Laminar airflow is an enclosed bench cabinet. It is designed to prevent contamination of biological samples or any particle-sensitive materials.
Principle:
The air is passed through a HEPA filter which removes all
airborne contamination to maintain sterile conditions.
Construction:
It is low cost and does not require more space. The cabinet
is made up of stainless steel without gaps or joints thereby preventing the
buildup of bacteria from collecting anywhere in the working zone. They are also
known as clean benches because the air for the working environment is
thoroughly cleaned by the precision filtration process. They consist of a
filter pad, a fan, a light with 100 lux, and UV tube to disinfect the bacterial
growth, and a HEPA filter. The fan sucks the air through the filter pad to trap
the dust particles. After that, the pre-filtered air has to pass the HEPA
filter where all the microorganisms are removed 99.97% of airborne particles
0.3 µm in diameter. Finally, sterile air flows into the working area without
risk of contamination. The air flows at a speed of 100 ft/min and sweeps dust
particles making the entire room free of particulate matter. This helps to
perform work under aseptic conditions.
Air Flow Pattern:
Generally, airflow patterns in clean rooms are of three
types viz. unidirectional airflow, non-unidirectional airflow, and combined airflow.
Unidirectional airflow is an airflow pattern in which essentially the whole
body of the air within a confined area moves with uniform velocity and in a single
direction with parallel air streams that means it is an airflow where a fluid
flows in one direction with no interruptions from turbulence. It should have
uniformed airflow at a speed of ± 15% and the speed of the air is measured as
it exits the HEPA / ULPA filter (Fig.1).
Fig.1: Unidirectional airflow
Non-unidirectional air flow is an air distribution where the supply air entering the clean zone mixes with the internal air using induction. The room air change rate per hour is calculated by the total airflow for the room divided by the room volume and a capture hood is used to measure the volume of air exiting the HEPA / ULPA filter (Fig.2).
Fig.2: Non-Unidirectional airflow
Combined air flow is a combination of both Unidirectional
and Non-Unidirectional air flows (Fig.3).
Fig.3: Combined airflow
Advantages:
• The persons working in the area do not feel the movement
of the air.
• The body of filters is made up of stainless steel which is
not favorable for bacterial growth.
• The HEPA filter can reduce the contamination.
Types:
Mainly two types Vertical laminar airflow bench and
Horizontal laminar air flow bench.
(a) Horizontal Laminar Flow Cabinets: In this
cabinet, the direction of airflow comes from above but then changes direction
and is processed across the work in a horizontal direction. The constant flow
of filtered air provides material and product protection (Fig.4).
Fig.4: Airflow in Horizontal Laminar equipment
(b) Vertical Laminar Flow Cabinets: It is also the same
as well as horizontal Laminar Flow Cabinets with the laminar air directed
vertically downwards onto the working area. The air can leave the working area
via holes in the base. Vertical flow cabinets provide greater operator
protection (Fig.5).
Fig.5: Airflow in Vertical Laminar Equipment
Biological safety cabinets come in several classes. For all
classes, the air is HEPA-filtered before being released as exhaust.
Class-I Laminar Flow Hoods: They are very simple
laminar flow-hood styles. They provide adequate protection to both the user and
the materials being worked with, but they do not protect the work substance
from contamination. They are similar to chemical fume hoods, which contain hazardous
fumes but do not disinfect.
Class-II Laminar Flow Hoods: They provide an aseptic
environment in addition to protection from fumes and gases. They protect
competently from the dangers of hazardous materials. They are safe and ideal
for that application.
Class-III Laminar Flow Hoods: They provide the
ultimate level of possible protection. They are gas-tight and so protect the
worker from the danger of exposure to human pathogens. They are used for any
applications involving potentially infectious substances.