Autoclaves for BSL-3 Facilities—Part 1: The Bio-Seal

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Written by: Scott Mechler

BS Mechanical Engineering, Mechanical Engineer

This is the first of three articles 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. In this article we explore the importance of the bio-seal, a feature that must be incorporated into a BSL-3 autoclave to ensure hazardous microbes like yellow fever and West Nile virus don’t pass between contained and non-contained rooms. Links to our second and third article can be found here:

Laboratories that work with microorganisms are given a “Biosafety Level” (BSL) designation. This is done in an effort to protect laboratory personnel, as well as the surrounding environment and community. Biosafety levels range from BSL-1 (least hazardous) to BSL-4 (most hazardous/dangerous). Read more about the difference in BSL levels here.

Most standard steam sterilizers (autoclaves) are suitable for use in BSL-1 and BSL-2 labs. BSL-3 and BSL-4 facilities, however, require autoclaves that possess additional features to a standard autoclave design. This article will focus on BSL-3 facilities only as BSL-4 is far less common and adds a lot more complexity to the discussion.

Let’s begin with the BSL-3 lab space. Perhaps the most important characteristic of a BSL-3 laboratory is that all bacteria and pathogens must be contained within the lab; hence, the name biocontainment lab. In other words, microbes must not escape from the room. This is accomplished by incorporating the following design features into the space and surrounding areas:

  • Separation:
    • Physical separation from access corridors
    • Self-closing, double-door access
  • Containment:
    • Exhausted air, not recirculated
    • Negative airflow into laboratory
  • Decontamination

These same design features for a BSL-3 room are applied to an autoclave utilized within that space. Most BSL-3 autoclaves have two doors where the flow of goods “pass through” the autoclave – from the contained room out to the non-contained room. The autoclave is installed in the wall-opening that separates the two rooms and must be sealed appropriately in the wall to prevent microbes from passing between the contained and non-contained rooms (double door, thru wall systems).

The Bio-Seal

To ensure the BSL-3 lab is contained, BSL-3 autoclaves are equipped with a biological sealing flange or bio-seal. A bio-seal provides separation and a positive seal between the hazardous side and safe side, which is imperative for the safety of personnel.

Top View of BSL-3 Autoclave situated into the wall opening



The bio-seal is comprised of a steel or stainless steel plate that is continuously welded to all four sides of the sterilizer. It extends out beyond the frame of the sterilizer to which the installer then attaches the barrier – a durable silicone gasket. The gasket extends between the barrier flange and the wall and is secured in place by stiffening bars to ensure a leak-tight fit. All penetrations through the barrier flange (for either wiring or plumbing) are fully potted to prevent air leaks.

Testing the Bio-Seal

By design, the biocontainment lab is under lower or negative air pressure relative to the hallway or adjacent lab. Proper testing of the bio-seal assembly is required to ensure the integrity of the seal and prevent biological contamination in the non-contained room. Testing should be performed by trained personnel who are proficient with the equipment and familiar with the appropriate testing standards. Further testing should be performed by an independent third party.

Here are a few testing guidelines:

  1. Test the bio-seal using the industry standard bulk smoke leak test. Smoke generated for this test has a particulate size no larger than 0.2 microns.
  2. For the duration of the test, the BSL-3 room should be maintained at a negative pressure differential of at least 0.002 PSIG. (Facility safety procedures may require an even deeper negative pressure during testing.)
  3. The seal is considered secure upon no visible penetration of smoke through the bioseal or by leakage standards established by the facility’s specifications, whichever is more restrictive.

Stay tuned for our next article on BSL-3 autoclaves where we will address other important design features. For more information on BSL-3 autoclaves please contact Consolidated Sterilizer Systems.

17 Questions to Ask Before Buying Your Next Autoclave

17 Questions to Ask Before Buying Your Next Autoclave

With so many models, sizes, options and components to choose from, how can you ever really know exactly what you need to make the most out of your investment?

These questions will help you to make informed decisions by outlining what is most important to consider and know about owning an autoclave.