Atmospheres and Decompression - UMDViolette’s Explosive Decompression Limits 12. Pulmonary...
Transcript of Atmospheres and Decompression - UMDViolette’s Explosive Decompression Limits 12. Pulmonary...
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
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Atmospheres and Decompression• Emergency and explosive decompression• Denitrogenation and decompression sickness• Tissue models• Physics of bubble formation• Atmosphere constituent analysis
1
© 2017 David L. Akin - All rights reserved http://spacecraft.ssl.umd.edu
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Effective Performance Time at Altitude
2
Altitude, m Altitude, ft Effective Performance Time5500 18,000 20-30 minutes6700 22,000 10 minutes7600 25,000 3-5 minutes8500 28,000 2.5-3 minutes9100 30,000 1-2 minutes
10,700 35,000 0.5-1 minute12,200 40,000 15-20 seconds13,100 43,000 9-12 seconds15,200 50,000 9-12 seconds
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Cabin Depressurization Rates• Fliegner’s Equation
– t=time of decompression (seconds)– A=cross-sectional area of opening (square inches)– V=cabin volume (cubic feet)– P=initial cabin pressure (psia)– B=external ambient pressure (psia)
• Decent approximation for aircraft cabins
3
t = 0.22V
A
�P �B
B
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Cabin Depressurization Rates• Haber-Clamann Model
– tc=time constant for cabin (sec)– V=cabin volume (cubic feet)– A=area of opening (square feet)– C=speed of sound (1100 ft/sec)– t=time of depressurization (sec)– P=initial cabin pressure (psia)– B=external ambient pressure (psia)
4
tc =V
ACt = tc
⇤1.68 ln
�P
B
⇥+ 0.27
⌅
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
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Cabin Depressurization Rates• Violette’s Equation
– t=time of depressurization (sec)– V=cabin volume (cubic meters)– A=area of opening (square meters)– P=initial cabin pressure– B=external ambient pressure
5
t =V
220Acosh�1 P
B
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S/C Depressurization (Sonic Orifice)• External environment at zero pressure• Any hole is a sonic orifice• Mass flow rate
• Switch to pressure (ideal gas, isentropic)
vflow
=p�RT
m =dm
dt= ⇢v
flow
Aorifice
dm
dt= AP
o
r�
RTo
✓2
� + 1
◆ �+1��1
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Sonic Orifice Analysis (2)
dm
dt= 0.04042
APop
To
For air, � = 1.4; R = 287
J
kg K
Solve for time to reach final pressure Pf
adiabatic: t =0.43pTo
V
A
"✓Po
Pf
◆0.143
� 1
#
isothermal: t =0.086p
To
V
Aln
✓Po
Pf
◆
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S/C Depressurization (Bernoulli)• Bernoulli’s Law
• g=0• Interior and exterior to spacecraft
• Inside vo~0, outside Pe=0
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P +1
2⇢v
2 + ⇢gh = constant
Po
+1
2⇢v2
o
= Pe
+1
2⇢v2
e
Po
=1
2⇢v2
e
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Bernoulli Analysis (2)
ve
=
s2P
o
⇢
dm
dt= ⇢Av
e
= A⇢
s2P
o
⇢= A
p2⇢P
o
⇢ = m/V
dmpm
= A
r2P
o
Vdt
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Cabin Leak Pressure Loss
10
0"
2"
4"
6"
8"
10"
12"
14"
16"
0" 50" 100" 150" 200" 250" 300" 350"
Cabin&Pressure&(p
si)&
Depressuriza1on&Time&(sec)&
Bernoulli" Sonic"Nozzle"
10 m3 cabin volume 1 cm2 leak area
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Lung Overpressure Following Decompression
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From Nicogossian and Gazenko, Space Biology and Medicine - Volume II: Life Support and Habitability, AIAA 1994
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Violette’s Explosive Decompression Limits
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Caissons• Pressurized chambers
for digging tunnels and bridge foundations
• Late 1800’s - caisson workers exhibited severe symptoms– joint pain– arched back– blindness– death
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Brooklyn Bridge• Designed by John Roebling, who
died from tetanus contracted while surveying it
• Continued by son Washington Roebling, who came down with Caisson Disease in 1872
• Competed by wife Emily Warren Roebling
• 110 instances of caisson disease from 600 workers
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Decompression Sickness (DCS)• 1872 - Dr. Alphonse Jaminet noted similarity
between caisson disease and air embolisms• Suggested procedural modifications
– Slow compression and decompression– Limiting work to 4 hours, no more than 4 atm– Restricting to young, healthy workers
• 1908 - J.B.S. Haldane linked to dissolved gases in blood and published first decompression tables
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Supersaturation of Blood Gases• Early observation that “factor of two” (50% drop in
pressure) tended to be safe• Definition of tissue ratio R as ratio between
saturated pressure of gas compared to ambient pressure
• 50% drop in pressure corresponds to R=1.58 (R values of ~1.6 considered to be “safe”)
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R =PN2
Pambient= 0.79 (nominal Earth value)
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Tissue Models of Dissolved Gases• Issue is dissolved inert gases (not involved in
metabolic processes, like N2 or He)• Diffusion rate is driven by the gradient of the
partial pressure for the dissolved gas
where k=time constant for specific tissue (min-1)P refers to partial pressure of dissolved gas
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dPtissue(t)dt
= k [Palveoli(t)� Ptissue(t)]
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Solution of Dissolved Gas Diff. Eq.• Assume ambient pressure is piecewise constant
(response to step input of ambient pressure)• Result is the Haldane equation:
• Need to consider value of Palveoli
where Q=fraction of dissolved gas in atmosphere ΔPO2=change in ppO2 due to metabolism
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Ptissue(t) = Ptissue(0) + [Palveoli(0)� Ptissue(0)]�1� e�kt
⇥
Palveoli =�
Pambient � PH2O +1�RQ
RQPCO2
⇥Q
Palveoli = (Pambient � PH2O � PCO2 + �PO2)Q
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Linearly Varying Pressure Solution• Assume R is the (constant) rate of change of
pressure - solution of dissolved gases PDE is
• This is known as the Schreiner equation • For R=0 this simplifies to Haldane equation• Produces better time-varying solutions than
Haldane equation• Easily implements in computer models
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Pt(t) = Palv0 + R
�t� 1
k
⇥�
�Palv0 � Pt0 �
R
k
⇥e�kt
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Tissue Saturation following Descent
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Tissue Saturation after Ascent
21
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Effect of Multiple Tissue Times
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Haldane Tissue Models• Rate coefficient frequently given as time to evolve
half of dissolved gases:
• Example: for 5-min tissue, k=0.1386 min-1
• Haldane suggested five tissue “compartments”: 5, 10, 20, 40, and 75 minutes
• Basis of U. S. Navy tables used through 1960’s• Three tissue model (5 and 10 min dropped) • 1950’s: Six tissue model (5, 10, 20, 40, 75, 120)
23
T1/2 =ln (2)
kk =
ln (2)T1/2
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Workman Tissue Models• Dr./Capt. Robert D. Workman of Navy
Experimental Diving Unit in 1960’s• Added 160, 200, 240 min tissue groups• Recognized that each type of tissue has a differing
amount of overpressure it can tolerate, and this changes with depth
• Defined the overpressure limits as “M values”
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Workman M Values• Discovered linear relationship between partial
pressure where DCS occurs and depth
M=partial pressure limit (for each tissue compartment)M0=tissue limit at sea level (zero depth)ΔM=change of limit with depth (constant)d=depth of dive
• Can use to calculate decompression stop depth
25
M = M0 + �Md
dmin =Pt �M0
�M
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PADUA (Univ of Penn.) Tissue ModelTissue T1/2 (minutes) M0 (bar)
1 5 3.042 10 2.5543 20 2.0674 40 1.6115 80 1.5816 120 1.557 160 1.528 240 1.499 320 1.4910 480 1.459
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Bühlmann Tissue Models• Laboratory of Hyperbaric Physiology at University
Hospital, Zurich, Switzerland• Developed techniques for mixed-gas diving,
including switching gas mixtures during decompression
• Showed role of ambient pressure on decompression (diving at altitude)
• Independently developed M-values, based on absolute pressure rather than SL depth
• “Zurich” 12 and 16-tissue models widely used
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Bühlmann M-Value Models• Modifies Workman model by not assuming sea
level pressure at water’s surface
Pamb=pressure of breathing gasb=ratio of change in ambient pressure to change in tissue pressure limit (dimensionless)a=limiting tissue limit at zero absolute pressure
• ZH-L16 model values for a and b
28
M =Pamb
b+ a
a = 2 T� 1
31/2 < bar > b = 1.005� T
� 12
1/2
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
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Physics of Bubbles• Pressure inside a bubble is balanced by exterior
pressure and surface tension
where γ=surface tension in J/m2 or N/m (=0.073 for water at 273°K)
• Dissolve gas partial pressure Pg=Pamb in equilibrium
• Gas pressure in bubble Pint>Pamb due to γ• All bubbles will eventually diffuse and collapse
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Pinternal = Pambient + Psurface = Pambient +2�
r
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Critical Bubble Size• Minimum bubble size is defined by point at which
interior pressure Pint = gas pressure Pg
• r<rmin - interior gas diffuses into solution and bubble collapses
• r>rmin - bubble will grow • r=rmin - unstable equilibrium
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rmin =2�
Pg � pambient
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
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Bubble Formation and Growth• In equilibrium, external pressure balanced by internal
gas pressure and surface tension• Surface tension forces inversely proportional to radius
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“Clinical” Discussion of DCS• Tissue models are predictive, not definitive• Every individual is different
– Overweight people more susceptible to DCS– Tables and models are predictive limits - there will be
“outliers” who develop DCS while adhering to tables
• Doppler velocimetry reveals prevalence of bubbles in bloodstream without presence of DCS symptoms - “asymptomatic DCS”
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
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Implications of DCS in Space Flight• Drop from sea level pressure to ~4 psi, 100% O2
pressure– Equivalent to ascent from fully saturated 120 ft dive – Launch in early space flight– Extravehicular activity from shuttle or ISS
• To have “safe” (R=1.4) EVA from shuttle requires suit pressure of 8.2 psi
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R =PN2
Pamb=
14.7(0.78)4
= 2.87
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Current Denitrogenation Approaches• Depress to 10.2 psi for 12-24 hours prior to EVA
– Full cabin depress in shuttle– “Campout” in air lock module of ISS
• Exercise while breathing 100% O2• In-suit decompression on 100% O2 (3.5-4 hours)
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Historical Data on Cabin Atmospheres
35
from Scheuring et. al., “Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Spacecraft Atmosphere Design Space
36
from Scheuring et. al., “Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Effect of Pressure and %O2 on Flammability
37
from Hirsch, Williams, and Beeson, “Pressure Effects on Oxygen Concentration Flammability Thresholds of Materials for Aerospace Applications” J. Testing and Evaluation, Oct. 2006
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Atmosphere Design Space with Constraints
38
from Scheuring et. al., “Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007
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Decompression/Neurovestibular Physiology ENAE 697 - Space Human Factors and Life Support
U N I V E R S I T Y O FMARYLAND
0.0#
2.0#
4.0#
6.0#
8.0#
10.0#
12.0#
14.0#
0# 200# 400# 600# 800# 1000# 1200#
Tissue
&Nitrogen
&Pressure&(psi)&
Time&(min)&
5*min#.ssue# 80*min#.ssue# 240*min#.ssue#
EVA Denitrogenation - 14.7 psi Cabin
39
Suit Pressure 4.3 psi 100% O2
Cabin Atmosphere 14.7 psi 21% O2
R Value = 1.4
![Page 40: Atmospheres and Decompression - UMDViolette’s Explosive Decompression Limits 12. Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support U N I V E](https://reader035.fdocuments.net/reader035/viewer/2022081516/6129e2774ed46a779579692e/html5/thumbnails/40.jpg)
Decompression/Neurovestibular Physiology ENAE 697 - Space Human Factors and Life Support
U N I V E R S I T Y O FMARYLAND
0.0#
1.0#
2.0#
3.0#
4.0#
5.0#
6.0#
0# 200# 400# 600# 800# 1000# 1200#
Tissue
&Nitrogen
&Pressure&(psi)&
Time&(min)&
5+min#/ssue# 80+min#/ssue# 240+min#/ssue#
EVA Denitrogenation - 8.3 psi Cabin
40
Suit Pressure 4.3 psi 100% O2
Cabin Atmosphere 8.3 psi 32% O2
R Value = 1.4
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Pulmonary Physiology and Decompression ENAE 697 - Space Human Factors and Life Support
U N I V E R S I T Y O FMARYLAND
Constellation Spacecraft Atmospheres
41
from Scheuring et. al., “Risk Assessment of Physiological Effects of Atmospheric Composition and Pressure in Constellation Vehicles” 16th Annual Humans in Space, Beijing, China, May 2007