Autoclaves for BSL-3 Facilities—Part 3: Effluent Decontamination Systems

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Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

This is the final article of a three-part series describing BSL-3 autoclaves, also commonly known as biocontainment sterilizers. These types of sterilizers are essential in handling microbes that can lead to serious or potentially lethal disease through inhalation. Links to our first and second article can be found here:

Our final article here examines effluent decontamination systems or ensuring that effluent (air, steam, and condensate) leaving the autoclave is free of harmful microbes. While this seems obvious, a study conducted by Tufts University Medical School demonstrated that a variety of autoclaves expel bacteria through the chamber drain during the preconditioning (purge) phase of the sterilizer cycle.

To clarify this phenomenon, consider the following steps of a typical sterilization process:

  1. The user loads the sterilizer with contaminated goods.
  2. The door is closed and a cycle is initiated through the autoclave’s control system.
  3. The air is purged from the chamber either by vacuum or by steam pressure.
  4. This air/steam effluent is discharged through the chamber’s drain port and into the floor drain throughout the entire cycle.

The potential for contamination arises in steps 3 and 4. As air is purged from the chamber, microbes may become aerosolized and discharge into the floor drain and surrounding environment. Effluent that flows through the chamber drain during the initial part of the cycle has not yet been fully exposed to the proper combination of time and temperature required to destroy microbes to the proper lethality of sterilization (i.e. log6 kill).

BSL-3 facilities work with microbes that may pose serious health risks, therefore, it is recommended the sterilizer effluent be contained, filtered, or decontaminated prior to exhausting into the environment. Verify with the facility’s safety officer to determine the effluent decontamination requirements for your lab.

Examples of Effluent Decontamination Systems

There are three acceptable methods for decontaminating the effluent from an autoclave.

Internal HEPA Filter

This method utilizes a 0.2-micron, ultra high-efficiency HEPA filter located within the autoclave chamber. The filter retains any bacteria that may become aerosolized from the contaminated goods within the chamber. The key aspect of this design is the placement of the filter (i.e. within the chamber as opposed to outside the chamber). This is significant because the steam that sterilizes the products within the chamber also sterilizes the filter (and the bacteria captured by the filter membrane) thereby making it safe to handle and replace without the need of a service technician.

External HEPA Filter

This technique utilizes a 0.2-micron HEPA filter mounted outside the autoclave chamber to purify the effluent discharging from the autoclave. This system directs the effluent through an orifice typically located in the top of the chamber. It then travels through the external filter before going to drain. The filter is encased in a housing that is heated by steam during the exposure phase thereby sterilizing the retained filter. A separate (or additional) temperature control system is used to control the temperature in the filter housing. With this method, it is imperative that condensate within the chamber does not drain until the end of the cycle thus ensuring its sterility. The filter should be monitored and replaced frequently and usually requires a service technician to do so.

External Decontamination Chamber

In this method, effluent is discharged to an external decontamination tank (or “kill tank”) where steam is added to destroy the bacteria. The tank must be large enough to ensure proper mixing and sufficient time for complete kill. It employs a separate (or additional) temperature control system in order to maintain the proper minimum temperature. Although this method is the most complex and costly it does allow the facility to capture effluent from multiple autoclaves and sources (e.g. washers, sinks, etc.).

BSL-3 steam sterilizers are designed with special components that allow researchers to safely handle potentially lethal microbes. Features such as bioseals, door-interlocks, and effluent decontamination systems are all necessary for maintaining a barrier between dirty (contained) and clean (non-contained) sides of the laboratory. In addition to the aforementioned sterilizer features, a BSL-3 facility should have clearly defined standard operating procedures (SOPs) and validation guidelines.

Stay tuned for future blog posts on validation. For more information on BSL-3 autoclaves please contact Consolidated Sterilizer Systems.

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