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Hypoxia Dr Simon Brown
The Prevalence
The Problem
The Physiology
The Prevention
Decompression & Hypoxia
The Prevalence of Decompression
UK [1990-99]: 77
Decompression Occurrence
Canada [1985-99]:
164
USA [1974-83]: 355
Australia [1990-99]:
5
GREECE [2005]: At least 1
UK [1990-99]: 77
Decompression Occurrence
Canada [1985-99]:
164
USA [1974-83]: 355
Australia [1990-99]:
5
Your Company ?
Selected Incidents
Greece 2005 - Boeing 737 Cabin probably did not pressurise in climb F/D crew did not don masks Cabin Crew and pax did don drop-down masks Autopilot levelled aircraft at 34,000 ft Interceptor saw FO “slumped” over controls Captain
not seen on flight deck
121 Fatalities
Selected Incidents
USA 1996 - Boeing 727 33,000 ft (cabin altitude horn warning sounded) Cabin altitude climbed to 14,000 ft, masks deployed Flt Eng inadvertently opened outflow valve - cabin
alt increased Captain, Flt Eng and No1 unconscious First Officer donned mask at first warning Captain, Flt Eng and No1 regained consciousness
in descent
Selected Incidents
UK 1998 - Boeing 737 35,000 ft (cabin altitude 20,000 ft) Captain couldn’t don oxygen mask quickly enough Senior cabin crew took off her mask to help Captain Captain and cabin crew member unconscious
F/O Had Donned Mask & Descended Aircraft Captain unaware he had been unconscious
Made various incorrect switch selections
“ . . .it is possible that neither fully appreciated the
nature of hypoxia.”
[UK AAIB, referring to the unconscious Captain and No1]
Cabin Decompression
How Cabin Pressurisation Works
[Picture of aircraft outflow valve]
[Animation of aircraft pressurisation system]
Not As Uncommon As You Think
Cabin Decompression
Causes Include: A/C Pack or Bleed Failures Outflow Valve Failures Door Seal/Latching Failures Structural Failures
“ . . .it is possible that neither fully appreciated the
nature of hypoxia.”
The Problem
What is Hypoxia?
Definition:
Hypoxia is a condition when oxygen available to tissues is insufficient to
meet their needs
Hypoxia is recognised to be the most serious single physiological hazard during flight at altitude
What Is Hypoxia
• Insufficient Oxygen for the Tissues
• Brain tissues most sensitive to lack of oxygen
• Therefore, first symptoms of hypoxia are related to higher mental function
HYPOXIA
Higher Functions
Lack of InsightLoss of Judgement
Loss of Self-criticismEuphoria
Feelings of UnrealityMental Incoordination
Loss of Memory
Unconscious DEATH
Physical Signs
Muscular IncoordinationIncreased Heart RateCyanosis (Blue Lips)
Hyperventilation+
Susceptibility to hypoxia increased by:Susceptibility to hypoxia increased by:
- final altitude- final altitude- time taken to climb- time taken to climb- exercise- exercise- cold- cold- illness- illness- fatigue- fatigue- drugs/alcohol- drugs/alcohol- smoking- smoking
HYPOXIAHYPOXIA
Signs & Symptoms of Hypoxia
Above 20,000 ft Exaggeration of all signs and
symptoms Comprehension and mental
performance decline rapidly Unconsciousness occurs with
little or no warning
Cabin Decompression
May be Slow or Fast
Cabin
Noise
Fogging/Dust
Temperature
Masks
Body
Ears/Sinuses
Hyperventilate
Faintness
Unconsciousness
Physiology of Hypoxia
How does oxygen get from the lungs into the bloodstream?
Respiration Respiration Physiology of Hypoxia
Capillaries
Alveolus
Respiration
Capillary
Physiology of Hypoxia
Alveolus
O2CO2
Respiration
Gas Exchange Takes Place
by Diffusion Only
Physiology of Hypoxia
Capillary
Alveolus
O2CO2
Respiration
This Requires
Pressure
Physiology of Hypoxia
Capillary
Alveolus
O2CO2
PressurePressure
[Film clip demonstrating pressure.]
The Atmosphere
Sea Level
14 psi (760 mm Hg or 1 bar)
18,000 feet
1/2 sea level pressure
34,000 feet
1/4 sea level pressure
40,000 feet
1/5 sea level pressure
Pressure
8,000 ft
1.5x
SL
1x
The Volume of a Gas Increases
as the Pressure Drops
Gas Expansion
Respiration
This Requires
Pressure
Physiology of Hypoxia
Capillary
Alveolus
O2CO2
RespirationRespiration
This Requires
Pressure
Capillary
Alveolus
OO22CO2
Physiology of Hypoxia
Sea Level
14 psi(760 mm Hg or 1 bar)
18,000 feet
1/2 sea level pressure
34,000 feet
1/4 sea level pressure
40,000 feet
1/5 sea level pressure
Holding your breath works down here . . .
. . . but not up here
Oxygen Saturation
Breathing RateSubject stops breathing
10 secs
100 %
50 %
Cabin Altitude 8,000 ft
25,000 ft
Physiology of Hypoxia
Nitrogen
78%
Other
Gases
1%
Oxygen
21%
Only 1/5 of the pressure is
Oxygen
A Bit More on Pressure- The Atmosphere
Nitrogen
78%
Other
Gases
1%
Oxygen
21%
Nitrogen
78%
Other
Gases
1%
Oxygen
21%
Now ALL of the pressure is
Oxygen
More Oxygen
A Bit More on Pressure- The Atmosphere
A Bit More on PressureA Bit More on Pressure
++ ++ ++ ++
++==
4040°°
==
88°°
Nitrogen
78%
Other
Gases
1%
Oxygen
21%
Nitrogen
78%
Other
Gases
1%
Oxygen
21%
Now ALL of the pressure is
Oxygen
More Oxygen
A Bit More on Pressure- The Atmosphere
Time of Useful Consciousness(TUC)
ALTITUDESITTING QUIETLY
MODERATE ACTIVITY
RAPID DECOMPRESSION
35,000 FT45
SECONDS30
SECONDS 20 SECONDS
Hypoxia Video
[Video clip of rapid decompression and hypoxia at 25,000 ft in QinetiQ’s hypobaric chamber.]
Time of Useful Consciousness(TUC)
ALTITUDESITTING QUIETLY
MODERATE ACTIVITY
RAPID DECOMPRESSION
35,000 FT45
SECONDS30
SECONDS 20 SECONDS
Prevention
Stay Below 10,000 ft!
Cabin Decompression . . .
. .or if you suspect hypoxia ? . . .
CARRY OUT THE ACTIONS IN THE SAFETY MANUAL
Prevention
GET ON OXYGEN GET ON OXYGEN AND AND STAYSTAY ON IT ON IT
DON’TDON’T HOLD YOUR BREATH HOLD YOUR BREATH
Holding your breath works down here . . .
. . . but not up here
Questions?