The Role Of Laminar Flow Hoods And Cabinets In The Lab

Laminar hoods, also called tissue culture cabinets

, are used in laboratories and industry to protect samples from contamination. They were first introduced in the 1960's as a smaller, more cost-effective alternative to a full scale cleanroom or as an extra-clean workspace within a cleanroom. Industrial cleanrooms can be thousands of square metres in size and require a long list of entry and maintenance procedures so the concept of a smaller scale option for laboratory and non-industrial environments was quickly accepted while the use of laminar flow workbenches within cleanrooms is now standard.

Laminar hoods take the form of an enclosed workbench area and use directional air flow and high efficiency particulate air (HEPA) filters to ensure a supply of sterile air to the work area. Air is drawn into the unit through a gross filter which traps dust and then through the HEPA filter where bacteria, fungi, spores and any other contaminants are removed.

There are different sizes of laminar hood which include individual stations and clean benches or free-standing enclosures where a number of technicians can work side by side. The smaller units are mobile and lightweight and can be placed where needed. The larger clean bench laminar stations are fixed units.

Apart from their size there are two main types of tissue culture cabinet, depending on the direction of their laminar flow. The first uses a horizontal flow, taking air in from the top of the unit, passing it through a HEPA filter and then sending from back to front, over the samples and into the room in even, parallel streams.

Vertical laminar flow brings in air from the top of the cabinet, filters it then passes it downwards towards the workbench. In some vertical laminar hoods, air is filtered before being passed out of the workspace. In these cases, the operator has some protection from any particulates that have been picked up as past of the tissue culture or manufacturing process although neither hood is specified for working with biologically hazardous material.

Laminar flow can describe the movement of a liquid or of air and in the case of laminar hoods describes the even passage of streams of air through the enclosed work spaces. It is important that the air is not impeded as this can cause dead spaces inside where particulates can build up or create eddies of backwash which allow unfiltered air to seep in from the laboratory.

An obstacle in a laminar hood is anything at all which disturbs the air flow including the operator's hand. In horizontal hoods the air flows towards and round obstacles creating less turbulence whereas in vertical hoods the air strikes the obstacle and creates more disturbance. In either case, some laminar hoods are vented to minimise turbulence and backwash.

Most of these products also has a UV germicidal lamp. It should be noted that the light emitted only kills germs that it actually comes into contact with and that operators should follow the standard precautions when utilising UV light.

Laminar hoods may come in many sizes and the two standard kinds may include many different variations but there is no question that they are widely used in the fields of manufacturing, biological and medical research, food technology and clinical laboratories everywhere.

by: Andrew Long

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