A laminar flow hood or cabinet is an enclosed workstation that creates a contamination-free work environment through filters. It is designed to protect the samples or materials inside the cabinet from being exposed to airborne particles, microbes, or contaminants from the outside environment. It also protects the operator and the surrounding area from the potential hazards of the materials being handled inside the cabinet.

A laminar flow hood works by creating a laminar flow of air, which means that the air moves in parallel streams with minimal turbulence. The air is drawn from the room through a pre-filter that removes large dust particles and then passes through a high-efficiency particulate air (HEPA) filter that removes 99.97% of particles that are 0.3 micrometers or larger. The filtered air is then blown into the cabinet through a diffuser that creates a uniform and constant velocity of air across the work surface. The air exits the cabinet through an opening at the front or bottom of the cabinet.

A laminar flow hood can be used for various applications in laboratories and industries that require a sterile and particulate-free environment for handling sensitive materials, such as tissue culture, media preparation, drug preparation, electronic device assembly, etc. Depending on the direction of airflow, there are two types of laminar flow hoods: vertical and horizontal.

A laminar flow hood consists of the following parts:

• Cabinet: The cabinet is the outer structure of the laminar flow hood that encloses the working space and protects it from external contamination. The cabinet is usually made of stainless steel with minimal gaps or joints to prevent the accumulation of dust or microbes. The front of the cabinet has a glass shield that can be opened partially or fully to allow access to the working space. The glass shield also prevents the escape of filtered air from the cabinet.

• Working station: The working station is the flat surface inside the cabinet where the operations are performed. The working station can accommodate various tools and materials such as culture plates, burners, loops, etc. The working station is also made of stainless steel to resist corrosion and facilitate cleaning.

• Filter pad/Pre-filter: The filter pad or pre-filter is located on the top of the cabinet and serves as the first stage of filtration. The filter pad traps large dust particles and some microbes from entering the cabinet. The filter pad also helps to create a uniform airflow across the cabinet.

• Fan/Blower: The fan or blower is situated below the filter pad and creates a suction force that draws in air from outside and circulates it inside the cabinet. The fan or blower also directs the air towards the HEPA filter for further filtration.

• UV lamp: Some laminar flow hoods have a UV lamp that emits ultraviolet radiation to sterilize the interior of the cabinet and its contents before and after each operation. The UV lamp should be turned on for at least 15 minutes before starting the operation and turned off before switching on the airflow. The UV lamp should not be exposed to human skin or eyes as it can cause damage.

• Fluorescent lamp: The fluorescent lamp provides adequate illumination for the operation inside the cabinet. The fluorescent lamp should be switched on during the operation and switched off after finishing.

• HEPA filter: The HEPA filter is the most important part of the laminar flow hood as it ensures a sterile environment inside the cabinet. The HEPA filter stands for High-Efficiency Particulate Air filter and can remove 99.97% of particles that are 0.3 microns or larger in size. The HEPA filter captures bacteria, fungi, and other particulate matter that may contaminate the operation. The HEPA filter should be replaced periodically according to the manufacturer`s instructions.

These are the main components of a laminar flow hood that work together to create a contamination-free work environment for various laboratory and industrial applications.

The principle of a laminar flow cabinet is based on the laminar flow of air through the cabinet. The device works by the use of inwards flow of air through one or more HEPA filters to create a contamination-free work environment.

The air is taken through a filtration system and then exhausted across the work surface as a part of the laminar flow of the air. The air first passes through the filter pad or pre-filter that allows a streamline flow of air into the cabinet. Next, the blower or fan directs the air towards the HEPA filters. The HEPA filters then trap the bacteria, fungi and other particulate materials so that the air moving out of it is particulate-free air.

Some of the effluent air then passes through perforation present at the bottom rear end of the cabinet, but most of it passes over the working bench while coming out of the cabinet towards the face of the operator. The laminar flow hood is enclosed on the sides, and constant positive air pressure is maintained to prevent the intrusion of contaminated external air into the cabinet.

The direction of airflow determines the type of laminar flow cabinet: horizontal or vertical. In a horizontal laminar flow cabinet, the air flows from behind the working bench towards the operator. In a vertical laminar flow cabinet, the air flows from the top of the cabinet towards the bottom. Each type has its advantages and disadvantages, which will be discussed in point 5.

The procedure to be followed while operating a laminar flow cabinet is given below:

• Before running the laminar flow cabinet, the cabinet should be checked to ensure that nothing susceptible to UV rays is present inside the cabinet.
• The glass shield of the hood is then closed, and the UV light is switched on. The UV light should be kept on for about 15 minutes to ensure the surface sterilization of the working bench.
• The UV light is then switched off, and a time period of around 10 minutes is spared before the airflow is switched on.
• About 5 minutes before the operation begins, the airflow is switched on.
• The glass shield is then opened, and the fluorescent light is also switched on during the operation.
• To ensure more protection, the working bench of the cabinet can be sterilized with other disinfectants like 70% alcohol.
• Once the work is completed, the airflow and florescent lamp both are closed and the glass shield is also closed.

Depending on the direction of movement of air, laminar flow cabinets are divided into two types: vertical and horizontal.

Vertical laminar flow cabinet

In the vertical flow cabinets, the air moves from the top of the cabinet directly towards the bottom of the cabinet. The air passes through a pre-filter and a HEPA filter before reaching the working station. The effluent air then exits through perforations at the bottom rear end of the cabinet.

A vertical airflow working bench has some advantages over a horizontal one:

• It does not require as much depth and floor space as a horizontal airflow hood, which makes it more manageable and decreases the chances of airflow obstruction or movement of contaminated air downstream.
• It is also considered safer as it does not blow the air directly towards the person carrying out the experiments.
• It provides better protection for the samples and products from contamination by the operator`s hands or arms.

Some disadvantages of a vertical laminar flow cabinet are:

• It may create turbulence in the airflow near the working station, which can affect the sterility of the environment.
• It may also cause discomfort to the operator due to the downward flow of air on their head and shoulders.

Horizontal laminar flow cabinet

In the horizontal laminar flow cabinets, the surrounding air comes from behind the working bench, which is then projected by the blower towards the HEPA filters. The filtered air is then exhausted in a horizontal direction to the workplace environment.

A horizontal airflow working bench has some advantages over a vertical one:

• It provides a uniform and laminar flow of air across the working station, which reduces turbulence and ensures sterility.
• It also allows better visibility and access to the samples and products on the working station.

Some disadvantages of a horizontal laminar flow cabinet are:

• It requires more depth and floor space than a vertical airflow hood, which can limit its placement and mobility in the laboratory.
• It also poses a higher risk of contamination as it blows the air directly towards the person carrying out the experiments, which can introduce particulate matter or microbes from their clothing or skin.

The following are some common uses of a laminar flow cabinet in the laboratory and industry:

• Laminar flow cabinets are used in microbiology and biotechnology laboratories for contamination-sensitive processes like plant tissue culture, media plate preparation, and culture of microorganisms. These processes require a sterile environment to prevent the growth of unwanted microbes or contaminants that can affect the results or quality of the products.
• Laminar flow cabinets are also used in electronics and nanotechnology industries for operations of particle-sensitive devices such as semiconductors, microchips, and nanomaterials. These devices require a dust-free environment to prevent damage or malfunction due to the accumulation of particles on their surfaces or circuits.
• Laminar flow cabinets are also used in pharmaceutical and medical industries for drug preparation techniques such as compounding, filling, and packaging. These techniques require a particulate-free environment to ensure the purity and safety of the drugs or medical products that are administered to patients or consumers.
• Laminar flow cabinets can also be made tailor-made for some specialized works such as DNA sequencing, cell culture, and forensic analysis. These works require a high level of precision and accuracy that can be achieved by using a laminar flow cabinet that provides a controlled and consistent airflow.
• Laminar flow cabinets can also be used for general lab techniques in the microbiological as well as the industrial sectors such as pipetting, weighing, and mixing. These techniques require a clean and stable environment to prevent errors or contamination that can affect the outcomes or quality of the experiments or products.

Precautions

While operating the laminar airflow cabinet, the following things should be considered:

• The laminar flow cabinet should be sterilized with the UV light before and after the operation. The UV light and airflow should not be used at the same time. No operations should be carried out when the UV light is switched on.
• The operator should be dressed in lab coats and long gloves. The operator should also avoid any unnecessary movements or talking inside the cabinet to prevent the generation of aerosols or droplets that might contaminate the work environment.
• The working bench, glass shield, and other components present inside the cabinet should be sterilized before and after the completion of work. A 70% alcohol solution or other suitable disinfectants can be used for this purpose.
• The materials and equipment to be used inside the cabinet should be kept to a minimum and arranged in an orderly manner. They should also be sterilized before placing them inside the cabinet. Any waste materials should be disposed of properly in a biohazard bag or container.
• The airflow should not be obstructed by any objects or persons during the operation. The operator should work at least six inches away from the front edge of the cabinet to avoid disrupting the laminar flow of air. The operator should also avoid placing their arms or hands over the work area or crossing them inside the cabinet.
• The laminar flow cabinet should be checked regularly for any signs of damage or malfunction. The filter pad, fan, UV lamp, fluorescent lamp, and HEPA filter should be replaced or serviced as per the manufacturer`s instructions. The airflow velocity and direction should also be monitored and adjusted if needed.

By following these precautions, the operator can ensure a safe and sterile work environment inside the laminar flow cabinet.

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