Standard Operating Procedure for laminar flow cabinet

The ultra clean workbench is the most fundamental and critical local cleaning equipment in the fields of microbiology, cell biology, and pharmaceuticals. Many operators consider themselves proficient in the process, but often make mistakes in several easily overlooked links, resulting in the failure of the entire aseptic operation. The following five details are the key points that must be strictly controlled during SOP execution.
 
1、 Insufficient startup self purification time, airflow has not reached a stable state
After the ultra clean workbench is started, the internal fan needs to circulate the air through the high-efficiency filter multiple times in order to form a uniform and unidirectional laminar airflow in the working area. If operated immediately after turning on, the airflow velocity and direction are fluctuating, and unfiltered air from the outside may flow back into the operating area with the person's arm. The SOP should clearly stipulate that at least enough time should be allowed for the airflow to fully replace and stabilize after turning on the machine before starting the experimental preparation.
 
2、 The placement of items disrupts the laminar flow path
The core value of laminar flow lies in its "single direction, vortex free" airflow cleaning effect. If items on the workbench are stacked too high, placed too densely, or large containers block the return air grid, it will directly change the direction of the airflow and form a local turbulent zone. In the turbulent zone, the risk of dust particles and microbial settling increases exponentially. The standard requires that all items should be arranged in a single layer in the order of use, from inside to outside and from clean to unclean. High equipment should be placed on both sides of the operating area and cannot block the overall passage of horizontal or vertical airflow.

3、 Crossing arms and frequent entry and exit disrupt the air curtain
The operator's arm is the biggest way to introduce external pollution. Every time the arm enters or exits the workspace, it will cause disturbances in the surrounding air. If the arm crosses back and forth directly above the tabletop, or frequently enters and exits, it will continue to damage the air curtain barrier at the work window. SOP must emphasize that all required equipment should be placed in one go before operation; During the operation, the arm should be extended parallel and slowly to avoid making large movements directly above the table; Try to maintain elbow stability and perform fine operations only on the wrist and forearm to reduce the number of entries and exits.
 
4、 The residual gas after UV lamp sterilization has not been completely discharged
Most operators immediately turn off the UV lamp and start operating after sterilization by UV irradiation. However, ultraviolet lamps generate ozone during operation, which has strong oxidizing properties and not only stimulates the human respiratory tract, but may also cause chemical damage to some samples or reagents. The correct process should be: after turning off the ultraviolet lamp, turn on the fan and keep the work area running empty for a specific period of time, so that residual ozone is completely discharged, and at the same time, let the high-efficiency filter re-establish a complete clean airflow environment. If this step is omitted, although the sterile environment is present, the chemical cleanliness has been compromised.
 

5、 Return air pollution before terminating operation
After the operation was completed, many personnel directly turned off the power and left. At this time, trace particles or aerosols generated during the operation are still suspended in the workspace. If the machine is stopped immediately, these particles will settle and adhere to the surface of the table or residual equipment due to gravity, becoming a source of pollution for the next round of operation. The standard finishing action should be: after cleaning the table, maintain the fan running for a period of time to allow the laminar airflow to carry out residual particles and trap them in the filter, then turn off the power and turn on the ultraviolet lamp for final disinfection.