To
-., I 85 29549
' INTERNALCONTAMINATION
! IN THE
.L| SPACE STATION
i' February 1984
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Prepared for:{
I NASA HeadquartersSpace StationTask ForceHuman ProductlvltyWorking Group
_-12_
1985021227-225
https://ntrs.nasa.gov/search.jsp?R=19850021237 2020-05-17T13:26:35+00:00Z
INTRODUCTION
This paper discussesatmospheretrace contaminantcontrol systems used in the
" past (LunarModule and Skylab) and present (nuclearsubmarinesand Shuttle),
a_d makes recommendationsfnr the futureSpace Station contaminantcontrol
system. The _reventionand control methods used are judiciousmaterial
selection,detection,and specific removalequipment. Sources and effectsof
contaminationrelating to crew and equipmentare also discussed.
• EFFECTSOF TRACE CONTAMINANTS
m
r Trace contaminantscan affect the crew, equipmentand experiments.D
EffectsOn The Crew
The compoundsfound in the trace contaminantscan be divided into categories
based on their major toxic effects. These categories,with examples
are(1)•
I. Irritants: aldehydes,ketones and esters.
2, Asphyxiants: carbonmonoxide,carbon dioxide*,fluorinatedhydrocarbons*
and methane*.
3. CentralNervous SystemDepressants: a11phatichydrocarbonsand alcohols.
4. SystemicPoisons: chlorina_d hydrocarbonsand aromatic hydrocarbons.
*Displaces oxygen at high concentrations
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An indicationof the toxic risk from a given atmosphericcontaminantis the
ratio of its concentration(C) to its SMAC (SpacecraftMaximum Allowable
Concentration)value. The relative toxic hazard index (RTHI)value of
compoundX would be expressedas Cx/SMACx. Any atmosphericcontaminantthat exceeds its SMAC value (RTHI> l) would be consideredto be at an
unacceptablyhigh level.
To some extent, multiple atmosphericcontaminantsthat are in the same
toxicologicalcategory exert an additive effect. The sum of all RTHI values
in one toxicologicalcategory of an atmosphericsample can be referred to as
the total relativetoxic hazard index (TRTHI). It may be expressed
c mathematicallyas follows:w
TRTHI = CI/SMACl + C2/SMAC2 + C3/SMAC3 + Cn/SMACn
Cx : concentrationof chemical
SMACx = SMAC value of chemical
The level of toxicitycan be subjectivelygraduatedfrom nuisance valve, to
reduced productivity,to health hazard, to life threatening.
Contaminationmay affect the drinkingwater supply, food storage and
preparationequipmentand air circulationequipment.
An additionalhazardof some contaminantsis their property as fuel for
propagatiorof fire and explosion. Examples are H2, CO, and CH4.
EffectsJn [quipment
Monomolecularlayerson microchipscan affect the conductivityof electrical
paths and capacitanceof elements. Surface degradationand adverse corrosion
can occur as well as clogging of microporousmembranes,filters and
operations. Optical surfacesare particularlyvulnerable.
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Effects on Experiments
Cross contaminationcan occur in biological experimentswhich can affect
i growth and fatality rates,thereby coloring conclusionsreferringto cause andeffect. Non-biologicalexperimentscan also be influencedby contaminat,on.
Crystal growth, plating, flow reduction,and assembly can be affected.
SOURCESOF CONTAMINATION
Contaminantshave been found to be generatedby the crew vehicle equipment,
experiments,operations,food and human waste disposal,cleaning fluids, and
repairs.
Crew
Principalsourcesof contaminantsfrom man are expired air, urine, feces,
flatus,perspiration,vomltus and saliva (sneezing). Major contaminants
generatedby metabolicprocessesof the crew are: CO2, NH3, CO, H2S,
H2, CH4, organic acids and mercaptans. In addition,bacteria,virus,
fungus, skin particlesand hair and nail clippingswill occur.(2)'(3)
Equipment
Compoundsgeneratedby equipmentgenerallyhave relativelyhigh vapor pressure
and are outgassedfrom solid materialsand lubrica)its.Although NASA has done
an outstandingJob eliminatingmost of these contaminantsin NASA owned
equipment,experimentersand developersof manufacturingprocessesmay not be
able to conform to the guidelinespresentedin NHB 8060.1B,"Flammability,
Odor, and Offgasslng Requirements&nd Test Proceduresfor Materials in
Environmentsthat SupportCombustion,"SeptemberIg81.(4)
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Experimentsand Crew Activities
Experimentscan release inorganic,organic, viral and bacteriological
contaminants.
Contaminantswill probably be released during food preparation,food anJ human
waste disposal,and crew clean3ing.
Accidents,Fire, Explosion,and Spillage
• In addition to contaminantspresent during normal operations,one must_J,_,I considerthe toxic atmospheresresultingfrom such upset conditionsas fire or
. equipmentfai!ure,as well as the products of therm"1 decompositiondue to
overheatingof electricaland hydraulicequipment. Carbon monoxide and
L- aldehydesare frequentbreakdownproducts in equipmentfires. Thermal
. degradationof plastics will yi_.Idmonomers and large chain fragmentssuch as
- methyl alcohol, hydrochloricand hydrofluoricacids, and hydrogen
cyanide.(5)
Accidentsmay occur during servicingof satellites,leading to an EVA'I
astronaut'sexposure to rocketfuels and oxidizers. These contaminantsmay
then be brought into the stationon EMU clothing or tools.
PAST CONTAMINANTCONTROL
: Lunar ModuleL
The lunar module contaminantcontrol systemconsistedof particulatefilters
and activatedcarbon, for odo_ control, both packaged in the LiOH cartridges
used to control CO2. The pressure suits worn by the crew also aidedcontaminantcontrol.
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]98502]227-229
Langley (MDAC)90-Da_ Manned Test - 1970
Objectivesof the 90-day operationalmanned test involved the evaluationof an
advanced regenerativelife support system similar to that of an orbiting
scientificlaboratoryunder closed-doorconditions. These objectives included
determinationof long-termoperatingcharacteristicsand power requirementsof
individua_subsystemsand the total system;measurementof mass and thermal
balances;determinationof the ability of the test crew to operate, maintain,
and repair onboard equipment;m_asurementof chemical and microbial
equilibriumof the closed life support system;assessment of the effect of
_ confinementon the psychologicaland physiologicalcharacteristicsof the test
. crew; and collectionof data to assist in determiningthe role of man in
performingin-flightexperiments.(6)
LThis test operated with no materials passed into or out of the test chamber.
" The compositionof the atmosphereduring the manned operationwas determined
on a continuousbasis and by individualsamples taken at frequent intervals.
Analysis was done by chromatographon direct samples. Concentratedsamples
were also obtained by freeze-outtechniquesand sent through the gas
chromatographto determinethe presence of organiccompounds. Inorganic
compoundswere measured by wet chemical analysison samples taken daily.(7)
Contaminantswere controlledduring the gO-daytest by employinga 1.5 cfm
toxin burner (i_tegratedwith a Sabatier reactor for therma_ efficiency),
along with part1:uletefilters, solid amine CO2 control, molecular sieve
CO2 control and a condensingheat exchanger. The cabin air was almost free
of contaminantsduring the unmanned and manned periods preceding the 90-day
test. During the gO-day test there were no inorganiccompounds noted. There
were no NOx compoundsuntil NH3 reached0.5 ppm. The NOx disappeared
when the toxin burner was shut down, indicatingNOx was formed from NH3 inthe toxin burner.
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]98502]227-230
Analysis of the CO2 just upstream of the Sabatier reactor showed the
presenceof Freon ll3. The average detected concentrationof Freon ll3 varied
from 9.0 ppm, when the solid a_,ineunit was operating,to 33.8 ppm, when the
molecularsieve unit was operating.Acetone and ethyl alcoholwere also
detected in the CO2 at low concentrations. These results indicate that the
CO2 scrubberswere able to remove some of the trace contaminants.
Skylab
The Skylabenvironmentalcontrol system had considerablecapabilityto scrub
the cabin air of generatedcontaminants. Principalelements of the system
were the charcoal canistersin the molecularsieve unit and waste management
systems,the condensingheat exchangers,and the Linde 13X and 5A molecular
sieve material.
_" The molecular sieve and charcoal canistersperformedtheir design function of
" removingodors, as well as removingcontaminants. The only means availableto
evaluatethe performanceof the odor removal system was via crew comments,but
all three crews indicatedthat the system performedvery well.
Ground tests in which air laden with various concentrationsof trace
contaminantswas passed throughspecial test bed molecularsieves, qual unit
molecularsievesand a Gemini condensingheat exchangerindicatedthat
molecularsieve material had I00% removal efficiencyfor all contaminants
testedwith the exceptionof H2 and CO as shown in Table I. No removal
capabilitywas noted for these two gases. The condensingheat exchangerhad
some capabilityfor contaminantremoval,especiallyfor Coolanol 15.
: 2-135
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]98502]227-23]
TABLE 1
SKYLABCONDENSINGHEAT EXCHANGERAND
MOLE-SIEVECONTAMINANTREMOVAL EFFICIENCY
Removal Efficiency,
Test Inlet Percent
Concentration,
Contaminant ppm CHX Mole-Sieve
-i__I I. Hydrogen 900 (I) 0
2. Ammonia 60 (1) lO0
3. Methyl Chloride 20 (1) lO0
4. Freon 12 500 (1) I00
5. Benzene 5 8.7 lO0
6. Freon If3 500 (1) lO0
• 7. Xylene 50 (1) 100
" 8. Toluene 50 (1) 100
g Acetone 500 (1) 1O0
10. Isopropyl Alcohol 100 (1) 100
1I. Acetaldehyde 50 2.6 I00
12. Methyl IsobutylKetone I0 33 I00
13. Dlchloromethane Z5 (I) I00
14. Carbon Monoxide 75 (I) 0
15. Methyl Chlorofo_ 90 15.2 100
lb. Methyl Ethyl Ketone I00 I.I I00
17. Coolanol 15 5C 89 lO0
(I) Not tested.
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i 98502i227-232
PRESENT CONTAHINANTCONTROL
Shuttle and Spacelab
The Shuttle and Spacelab trace contaminantcontrol systemseach include
activatedLiOH canisters,a condensing heat exchangerand a carbon monoxide
oxidizer.
Four atmosphericsamples were collectedat approximately12-hour intervalsin
the orbiter crew cabin during the 56-hour STS-I mission on April 12-14,
1981.(8) Post-missiongas chromatographic/massspectrometeranalysis showed
57 differentchemical contaminants;38 were structurallyidentified. The
total quantity of gases in each toxicologicalcategorywas below the SMAC
value of any one of its constituents. The only categoriesof gases that
approachedthe SMAC value for any one gas in their category were the systemic
poisons and asphyxiants. However, in both cases, these valueswere below the
concentrationof gases with the lowest SMAC value. The catalytic oxidizer forJ
CO controlwas not presenton the STS-I mission. +
Submarines
In view of the convergenceof the requirementsfor spacecraft and submarine
l_fe support systemsa t_udy, jointly funded by the Navy NAVSEC and NASA was
preparedby Hamilton Standard in 1974(9).
In this study, for submarines,activatedcarbon was selected to control trace
contaminants,as well as odors, hydrocarbonsand "Freon"spills. On present
submarines,aerosols are controlledwith strategicallyplaced filters and
electrostaticprecipitators. A Hopcalitecatalyst operated at hig_
temperatureis now used to control CH4, H2 and CO.
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1985021227-233
Detectionof trace contaminantson submarinesis accomplishedby a
Perkin-ElmerCentral AtmosphereMonitoring System (CAMS)which uses a mass
spectrometerto monitor all trace contaminantsexcept CO. An infrared
analyzermonitors CO.
SPACE STATION
Contaminantsexpected in the Space Station can be divided _nto the following
main categories:
- Those present duringnormal operation
Contaminantsgeneratedby the crew and equipment
+ Contaminantsgeneratedby experimentsand manufacturing
- Contaminantsgeneratedby fire and explosion
As demonstratedby previous Skylab flightsand STS-I, the combinationof
prevention (selectionof materials),proper waste handling,and minimal
removalequipmentresulted in odor-free flighton Skylab and no contaminant
reaching its SMAC value on STS-I.
However, It is expected that the de,Ire to open the station to a broad user
colaunltywlll necessltatesome relaxationof NHB 8060.IB. Therefore,higher
levels of particulateand gaseous contaminantswlll be generated,requiring
control equipmentwhlL_,is more sophisticatedand has larger throughputthan
that used on SIKylaband Shuttle.
In addition,the cabln volumeand crew size w111 increase In proportionto the
space statlon size whlle cabin alr leakagecan be expected to decllne,
partlcularlyfor non or low EVA actlvlty misslons.
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'I98502"I 227-234
As a result, the need to control low molecularweight contaminants,
particularlyCH4, will require a high temperature(600°F)catalyst.
Tne high temperaturecatalyticoxid zer developedby Hamilton Standard is
relativelyinsensitiveto the norma_ humidity levels found in the
environment. Additionalbase sorbent beds such as LiCO3 should be placed
upstream o, the catalyst bed to protect it from acid gases such as SO2,
H2S and HCf. A base sorbent bed should be placed downstreamof the high
temperaturecatalyst to stop acid gases which may be produced in that catalyst
bed, such as HCl and HF.
_ As noted earlier, the condensingheat exchangercan be used to control some of
_ the trace contaminants,such as a_nonia, methyl isobutyl ketone, methyl
chloroformand benzene which have been demonstratedin laboratorytests to be
removed in the condensatewater, thiswater must then be filtered to remove
these contaminantsif it is to be r=.used.
Particulatesand aerosols can be controlled using absolute filters placed
upstreamof the fan and a condenslnfh_at exchangerto remove particles
L greater than 0.3 microns includingoacteria. The absolute filter prevents
growth in the activatedcarbon and condensing heat exchanger. Debris traps
shouldbe placed upstreamof the absolute filters to stop coarse particles
(wetand dry) which make up the bulk of the particulatematter and may quickly
clog the absolute filter.
Post-FireAtmosphereCleanup
In the event of a fire within the space station,the routine proceduresfor
controllingand (xtinguisningthe blaze should includeshutting down the
environmentalcontrol equipmentin or serving the affected section. This
action helps to lower the oxygen concentrationin the area of the fire and
restrictsthe distributionof the combustionproducts in the atmosphereto a
local area around the fire site.
t
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i98502i227-235
Once the fire is extinguished,the local atmospheremust be cleaned to remove
suspendedparticulatematerialsand objectionableor toxic gases generatedby
the combustionbefore the ECLSS is returned to duty in order to prevent
spreadingthe fire-generatedcontaminantsto other parts of the station.
Portableoxygen systems or other self-containedbreathingapparatus should be
includedin the on-board emerg,,ncyequipment.
One method of cleaning the fire-contaminatedatmospherewould be to dump it by
depressurizingthe affected section. Depressurizationinvolves added risk
such as the bends if the crew had no other area in which to seek protection.
. _ In addition,depressurizat_onof a large sectionof the space stationwill
requirethe replacementof the N2 and 02 required. For example, a 5000- 6
ft3 sectionwill contain 300 Ibs of N2 at standardconditions. In
addition,there is a possibilitjof contaminatingexperimentsor sensors
outside the pressurizedvolume.
A portable post-fireair purificationunit proposedby Hamilton Standard for
use in U.S. Navy ships can provide the requiredcleanup capabilitywithout any
interfacewith the ECLSS. The unit is entirely self-containedand requires
only a sourceof electric power to operate its fan. It can reduce the level
of carbonmonoxide in a 5000 cubic foot enclosed volume from a fatal one-hour
exposurelevel of 5000 parts per million to a safe one-hour inhalationlevel
of less than 500 parts per million in about 20 minutes.
To clean up a contalnated ccapartjaent,the un(t need only be allowed to run
unattendedwithin the closed volu_ until contaminantlevels are sufficiently
reducedas indicatedby the ECLSS Monitor and Control sensors in the
compartmentor until visual and olfactoryobservationsindicate the removal of
smoke and odors.
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1985021227-236
f.u
v
SUI_ARY
Skylab and Shuttle results have indicatedthat the combinationof materials
selection,onboard removaldevices, and preflightoffgassing tests can be an
effectivemeans of controllingspacecraftcontaminantlevels.
The followingare recommendationsfor atmosphericcontaminationcontrol on
Space Station:
I. The maximum allowablelevels of contaminantsshould be establishedby
_ NASA.
) Z. An effectivematerialsscreeningprogram should be carried out to
eliminatematerialswith offgassingcharacteristicsabove established
criteria; i.e., NASA shouldproduce a list of acceptablematerials.
3. Contaminantsshould be selectivelymonitoredusing a CAMS or similar
unit.
4. A _mple,standardprocedureshould be developedto test the
flammabllityand outgassingof flight payloads and experiments.
Standard cabinets shouldbe considered,especiallydesigns which
accommodatespecial sorbent beds and interfacewith the catalytic
oxidizer so that unique contaminantscan be efficientlycontrolled.
Table 2 defines the elements of a contaminantcontrol system envisionedfor a
Space Station. Additionalequipmentor designed-ln,controlledcabin leakage
may later be required.
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TABLE 2
TYPICAL SS CONTAMINANTCONTROL SYSTEM
ITEM TO CONTROL
Absolute Filters Particulates,Bacteria and Aerosols
CondensingHeat Exchanger Humidity Control (Moisture)and Water
c Soluble Compounds
t
; CO2 Removal Hardware Carbon Dioxide Leve;
ActivatedCharcoal High MolecularWeight Hydrocarbonsand
(Treatedand Untreated) Mwmw)nia
High TemperatureCatalytic Cabin Monoxide,Hydrogen and Low
Oxidizer with Pre- and Post- MolecularWeight Hydrocarbons;
Filters acid gases and productsof oxidation
_ 2-I_2;, |
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]98502]227-238
4
REFERENCES
I. "ToxicologicalAssessmentof the STS-I 56-Hour Outgassin9Samples,"S.L.
Pool, M. E. Coleman, 6-26-81, SD/Chief,Medical Sciences Oivision,Johnson
Space Center, NASA.
2. "A Detailed Study of ContaminantsProduced by Man in a Space Cabin
Simulatorat 760 mm Hg." J. P. Conkle Mar 1967, SAM TR-67-16,USAF School
of AerospaceMedicine,_erospaceMedical Division AFSC, 6roo,_sAir Force
Base, Texas.i
s
: 3. "BioastronauticsData Book," 2nd ed, NAF, SP 3006, 1973.
4. "Flammability,Odor and OffgassingRequirementsand Test Proceduresfor
Materials in Environmentsthat Support Combustion,"NHB 8060.IB, Sep 1981.
5. "Compendiumof Human Responsesto the AerospaceEnvironment,"Vol Ill Sec
: 13, NASc CR-1205 Nov 1968.
6. "PreliminaryResults from an Operational90-Day Manned Test of a
" RegenerativeLife Support System," Nov 17, 1970, NASA SP-26], Langley
ResearchCenter, NASA.
7. "Test Report - Test Results - OperationalNinety-DayManned Test of a
RegenerativeLife Supp(JrtSystem," NASA CR-I11881,MDC G2282, Langley
ResearchCenter, May 1971.
8. "SkylabAbaosphereContaminationControl,"NASA TM k-64900, M_rshall
Spacef,ightCenter,NASA.
9. AdvancedLife SupportApplicationStudy - Design Notebook N00024-74-C-5422
for Naval Sea SystemsCommand, HSD No. SVHSER 6536.
_ 2-143
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]98502]227-239
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