In laboratories, the operators are exposed to varying kinds of pathogens and harmful chemicals. There are many experiments and processes that are carried out which might contaminate the environment in the laboratory. To deal with these two factors – protecting the personnel and the environment, biosafety cabinets are used. In addition to protecting, some types of biosafety cabinets also ensure the protection of the sample against contamination.
Classification of the different types of Biosafety cabinets
The different types of Biosafety cabinets are classified by the United States Centre for Disease Control and Prevention or CDC. These classifications and types of biosafety cabinet are categorized on the basis of two main factors:
- The extent to which the user and environmental protection provided by the biosafety cabinets
- The extent to which the product or sample protection provided by the biosafety cabinets.
HEPA filtration
One of the main technologies used in the biosafety cabinet is HEPA filtration. High-Efficiency Particulate Air or HEPA is an air efficiency standard that helps to effectively remove particles of the size of 0.3 microns or greater. The heart of every biosafety cabinet is HEPA. The standard set by organizations mandates 99.95% of the particles passing through the air filter to be removed for it to be certified as a HEPA filter. HEPA filters are distinctly in different types of Biosafety cabinets to achieve the desired protection levels.
Types of Biosafety cabinets and their uses
Biosafety cabinets are broadly classified into three classes – Class (I, II and III). Class II biosafety cabinet is further divided into five different types. The explanation and use of each are given below.
Where should biological safety cabinets be located?
What is Class I biosafety cabinet and how they work?
Class I Biosafety cabinets are ventilated cabinets that are used to work with agents that need treatment as per Biosafety Level 1-3 processes. These cabinets prevent the user and the environment around the cabinet from getting contaminated. However, they have no specific feature to secure the product. This can result in contamination of the samples that are being manipulated.
The inward airflow is at an average velocity of 75 fpm. The outward airflow can either be recirculated in the laboratory or exhausted through the building ducts. HEPA filtration of the exhaust air sterilizes it from contamination. These biosafety cabinets are generally used for protecting specific equipment or processes that release aerosols. Due to their inability to protect the samples, use of Class I cabinets is very limited.
What is Class II biosafety cabinet and how they work?
Class II biosafety cabinets are extensively used in the pharmaceutical industry and in microbiological work. It is further divided into 5 types of Biosafety cabinets – (Type A1), (Type A2), (Type B1), (Type B2) and Type C1. This division is based on the basis of the nature of inflow airflow, exhaust airflow and construction patterns of the cabinets.
In class II types of Biosafety cabinets, the air inside the cabinet is also HEPA filtered. This prevents the sample from getting contaminated. Like the type of Class I BIOSAFETY CABINET, these are also used to treat agents that require Biosafety level 1 – 3 procedures.
The front part of the cabinet is open and the air flows inward, ensuring user protection. Downward, laminar airflow with HEPA filtration ensures product protection. The outward airflow ensures environmental protection. The exhaust air is also passed through a HEPA filter. In class II cabinets, the biologically contaminated areas are subjected to negative pressure or enclosed by ducts that have negative pressure.
In addition to the user and environment protection, Class II biosafety cabinets provide product protection against contamination. Biosafety Cabinet is a closed and ventilated work area in a laboratory or research facility. These are used to work with materials that are potentially contaminated with pathogens. Depending upon the biosafety requirement levels of pathogens, there are different types of BIOSAFETY CABINETs.
Biosafety Cabinets Type A1
These cabinets have air inflow speed with an average velocity of 75 fpm. The downward airflow is screened through a HEPA-filter to protect the product from getting contaminated. The air is then drawn downward and brought up through a duct, from the back. This air is consequently blown to positive pressure. Following this, the air might be recirculated into the plenum after HEPA filtration or exhausted out of the cabinet. The exhausted air is HEPA filtered. A1 can be used to work with biological agents but is not suitable to work with hazardous chemicals.
Biosafety Cabinets Type A2
These biosafety cabinets need to have an average air inflow of 100 fpm. A2 type cabinets are also similar to A2 type cabinets. The major difference is in the speed of inflow air. A2 cabinets that have a canopy attached to them can be used for treating biological agents that have fragrant quantities of hazardous chemicals. The cabinet can also come in use to a couple of small amounts of radionuclides. Radionuclides will not interfere with the processes if they are recirculated in the downward direction.
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Biosafety Cabinets Type B1
The B2 cabinets have a minimum air inflow speed of 100 fpm from the front opening. These do not recirculate the air that is contaminated flows downward from the cabinet. Instead, they send the air out through the exhaust duct after HEPA filtration. The airflow is split in such a way that the air behind the smoke split is sent out through the exhaust system. The air between the user and smoke split mixes with the incoming air and is recirculated downward. As the air that is exhausted from the cabinet drawn from the rear end, it is suggested to carry out all work with hazardous substances at the rear end of the cabinet, Type B1 cabinets can be used to work with small quantities of volatile chemicals and finer radionuclides. When these substances are used, the work must be conducted at the rear end of the cabinet.
Biosafety Cabinets Type B2
Type B2 cabinets need to maintain a minimum air velocity of 100 fpm. For an inward flow of air, these cabinets draw air directly from the laboratory or from the outside. The air is then HEPA-filtered and cast over the work area. Since they do not recirculate the air, all the downward airflow is excreted out into the atmosphere after treating the air with HEPA filters. They do not recirculate the air inside the cabinet or lab. These are sometimes termed as 100% Exhaust cabinets. They are commonly used to work with biological agents that may need to be supplemented with materials that are toxic and radionuclides while performing microbiological processes.
Biosafety Cabinets Type C1
Type C1 of Class II biosafety cabinets need to maintain a minimum air inflow speed of 105 fpm. Type C1 cabinets were designed to reduce costs and increase flexibility in research laboratories. The unique characteristic of C1 type cabinet is that it can perform both as A1 type while recirculating the air or as B2 type while exhausting the air outside the cabinet. The cabinet can be switched easily by disconnecting or connecting to an exhaust system and realigning the cabinet. It also offers two distinct areas for work and storage. The work area has a dedicated exhaust line to work with hazardous chemicals or radionuclides and a delineated space for storage.
A2 vs B2 Type Biosafety Cabinet
There is a general misconception that B2 is safer than A2. But actually both are kind of similar. The safety actually depends upon the biological agent in consideration. Both of them help to protect the user and the sample under consideration. However, B2 BIOSAFETY CABINET provides additional precaution while working with vapors and gaseous elements. B2 is able to achieve greater dilution by preventing the recirculation of volatile chemicals in the cabinet work area. Both A2 and B2 cannot be used with inflammable or explosive materials.
In terms of cost and resources, B2 has greater requirements. The investment and operating costs of B2 type is considerably higher than A2 type. In addition to that, B2 exhausts 2.5 times the air from the cabinet over the volume of air exhausted by A2. This requires the same quantum of air to flow inside the cabinet. Which makes it necessary to have a sustained and conditioned supply of air inflow. This translates into higher energy consumption and carbon footprint.
The decision to employ A1 or B2 should be carefully considered. The type of hazardous chemicals that might be used in the biological treatment and the impact of the same on the user should be considered before going ahead and making a decision. B2 type cabinet has considerably higher costs and resource requirements.
Which class of biosafety cabinets provides the most protection?
Class III (biosafety cabinets) are considered the most secure and full proof of biosafety cabinets. These are ventilated cabinets which are gas-tight and leak-proof. There is a rubber glove that is attached to the cabinet which is used to perform operations inside the cabinet. This prevents direct contact of the user with the hazardous materials. A transfer chamber is attached to the cabinet that sterilizes the materials before leaving the compartment. The cabinet is kept subjected to (negative)/-ve pressure. The inflow air is passed through HEPA filters. Exhaust air is either treated by HEPA or by double HEPA filtration. Class III (BIOSAFETY CABINETs) are used to work with agents that require Level 1-4 containment for biosafety. These are also known as glove boxes. Mostly, these are installed in industries and laboratories that require maximum containment.