Hypoxia
Dr Simon Brown
Decompression &
Hypoxia
The Prevalence
The Problem
The Physiology
The Prevention
The Prevalence of
Decompression
Decompression Occurrence
UK [1990-99]:
Canada [1985-99]:
77
164
5
Australia [1990-99]:
USA [1974-83]:
GREECE [2005]:
355
At least 1
Decompression Occurrence
UK [1990-99]:
Canada [1985-99]:
Australia [1990-99]:
USA [1974-83]:
Your Company
77
164
5
355
?
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]
Cabin Decompression
Causes Include:
A/C Pack or Bleed Failures
Outflow Valve Failures
Door Seal/Latching Failures
Structural Failures
Not As Uncommon As You Think
The Problem
“ . . .it is possible that
neither fully appreciated
the nature of hypoxia.”
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
Physical Signs
Lack of Insight
Loss of Judgement
Loss of Self-criticism
Euphoria
Feelings of Unreality
Mental Incoordination
Loss of Memory
Muscular Incoordination
Increased Heart Rate
Cyanosis (Blue Lips)
Hyperventilation
Unconscious
+
DEATH
HYPOXIA
Susceptibility to hypoxia increased by:
- final altitude
- time taken to climb
- exercise
- cold
- illness
- fatigue
- drugs/alcohol
- smoking
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
Cabin
Body
Noise
Fogging/Dust
Temperature
Masks
Ears/Sinuses
Hyperventilate
Faintness
Unconsciousness
May be Slow or Fast
Physiology of Hypoxia
How does oxygen get from the lungs into the
bloodstream?
Physiology of Hypoxia
Respiration
Alveolus
Capillaries
Physiology of Hypoxia
Respiration
Alveolus
O2 CO2
Capillary
Physiology of Hypoxia
Respiration
Gas Exchange Takes Place
by Diffusion Only
Alveolus
O2 CO2
Capillary
Physiology of Hypoxia
Respiration
This Requires Pressure
Alveolus
O2 CO2
Capillary
Pressure
[Film clip demonstrating pressure.]
The Atmosphere
40,000 feet
1/5 sea level pressure
34,000 feet
1/4 sea level pressure
18,000 feet
1/2 sea level pressure
Sea Level
14 psi (760 mm Hg or 1 bar)
Pressure
Gas Expansion
1x
The Volume of a
Gas Increases
as the Pressure
Drops
SL
1.5x
8,000 ft
Physiology of Hypoxia
Respiration
This Requires Pressure
Alveolus
O2 CO2
Capillary
Physiology of Hypoxia
Respiration
This Requires Pressure
Alveolus
40,000 feet
1/5 sea level pressure
34,000 feet
1/4 sea level pressure
18,000 feet
O2 CO2
1/2 sea level pressure
Sea Level
14 psi(760 mm Hg or 1 bar)
Capillary
Holding your breath
works down here . . .
. . . but not up here
Physiology of Hypoxia
Subject stops
breathing
Breathing Rate
10 secs
Oxygen
Saturation
100 %
50 %
Cabin
Altitude
8,000 ft
25,000 ft
A Bit More on Pressure
- The Atmosphere
Nitrogen
78%
Oxygen
21%
Other
Gases
1%
Only 1/5 of the
pressure is
Oxygen
A Bit More on Pressure
- The Atmosphere
Nitrogen
More Oxygen
78%
Oxygen
21%
Other
Gases
1%
Now ALL of the
pressure is
Oxygen
A Bit More on Pressure
40°
=
+
8°
=
+
+
+
+
A Bit More on Pressure
- The Atmosphere
Nitrogen
More Oxygen
78%
Oxygen
21%
Other
Gases
1%
Now ALL of the
pressure is
Oxygen
Time of Useful Consciousness
(TUC)
ALTITUDE
SITTING
QUIETLY
MODERATE
ACTIVITY
RAPID
DECOMPRESSION
35,000 FT
45
SECONDS
30
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)
ALTITUDE
SITTING
QUIETLY
MODERATE
ACTIVITY
RAPID
DECOMPRESSION
35,000 FT
45
SECONDS
30
SECONDS
20 SECONDS
Prevention
Stay Below 10,000 ft!
Prevention
Cabin Decompression . . .
. .or if you suspect hypoxia ? . . .
CARRY OUT THE
ACTIONS IN THE
SAFETY MANUAL
GET ON OXYGEN
AND STAY ON IT
DON’T HOLD YOUR BREATH
Holding your breath works
down here . . .
. . . but not up here
Questions?