Carbon monoxide poisoning

Carbon monoxide (CO): anaemic hypoxia (TC AIM AIR 3.2.2).

Source:

• Exhaust leaking through cabin heater (TC AIM AIR 3.2.2)
• Exhaust gases contain large amounts (PHAK ch.7)

Exhaust system (PHAK ch.7):

• Vents burned gases overboard via: pipes from cylinders, muffler, muffler shroud
• Shroud heats outside air for cabin heat and defrost, via exhaust manifold heat exchanger (TP 1102 Heating and Ventilation)
• Must be free of cracks: a leak lets CO into the cabin through the heater vents

Properties:

• Colourless, odourless, tasteless (TC AIM AIR 3.2.2)
• Binds haemoglobin over 200 times more readily than oxygen (TC AIM AIR 3.2.2)
• Severe poisoning can be fatal (PHAK ch.17)
• Dangerous levels can build with no smell: CO detector more reliable than exhaust odour

Signs (TC AIM AIR 3.2.2):

• Early: inability to concentrate, blurred thinking
• Later: dizziness, headache

Action: shut off heater, open fresh-air vents, use 100% oxygen, land.

Catalytic heaters: consume oxygen, produce CO. Never use in aircraft (TC AIM AIR 3.2.2).

Smokers (TC AIM AIR 3.2.2):

• Always carry CO: may run 5-10% of haemoglobin saturated
• Can become hypoxic below 10,000 ft
• Smoking also impairs night vision (TC AIM AIR 3.5)

Trap: cherry-red skin (a CO sign) does not mean hypoxia; oxygen-starved tissue turns blue. An exhaust crack is a CO hazard, not a heat-only problem.

Practice