HYPOXIA - TRAP IN THE AIR

HYPOXIA - TRAP IN THE AIR

What is HYPOXIA? (AIM §8-2)
Hypoxia is a state of OXYGEN deficiency in the body sufficient to impair functions of the brain and other organs.

Cabin depressurization effects on human physiology

Carbon dioxide and water vapor pressure affect alveolar Oxygen.

Mean Sea Level - MSL

IN THE AIR

Barometric pressure in standard day is 760 mm Hg

Oxygen pressure is 159 mm Hg

Oxygen saturation 97%

IN ALVEOLI (in the Lungs)

Oxygen pressure is 104 mm Hg

Carbone dioxide pressure is 40 mm Hg

Alveolar ventilation is 40 mm Hg

29000 Flight Level

IN THE AIR

Barometric pressure is around 226 mm Hg

Oxygen pressure is 47 mm Hg

Oxygen saturation 24%

IN ALVEOLI

Oxygen pressure is 18 mm Hg

Carbone dioxide is 24 mm Hg

Alveolar ventilation is 7 mm Hg (due to breathe increase)

39000 Flight Level

Barometric pressure is around 141 mm Hg

Oxigen pressure is 29 mm Hg

49000 Flight Level

Barometric Pressure is around 87 mm Hg

Oxygen pressure is 18 mm Hg

Suppose we would be able to make flight on Flight Level 29000 feet without PRESSURIZATION.(somewhat near Everest top)

Barometric Pressure is 226 mm Hg

minus H2O water vapor pressure which is 47 mm Hg (normal body temperature)

minus CO2 Carbone dioxide alveolar pressure is 7 mm Hg

Remaining pressure is 172 mm Hg

(whether there were no other Oxygen application)

One fifth would be Oxygen (34.4 mm Hg)

four fifth would be Nitrogen (137.6 mm Hg)

We would only get one fifth of Oxygen pressure for the bloodstream (34.4 mm Hg) instead of 104 mm Hg at Mean Sea Level.

What is hyperventilation? (AIM §8-2)

It is an abnormal increase in the volume of air brethed in and out of the lungs. It can occur subconsciously when a stressful situation is encountered in flight. This results in a significant decrease in the Carbon dioxide content of the blood. Carbon dioxide, of course, is needed to automatically regulate the breathing process.

Alcohol and Drugs

Histotoxic Hypoxia can be induced by the introduction of substances like alcohol or Drugs into tissue, reducing its ability to accept OXIGEN from bloodstream.

Anaemic Hypoxia is a reult of the blood being unable to carry OXYGEN, e.g. caused by exposure to Carbon MONOxide.

When a pilot take only carbohydrate in her/his diet the Respiratory Quotient is 1.00.

R.Q. is the ratio of the volume of Carbon dioxide released to the volume of oxygen consumed by a body tissue or an organism in a given period.

Otherwise, when pilots eat fatty food only, the R. Q. decrease to 0.7.

In normal diet for Carbohydrate, Fat and Protein the R.Q is 0.825.

Stagnant Hypoxia results from the body's inability to carry OXIGEN to the BRAIN, which can result from high-gravity forces causing blood to pool in the lower extremities of the body.

Time of Safe Unconsciousness

Some experts believe that for passengers - in contradiction to the crew - a short period of unconsciousness during cabin depressurization can be tolerated since they are not performing an operational task. Unconsciousness is a clear sign of insufficient OXIGEN supply to the BRAIN and it is obvious that this time can only be very short before permanent brain demage occurs.

It is believed that a safe time of unconsciousness is somewhere between 90 seconds and 4 minutes.

Time of Uncounsciousness

20000 feet

All unacclimatized persons lose useful consciousness within 10 minutes

25000 feet

Useful consciousness is lost after 2.5 minutes or less

30000 feet

Approximately 30 seconds

37000 feet

Approximately 18 seconds

45000 feet

Approximately 15 seconds

Very large numbers of aircrew and passengers have been exposed to breathing air at cabin altitudes up to 8000 feet over the last 60 years cithout significant deleterious effect. Although exposure to this altitude reduces the OXYGEN partial pressure in the pulmonary tract the tissues of the body are maintained well above the required level.

Carbon MONOxide has a 240-times greater tendency than Oxygen to attach red blood haemoglobin, thus inactivating a large amount of haemoglobin as an Oxigen carrier.

REQUIREMENTS

GENERAL

CS/FAR 25.841 (a): Maximum cabin pressure altitude under normal operation: 8000 feet

CS/FAR 25.841 (a): Maximum cabin pressure altitude after any probale failure condition in the pressurization system: 15000 feet.

FAR 25.841 (a) (2) (i): Maximum exposure time to cabin presure altitude exceeding 25000 feet: 2 minutes

FAR 25.841 (a) (2) (ii): Exposure to cabin pressure altitude that exceeds 40000 feet: NOT ALLOWED

CABIN OCCUPANTS

CS/FAR 25.1443 (c): Provides oxigen system performance data on oxygen flow and required partial pressure of oxygen

CS/FAR 25.1447 (c): The total number of masks in the cabin must exceed the number of seats by at least 10%

CS/FAR 25.1443 (d): Defines oxygen flow for first-aid oxygen equipment ( for cabin depressurization treatment)

JAR OPS 1.760/FAR 121.333 (e) (3): Requires first-aid oxygen for at least 2% of passengers

JAR OPS1.770 (b) (2) (i)/FAR 121.329 (c): Defines the percentage of passengers that need to be provided eith supplemental oxygen (cabin pressure altitude dependent)

FLIGHT CREW

CS/FAR 25.1443 (a) and (b): Provides oxygen system performance data on oxygen flow and required partial pressure of oxygen

CS/FAR 25.1447 (c) (2) (i): For aircraft operating above 25000 feet quick donning oxygen masks are required for the flight crew wich can be donned with one hand within 5 seconds

FAR 121.333 (c) (2) (i) (A): One flight crew member needs to wear permanently his oxygen mask when the aircraf is operated above Flight Level 41000 feet

FAR 121.333 (c) (3): In case of one flight crew member leaves the control the remaining pilot needs to use his oxygen mask when the aircraft is operated above 25000 feet

Any delay in donning a mask will significantly increase the risck of losing consciousness.