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The hitchhiker's guide to biosafety cabinet

31 May 2022

Ensuring the safety of personnel is very important when setting up a laboratory. Regardless of the type of work being performed, it is imperative to take steps to address any situation that could pose a potential risk. This means considering the overall design of the lab space to avoid overcrowding and minimize footfall; configuring the layout of furniture and equipment so that the lab is neat and easy to clean; selecting appropriate safety equipment, including in handling and disposing of biohazardous materials.

Introduction

The biosafety cabinet is designed to protect personnel, the environment and product from contamination when the operator handles materials. In this case, BSL1 as the lowest level of biosafety does not require special safety equipment; these are usually given to agents such as Bacillus subtilis or canine hepatitis which pose only very minimal risk and can be manipulated in an open laboratory bench. On a different scale, BSL4 which has a hazardous or exotic agent associated with a very high risk of a life-threatening disease or an associated agent for which the risk of transmission is unknown; is used to classify agents such as the Ebola virus or the Marburg virus, whose infections are often fatal and often have no known cure.

How does it work?

Biosafety cabinets function by causing the air to move in a precise pattern, as well as filtering the air to remove hazardous particles. This capability requires advanced engineering in areas such as airflow dynamics, usability ergonomics, enclosure design, and electrical design of motors, blowers and control systems.

The origin of the biosafety cabinet

The history of BSC development has been a long process, as described by the 1991 Clinical Microbiological Review paper, Biological Safety Cabinet, about infections resulting from exposure to substances in the laboratory came in 1893. The first surveys in the laboratory Acquired disease, typhoid fever, was mainly due to the use of pipettes, began in 1915. In the mid-1900s, the relationship between laboratory practice and the potential for contamination and infection intensified. A 1950 survey reported at the annual meeting of the American Public Health Association noted that 5,000 laboratories recorded 1,342 cases of laboratory-acquired infection. 39 deaths occurred. Of the 1,342 infections, only 467 were previously published. This pattern of infection continued in the following decades, as reported by the Centers for Disease Control and Prevention (CDC) and the National Centers for Animal Diseases.

The forerunner of the biosafety cabinet appeared in 1909 when a company offered a ventilated hood to prevent tuberculosis infection when preparing tuberculin. Closed cabinets were first mentioned in the scientific literature in 1943. In the early 1950s, the U.S. Army Biological Laboratory at Fort Detrick, Maryland developed and implemented advanced containment cabinet technology.

The use of containment cabinets began to spread, continuing to this day. Currently BSC is considered standard in the laboratory to prevent a variety of potential contaminants. Although the BSC must provide safety for personnel and improve accuracy in testing and production through air contamination control, the terms "safety" and "air contamination control" are relative terms. Is there an acceptable level of exposure in a particular instance? Is there a standard that can be used to measure the effectiveness of BSC from different factories?

How biological safety cabinets are classified

For these reasons and others, NSF International, a standards development organization, helped create BSC standards and classifications, according to the amount of protection they are supposed to provide. What meets the needs of one lab may be excessive or insufficient for another. Minimum standards allow lab managers and safety personnel to know, at a minimum, what they can rely on. To understand the BSC in relation to lab safety requirements, further review of the BSC is needed. Biosafety Cabinet Standards and Types There are 3 main types of BSCs in common use:

Class I
Cabinets that can be recirculated to the laboratory or removed via the HVAC system. It uses negative pressure from the interior blower motor or external exhaust system, creating an air barrier across the front of the cabinet at a minimum speed of 75 linear feet per minute with air then circulating through the cabinet. Negative pressure prevents air from spilling back into the lab environment. The cabinet draws air from the supply outlet usually at the front of the cabinet. Exhaust air from the cabinet is passed through a HEPA filter. Class I cabinets are designed for low to moderate risk biological materials. They protect lab personnel and the environment but do not protect cabinet work.

Class II
Cabinet with front which are partially open to workers' access. Class II is similar to Class I in that it uses negative pressure to prevent air from moving through the supply openings and access panels. The main difference between Class I and Class II cabinets is that Class II cabinets create an air barrier at the front of the cabinets by creating a vacuum using airfoils that direct air under the work surface, not over the work area. It also filters the air supply to the internal work area and uses laminar airflow to eliminate turbulence, and possible cross-contamination within the cabinet. Air is split at the work surface and drawn into the grills located at the front and back of the cabinet. Some of the air will be drawn from the side of the work area and under the work surface directed to ducts located at the rear of the cabinet then recirculated to the work zone, exhausted, or a combination of both depending on the cabinet subtype. There are four subtypes of Class II cabinets. Air is drawn through the front opening of the cabinet at a minimum speed of 75 linear feet per minute or 100 linear feet per minute, depending on the subtype. Some or all of the air is returned to the working area of the cabinet through the supply HEPA filter or returned to the laboratory or building exhaust system through the exhaust HEPA filter. Class II BSCs are designed for low to moderate risk biologics.

Class III
Closed cabinet that protects personnel and the environment. Usually designed for biosafety level 4 pathogens. Users put their hands into attached gloves that pass through unopened windows and manipulate all work in that way. The blower creates a negative pressure of at least 0.5 inches of water gauge. Air enters the cabinet through the HEPA filter. The exhaust air passes through two separate HEPA filters, or a HEPA filter and an air incinerator, and finally through a duct for exhaust to a separate exhaust system from the general laboratory exhaust system. Class III BSCs typically do not offer laminar airflow within the internal work area. Materials enter the workspace through a dunk tank on the cabinet floor or through a double-door decontaminated box between uses. Cabinets are designed for high-risk biological substances.

Simplify BSCs by staying basic

As shown by the BSC categories and types, it’s easy to get caught up in the complexity of this range of products, but that’s not necessarily productive. Before considering bells and whistles, consider what adds value in terms of improving protection and continuing to offer that protection cost-effectively and ergonomically over the long-term.

Confused? Let us help you to make it easier. Our trained team of professionals is ready to help you through the selection process from start to finish. Reach out today to start the conversation. Call us at +603 8065 3889 today or send us a message at marketing@gaiascience.com.my.

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