Aerospace Physiology - University Of Maryland · Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design U N I V E R S I T Y O F MARYLAND Solution of Dissolved Gas
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Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
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 implemented in computer models
27
Pt(t) = Palv0 + R
�t� 1
k
⇥�
�Palv0 � Pt0 �
R
k
⇥e�kt
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
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)
28
T1/2 =ln (2)
kk =
ln (2)T1/2
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
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”
29
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
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
30
M = M0 + �Md
dmin =Pt �M0
�M
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Effect of Multiple Tissue Times
31
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
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)
• Dissolved gas partial pressure Pg=Pamb in equilibrium
• Gas pressure in bubble Pint>Pamb due to γ • All bubbles will eventually diffuse and collapse
32
Pinternal = Pambient + Psurface = Pambient +2�
r
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
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
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Historical Data on Cabin Atmospheres
34
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
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Spacecraft Atmosphere Design Space
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
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Effect of Pressure and %O2 on Flammability
36
from Hirsch, Williams, and Beeson, “Pressure Effects on Oxygen Concentration Flammability Thresholds of Materials for Aerospace Applications” J. Testing and Evaluation, Oct. 2006
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Atmosphere Design Space with Constraints
37
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
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
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
38
Suit Pressure 4.3 psi 100% O2
Cabin Atmosphere 14.7 psi 21% O2
R Value = 1.4
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
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
39
Suit Pressure 4.3 psi 100% O2
Cabin Atmosphere 8.3 psi 32% O2
R Value = 1.4
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Constellation Spacecraft Atmospheres
40
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
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Categories of Sensing• Proprioception (internal to body)
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
Allowable Rotation Rates• Select groups (highly trained, physically fit) can
become acclimated to 7 rpm • 95% of population can tolerate 3 rpm • Sensitive groups (elderly, young, pregnant
women) may have tolerance levels as low as 1 rpm
54
Aerospace Physiology ENAE 483/788D - Principles of Space Systems Design
U N I V E R S I T Y O FMARYLAND
References• R. L. DeHart, ed., Fundamentals of Aerospace
Medicine, Second Edition Williams and Wilkins, 1996 • A. E. Nicogossian, C. L. Huntoon, and S. L. Pool, Space
Physiology and Medicine, Third Edition Lea and Febiger, 1994
• A. E. Nicogossian, S. R. Mohler, O. G. Gazenko, and A. I. Grigoriev, eds., Space Biology and Medicine (Volume III, Book 1: Humans in Spaceflight) American Institute of Aeronautics and Astronautics, 1996
• J. T. Joiner, ed., NOAA Diving Manual: Diving for Science and Technology, Fourth Edition Best Publishing, 2001