Decontamination is a broadly used term that describes a number of techniques or strategies for reducing or eliminating the presence of hazardous microorganisms and biological toxins from various surfaces, materials and equipment. Decontamination is important from a safety perspective as well as preventing cross contamination and maintaining the integrity of the work.
Critical elements involved in the process include choice of decontaminant, site conditioning, biological indicator choice and monitoring for gas or vapor. Chemicals frequently used in the decontamination process include: chlorine dioxide gas, 70% ethanol, gaseous paraformaldehyde/formaldehyde, liquid sodium hypochlorite/bleach, and hydrogen peroxide vapor.
When selecting a decontaminating agent a number of factors have to be considered to include the susceptibility of the organism to the decontaminating agent; contact time, temperature and relative humidity required; stability of the decontaminating agent; and the physical characteristics, material compatibility and surface properties of what is being decontaminated. Decontaminating agents are typically harsh and can damage or leave a residue on gloves, stainless steel, electronics and other materials inside the BSC.
Site preparation is a requirement regardless of which decontaminating agent is being used. It entails pre-cleaning the interior of the BSC to remove bioburdens and other compounds that may interfere with decontamination such as protein, organic matter, salts, absorptive materials, and liquids and solid wastes to be autoclaved. In the case of gaseous decontamination, the Class III BSC and its filter housings must be capable of being sealed to prevent the leakage of gas into inhabited spaces resulting in personnel exposure, and to prevent dilution of the concentration required for microbial killing. Supply and exhaust vents, drain traps or dunk tanks, and any penetrations must be air tight and sealed. All areas requiring decontamination should be accessible for gas penetration, and a fan(s) may be required to disseminate the gas.
Different biological indicators may be used for different gas decontaminants, and optimally contain the equivalent of 106 organisms per BI to measure the effectiveness of the process. Indicators should be distributed throughout the enclosure to be decontaminated with attention to stratification across height and areas that may be more difficult for gas or vapor to reach. Users of BI’s should follow manufacturer instructions regarding incubation parameters and the type of decontamination systems for which they have been validated. BI’s are not used when decontamination is by bleach or 70% ethanol wipe down. In this case, successful decontamination can be confirmed by performing swab sampling throughout the area decontaminated and monitoring those swabs for growth of organisms.
If BSC are to be decontaminated using gas or vapor, the room should be monitored for leaks of the decontaminant. Dräger tubes, automated Dräger technology, Calibrated Miran SapphIRe 205B, or other equivalent systems are commonly used for monitoring leakage and the presence of monitor for chlorine, hydrogen peroxide, formaldehyde, and ammonia gases during and after decontamination. The sensitivity of different technologies and models vary. It is important that the monitoring system is sensitive and has adequate specificity so it can reliably and reproducibly measure concentrations below the OSHA permissible exposure level (PEL) with 95% confidence.
References:
Favero, M. S. and Bond, W. W. (1991). Chemical disinfection of medical and surgical materials, in Disinfection, Sterilization, and Preservation, 4th ed. (Ed. Block, S.), Lea & Febiger, Philadelphia, PA, 621.
Environmental Protection Agency (March 2005). Compilation of Available Data on Building Decontamination Alternatives Publication # EPA 600/R05/036.
http://www.epa.gov/NHSRC/pubs/600r05036.pdf
Czarneski, M.A. (2007). Selecting the Right Chemical Agent for Decontamination of Rooms and Chambers. Applied Biosafety, 12(2), 85-92.
Lever, M.S., Howells, J.L., Bennett, A.M., Parks, S. and Broster, M.G. (2008). The Microbiological Validation of a New Containment Level 4 Cabinet Line. Applied Biosafety, 13(2), 98-104.