Carbon Monoxide

[sdogg0]

Ive always been a little concerned after catching my first glimpse of an aircraft heating system. Has anyone ever had issues with exhaust cracks causing carbon monoxide in the cabin? What happened? Im kind of curious because carbon monoxide is a undectable gas using human senses.

[Heliian]

Go out and buy a bunch of those cheap stick on CO detector spots for starters and if you are concerned about CO poisoning, you can get an electronic detector installed which is a little more reliable. If you start to feel giddy, tired or lightheaded or smell exhaust, open a window. Shroud heaters are always cracking, that's why there is a 100hr AD requirement to check them for cracks. In fact I'm pretty sure if you have a shroud heater, you need a CO detector of some sort. Ventilating with fresh air will clear out the CO in no time. Either way, they are still lighter and easier to maintain than a combustion heater.

Safe Skys

[tkdowell]

Has anyone ever had issues with exhaust cracks causing carbon monoxide in the cabin?

No, haven't experienced it myself, not that I am aware of at least. You are absolutely correct, a crack in the exhaust could allow exhaust to creep into the cabin. The aircraft I have flown have a carbon monoxide detector -> the simplest being a little fuzzy dot that turns black and more complex ones giving a light or sounds (I don't trust these as much, I prefer the simpler ones). One of my friends I did training with encountered this and she said it was quite noticable since, well, it was exhaust not just CO (think about how 'foggy' it would get if you left the car running in the garage -> I think that's CO2 (carbon dioxide, not so bad...) for awhile too due to the catallitic converter but once incomplete combustion sets in it does become CO (carbon monoxide, quite a bit worse) -> probably best not to try anyways).

Anyways we talked about it in a human factors course I took and the term is Anemic Hypoxia. From Human Factors for General Aviation 6-6:

Carbon monoxide is more than 200 times more attractive to the hemoglobin in the blood than oxygen. When carbon monoxide is present in inhaled air, a disproportionate amount of carboxyhemoglobin is formed causing an oxygen deficiency throughout the body. In small amounts, this causes impairment of brain functions and sight; in larger amounts, it causes death.

Basically the CO 'latches' onto the blood cells that would have otherwise carried oxygen (hemoglobin) and then starves the body.

Here's some other symptoms if you're watching some suffering from hypoxia, also from above:

• Mental -> Euphoria, Poor Performance, Confusion, IMpaired judgment
  Physical -> Increase respiration poor coordination, unconsciousness
  Behavioral -> Aggressiveness

Here's what you'd actually feel if you were suffering from hypoxia, also from above:

• Mentally -> Euphoria, good performance (like sex)
  Physically -> Dizziness, Nausea, Headaches, tingling
  Vision -> Blurring, Tunnel Vision

Everyone is a bit different. I once did a stint in an altitude chamber and I just got a really bad headache myself. If it were to happen in flight, I'd check the fuzzy dot above, and shut off the cabin heat and open some windows. Another good reason to dress for the weather. Oh, and don't forget to put out your cuban cigar.

Cheers, TD

[old_man]

Old VWs and Porches have a similar heating set up. They usually don't get inspected every 100hrs. However, from my inexperienced knowledge you can tell when they start leaking. Much like a home furnace, they all work on heat exchangers. I wouldn't worry too much. However, if you smell something, shut the heat off and open the windows. I am sure there is a 'red page' for smoke in the cabin in your POH.

[polar one]

I have had a bout with CO., and but for pure luck, am still here. All the symptons you read in the textbooks were there..The problem is you dont recognize them as you are a little dopey.

The only, and I believe only way, is to get CO detectors, put them in a visable place, and replace them when they are due. If you see them change color, turn off the heaters, open window, vents etc, and land soon. If it hits all the classroom learning in the world wont help.

As an aside, we had some problems over the years with shroud heaters. The root casue was a. improper cool down by pilots (ie. forgetting), b. impoper use on the ground (fogetting the limitations), and c..NOT TELLING ANYONE WHEN THEY FORGOT.

Seems some who shut them down imporperly decided not to mention it...

[The Old Fogducker]

Had it happen to me once on a long flight in the Yukon ... long distances to the next runway.

I opened the window and sucked all my air from outside, but CO has a strong affinity for the hemoglobin, and takes a long time to be washed out of the bloodstream by oxygen, so don't expect things to improve in a hurry.

The thing I recall most was how terrible the headache was after I got on the ground, and how long it took for my head to stop pounding. I broke into the first aid kit and about 6 Asprin just barely touched it.

That's when I learned that the little black dot detectors have a very short shelf life.

Replace them regularly.

The Old Fogducker

[Liquid Charlie]

The cheap detectors don't work for subtle amounts of CO - had a crack in a burner can in a C402 - complained to the engineer about a leak -- I recognized the symptoms and turned it off - He tested it and nothing -- took a carterage and blew cigarette smoke on it and it turned immediately black. I came to work the next morning and the engineer was freeking out. All the test sensors were black but it took sitting in the shop overnight to turn them.

Those heaters are dangerous and the only way to keep them safe is continuous inspections -- The crack they found this time in the burner can was so small there were only very small amounts of CO escaping into the cabin but it was enough to cause headache -- shortness of breath and drowsiness -- I usually flew between 10 and 12 thousand and it was the shortness of breath that got my attention first -- then the headache started. --

[Captain Obvious]

I was on a local flight in my 172 one winter night when I thought I could smell exhaust. The carbon monoxide detector, the fuzzy dot kind, was difficult to read in a dark cabin, even with a flashlight. It looked darker but I couldn't really tell for certain. I decided to play it safe, so I turned off the heater, opened the vents and returned to the airport. The next day I discovered that there was a crack in the exhaust.

[Heliian]

I would speculate that if you inspected 100 piston engine exhaust shroud heater systems, you would find about 75 with cracks. Also some cracks may not be detectable until the exhaust is at operating temperature. The biggest giveaway will be the smell of exhaust in the cockpit, same thing applies to combustion heaters. IMO the southwind style of combustion heater is the safest and most user friendly.

[laticsdave]

Had a dose of CO during a run-up in a PA31. Both myself and my FO started to notice the effects after a few minutes (headache, tingling fingers and lips, and also for myself, a swollen tongue!).
A couple of hours on oxygen at the local clinic sorted everything out.
As a post script, the "cheap" CO detector card did not turn dark. It also took over a minute to go dark when held directly in the exhaust flow from a car. Not very reliable - better to get an electronic alarm from your local hardware store and place it under your seat - just don't forget to check the batteries!

[pelmet]

Sent to me in the mail recently.....

https://www.tc.gc.ca/en/services/aviati ... craft.html

Has some other links that I am slowly reading through.

As for the safety alert, the recommended actions are....

When accomplishing the inspections required by AD CF-90-03R2, accomplish a pressure/leak test in addition to the visual inspection, instead of performing the leak check only if the visual inspection indicates a possible problem.

Conduct engine run-up tests with cabin heat on and check for CO in the cabin with a hand-held CO detector during 100 hour and annual inspections.

Continue to inspect the complete engine exhaust system during 100 hour/annual inspections and at inspection intervals recommended by the aircraft and engine manufacturers in accordance with their applicable maintenance instructions.

Use a CO detector while operating your aircraft. A CO warning device is a very sensible investment for owners and operators of GA aircraft. A suitable CO detector that is located appropriately and equipped with a properly set alarm will provide reliable, early warning of elevated levels of this poisonous gas allowing the pilot to take appropriate actions.

[GoinVertical]

The little dot detectors are not great at detecting small amounts of CO, and it must be kept in mind that chronic exposure to low amounts of CO can have pretty drastic consequences.

The electronic detectors are the way to go if you're spending any serious amounts of time in an aircraft with exhaust shroud heaters.

[Squaretail]

I had a bad bout with CO once in a Pacer that it turned out the owner had done some "mods" to the exhaust. It was rather immediate, though you could smell the exhaust in the cabin, so it was pretty unmistakable. Took the rest of the day to shake off the effects of it, brutal headache and a lot of nausea. It was not equipped with a dot detector. The dots do work pretty immediately when I had a problem with the front burner in the navajo once, though they don't turn back to orange with fresh air like they say. They seem to be single use warning. I also doubt they have a very long shelf life, in spite of the sealed package. Make sure its replaced yearly if you're concerned.

[fleetcanuck]

The best CO detector I have found is made by CO Experts and is available through Aeromedix, or better yet, pick one up at OSH.

[Helno]

I use a sensorcon.

If you do a bit of searching they usually have a discount code for pilots buying them.

[EastCoastWings]

Guy at my school ran in CO problem one night while flying with his girlfriend, he wasn't feeling well but didn't want to say anything and it wasn't until she mentioned not feeling well that he realized something must be wrong for them to both not feel well and looked at the CO detector and noticed it was black. Only work if you check them lol

[pelmet]

Decided to search for a good CO detector today. Basically, I am willing to carry a larger one but I want something that is loud so I can hear it over the engine noise and be able to keep it in the flight bag and still hear it. I would also like a digital display so I know if it is a lot or just a miniscule amount that was detected. Plus a low batter chirp to remind me to put in a new battery as it will otherwise get forgotten. So it seems to me that a battery powered household detector could be perfect.

Decided to look at some of the household detectors and then went to an Aviation Consumer review and it pointed out this critical information......

"There are dozens of household CO detectors, some with prices not much above those of the chemical spot detectors. We do not recommend any of the residential detectors as most follow Underwriters Laboratories spec UL-2034, which requires a time delay before the unit will alarm once a given level of CO is present. That’s to cut down on calls to 911 for false alarms. Under the UL spec, if the unit has a digital readout, it cannot show CO concentrations below 30 PPM. The unit will not sound an alarm until CO reaches 70 PPM and remains there for four hours. At a concentration as high as 400 PPM, the unit will generally not alarm for 15 minutes.

Given the effect of flight at altitude in combination with low-level CO poisoning, we think it’s quite likely a pilot would be incapacitated well before a household detector would alarm in flight."