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