The Class II Biosafety Cabinet in a pharmaceutical laboratory
A Class II Biological Safety Cabinet is a device that utilizes directional airflow and HEPA filtration to protect a user, the environment and product or culture from airborne particulates. As the name implies, the particulates that are being 'targeted' are of a biological nature: bacterial hazards, cellular hazards or their components that can also be toxic. Fortunately, the design and operation of these cabinets lend themselves to applications outside of (micro)biology.
USP <797> sets guidelines, procedures and compliance criteria for sterile compounding facilities in order to reduce the risk of infection to patients receiving drugs, and to the pharmacy personnel that prepare the product. This set of standards is important and should be studied by hospital and pharmacy administrators and clinical staff, as well as hospital design, construction and facilities support professionals.
The laminar air supplied by the BSC's HEPA filters meet Class 5 conditions per ISO 14644-1 and 2 (formerly Class 100). This also happens to be the classification of room air required for compounded sterile preparations (CSPs) according to USP <797>.
This makes the Class II a great option for smaller (or private) pharmacy facilities that cannot afford to operate a clean room. A Class II BSC (typically a Type B2, total exhaust cabinet) or a Barrier Isolator (Pharmaceutical Glove Box) can be used to provide user protection and a clean room-like environment for sterile compounding.
However, to make a Class II BSC suitable for pharmaceutical usage, there are a few modifications and requirements that need to be included in the design:
HEPA filters are typically tested and rated by their “most penetrating particle size” or, mpps. Class II BSCs utilize HEPA filters that are rated at 99.99% with an mpps of 0.3 micron. In a nutshell, this means that the HEPA filters worst performance occurs when using particles that are 0.3 micron in size and it does so with a capture rate of 99.99%. Particles bigger or smaller than 0.3 micron are captured at increasing efficiencies.
Pharmaceutical powders or aerosols are typically much larger than 0.3 micron and thus are trapped at an extraordinary rate with standard HEPA filters. However, their added size and the propensity for which these aerosols are produced also takes a heavy toll on the HEPA filters load capacity; they load the filter much faster and can take years off of a HEPA filter's life.
For this reason, BSCs can be outfitted with pre-filters that can prolong the life of the HEPA filter. More importantly, doing so will decrease the operational and maintenance costs associated with the BSC.
Stainless Steel Interior:
Most Class II BSCs are built with stainless steel interiors (work surface, side and back walls, etc.). Stainless steel dissipates static charges that can cause powders to 'jump' and it has superior cleanability characteristics over other construction materials.
Bag-In/Bag-Out Exhaust HEPA filters:
This is probably one of the most overlooked modifications needed to adapt a Class II Type B2 BSC for pharmaceutical applications.
In typical microbiological scenarios, the hazards associated with such work are living organisms, viral agents, or cellular bi-products/fragments. These hazardous agents can be and are neutralized in a gaseous decontamination process whenever a BSC undergoes HEPA filter or blower maintenance.
Pharmaceutical powders, on the other hand, cannot be chemically neutralized in the same way as these biological agents. There has to be protection from the contents of the contaminated containment plenum for the service representative, the laboratory environment and anyone else within.
For this reason, it is common to see HEPA filtered enclosures (including BSCs) with what is called a Bag-In/Bag-Out (or simply BIBO) system. A BIBO adaption allows the filter to be removed through a series of sealed containment bags without ever exposing the laboratory to its hazardous contents. BIBO systems can be added to B2 BSCs, but are typically not available for retrofit or on A2 BSCs.
Appropriately outfitted, a Class II BSC can provide great flexibility to a pharmaceutical setting. Risk assessments should always be performed and never underestimated when making engineering control or capital safety equipment decisions. Nor should human safety be a commodity. The importance of due diligence when deciding on safety equipment (class, type, brand, manufacturer, dealer, etc.) cannot be overstated.