Airflow Pattern in Biosafety Cabinets and Laminar Flow Hoods | TechSule

Airflow Pattern in Biosafety Cabinets and Laminar Flow Hoods

Laminar Flow Hood is a container which is like a bench that provides a sterile environment, free from contamination. It provides a sterile environment for work but doesn’t protect the operator.

This type of equipment is used in laboratories to handle semiconductor wafers, biological samples or other substances that require purity. There is a constant passage of pure air in a Laminar Flow Hood. The air is passed through a High-Efficiency Particulate Air or HEPA filter and purified. This filter can remove airborne substances that can contaminate a sample. The sample is protected but not the user.

Biosafety Cabinets can be used when protection is required for an operator and the environment. This is similar to a glove box where the box is sealed.

Biosafety Cabinets Contain Several Options for Protection

  • Class I for the protection of the operator.
  • Class II and Class III for the protection of the specimen or product, the environment from any contamination and the user.
  • Class II cabinets allow open access to the working area while the Class III ones, known as glove boxes, have a barrier between the workspace and the operator.
  • The Class III cabinet is important for working with Level 4 agents of biosafety or other hazardous materials like pathogens or aerosols.


In a Laminar Flow Cabinet, the airflow can be vertical or horizontal. The air moves in one direction at the same speed. There is a minimal cross-over of air streams. In a Vertical Laminar Flow Hood, the air flows from the top to bottom where the filter is positioned on the top of the work area.

In a Horizontal Laminar Flow Hood air flows horizontally from a filter behind or on the back side of the work surface. In a vertical flow hood, the laminar flow is downwards, reinforcing gravity and sweeping particles out of the enclosure. However here the obvious obstacle is the work surface.

In a Horizontal Laminar Flow Hood, the air flows from the back wall of the work surface toward the opening. The air movement is horizontal from the viewpoint of the operator and eventually hits the operator’s face.

This type of flow may be risky as all particles flow towards the user or operator. The workbench is contaminant free, but those contaminants may be hitting the user. As such, if the operator also needs to be protected then the other option is a Biosafety Cabinet.

In a Biological Safety Cabinet, the air that flows across the workbench follows a parallel pattern. The cabinet has a negative pressure within, to prevent contaminants from escaping into the work area. Incoming air is passed through a HEPA filter and then to the work area.

It enters the plenum and 70% of the air is recirculated while the 30% is released safely outside through an exhaust after passing through a HEPA filter. These are best for Biohazards as the air isn’t pushed towards the operator.

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