Chapter 7: The Silent Killers | Human Performance & Limitations

§ 11Carbon Monoxide (CO) Poisoning

11.1 The Colourless Killer

What CO is Carbon monoxide is a colourless, odourless, tasteless gas that is a product of incomplete combustion.

Why CO is so dangerous — the 200× rule Haemoglobin, the oxygen-carrying chemical in the blood, picks up carbon monoxide over 200 times more readily than it picks up oxygen.

Thus, even minute quantities in the cockpit (often from improperly vented exhaust fumes) may result in pilot incapacitation. Exhaust gases from piston engines can consist of as much as 9 % carbon monoxide. So, gases from leaking exhausts can cause carbon monoxide poisoning in pilots.

Carbon monoxide binds haemoglobin over 200 times more strongly than oxygen — Figure 7.1 — Carbon monoxide binds haemoglobin more than 200× more strongly than oxygen, crowding oxygen off the blood.

Sources of cockpit CO — the usual suspects

Improperly vented exhaust fumes entering the cabin via the heating system.
Leaking exhaust manifolds / muffler shrouds (especially common in piston singles where cabin heat is drawn over the exhaust).
Engine combustion gases, which can contain up to 9 % CO.
Tobacco smoke in confined cabins.

11.2 Symptoms · Actions · Prevention

Carbon Monoxide Poisoning – Symptoms

Initially, there is an INABILITY TO CONCENTRATE
Headache
Dizziness
Nausea
Impaired vision
Lethargy or weakness
Impaired judgment
Personality change
Impaired memory
Flushed cheeks and cherry-red lips (classic CO sign)
Convulsions

Actions if CO Poisoning is Suspected

Turn off cabin heating
Open cabin ventilators
Consider using oxygen if available
Land as soon as possible
Take medical aid
Do not fly till cleared by doctor

DGCA-quoted prevention rule — copy verbatim into your exam answer AT ALL TIMES WHEN THE CABIN HEATING IS USED, FRESH AIR MUST BE CIRCULATED TO REDUCE PRESENCE OF CO.

Why the "cherry-red" colour? Carboxyhaemoglobin (Hb-CO) is a bright cherry red — much brighter than oxygenated Hb. The pilot's cheeks and lips therefore flush bright pink/red. Don't confuse this with the bluish CYANOSIS seen in hypoxic hypoxia. They look opposite:

Hypoxic Hypoxia → blue extremities (cyanosis)
CO Poisoning → bright cherry-red lips/cheeks

Carbon monoxide — symptoms, actions and prevention — Figure 7.2 — Carbon monoxide poisoning: symptoms, immediate actions and prevention.

CO affinity for Hb (vs O₂)

> 200 ×

CO in piston-engine exhaust

up to 9 %

First symptom

Inability to concentrate

Classic skin sign

Cherry-red lips

First action

Turn off cabin heat

Hypoxia type involved

Anemic (Type b)

§ 12Hyperventilation

Definition — "over-breathing" "Hyperventilation" is another word for "over-breathing" and may be defined as lung ventilation in excess of the body's needs. Good training is the best way to avoid Hyperventilation in pilots.

Mitigation for passengers The chances of Hyperventilation affecting your passengers can be reduced by giving them a thorough pre-flight briefing on every aspect of the flying sortie. (Briefed passengers = calm passengers; calm passengers don't hyperventilate.)

12.1 Causes at Low Altitude

At low altitude — where hypoxia is not a factor — the most common causes of hyperventilation are psychological or environmental rather than physiological.

The most common causes of Hyperventilation at low altitude
Category	Cause
Cognitive load	Intense concentration on a difficult task
Emotional	Fear
Emotional	Anxiety
Physical	Motion sickness
Physical	Shock
Environmental	Vibration
Environmental	Heat
Aerodynamic / Manoeuvring	High G-forces

12.2 Symptoms · Treatment · the Paper-Bag Trick

Symptoms of Hyperventilation

Dizziness
Tingling
Visual disturbances
Hot or cold sensation
Anxiety
Loss of muscular co-ordination
Increased heart rate
Spasms
Loss of consciousness
Cramping and spasms of the hands and feet
Cold clammy skin
Paleness

Treatment of Hyperventilation

Breathe oxygen at 100 percent. If hypoxia is the cause, the symptoms will improve markedly after three or four breaths.
If the symptoms persist, consciously slow the rate of breathing to 10–12 breaths per minute and do not breathe deeply.
If you are flying below 10,000 feet, hypoxia is unlikely and hyperventilation may be assumed.
If you suspect that any occupant of your aircraft is suffering from hyperventilation, try to calm them down. Give them a simple task to fulfill that might take their mind off their anxiety.
One of the direct causes of hyperventilation is a reduction in the carbon dioxide level in the blood. The condition may be alleviated by getting the sufferer to breathe into a PAPER BAG. This action will increase the blood's carbon dioxide level, causing the brain to reduce the breathing rate.

The science behind the paper bag Hyperventilation drives off too much CO₂ from the blood (respiratory alkalosis). Since the brain's breathing centre is regulated by CO₂ (see §8.4), low CO₂ causes the urge to keep over-breathing — a vicious circle. A paper bag traps exhaled CO₂ which is then re-inhaled, raising blood CO₂ back to normal and breaking the loop.

Hyperventilation — causes, symptoms and treatment — Figure 7.3 — Hyperventilation: causes, symptoms and treatment, including the paper-bag technique.

12.3 Hypoxia vs Hyperventilation — Telling Them Apart

A vital distinction — the symptoms overlap Many symptoms of hypoxia and hyperventilation overlap (dizziness, tingling, visual disturbances, loss of consciousness). The DGCA syllabus gives you a clean altitude rule to distinguish:

If flying BELOW 10,000 ft → hypoxia is unlikely → assume HYPERVENTILATION.
If flying AT or ABOVE 10,000 ft → hypoxia is plausible → provide O₂ AND descend. If symptoms clear after 3–4 breaths of 100 % O₂, it was hypoxia.

Hypoxia vs Hyperventilation — side-by-side
Parameter	Hypoxia	Hyperventilation
Typical altitude	> 10,000 ft	Any altitude (often below 10,000 ft)
Onset	Insidious, slow	Rapid — linked to a trigger (stress, fear)
Skin sign	Cyanosis (bluish)	Paleness · cold clammy skin
Heart rate	Often increased	Increased
Feeling of well-being?	Yes — euphoria	No — anxiety, fear
Blood CO₂ level	Variable / often normal	LOW
First-line treatment	100 % O₂ + descend below 10,000 ft	Slow breathing to 10–12/min, or breathe into paper bag
How to confirm in flight	Symptoms improve in 3–4 breaths of 100 % O₂	Symptoms persist on O₂; resolve with re-breathing technique

Examiner's favourite trap A pilot at 9,500 ft reports tingling in the fingers and dizziness. Hypoxia is unlikely below 10,000 ft → assume hyperventilation. Slow your breathing, calm down, optionally use a paper bag — do not declare an emergency and descend for a hypoxia event that isn't happening. (However — if O₂ is available, the standard advice "breathe 100 % O₂; if symptoms clear in 3–4 breaths it was hypoxia" lets you confirm safely.)