Animal Transfer Stations Vs. Animal Handling Biological Safety Cabinets

Important Distinctions in Airflow Fundamentals, Designs, Operational Techniques, and Intended Uses

In the vivarium, protecting both personnel and animals must always remain top priority. To ensure their protection, technicians must only handle animals within proper equipment designed specifically for animal handling to avoid cross-contamination. Animals may be immunocompromised or have specific pathogen free (PDF) status making them susceptible to microorganisms and infections.

Since elimination and/or substitution of risk is rarely achievable in the vivarium, engineering controls, administrative controls, and personal protective equipment (PPE) provide the primary means of protection. Typically, Animal Transfer Stations (ATSs) and Animal Handling Biological Safety Cabinets (AH BSCs) serve the role of engineering controls in this context. Understanding the capabilities and differences between these two controls will help eliminate unnecessary costs and loss of resources due to compromised animals and research.

Key Operational and Design Fundamentals

Both ATSs and BSCs utilize vertical laminar downflow of HEPA-filtered air inside the work zone where the animals are being handled. HEPA stands for high efficiency particulate air (filter). To comply with the National Sanitation Foundation’s (NSF) standards, Class II biosafety cabinets must utilize HEPA filters that are at least 99.99% efficient at 0.3 microns for the supply and exhausted airflow. The constant downflow of air pulls dander and microorganisms straight down into the air intake grills located on the bottom of the work zone. To extend the lifespan of HEPA filters, washable mesh pre-filters are often employed to remove larger particles, such as hair, dander, and dust, before reaching the HEPA filters.

On a Class II Type A2 biosafety cabinet, ambient air will also be pulled into the inflow air grill at the leading edge of the cabinet. These airflow dynamics are often referred to as a dynamic air barrier, separating personnel from the product(s) inside the work zone.

Although both devices utilize similar airflow fundamentals, notable differences in design, operational technique, and intended uses still exist between ATSs and AH BSCs.

What is an Animal Handling Biological Safety Cabinet (AH BSC)?

A Biosafety Cabinet (BSC) is an enclosed laboratory workspace for safely handling potentially contaminated or otherwise hazardous materials requiring a predefined level of biosafety. Because of the increased protection granted by a BSC, personnel can practice procedural tasks in the work zone, such as injecting, manipulating, or examining the product.

Three different classes (I, II, or III) of biosafety cabinets currently exist, defined by the varying degrees of biocontainment required. Class I cabinets are designed to provide maximum protection of the operator and environment by preventing outflow of pathogens or air-borne contaminants. Class II cabinets provide mid-range protection while Class III devices offer the highest containment with contents only accessible using physical barriers such as glove boxes.

Multiple types also exist within those classes, dictated by what proportion of the air passing through the work zone gets exhausted or recirculated. Unlike traditional BSCs designed for microbiology research, animal handling BSCs accommodate the specific needs of animal researchers with unique modifications, such as pre-filters, built-in waste chutes, and/or cage pass-through chambers. The higher level of containment provided by biosafety cabinets protect animals that may be immunocompromised, biohazardous, or designated as unknown infection status.

Most ATSs utilize a “push-pull” downward airflow pattern. An air supply impeller at the top of the cabinet creates the “push” action by directing air straight down through the work zone while a second motor beneath the work surface “pulls” the air through the air slots located on the edges of the work surface.  Due to the lack of regulatory agencies, ATSs can vary widely in design and functionality. However, as mentioned, one must still regularly certify the ATS functions according to manufacturer specifications.

The ATS workspace can be accessible from one or two sides, depending on the intended usage. Typically, one-sided stations create a stronger air barrier than their dual-sided counterparts. Two-sided ATSs offer greater convenience, but the additional access opening increases the surface area of the air barrier, making it markedly less stable.