1. Lecture 3: Aviation Human Factors
4/20/2017 6:40 PM
Lecture 3: Aviation Human Factors
© 2008 Microsoft Corporation. All rights reserved. Microsoft, Windows, Windows Vista and other product names are or may be registered trademarks and/or trademarks in the U.S. and/or other countries.
The information herein is for informational purposes only and represents the current view of Microsoft Corporation as of the date of this presentation. Because Microsoft must respond to changing market conditions, it should not be interpreted to be a commitment on the part of Microsoft, and Microsoft cannot guarantee the accuracy of any information provided after the date of this presentation. MICROSOFT MAKES NO WARRANTIES, EXPRESS, IMPLIED OR STATUTORY, AS TO THE INFORMATION IN THIS PRESENTATION.

2. Outlines Cabin Pressurization Decompression Awareness Atmosphere
Gas Laws

3. What is Cabin Pressurization?
Cabin pressurization is the active pumping of compressed air into an aircraft cabin .
The purpose of these systems is to provide a safe and comfortable cabin environment, and to protect all cabin occupants from the physiological risks of high altitudes (hypoxia, decompression sickness).
Pressurization is essential above 10,000 feet
Flying at high altitudes is more fuel efficient and it allows the aircraft to fly above most undesirable weather conditions 3

4. How Pressurization Works4

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

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

7. Cabin Decompression Awareness

8. What is Decompression?
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

9. Types of Decompression
There are two types of decompression:
1. Slow Decompression
Total loss of cabin pressurization happen more than 10 seconds. It happens in case of a small air leak.
2. Rapid or explosive decompression
Total loss of cabin pressurization within a few seconds. It happens in case of big air leak.

10. Qantas Flight Decompression, Big Hole in the Fuselage
Rapid Decompression
Qantas Flight Decompression, Big Hole in the Fuselage

11. Factors Affecting Severity of Decompression
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)

12. Time of Useful Consciousness
The time of useful consciousness is the time available to recognize that hypoxia exists and to be able to do something about it.
Altitude (Feet)
Times of useful consciousness
18,000
30 minutes
22,000
4 to 8 minutes
30,000
30 seconds to 1 minute
The time available to individuals to perform their tasks, after they have been deprived of oxygen, but are still aware of their environment and capable of controlling their actions.
It is important to emphasize that this table is only a guideline, and provides average values that can increase or decrease, depending on the skills needed to accomplish a task, on the individual’s health, and on the amount of activity. For example, the time of useful consciousness for a cabin crewmember involved in moderate activity is significantly less, compared to a passenger that is sitting quietly. 12

13. Effects of Decompression
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 Effects
Hypoxia, Hyperventilation, Decompression sickness, Trapped gas expansion.

14. Oxygen Systems 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.

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

16. Atmosphere

17. Earth's atmosphere
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.

18. Functions of the Atmosphere
Source of oxygen and carbon dioxide
Protection for the human on the Earth from the harmful cosmic ray, solar radiation and ultraviolet (UV) ray.
Source of rain
Maintains the temperature and climate that sustain life on earth

19. Atmospheric Pressure
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 gravity
The 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

20. Pressure and Temperature decrease with altitude
Altitude (Feet)
Pressure (mm/ Hg)
Temperature (degree Celsius)
760
15.0
18,000
380
-5.3
34,000
190
-62.3
48,000 95
-67.3
63,000 47
-67.04

21. Pressure & Temperature
Air Pressure
At sea level, the air pressure is about 760 mm/Hg.
As the altitude increases, the air pressure decreases (and there is less oxygen to breathe).
Temperature
As we ascend from the surface, the temperature falls steadily with altitude.
Temperature decreases at about 2°C per 1,000 feet .

22. Atmosphere Layer Troposphere: Stratosphere:
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 temperature
Little water turbulence
Above 60’000 ft

23. Physiological Zones of the Atmosphere
Atmosphere can be divided into 2 physiological zones, which are efficient and deficient.
These zones can affect us medically and physiologically.
63,000 ft
50,000
DEFICIENT ZONE: 10,000 to 50,000 feet
18,000 ft
10,000
EFFICIENT ZONE: Sea level to 10,000 feet

24. Physiological Zones of the Atmosphere
Physiological-efficient zone
Physiological-deficient 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.
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.

25. GAS LAWs

26. Gas Laws relevant to aviation medicine
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.
Boyle’s Law:
At a constant temperature, a given volume of gas is inversely proportional to the pressure surrounding the gas
A volume of gas expands as the pressure surrounding the gas is reduced
As altitude increases / gas expands and as altitude decreases / gas compresses.
Dalton’s Law
As altitude increases – gases exert less pressure
Describes the pressure exerted by a gas at various altitudes (pressures)
The sum of the partial pressures is equal to the total atmospheric pressure
Explains the hypoxia that occurs with flight to higher altitudes
Example
Oxygen at sea level
O2 = 21% and PO2 = 21% x 760 mm Hg = mm Hg
Oxygen at 8,000 feet
O2 = 21% and PO2 = 21% x 565 mm Hg = mm Hg
THE PECENTAGE OF OXYGEN REMAINS THE SAME with changes in altitude
Henry’s Law
The amount of gas in solution is proportional to the partial pressure of that gas over the solution
As the pressure of the gas above a solution increases, the amount of that gas dissolved in the solution increases
Reverse is also true, as the pressure of the gas above a solution decreases, the amount of gas dissolved in the solution decreases and forms a “bubble” of gas within the solution.
Example: Example: Bottle of soda
With the cap on, the gas within the solution is at equilibrium
With the cap removed, the gas pressure decreases and bubbles are released into the solution
In normal physiologic function, this law can be seen in the transfer of gas between the alveoli and the blood
This is significant physiologically for the occurrence of evolved gas disorder, aka decompression sickness
Explains the hypoxia experienced with increasing altitude – as the pressure of gases is reduced with ascent, the amount of gases dissolved in solution decreases and this leads to hypoxia and may lead to nitrogen bubble formation

27. Gas Laws relevant to aviation medicine
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
Graham’s Law
Law of gaseous diffusion
Gases diffuse or migrate from a region of higher concentration (or pressure) to a region of lower concentration (or pressure) until equilibrium is reached
The physiological significance is in the explanation of gas exchange
Oxygen moves from the alveoli into the blood and from the blood into the tissues due to this phenomenon
Charles’ Law
The pressure of a gas is directly proportional to its temperature with the volume remaining constant
Temperature increases make gas molecules move faster, and greater force is exerted and volume expands
The law explains the temperature changes associated with rapid decompression, and pressure changes inducing temperature changes with an oxygen cylinder
Example
Shaving cream can placed into fire

29. GROUP EXERCISES
Draw and define SHELL Model Components. Why ‘Liveware’ component is important?
How does the lung being affected when the human goes to higher altitude?
Define Hypoxia. What are the causes of hypoxia according to their types.
Briefly explain SIX symptoms of Hypoxia by relate them with the brain and heart functions?
Explain how Hypoxia can be prevented.

30. How does the lung being affected when the 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.

31. Prevention & Treatment of Hypoxia
Prevention of Hypoxia
Make sure cabin pressurization system functioning well.
Treatment of Hypoxia:
Put on the Oxygen Mask
Turn 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 clearance
Landing at the nearest airport as soon as possible.