assessment of gaseous decontamination technologies for … · value for gs, then steris vhp and...
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Assessment of Gaseous Decontamination Technologies for use on Spacecraft
Tom Pottage
Health Protection Agency
Porton Down
UK
EBSA 2011
Why worry?
Exposure of Bacillus spores to space for 2 weeks showed a ≤1 x 106 knock down
in spore numbers, but the survival rate was increased by a factor of 5 with the
inclusion of soiling (meteorites, rock and clay)
Horneck, G. et al. Origins of Life and Evolution of the Biosphere. 31: 527-547, 2001
Biological contamination limits must be achieved on spacecraft and their components prior to
launch – Planetary Protection (PP)
PP categories, I-V, depend on target body of mission
Max values for exposed internal / external surfaces is 3x105 spores, max density of 300 spores/m2
Levels of contamination must be demonstrated before launch
Existing Spacercraft Decontamination
At present the only certified decontamination process
is Dry Heat Microbial Reduction
DHMR >110°C for 30+hrs
Issues with material compatibility raised on the
EXOMARS project
Technology Selection
• A review was carried out on existing gaseous decontamination technologies
• A trade off matrix was produced to choose the most appropriate of these
technologies
• Trade off matrix produced
Scoring Factor Importance Weighting
Material Compatibility High 3
History of Use High 3
Residue Formation High 3
Control Medium 2
Cost Low 1
Technology Selection Trade Off Results
Technology Small Enclosure Large Enclosure
Steris (VHP) 71 71
Bioquell (HPV) 71 70
ClorDiSys (ClO2) 65 64
Formaldehyde 61 51
Ethylene Oxide 54 51
Plasma 65 35
Ozone 57 29
Technologies selected
Steris
• Steris ARD-1000 generator uses Vapour
Hydrogen Peroxide
• ‘Dry’ system – no surface condensation
• Continual VHP injection
• Technology previously used in a previous
study by JPL – MD2000 vacuum chamber
steriliser
Bioquell
• Bioquell RBDS generator uses Hydrogen
Peroxide Vapour
• ‘Wet’ system – surface microcondensation
• HPV injected once
• Widely used especially in hospitals
ClorDiSys
• ClorDiSys Minidox M generator produces ClO2 gas, by passing chlorine gas through
sodium hypochlorite cartridges within the generator
• ‘True gas’
• Continual ClO2 injection
• Widely used during anthrax letter clean up
General Test Procedure
• Studies carried out in a environmental chamber (22m3)
• Temperature controlled at 35°C for H2O2 systems, 25°C for ClO2
• The BIs were kept in a sealed box until the correct concentration of decontaminant was achieved and the BIs were then exposed
• BIs removed and placed in PBS at chosen time points (in triplicate) by operator using gauntlets
Biological Testing
Two commercially available indicators were chosen after initial assessment:
- Geobacillus stearothermophilus (GS, Steris) and Bacillus atrophaeus (BA,
SGM Biotech)
Three Naturally Occurring Organisms were chosen by ESA - Spacecraft
assembly facility isolates:
Bacillus megaterium, Bacillus safensis and Bacillus thuringiensis (BM, BS &
BT)
The commercially available indicators were exposed to triplicate cycles of 3
different decontaminant concentrations
The NOOs were exposed to one cycle
chosen by ESA
Material Testing
• 30 materials Supplied by ESA including
• Adhesives
• Films & Coatings
• Lubricants
• Bulk materials (PCB & Windows)
• Exposed to 3 cycles of chosen concentration on rack
• Repackaged and sent to ESA for testing
Residue analysis
• Silicon wafers - SEMI standard single side polished,
100mm in diameter
• Exposed to 3 decontaminant cycles, vacuum packaged
and sent to RAL for analysis
• Analysis using Raman spectroscopy and Time-of-Flight
secondary ion mass spectrometry (TOF-SIMS)
Biological Results - Steris
Organism Conc. D-value
GS 750ppm 159.8s
625ppm 493.3s
500ppm 585.4s
BA 750ppm 48.4s
625ppm 76.9s
500ppm 92.7s
BM 750ppm 45.8s
BS 750ppm 68.6s
BT 750ppm 175.4s
D-value is the amount of time it takes to achieve a one log reduction at a given
temperature
Exposure period / Minutes
0 20 40 60 80
Su
rviv
al fr
acti
on
/ N
/No
10-7
10-6
10-5
10-4
10-3
10-2
10-1
100
750ppm concetration cycle
625ppm concentration cycle
500ppm concentration cycle
Biological Results - Bioquell
Organism Injection
period
D-value
GS 10 min 66.0s
7.5 min 176.5s
5 min 140.3s
BA 10 min 90.7s
7.5 min 152.0s
5 min 97.3s
BM 10 min 60.7s
BS 10 min 37.5s
BT 10 min 132.5s Exposure period / minutes
0 20 40 60 80
Su
rviv
al
fracti
on
/ N
/N0
1e-7
1e-6
1e-5
1e-4
1e-3
1e-2
1e-1
1e+0
10 minute injection cycle
7.5 minute injection cycle
5 minute injection period
Biological Results - ClorDiSys
Organism Conc D-value
GS 1.1mg/l 726.7s
BA 1.1mg/l 924.4s
BM 1.1mg/l 757.8s
BS 1.1mg/l 627.8s
BT 1.1mg/l 6.6hrs
Ct / (mg/l)s
0 20 40 60 80
Su
rviv
al
fra
cti
on
/ N
/N0
1e-7
1e-6
1e-5
1e-4
1e-3
1e-2
1e-1
1e+0
G. stearothermophilus
B. atrophaeus
D-value for BT similar to previous work completed by Han et al, Journal of
Environmental Health, 2005
Material Testing Results
• No significant changes in material properties identified for
all hydrogen peroxide decontamination processes
• Chlorine dioxide sterilisation resulted in observable
degradation:
– Germanium coating of Kapton/Ge film
– Bulk adhesives CV 1152, CV 1142, Solithane 113
– Bleaching of Alodine 1200 coating
Rohr et al, 2009, 11th International Symposium on Materials in Space Environments, Aix-en-Provence,
France
Residue Analysis Results
Analysis
Technique
Steris Bioquell ClorDiSys
Raman
Spectroscopy
No change No change No change
TOF-SIMS
Least contaminated
sample. Contamination
mainly nitrogen
hydrocarbons with
sodium being the main
elemental
contamination
Contaminated with
nitrogen hydrocarbons.
Sodium, Calcium and
magnesium were
elemental contaminants
Most contaminated
sample. High levels of
hypochlorides, sulphates
and nitrogen
hydrocarbons. Chlorine
and sodium were
elemental contaminants
Ellipsometer
measurements*
(silicon oxide
thickness)
~10nm ~6nm ~6nm
* Silicon oxide on unexposed reference wafer was 4nm
Summary of Results
• The Bioquell HPV decontamination technology produced the fastest D-
value for GS, then Steris VHP and ClorDiSys. BT is shown to be as
resistant, if not more (ClO2), to the decontamination processes as GS
• Microcondensation appears to increase the decontamination speed but
formed more residues, problems with control
• Both H2O2 systems showed good material compatibility
• ClorDiSys produced most residues and had material compatibility issues
Steris VHP technology was chosen by the ESA and NASA
for future decontamination
Issues Raised Using BIs
• Is the size and loading of the BIs appropriate to their use? Lower
numbers of organisms are witnessed in the clean rooms of spacecraft
assembly facilities (approx 4 CFU/cm2)
• Indicator organism choice?
• Tighter regulation of the conditions by the generators could lead to more
reproducible results. The Bioquell system did not regulate the humidity
influencing the microcondensation levels, whilst Steris system needed
an external heater, problems with high temperature for ClorDiSys.
Acknowledgements
• European Space Agency, The Netherlands
• Systems, Engineering and Assessments, UK
• Science and Facilities Technology Council, UK
• Bioquell, UK
• Steris, UK
• ClorDiSys, USA
• JPL, US