Share thisAfter reading, “Design Considerationsfor Placement of Autoclaves in BSL and ABSL Containment Facilities” (ALN® Magazine, January/February 2006), I would like to offer my viewpoint on design considerations for the vacuum system, filtration of the sterilizer, and the containment of any hazardous materials within.
For any sterilizer used in a BSL3 or BSL4 application, the issues of safety and containment stems from what occurs during the various phases of the sterilization cycle. For any sterilization cycle, there are two conditions that need to be addressed from a containment standpoint — the air evacuation phase and the steam bleed during the sterilization dwell period. It is during these conditions where potentially harmful pathogens and/or viruses can be emitted to the building drain system and/or the surrounding environment. Therefore, the design of the piping system must incorporate the mechanical features needed in order to provide the necessary containment during these conditions.
In respect to incorporating a steam ejector or a sintered steam filter, neither the steam ejector nor the sintered filter designs will provide 100% guaranteed sterilization of the exhaust stream, containment of hazardous materials, or the protection required for such a critical application. Hazardous materials can exit the sterilizer in the exhaust stream during any air evacuation or steam bleed from the sterilizer chamber. Neither design protects the end users or service personnel from being exposed to any harmful pathogens or viruses that may be present within the drain piping system of the autoclave or in the evacuated air coming from the chamber.
The use of a steam ejector in a BSL-3 or BSL-4 application cannot guarantee that any hazardous material traveling through the ejector will be killed since any pathogens or viruses will be exposed to elevated steam temperatures for only a matter of seconds at best. The industry standard for bio-indicators used to determine sterility for all saturated steam sterilizers is Bacillus Stearothermophilus. This spore was selected since it can withstand steam temperatures of 121°C for more than five minutes. So how will hazardous materials be inactivated if they are exposed to elevated steam temperatures for only a matter of seconds in the ejector design? Inactivation will not be guaranteed 100% in an area where it is required, thus compromising the safety and well-being of the lab personnel using the equipment.
In addition, any contaminated condensate collecting in the autoclave chamber will be sucked out of the chamber during the air evacuation phases of the sterilization cycle since there is not a 0.2 µm hydrophobic HEPA filter employed in the exhaust line of the autoclave to prevent this. The contaminated condensate will simply be discharged to the building drain whether it has been sterilized or not. This is the same principle as to why vacuum is never employed in a liquids cycle on an sterilizer -because of the potential to evacuate the liquid out the glass containers holding the media.