The simplest and best solution in this case are so-called FFP3 masks (FFP stands for filtering face piece), which have to fit as closely as possible over the wearer’s mouth and nose. Filter materials behind the exhalation valve vary and include activated carbon, which filter many particles from the air. The major drawback of these masks is that they must be tight-fitting. The fit largely depends on the wearer’s physiognomy, but beards can be a problem in this case. What’s more, breathing is difficult if the mask is worn for long periods of time.
Another alternative are wearable filter systems, which can be combined with helmets or hoods and a tight, secure-fit visor. They use HEPA (high efficiency particulate air) filters to purify the air by using fiberglass fibers to trap and capture particles that are smaller than 1 µm. These systems make breathing easier and provide a better and more secure fit than FFP3 masks. Generally, however, this equipment cannot be worn indefinitely because it is physically demanding and the filter materials don’t last forever and have to be changed.
To prevent biological agents from escaping the lab or avoiding exposure, labs typically use so-called biosafety cabinets or microbiological safety cabinets. This is an enclosed, ventilated laboratory workspace that can be adjusted by positioning the safety glass sash. The employee works in the space that’s created under the opened window sash. To prevent the escape of aerosols, the air is extracted from inside the cabinet and passed through a particulate air filter. Laminar airflow provides an extra layer of protection. Air is blown from the top of the hood straight down and suctioned. This airflow serves as an additional barrier against particles from inside the biosafety cabinet. It is very precisely adjusted and can be easily disturbed by devices inside the cabinet or external turbulence in the lab such as the air conditioning system.
An even safer option is a totally enclosed, ventilated cabinet with leak-tight construction and attached rubber gloves for performing operations in the cabinet. Materials have to be brought in and removed through an airlock. Both types of biosafety cabinets are maintained under negative pressure and supply air is drawn in through HEPA filters. This ensures that aerosol generated within the cabinet is contained within the cabinet even in case of damage.