Cabin PressurizationCabin PressurizationDecompression AwarenessDecompression AwarenessAtmosphereAtmosphereGas LawsGas Laws

Cabin pressurizationCabin pressurization is the active pumping of is the active pumping of compressed compressed airair into an into an aircraft cabinaircraft cabin . .

The purpose of these systems is to provide a The purpose of these systems is to provide a safe and comfortable cabin environment, and safe and comfortable cabin environment, and to protect all cabin occupants from the to protect all cabin occupants from the physiological risks of high altitudes (hypoxia, physiological risks of high altitudes (hypoxia, decompression sickness).decompression sickness).

Pressurization is essential above 10,000 feetPressurization is essential above 10,000 feet

Outside air continuously enters engine. Outside air continuously enters engine. Air is compressed by the compressor in the Air is compressed by the compressor in the engine and then passes through cooling packs.engine and then passes through cooling packs.Cool outside air goes into mixing chamber and Cool outside air goes into mixing chamber and mixed with re-circulated air from the tanks.mixed with re-circulated air from the tanks.Air from mixing chamber then continuously Air from mixing chamber then continuously supplied to the cabin from overhead outlets.supplied to the cabin from overhead outlets.Outflow valve then control the air flow by open Outflow valve then control the air flow by open and close the valve to maintain the suitable and close the valve to maintain the suitable pressure.pressure.

The cabin pressure of a pressurized cabin is The cabin pressure of a pressurized cabin is controlled by changing the position of outflow controlled by changing the position of outflow valve.valve.If outside pressure is greater than cabin If outside pressure is greater than cabin pressure, the outflow valve is opened in order pressure, the outflow valve is opened in order to equalize the pressure (example: when to equalize the pressure (example: when aircraft ready for landing)aircraft ready for landing)

Decompression means aircraft loss of cabin pressurization.It is a gradual reduction of air pressure.It can occur because cabin pressurization system not functioning well, the damage to the aircraft that causes a break in the aircraft structure which enabling cabin air to escape outside the aircraft

There are two types of decompression:

1. Slow DecompressionTotal loss of cabin pressurization happen more than 10 seconds. It happens in case of a small air leak.

2. Rapid or explosive decompressionTotal loss of cabin pressurization within a few seconds. It happens in case of big air leak.

Qantas Flight Decompression, Big Hole in the Fuselage

Size of cabin, the larger the cabin, the longer the decompression time. Size of the opening (air leak) ,the larger the opening, the faster the decompression time.Differential ratio, the greater the pressure differential between the cabin pressure and the external environmental pressure, the more forceful the decompression. Flight altitude, higher altitudes create greater threats for physiological consequences

Remember your Time of Useful Consciousness (TUC)

The time of useful consciousness is the time The time of useful consciousness is the time available to recognize that hypoxia exists and to available to recognize that hypoxia exists and to be able to do something about it.be able to do something about it.

Altitude (Feet) Times of useful consciousness

18,000 30 minutes22,000 4 to 8 minutes30,000 30 seconds to 1

minute

Physical effects :Noise: there is a loud and popping noise. The rush of air from inside an aircraft structure to the outside is of such force that items not secured may be ejected from the aircraft.Cooler temperature as cabin temperature equalizes with the outside ambient temperature.

Physiological EffectsHypoxia, Hyperventilation, Decompression sickness, Trapped gas expansion.

Portable Oxygen Cylinders Oxygen cylinders are located throughout the cabin. The number and location of the oxygen cylinders varies, depending on the aircraft cabin configuration.

Airline crews modify the pressure and temperature of the air in Airline crews modify the pressure and temperature of the air in the airplane cabin in order to make airline passengers more the airplane cabin in order to make airline passengers more comfortable. The system that they typically use allows pilots to comfortable. The system that they typically use allows pilots to set a pressurization controller to a comfortable pressure. In set a pressurization controller to a comfortable pressure. In response, air slowly leaks in and out of the cabin until the response, air slowly leaks in and out of the cabin until the desired pressure is achieved. Usually the pressure in the cabin desired pressure is achieved. Usually the pressure in the cabin is a little lower than the pressure of air when the airplane took is a little lower than the pressure of air when the airplane took off. This is because the airplane is not completely airtight, so off. This is because the airplane is not completely airtight, so the air pressure will decrease as the airplane flies in a low-the air pressure will decrease as the airplane flies in a low-pressure region (high altitude). This is why your ears often pop pressure region (high altitude). This is why your ears often pop after takeoff or during descent.after takeoff or during descent. a) When at cruising altitude, is the pressure inside the airplane a) When at cruising altitude, is the pressure inside the airplane more or less than the pressure outside the airplane? more or less than the pressure outside the airplane? b) If a window were to open, would air rush into or out of the b) If a window were to open, would air rush into or out of the airplane, in order to equalize pressure?airplane, in order to equalize pressure?

The Earth's atmosphere is a thin layer of gases that surrounds the Earth. It composed of 78% nitrogen, 21% oxygen, 0.9% argon, 0.03% carbon dioxide, and trace amounts of other gases.

Source of oxygen and carbon dioxideProtection for the human on the Earth from the harmful cosmic ray, solar radiation and ultraviolet (UV) ray.Source of rainMaintains the temperature and climate that sustain life on earth

Atmospheric pressure is the combined weight of all the atmospheric gases, creating a force upon the surface of the earth – the cause of this force is gravityThe atmospheric pressure can be measured in force / unit area (Pounds per square inch [Psi] or Millimeters of mercury [mm/Hg])The standard atmospheric pressure at sea level is 760 mm/Hg.It is the combination of:

Gases Pressure [mm/Hg]

Oxygen 100

Carbon dioxide 40

Nitrogen 573

Water Vapor 47

Total 760

Altitude (Feet) Pressure (mm/ Hg)

Temperature (degree Celsius)

0 760 15.0

18,000 380 -5.3

34,000 190 -62.3

48,000 95 -67.3

63,000 47 -67.04

Air PressureAt sea level, the air pressure is about At sea level, the air pressure is about 760 mm/Hg.As the altitude increases, the air pressure decreases As the altitude increases, the air pressure decreases (and there is less oxygen to breathe). (and there is less oxygen to breathe).

TemperatureAs we ascend from the surface, the temperature falls As we ascend from the surface, the temperature falls steadily with altitude.steadily with altitude.Temperature decreases at about 2°C per 1,000 feet .Temperature decreases at about 2°C per 1,000 feet .

Troposphere:Temperature decreases constantly with increasing altitude. Has water vapor (humidity) which produces weather. 30’00o ft at the poles and 60’000 above the equator.Almost commercial aircrafts fly in this layer.

Stratosphere:Constant temperatureLittle water vapor @ turbulenceAbove 60’000 ft

Atmosphere can be divided into 2 Atmosphere can be divided into 2 physiological zones, which are efficient and deficient.zones, which are efficient and deficient.These zones can affect us medically and physiologically.

EFFICIENT ZONE: Sea level to 10,000 feet

DEFICIENT ZONE: 10,000 to 50,000 feet

10,000

50,000

18,000 ft

63,000 ft

Physiological-Physiological-efficientefficient zone zone

Between sea level to approximately 12,000 feet Represents where the human body can adapt the environment. The oxygen levels are usually sufficient for human body requirements.

Physiological-Physiological-deficientdeficient zone zone

Between 12,000 feet to about 50,000 feet.Human cannot adapt unless they are in a pressurized cabin.Here, there is increased risk of problems, especially hypoxia, trapped-gas, and evolved-gas situations.

The body responds to barometric pressure changes in temperature, pressure, and volume.Boyle’s Law: The volume of a gas is inversely proportional to its pressure; temperature remaining constant. Explains trapped gas in the body.

Dalton’s Law: As altitude increases – gases exert less pressure. Explains the hypoxia that occurs with flight to higher altitudes.

Henry’s Law: When the pressure of a gas over a certain liquid decreases, the gas in the liquid will also decrease (Ex: Carbonated drink).Explains the transfer of gas between the alveoli and the blood.

The body responds to barometric pressure changes in temperature, pressure, and volume.

Graham’s Law: Gas of high pressure exerts a force toward a region of lower pressure. Explain the inhalation process during air breathing.

Charles’ Law: The pressure of a gas is directly proportional to its temperature (volume constant). Temperature increases make gas molecules move faster, and greater force is exerted and volume expands. Explains the temperature changes associated with rapid decompression, and pressure changes inducing temperature changes with an oxygen cylinder

1.1. Draw and define SHELL Model Draw and define SHELL Model Components. Why ‘Liveware’ component Components. Why ‘Liveware’ component is important?is important?

2.2. How does the lung being affected when How does the lung being affected when the human goes to higher altitude?the human goes to higher altitude?

3.3. Define Hypoxia. What are the causes of Define Hypoxia. What are the causes of hypoxia according to their types.hypoxia according to their types.

4.4. Briefly explain SIX symptoms of Hypoxia Briefly explain SIX symptoms of Hypoxia by relate them with the brain and heart by relate them with the brain and heart functions?functions?

5.5. Explain how Hypoxia can be prevented.Explain how Hypoxia can be prevented.

How does the lung being affected when the How does the lung being affected when the human goes to higher altitude?human goes to higher altitude?

Lung functions to exchange O2 and CO2 from the outside air into the alveoli in the lung.All gas movement within the body is dependent on the difference in partial(total) pressure.At high altitude partial pressure goes down, thus the movement of O2 into the alveoli & from alveoli into the blood cells is impaired (insufficient).At high altitude, rate and depth of breathing also increased in order to get more O2

The lack of oxygen for the body cells & tissues requirements lead to the HYPOXIA.

Prevention & Treatment of Hypoxia

Prevention of HypoxiaMake sure cabin pressurization system functioning well.

Treatment of Hypoxia:Put on the Oxygen MaskTurn On the Oxygen and make sure 100% Oxygen is being delivered.Slow down breathing rate.Descends to altitude below 10’000 ft.Contact ATC for emergency landing clearanceLanding at the nearest airport as soon as possible.