What is a Laminar Flow Cabinet?
This type of cabinet is a mechanically ventilated device that discharges uni-directional airflow at a controlled speed across a defined workspace. The device provides a zone of particle free ‘clean’ air in which sensitive work can be conducted. They are used in the pharmaceutical, medical, electronic, and industrial sectors and vary in size to suit the application.
These cabinets generally comprise a structure housing a fan unit, high efficiency particulate air (HEPA) filter and a work surface. They provide protection to a product or sample being held within the controlled ‘clean’ zone but unlike a microbiological safety cabinet they do not provide protection to the operator.
Laminar flow cabinets are also known as flow cabinets, clean benches, laminar flow benches.
Types of Laminar Flow Cabinet
There are two common types, Vertical and Horizontal, describing the airflow direction.
Vertical Laminar Flow Cabinet:
These units discharge particle free air vertically downwards onto the work zone where it changes direction and then leaves the cabinet horizontally via a fixed opening or aperture. The constant outflow of air provides a barrier to prevent airborne contaminates from entering the working chamber.
This type of cabinet is also known as a Downflow Cabinet.
Horizontal Laminar Flow Cabinet:
A Horizontal Laminar Flow Cabinet discharges particle free air horizontally, out of the cabinet towards the operator. The constant flow of uni-directional or laminar HEPA filtered air acts as a barrier and prevents airborne contaminants from entering the work zone.
There is no need for a specific design and performance standard for flow cabinets. The only reference standard generally used is BS EN ISO 14644-1:1999 ‘Cleanrooms and associated controlled environments. Classification of air cleanliness’.
BS EN ISO 14644-1:2015 covers the classification of air cleanliness in cleanrooms and associated controlled environments. This is based solely on the concentration of airborne particles. Only particle populations having cumulative distributions based upon threshold sizes, ranging from 0.1μm to 5μm, are considered for classification purposes.
Most clean air cabinets are designed to maintain ISO 14644 Class 5 air cleanliness within their defined clean zone. ISO Class 5 air must have no more than 3,520 particles at or below 0.5 µm in size and no more than 29 particles at or below 5 µm. ISO Class 5 is equivalent to the old Class 100 Federal Standard 209E.
Where the cabinets are used for pharmaceutical processes in Europe the EU GMP standard will apply. A laminar flow cabinet can achieve a grade A cleanliness classification if the surrounding air is maintained and classified as Grade B.
Different grades of HEPA filter can be installed within the cabinet; the most common grade is H14 as defined by the European standard EN 1822.
Cabinets can be fitted with Ultra High Efficiency Filters (ULPA) and the standard grade is U15. It should be noted that filter efficiency quoted by some manufacturers is misleading. The term ‘ULPA’ filter as defined by IEST-RP-CC001.3 is used rather than that of EN 1822. The efficiency of a U15 grade ULPA filter should be 99.9995% @ 0.1 – 0.2 µm at the ‘Most Penetrating Particle Size’ (MPPS).