Biological Safety Levels: BSL-1, BSL-2, BSL-3, BSL-4

Posted: January 31, 2019

Categories: Cleanrooms

What is BSL?

Biological Safety Level (BSL) is a biocontainment designation system with requirements intended to protect personnel from potentially harmful pathogenic exposure in a research or manufacturing environment.

What are the differences among the BSL designations?

The Centers for Disease Control (CDC) specifies four broad Biological Safety Levels, each of which corresponds to a level of exposure danger and a set of design features and operational protocol. Each increasing level builds on the previous level(s):

BSL-1: Required in the presence of microbes that do not consistently cause disease, such as E. coli. Work can be done on an open bench, and minimal Personnel Protective Equipment (PPE) is required. Doors separate the BSL-1 lab from the rest of the facility.
BSL-2: Required in the presence of moderately hazardous microbes, such as Staphylococcus aureus. The lab is restricted behind self-closing doors. Personnel wear minimal PPE plus face shields; many operations are performed within biological safety cabinets (BSCs – see explanation below). Negative-pressure containment is generally advised, and exhausted air may require filtration.

BSL-3: Required in the presence of potentially lethal, often “exotic” airborne microbes, such as tuberculosis. The lab is restricted behind two sets of doors. Workers may require immunizations, and PPE plus respirators are advised. All work is performed within a BSC. Filtered room air must be exhausted.
BSL-4: Required in the presence of high risk of airborne transmission; infections are frequently fatal, as from Ebola. Decontaminate all material before exiting lab; shower after exiting. Full body, positive-pressure cleanroom suit. All work performed in Class III BSC. Lab is in a separate building.

All BSL facilities require that personnel follow “standard microbial practices”: no food or drink; no cosmetics; hands and gloves are frequently washed and surfaces routinely decontaminated. Sterilization and entry/exit protocol vary by BSL level.

How do BSL designations correlate to cleanroom levels (e.g, ISO 5 or ISO 6)?

There is no necessary correlation between a BSL and an ISO cleanliness level since they correspond to two different sets of concerns: protection of personnel and the environment from biological exposure vs. protection of a sensitive sample from contaminant exposure.

Any BSL environment can require any ISO cleanliness standard, depending on the sensitivity of the process to airborne particulates (including aerosols and germs). BSL applications that involve storage or handling of packaged pathogens may tolerate a relatively “dirty” environment, such as ISO 8, whereas processing unpackaged pathogens susceptible to contamination by airborne particles might require an ISO 5 environment.

As a practical concern, the most challenging applications involve hazardous microbes (BSL-2 or higher) that are also highly sensitive to particulate contamination (requiring ISO 5 or cleaner). These situations require a high volume of micro-filtered air passing through the enclosure to guarantee cleanliness, and therefore also a high volume of exhausted air to ensure negative-pressure containment. Such systems typically incorporate high-capacity exhaust fans and ductwork, often with system redundancy, and sophisticated airflow monitoring systems.

Can Terra Provide a BSL Cleanroom?

Yes, but it depends on your specific application. Modular cleanrooms are rarely appropriate for BSL-3 and BSL-4 applications, which typically require sophisticated facility integration involving air handling systems and environmental monitoring equipment.

Terra provides BSL-2 modular cleanrooms, but how a given BSL specification affects cleanroom design and construction is not always clear. Some operations that fall under BSL-2 may require single-pass air that is filtered before being exhausted to the outside; others may allow recirculation of air and release of unfiltered exhaust air.

For this reason, Terra requests that any BSL application receive careful review by the appropriate process validation expert, who can translate the process and BSL requirement into specific environmental design specifications involving ISO cleanliness level, pressure levels, air change rates, air circulation, and exhaust air treatment, among other factors.

Once these issues are clear, Terra can propose the most economical way to address your BSL application.

See our Modular Cleanroom here.