Contamination Control by Use of Ethylene Oxide

/ CONTAMINATION CONTROL BY USE OF ETHYLENE OXIDE TECHNOLOGY SUMMARY (Task 12) Contract NASw-2062 National Aeronautics and Space Ad .. t t' minIS ra Ion Planetary Quarantine Office Washington, D. C. 20546 :NASA-CR-126034) CONTAMINATION CONTROL BY JSE OF ETHYLENE OXIDE R.H. Stroud, et al ;Exotech, Inc.) Apr. 1972 42 P CSCL 06" EXOTECH SYSTEMS, INC. 525 School Street, S.W. Washington, D. C. 20024 Roproduced by NATIONAl TECHNICAL INFO~~V,,\ r:c~~ SeRVICE TR72-11 US Deportment of Commerce Springfield VA 22151 FOREWORD This document is a state-of-the-art summary prepared by Exotech Systems Inc. in partial fulfillment of contract NASW-2062, under the cognizance of the NASA Planetary Quarantine office. The initial purpose of the report had been to summarize the technological advances in the application of ethylene oxide, which had been developed under the NASA Planetary Quarantine program. After a review of a preliminary draft, the scope of this paper was expanded to include the technological advances developed for non-space applica tions. This state-of-the-art report should, therefore, be useful in evaluating the potential for new and further uses of ethylene oxide as a decontaminant for Planetary Quarantine related applications. i TABLE OF CONTENTS FOREWORD 0 • • 0 • • • •••0••••0•• i INTRODUCT10N. .••• • 0 • •• 1 I. APPLICATIONS AND LIMITATIONS. •• 2 IT. CHEMICAL AND PHYSICAL PROPERTIES • •• 6 lIT. GERMICIDAL ACTIVITY. •••••.••.. 8 A. INDEPENDENT VARIABLES. • 0 8 1. Sterilant Concentration. .. 0 0 0 •• 8 2 • Exposure Time. .••..••• 0 •• 9 3. Temperature. •.......• 0 • • • 0 12 4. Humidity. .•. 0••••••0••• •• 12 5. Microorganism Age •••.•...• •• 16 B. STERILANT MIXTURES. •• '''. ••••• •• 19 C. PENETRATING ABILITY. •.. • •• 22 D. RELIABILITY •• •••••••••• •• 28 IV. METHODS OF APPLICATION. 0 ••••••• •• 32 SPECIAL HANDLING. •••••• •. ••• •• 32 V. EFFECTS ON PERSONNEL. .••••••.•• 0 33 REFERENCES. •••••• 0" 0•••••••••0• o. 35 ii LIST OF FIGURES Figure 1 B. Subtilis Spores on Cotton, Time and Percent Recovery. •••.• 0 • • • • • • .. 14 LIST OF TABLES Table I Decimal Reduction Values ETO on B. subtilis var 0 niger Spores ••• 0 •• 10 II Decimal Reduction Values ETO on Non-Sporeforming Organisms. •. 11 TIl Sporicidal Effect of ETO on B. subtilis .' .• .. 18 iIV Sporicidal Effect of ETO on B. subtilis 0 Spores at 20 C 0••••••••0••0 .~ • • 0 • 18 V Percent of Kill in Olive Oil and Water. • • • 0 • • 21 VI Decimal Reduction of Spores Dried and Enclosed.. ......... 0 • 0 • • • • 0 • • •• 23 VII Effectiveness of Dry Heat on Spores On and Between Surfaces • 0 ••••••••• 0 • • • •• 26 VIII Effectiveness of ETO on Spores On and Between Surfaces ••• 0 • 0 • • • • • • 0 . .. 27 IX Number of Unsuccessful Trials at Varying "Concentrations cf ETO n '" 0 o. 28 X Number of Unsuccessful Trials for Varying Exposure Times ••• 0 • • 0 0 • 0 0 •• 30 iii INTRODUCTION The requirements for Planetary Quarantine have prompted a review of spacecraft decontaminating agents to evaluate their effectiveness, and the feasibility of their use. Ethylene oxide (ETO) is a highly penetrating and effective decon taminating gas, convenient to use, versatile, and effective at room temperature. It can kill all forms of microorganisms, including resistant soil varieties. The level of its effectiveness depends on such environmental variables as temperature, relative humidity, gas con centration, and duration of exposure. Other factors that affect the lethality are the age, and physical state, of the microorganisms. While the probability of complete sterility through the use of ethylene oxide is less than that obtainable by the use of dry heat, the experimental data reviewed showed that at least a three order of magnitude reduction of the microorganism population could be achieved without difficulty . The incompatibility of the ethylene oxide decontamination process with many materials that may be used on spacecraft is the greatest deterrent to its acceptability in spacecraft contamination control. In the decontamination process, the ethylene oxide and any water vapor that .may be present can alter both chemical and physical properties of . many metals and plastics 0 Prior to any use on spacecraft, therefore, care mustbe exercised in assuring the compatibility of all exposed materials. 1. I APPLICATIONS AND LIMITATIONS e. Ethylene oxide has been known as an effective insjcticidal fumigant since the 1920's. Its bacteriological activity was noted shortly thereafter. The main commercial application of ethylene oxide for sterilizing purposes appears to have been the treatment of spices which were often a source of food spoilage. It has also been used in medical and surgical practices, and in the pharmaceutical industries, to sterilize bedding, bandages, various types of medical instruments, and certain medical and biological preparations, including pinicilin and culture growth media. Ethylene oxide has now been suggested as a possible surface decontaminent to reduce microbial populations on spacecraft (refs. 1 and 2). To date, it has not been used on any planetary flight project. Several factors indicate that great care must be taken to avoid contact between ethylene oxide and certain materials that may be used in spacecraft. The most immediate hazards of ethylene oxide exposure are: (a) Corrosion, caused by humidity, or condensed water, combined with a somewhat elevated temperaiure; (b) Polymerization reactions, caused by catalytic properties of some materials; (c) Chemical reaction with some of the materials used within the chambers (refs. 3, 4, and 5); 2. (d) Parameter drift of some devices (refs 0 6 and 7). Compatibility tests have been conducted on many materials used in spacecraft. In these tests, corrosion of metals, particularly of magnesium, was encountered 0 This was traced to a softening of conformal coating, with subsequent penetration of moisture which caused the corrosion. Polymerization reactions are catalyzed by bases and organic salts. Resulting compounds are of low volatility, and may degrade electrical contacts and thermal control surfaces. Silver and copper can catalyze polymerization of ethylene oxide if moisture is present, and they can cause explosive reactions if acetylene contaminants are present in the ethylene oxide. The compatibility tests included tests on adhesives, coatings, encapsulating compounds, elastomers, reinforced and unreinforced plastics, films and tapes (ref. 4). The tests consisted of exposing the materials to two environments: (a) heat of l500 C for three intervals of 40 hours each, and (b) a combination of 12 percent ethylene oxide and 88 percent Freon 12 for two periods of 24 hours. About 20 to 25 percent of the materials evaluated were considered unacceptable after the heat sterilization. Only two materials (out of approximately 160) were appreciably degraded by ethylene oxide. Adverse long term effects, however, have been associated with ex posure to ethylene oxide, indicating that it had been absorbed and re tained in components (ref. 5). Liquid ethylene oxide is also a solvent 3. of such acrylic plastics as lucite and plexiglass, and will react with plasticizers employed in plastics for binding purposes. Limited testing was also performed at Boeing (refs. 6 and 7) to establish the magnitude of the potential problems arising from ethylene oxide exposure. To accelerate short term results, parts were tested out of their normal-use environment, i.e. , hermetic seals were breached and no protective conformal coating was used. Approximately 250 piece parts, of about 80 different types, were examined. The assortment of parts types included silicon transistors (both npn and pnp small signal and power devices), germanium semi conductors, various types of resistors and capacitors, typical integrated circuitry, and selected relays. All parts were of high reliability quality. The general test technique was to operate the devices in a normal mode, with power supplied for a full 24 hours at 400 C., in an ethylene oxide-Freon-water vapor decontamination gas. Some difficulties were uncovered. The moisture associated with the process affected parameters that included transistor character istics, loss of dielectric strength, minor drifts in capacitors, and similar difficulties. In every case, however, when the parameter drift was encountered, the defective device was repaired by high temperature bakeout. On test, drift was recreated by exposure to nitrogen and water vapor. The paints and labels on .some relays were softened by the ethylene oxide exposure. Although the softening 4. was also reversible, sterilizable parts should not employ paints or varnishes that are soluble in ethylene oxide because of the potential long term degradation previously described. 5. II CHEMICAL AND PHYSICAL PROPERTIES Ethylene oxide is highly penetrating and effective at room temperature (ref. a). It is a colorless gas, liquifies readily at 10.aOc, and freezes at -111. 30C (ref. 9). The liquid is miscible with water as well as with other common organic solvents. It is the simplest cyclic ether or epoxy compound. As little as 3.6 percent of ethylene oxide vapor in air is explosive and will support combustion (ref. 10). Therefore, other gases, such as carbon dioxide or the fluorinated hydrocarbons, which are biologically inert, are added to make a nonflammable mixture. When mixed with 90 percent carbon dioxide, or about the same percent of various fluorinated hydrocarbons, the resulting mixture can in turn be mixed with air in all proportions without passing

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