Assessment of Gaseous Decontamination Technologies for use on Spacecraft

Transcription

1 Assessment of Gaseous Decontamination Technologies for use on Spacecraft Tom Pottage Health Protection Agency Porton Down UK EBSA 2011

2 Why worry? Exposure of Bacillus spores to space for 2 weeks showed a 1 x 10 6 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: , 2001

3 Existing Spacercraft Decontamination 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 3x10 5 spores, max density of 300 spores/m 2 Levels of contamination must be demonstrated before launch 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

4 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

5 Technology Selection Trade Off Results Technology Small Enclosure Large Enclosure Steris (VHP) Bioquell (HPV) ClorDiSys (ClO 2 ) Formaldehyde Ethylene Oxide Plasma Ozone 57 29

6 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 ClO 2 gas, by passing chlorine gas through sodium hypochlorite cartridges within the generator True gas Continual ClO 2 injection Widely used during anthrax letter clean up

7 General Test Procedure Studies carried out in a environmental chamber (22m 3 ) Temperature controlled at 35 C for H 2 O 2 systems, 25 C for ClO 2 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

8 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

9 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)

10 Biological Results - Steris Survival fraction / N/N o ppm concetration cycle 625ppm concentration cycle ppm concentration cycle Exposure period / Minutes 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

11 Biological Results - Bioquell Organism Injection period D-value 1e+0 1e-1 10 minute injection cycle 7.5 minute injection cycle 5 minute injection period GS 10 min 66.0s 7.5 min 176.5s Survival fraction / N/N 0 1e-2 1e-3 1e-4 1e-5 1e-6 5 min 140.3s BA 10 min 90.7s 7.5 min 152.0s 5 min 97.3s BM 10 min 60.7s 1e Exposure period / minutes BS 10 min 37.5s BT 10 min 132.5s

12 Biological Results - ClorDiSys 1e+0 1e-1 G. stearothermophilus B. atrophaeus Organism Conc D-value GS 1.1mg/l 726.7s Survival fraction / N/N 0 1e-2 1e-3 1e-4 1e-5 BA 1.1mg/l 924.4s BM 1.1mg/l 757.8s BS 1.1mg/l 627.8s 1e-6 BT 1.1mg/l 6.6hrs 1e Ct / (mg/l)s D-value for BT similar to previous work completed by Han et al, Journal of Environmental Health, 2005

13 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, 11 th International Symposium on Materials in Space Environments, Aix-en-Provence, France

14 Residue Analysis Results Analysis Technique Raman Spectroscopy Steris Bioquell ClorDiSys 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

15 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 (ClO 2 ), to the decontamination processes as GS Microcondensation appears to increase the decontamination speed but formed more residues, problems with control Both H 2 O 2 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

16 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/cm 2 ) 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.

17 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

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