Laminar Air Flow.

Introduction:

Also called a “Laminar Airflow Hood / Laminar Aseptic Hoods”.
A Laminar Airflow Hood (LAFH)/ Laminar Aseptic Hoods, or a workbench, is a primary engineering control device which provides the following services during aseptic compounding,

1) Clean air to the critical sites (immediate aseptic compounding area),
2) Constant flow of air out of the work area to prevent the entry of room air, and
3) Outward flow of air from the hood that suspends and removes contaminants which have been introduced in the work area by personnel.

A High Efficiency Particulate Air (HEPA) Filter is the most important part of a LAFH.
The air within the room is taken into this filter and passed through a pre-filter which removes the gross contaminants (lint, dust, etc.).
The air is then blown at a uniform velocity through the hood and HEPA filter in a unidirectional (laminar flow) manner over the aseptic area.
HEPA filter is a particulate filter which traps the airborne particles and microbes; but allows the gases to pass through.
HEPA filters should be fitted either at or near to the clean room inlet.
A pre-filter is fitted upstream of the HEPA filter, thus extending the final filter's life.
A fan is also fitted which pumps the air through the filter.
The filter medium used in HEPA filters 1S made up of pleated fiberglass paper.
Parallelly arranged pleats not only increase the filter surface area but also the air flow through the filter.

This parallel arrangement of filter medium also allows the filter to retain a compact volume.
The filter material is sealed to an aluminium frame within the filter.
One side of the filter is protected with a coated mild steel mesh. HEPA filters provide,

HEPA filters remove larger, medium, and smaller particles from the air by inertial impaction, direct interception, and by Brownian diffusion, respectively.
The HEPA filters are least efficient in removing particles of about 0.3um size.
However, its efficiency of removing particles is affected by air velocity and filter packing.
It removes larger and smaller particles with more efficiency.

These hoods sweep the filtered air from the back to the front of the hood.
An electrical blower draws the contaminated room air using a pre-filter, to remove gross contaminants.
The air after passing through the pre-filter is accelerated so that a consistent airflow distribution reaches the final filter (HEPA filter), present at the back portion of the hood's working area.
HEPA filter removes 99.97% of 0.3µ or larger sized particles, thus removing most of the 0.5µ or larger sized airborne microorganisms.

These hoods sweep the filtered air vertically.
The air passing through HEPA filters merges from the top and passes downward through the working area.
When a foreign object comes in between the sterile object and the HEPA filter, the wind turbulence in the critical area increases, and foreign contaminants are carried to the sterile work surface, thus contaminating the injection port, needle, or syringe.
For ensuring complete sterility, nothing should pass behind a sterile object in a horizontal airflow hood; and in case of vertical airflow hood, nothing should pass above the sterile object.
The materials within the compounding work area interrupt the pattern of air blowing from the HEPA filter.

It should be placed away from traffic, doors, air vents, or anything that can produce air currents, to avoid entrance of contaminants.
It should remain on for 24 hours otherwise, non-filtered, non-sterile air occupies the compounding work area.
Before using the LAFH, its interior working surfaces should be disinfected using 70% isopropyl alcohol and a clean, lint-free cloth.

Plexiglas sides present in some types of LAFHs, should not be cleaned using alcohol but with warm water and a germicidal detergent (e.-g.Lysol).
HEPA filter grill (protective grill) should be cleaned in such a way that it does not get wet.

Other objects like Paper, pens, labels, or trays should not be placed in this area.

The operators during compounding should not wear any jewellery on hands or wrists since they affect the integrity of personnel clothing (gowns and gloves).
The operators should minimise talking and should cough away from the compounding work area.
The operators should avoid or reduce the unnecessary movement within or around the LAFH to minimise the airflow turbulence.
Smoking, eating, gum chewing, and drinking are strictly prohibited in the aseptic environment.
The objects should be arranged to get full benefit of the laminar air flow.
Critical items should be placed close to the air source.
The objects in the horizontal hood should not be placed closer than 3 inches from the back of the hood (ensuring that nothing should be in direct contact with the filter).
Testing should be done on a regular basis by qualified personnels.

It has various applications, especially where an individual clean air environment is required for smaller items, e.g., particle sensitive electronic devices.
It is used for special operations in laboratories.
It can be tailor made to the specific requirements of laboratories and are also used for general lab work, especially in medical, pharmaceutical, electronic, and industrial sectors.

A laminar airflow hood Should remain on for 24 hours. lf it is turned off; it should be left on for at least 30 minutes for its disinfection before use.