What are Biosafety Cabinets?

Biological Safety Cabinet is the primary engineering control that provides user, sample, and environment protection against biohazards. A biosafety cabinet’s airflow consists of an inflow barrier that prevents the accidental release of biohazards from the cabinet’s working area. It also has a downflow air that removes contaminants from the work zone, providing a sterile area for the samples.

A BSC should be selected based on the following criteria: type of work, classification of biohazards (Risk Group 1-4); personnel protection against exposure to radionuclides and volatile toxic chemicals; or a combination of these. The table below shows which BSCs are recommended for each type of protection.

Source: Laboratory Biosafety Manual. 3rd ed (revised). Interim guidelines. World Health Organization. p52.

Esco Lifesciences is a world leader in biological safety cabinets, offering the industry’s widest product range, with thousands of installations in leading laboratories in more than 100 countries around the globe. Esco biological safety cabinets have earned more independent certifications in more countries, in more languages, than any other product, demonstrating our commitment to the industry’s best safety and quality. 

Class I Biological Safety Cabinets 

The Class I biosafety cabinet has the most basic and rudimentary design of all BSCs available today. It offers protection to the operator and the environment from exposure to biohazards and is suitable for work with microbiological agents assigned to biosafety levels 1, 2, and 3. 

Class II Type A2 Biological Safety Cabinets

The Class II Type A2 biological safety cabinet is the most common Class II BSC. It is also the most common biosafety cabinet of all the different types available. It has a  plenum from which 30% of air is exhausted, and 70% is re-circulated to the work area as the downflow. It protects the operator and the environment from exposure to biohazards and protects products from contaminated room air and cross-contamination. 

If trace amounts of toxic chemicals are employed as an adjunct to microbiological processes, Type A cabinets should be exhaust-ducted. 

Class II Type B2 Biological Safety Cabinets 

A Class II Type B2 biological safety cabinet is designed to have no recirculation within the cabinet. The inflow and downflow air is exhausted after HEPA filtration to the external environment. Type B2 biosafety cabinets are suitable for work with toxic chemicals employed as an adjunct to microbiological processes as there is no recirculation. In theory, Type B2 BSCs may be considered as the safest of all Class II BSCs since the total exhaust feature acts as a fail-safe if the downflow and/or exhaust HEPA filtration system cease to function normally. 

Class III Biological Safety Cabinet 

The Class III biological safety cabinet provides an absolute level of safety, which cannot be attained with Class I and Class II biosafety cabinets. It is suitable for work with microbiological agents assigned to biosafety levels 1, 2, 3, and 4. It is frequently specified for work involving the most lethal biological hazards.

Selection Based on Biosafety Level

Biosafety levels are measures to contain or isolate harmful infectious agents in a laboratory. For risk assessment of harmful agents, a Biological Safety Officer (BSO) and Institutional Biosafety Committees (IBC) may be of help. There are four biosafety levels:

Biosafety Level 1 is for undergraduate and secondary educational training, teaching laboratories, and for other laboratories that use microorganisms that are not pathogenic. Examples are Bacillus subtilis, Naegleria gruberi, and infectious canine hepatitis virus. Thus, BSL-1 containment only requires a sink for handwashing.

Biosafety Level 2 is appropriate for clinical, diagnostic, teaching, and other laboratories which deal with indigenous moderate-risk agents linked with human disease and is present in a community. Examples are the Hepatitis B virus, HIV, Salmonella, and Toxoplasma. These microorganisms may be used on the open bench as long as there is low production of aerosols. Hazards may be acquired through ingestion of or exposure of the mucous membrane from the microorganisms. Certain precautions should be taken in handling contaminated materials (i.e. sharp objects). Similarly, procedures involving aerosol should be undertaken in BSC or safety centrifuge cups. Personal protective equipment is also effective together with handwashing sinks and waste decontamination facilities.

Biosafety Level 3 applies to clinical, diagnostic, teaching, research, or production facilities handling indigenous or exotic agents with a potential for respiratory transmission that may be a cause for lethal infection. Examples are Mycobacterium tuberculosis, St. Louis Encephalitis virus, and Coxiella burnetii. Hazards may be acquired through autoinoculation, ingestion, and exposure to infectious aerosols. For containment, procedures should be done in BSC or a gas-tight aerosol generation chamber. Ventilation systems should also be appropriate to reduce the release of hazardous aerosols.

Biosafety Level 4 is appropriate for life-threatening hazardous agents or pathogens which may be spread through the aerosol route and has no available vaccine or therapy. Examples are Marburg or Congo-Crimean hemorrhagic fever. Hazards may be acquired through infectious aerosols, skin membrane exposure to hazardous droplets, and autoinoculation. To isolate the infectious agents completely, procedures should be done in Class III BSC or while in a full-body air-supplied positive-pressure personnel suit. The BSL-4 laboratory is located in an isolated complex with specialized ventilation and waste management systems. The entire operation of the laboratory should be handled by a laboratory director. A supplement to this will be the presence of trained laboratory personnel, safety measures/manuals, safety equipment, appropriate design of facilities, personal protective equipment, and biosafety level practices.

Selection Based on the Filtration system

One of the most important components of a BSC is the filter. Currently, there are two kinds of filters that a biological safety cabinet utilizes:

• High-Efficiency Particulate Air (HEPA) filter that is 99.99% efficient at MPPS (typically at 0.30 micron).
• Ultra-Low Particulate Air (ULPA) filter that is 99.999% efficient at MPPS (typically at 0.12 micron).

ULPA filter is 10 times more efficient than the HEPA filter, thus a biosafety cabinet with an ULPA filter can provide better operator, product, and environmental protection.

Selection Based on Possibility to Block Inflow Grille

The operator and product protection are achieved through the air curtain created by both the inflow and downflow that goes into the front air grille. The user needs to select a BSC design that can prevent accidental blocking on the grille by operator arms or samples.

There are several ways to prevent the inflow grille blocking:

1. Use a raised armrest.
2. Put armrest above inflow grille
3. Curve the inflow grille up (like an A-shape)
4. Curve the inflow grille down (like a V-shape)
5. Put the inflow grille lower than the front nosing of the cabinet and the work tray

Figure 1. Combination of raised armrest and curved inflow grille to prevent accidental blocking.

Selection Based on Airflow Alarm

There are different possibilities for alarms and control systems used by biosafety cabinets:

1. Simple switches – the simplest control system with buttons to turn blower and lights on and off. Has audio and visual alarms to indicate airflow failure.
2. Analog display – shows the airflow velocity and provides an overview on how far the current velocity is from the fail point.
3. Digital microprocessor – displays the cabinet’s basic parameters such as airflow values to sash status and alarms. It has easy-to-use buttons for the cabinet’s operation and an LCD screen that enables the user to diagnose the status of the cabinet and program different features such as setting the experiment timer.

Selection Based on Front Window Mechanism, Material, and Angle

A biosafety cabinet has different window mechanisms wherein the user must select the most convenient type without compromising containment.

• Hinged window. The advantage is the ease to get the nominal aperture opening height because it is fixed. However, the operator must attach an optional front cover to cover the aperture when the UV light is on.
• Manual sash window. The operator must observe the correct nominal window opening height, as indicated by the guide mark and supported by the sash alarm. The sash window must be fully closed before the UV light is activated.
• Motorized sash window. This is similar to the manual sash window version, but the user just needs to press one or two buttons to move the window. Typically, two buttons are used for safety to ensure that both of the operator’s hands are outside the path of the traversing window.