exhaust staining on the lower edge of the rudder and if there is somewhat lower pressure inside the fuselage then the exhaust may be moving forward in the fuselage. Anyone have thoughts about this theory? Solutions?

Your suspicions are possible.

Undesirable airflow entering the cockpit, besides effecting cabin heat performance, can bring engine exhaust with it as well.

A possibly relevant post from another thread.....

http://www.vansairforce.com/community/showpost.php?p=1238288&postcount=42
 
CO

There is a noticeable ?breeze? that comes through the corrugations in the baggage compartment bulkhead. This can be stopped by using triangle shapped foam pieces to seal it. Helps with heating in cold flights, too.

There is still the problem of the elevator push-pull tube and its channel. I do not think it is a good idea to put boots either here or on the wing roots. If these ever come loose they could jam your flight controls. If you put anything there, make sure it can?t effect your controls.
 
Upon careful inspection of the firewall, I noticed there are numerous small gaps around the perimeter of the firewall between the flanges. I did not seal these during construction but plan to do so now as I could find no other way for the CO to get into the cockpit. What have others done about these small gaps and does this sound like a reasonable explanation for the low level CO that I am detecting? I expect just putting a bead of red silicone around the perimeter may solve this....any better or alternative ideas?

I didn't want to climb under the panel do it from the inside, so just smeared a small dab of silicone into each little slot in the firewall from the engine side. Use some finger pressure to push the silicone well into the slot. Then leave a little build up.

Larry
 
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