The microbiology laboratory handles many infectious and hazardous materials. The handling risks the contamination of the environment and increases the risk of infection in laboratory personnel. So, safety cabinets are preferred for safe and contamination-free handling of microbial cultures. These help in the containment of infectious aerosols. The types of safety cabinets commonly used are biological safety cabinets and laminar air flow cabinets.
A laminar airflow cabinet is a closed workstation that has HEPA (high-efficiency particulate air) filters for providing a unidirectional flow of air at a steady velocity. The laminar airflow cabinet offers an area for contamination-free handling of hazardous and infectious material. It is ideal for preparing sterile culture media, assembly of sterile components into complete units, and other aseptic transfers.
Parts of Laminar Airflow Cabinet
The parts of the laminar airflow chamber are; the cabinet, workstation, HEPA filter, filter pad, blower, fluorescent, and UV lamp.
- Cabinet: It is the outermost part of the hood. It is made up of stainless steel. The cabinet provides an enclosed system of insulated air throughout the working station. The front part of the cabinet consists of a sliding glass door. The sliding door should be closed completely when the hood is not in use because it shields the inner sterile condition from the outside environment.
- Working platform: It is the sterile space inside the cabinet. The platform is also made up of stainless steel and serves as an area for performing all the desired tasks.
- Filter pad: it is the primary filter for absorbing pollutants of air entering inside the cabinet.
- Blower/Fan: It draws the semi-filtered air from the filter pad and passes it into the HEPA filter.
- HEPA filter: It is the second filter that traps 99.99% of air pollutants and particles as low as 0.3 µm. The HEPA filter then passes the sterile air throughout the chamber at uniform velocity.
- Fluorescent lamp: It is helpful for illumination inside the cabinet for performing tasks.
- UV lamp: It is useful for sterilizing laboratory work glassware, chambers, and media.
Working Principle of Laminar Airflow Chamber
The operation of the laminar airflow chamber is based on the unidirectional flow of filtered sterile air with constant velocity. The prefilter/filter pad of the hood traps the outside non-sterile air; the air is slightly filtered by it. The prefilter air is then blown to the HEPA filter with the help of a fan/blower. The HEPA filter is a highly efficient filter capable of trapping air pollutants with a size of 0.3 µ or larger. Now, the completely sterile air passes through the working area of the hood. This way, the non-sterile air is trapped, filtered, and sterilized to pass through the working area.
Sometimes the objects used inside the hood might be non-sterile or exposed to the outside air. The exposure may risk the contamination of the hood, so using the UV lamp while using metals, glassware, and media before performing the task helps maintain sterility.
Operating a Laminar Airflow Cabinet
The following steps are required for the operation of the laminar airflow cabinet:
- Firstly, turn on the hood’s main switch and ensure the manometer displays zero before using it. If the reading is more than zero, leave the button on for 30 minutes to an hour until the manometer shows zero.
- Then turn on the airflow switch for circulating air in the hood.
- Place all the required objects, media, glassware, and metal instrument inside the hood and turn on the UV lamp to sterilize the materials.
- Turn off the UV lamp after about 30 minutes and turn on the fluorescent lamp to start performing the task in a sterile environment.
Cleaning the Laminar Airflow Hood
- Turn the airflow and UV switch off for cleaning the working space.
- Use a clean dry cloth for cleaning the HEPA filter grill (protective grill). Do not wet the grill.
- Now clean the interior working area using a clean cloth and sterile water. Then, spray the 70% alcohol (isopropyl alcohol) and wipe with another clean cloth on the work surface.
- After that turn on the UV lamp for sterilization.
- Operators should wear personal protective equipment such as gloves and gowns. They should also avoid unnecessary movements and minimize talking and coughing near the hood.
- Eating, drinking, and smoking are strictly prohibited near the hood.
- The arrangements of the critical object should be near the air source.
- Maintenance of the filters and blowers should be carried out timely.
- Carrying out the aseptic procedures should be 6 inches away from the sides and front edge of the hood.
- Operators must not avoid jewelry on their hands and wrists.
- Replace UV light after 999 hours of use.
Types of Laminar Airflow Chamber
Based on the movement of air, the laminar airflow cabinet is of two types which are; horizontal and vertical airflow cabinets.
Horizontal Airflow Cabinet
The air movement in these cabinets is from the back to the front of the hood. The electrical blower pulls the contaminated air from the room using a pre-filter or filter pad. The air passage through the filter pad accelerates for the consistent airflow distribution to the HEPA filter (final filter). The HEPA filter is at the bottom of the hood’s working platform. Since the HEPA filter removes 0.3 µm or larger particles, it can easily remove the common airborne microorganism of size 0.5 µ or larger. For complete sterility, nothing should pass behind the sterile object.
Vertical Airflow Cabinet
The movement of air is vertical. The air passing through the HEPA filter joins from the top and moves downward through the working area. The air then leaves the hood through the holes in the base of the working area. The interruption in the airflow between the HEPA filter and the sterile air due to placing materials creates a zone of turbulence in the critical area. The increase in the zone of turbulence carries the contaminants to the sterile area hence contaminating the area. So, nothing should pass above the sterile object.
Uses of Laminar Airflow Cabinet
The laminar airflow cabinet is helpful in the following laboratory works:
- Preparing culture media for bacterial and fungal isolation and culture.
- Performing plant cell and tissue cultures.
- Conducting other tasks that require aseptic conditions, like the operation of particle-sensitive electronic devices.
- Preparing and quality testing of pharmacological products.
- Performing general laboratory tasks by adjusting settings as per need.
Advantages of Laminar Airflow Cabinet
The advantages of the laminar airflow cabinet over the biosafety cabinet and other methods of sterilizing workspace are as follows:
- Since heat or harsh chemicals are not used in laminar airflow cabinets, it prevents chemical irritation and heat-related damage to samples and reagents.
- The sterile working area is spacious compared to the biological safety cabinet, so larger containers can be used inside the cabinet.
Limitation of Laminar Airflow Cabinet
Although the laminar airflow cabinet is helpful and spacious, it has certain limitations. They are:
- Airflow velocity can sometimes increase. A zone of turbulence is created to prevent the increase of airflow velocity, which increases the risk of introducing contaminants inside the sterile environment of the hood.
- Operation time might increase if the hood is not turned on for 24 hours.
- If the filter pad and HEPA filter are not cleaned correctly and timely, the risk of contamination increases.
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