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.

Outlines Cabin Pressurization Decompression Awareness Atmosphere Gas Laws

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

How Pressurization Works 4

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.

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

Cabin Decompression Awareness

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

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.

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

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)

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

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.

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.

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?

Atmosphere

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.

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

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

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

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 .

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 vapor @ turbulence Above 60’000 ft

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

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.

GAS LAWs

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 = 159.22 mm Hg Oxygen at 8,000 feet O2 = 21% and PO2 = 21% x 565 mm Hg = 118.65 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

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

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.

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.

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.