LABORATORY SAFETY CABINETDr Fadhl Alakwa

http://fadhl-alakwa.weebly.com/

BIOLOGICAL SAFETY CABINET USES

Biological Safety Cabinets offer protection from microbiological contamination in the laboratory environment, including both operator and product protection.

Application: pharmaceutical, medical, clinical research, defense, education and general healthcare sectors.

BIOLOGICAL SAFETY CABINET NAMES

microbiological safety cabinet. Other frequently used names include safety cabinet, bio-safety cabinet, biological cabinet and laboratory safety cabinet.

clean rooms, laminar flow equipment and fume extraction systems.

BIOLOGICAL SAFETY CABINET CLASSES

There are several different main types of Biological Cabinet, specified by purpose and construction.

There are three main classes of Biological Safety Cabinet.

Class 3 cabinets offer the greatest protection.

Class 1 Biological Safety Cabinet

Class 2 Biological Safety Cabinet

Class 3 Biological Safety Cabinet

CLASS 1 BIOLOGICAL SAFETY CABINET A Biological Safety Cabinet

with a working front aperture through which the user can carry out manipulations inside the cabinet.

It offers operator protection via inward airflow allowing the escape of airborne particles generated within the cabinet with the aid of HEPA filtration of the exhaust air.

This type of Biological Safety Cabinet is suitable for work with all types of biological agent, except Hazard Group 4.

Class I Cabinets offers protection for the user but no protection for the work.

CLASS 2 BIOLOGICAL SAFETY CABINET

A Class 2 Biological Safety Cabinet has a front aperture through which the operator can carry out work inside the cabinet. Notably, it provides both worker and materials protection.

Class 2 Biological Safety Cabinets are the most in use bio-containment devices protecting worker, product and environment from potentially dangerous microbiological agents.

A Class 2 Biological Safety Cabinet is designed to control airborne contamination of the work and reduce risks of exposure of the operator to any airborne particles dispersed within the cabinet from the work procedures.

CLASS 2 BIOLOGICAL SAFETY CABINET The process is controlled by re-

circulating filtered air over the work area combined with inflow air passed through the working aperture.

The escape of airborne particles generated within the cabinet is controlled by means of an inward airflow at the front of the cabinet which is filtered before circulation within it, while the downflow filtered air over the working surface protects the work.

While both Class 2 Biological Cabinets provide additional protection to the work in the case of both the Class 1 and Class 2 type of safety cabinet the pattern of air flow through the working aperture can be disturbed by sudden movements by the operator or around the cabinet. Class 3 Cabinets provide greater protection still.

CLASS 3 BIOLOGICAL SAFETY CABINET

Class 3 Microbiological Safety Cabinets provide total barrier protection for the operator and are suitable for extreme bio-hazard work. Inflow air is HEPA filtered before entering the Class 3 Biological Safety Cabinet via a side mounted inlet filter chamber.

Exhaust air is HEPA filtered before leaving the safety cabinet via a single or double HEPA filter, dependent on the customer’s specific technical requirements. Total enclosure of the working

area User separated from the work by a

physical barrier Filtered air continuously supplied

to the safety cabinet Exhaust air treated to prevent

contamination Creates total protection for user

and materials

CLASS 3 BIOLOGICAL SAFETY CABINET

Manipulations within the Class 3 Biological Safety Cabinet are carried out via gloves mechanically attached to the cabinet providing a total seal against any particulate contamination released within the main working area.

Only Class 3 cabinets which are totally enclosed units are suitable for work with Group 4 hazards.

MICROBIOLOGICAL HAZARD GROUPS AND SAFETY CABINETS

Bio agents unlikely to cause disease

May cause disease but a low hazard with the spread of disease unlikely and with prophylaxis/treatment available.

Hazard Group 1 Hazard Group 2

Can be handled on an open bench with no containment or clean air technology required.

Could be handled on an open bench but aerosol emissions will require containment, i.e. in a Biological Safety Cabinet.

Containment Level 1 Containment Level 2

MICROBIOLOGICAL HAZARD GROUPS AND SAFETY CABINETS

Possibility of a severe disease with spread of disease possible although prophylaxis/treatment is available.

Causes severe disease with serious bio-hazard risk and a high risk of spread of disease. With prophylaxis/treatment not normally available this is the most serious bio-hazard risk group.

Hazard Group 3 Hazard Group 4

Should be handled in a Biological Safety Cabinet.

Must be handled in the maximum bio-containment facility, i.e. a Class 3 Biological Safety Cabinet.

Containment Level 3 Containment Level 4

BIOLOGICAL SAFETY CABINET TESTING

Microbiological Safety Cabinets must be designed, sited, installed and operated in accordance with Standards and should be maintained in efficient working order, and managed by a suitably qualified person who adheres to the importance of regular containment and filter integrity tests.

It is a legal requirement that Biological Safety Cabinets receive ongoing testing to ensure their effectiveness is not compromised.

This includes examining HEPA filters and ensuring performance and containment criteria are met.

BIOLOGICAL SAFETY CABINET TESTING

A certificate of testing must be kept clearly visible on each cabinet. Inspection reports should also be made readily available for inspection by enforcing authorities

BIOLOGICAL SAFETY CABINET STANDARDS

BS EN 12469:2000 BS 5726:2005 BS EN 61010-1, BS

EN 292-1 and BS EN 292-2.

NSF/ANSI standard 49

HOW HEPA FILTERS WORK IN BIOSAFETY CABINETS

An essential component in any clean bench or biosafety cabinet is the high efficiency particulate air filter, commonly called a HEPA filter.

The HEPA filter removes particulates (generally called aerosols) such as micro-organisms, from the air. The HEPA filter does not remove vapors or gases.

HEPA filters used in clean benches and biosafety cabinets should have a minimum filtration efficiency of 99.99% against airborne particles 0.3 microns in size.

COMPONENTS OF A HEPA FILTER HEPA filters are made of

boron silicate microfibers formed into a flat sheet by a process similar to making paper.  Flat filter sheets are pleated to increase the overall surface area. 

Pleats are separated by aluminum baffles which direct the airflow through the filter.  Filter media is very delicate and should never be touched.

HOW A HEPA FILTER OPERATES:

A HEPA filter is designed to target very small particles, and therefore doesn’t work like a typical membrane filter, where particles larger than a given pore size of a filter are captured.  Instead, HEPA filters rely on a combination of three mechanisms to trap particles.

HOW A HEPA FILTER OPERATES:INTERCEPTION

where particles being carried in the airflow around the filter fibers adhere to the filter.  Particles must be within one radius of the filter fiber to be captured.

HOW A HEPA FILTER OPERATES:IMPACTION

Larger particles are often captured by the second mechanism, impaction.  Due to their size, these particles cannot adjust to sudden changes in airflow around the filter and essentially run into the filter fiber and become embedded. 

HOW A HEPA FILTER OPERATES: The final mechanism is

diffusion that occurs because of the way microscopic particles move and interact with surrounding molecules. 

This is described as Brownian motion, where molecules move in a random, zig-zag pattern because they collide with surrounding molecules.

This motion slows down a particle’s path through the HEPA filter and increases the probability that the particle will be captured by either interception or impaction.

HEPA FILTER EFFECTIVENESS The ability of a HEPA filter to remove particles

depends of the size and velocity of the particles.  Due to the mechanisms mentioned above, a HEPA

filter does not remove particles only ABOVE a certain size.  It can effectively remove particles both above AND below 0.3 microns. 

In general, large particles (greater than 0.3 microns in diameter) are captured by both the impaction and interception mechanisms, whereas small particles (less than 0.1 micron in diameter) are captured by the diffusion mechanism. 

Medium particles (from 0.1 to 0.4 microns in diameter) are captured by both the diffusion and interception mechanisms.  The most penetrating particle size is 0.3 microns.

HEPA FILTER MAINTENANCE

As the cabinet operates, the HEPA filter will collect particulates. The room and cabinet particulate levels along with the capacity of the building exhaust fan determines the life of a HEPA filter.

Under most laboratory conditions, you should expect a long filter life. However, misuse or a heavy particulate load within the cabinet will shorten any filter's life. 

When the cabinet can no longer maintain proper airflow balance due to the loading of the filters, they will need to be replaced.

REFERENCES

http://www.phac-aspc.gc.ca/publicat/lbg-ldmbl-04/ch9-eng.php

http://www.nsf.org/services/by-industry/pharma-biotech/biosafety-cabinetry/

http://www.biologicalsafetycabinet.co.uk/ http://

info.bakerco.com/blog/bid/252645/How-HEPA-Filters-Work-in-Clean-Benches-and-Biosafety-Cabinets