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Coronavirus Handling & Microbiological Safety Cabinets (MSCs)

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In our earlier article, Coronavirus Handling & Biosafety Levels we explained the UK government’s interim advice on the safe handling of samples of Coronavirus (SARS-CoV-2) and the disease it causes (COVID-19) in clinical diagnostic laboratories (COVID-19: safe handling and processing for samples in laboratories), different hazard group classification and corresponding biosafety/containment levels.

In the guidance, use of a MSC (Microbiological Safety Cabinet) for certain laboratory activities has been mentioned. In this article, we outline some basics about the different classes of MSCs and their functions.

Microbiological safety cabinets, also commonly known as biological safety cabinets (BSCs), are enclosed, ventilated laboratory enclosures/workstations designed to protect the user handling biological agents, the surrounding environment from release of pathogens and the product handled e.g. cell culture. All exhaust air is HEPA (high efficiency particulate air) filtered to remove hazardous agents such as viruses and bacteria.

MSCs are used in many laboratories including clinical, research and development labs but they are not designed to contain radioactive, toxic or corrosive substances.

MSCs are divided into the following classes.

GMP picture

Class I: An open-fronted cabinet through which air is drawn to minimise aerosol escape and is filtered through a HEPA filter before discharging to the laboratory air for re-circulation or ducting to the exterior of the building.

Class I cabinets protect the worker and the environment from contamination but provide no protection for the material handled, as unfiltered air is drawn inside the cabinet.

They are suitable to use for all types of biological agents except Hazard Group 4, HG4 (See Advisory Committee on Dangerous Pathogens (ACDP) document ‘The management, design and operation of microbiological containment laboratories’ for details). They are also useful to enclose equipment such as centrifuges, small fermenters or procedures that generate aerosols.

Class II: An open-fronted cabinet flushed with a downward draught which is HEPA filtered and re-circulated. 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 of HEPA filtered air over the working surface protects the work. Class II cabinets protect the worker, the environment, and the material handled and are suitable to use for all categories of biological agents except HG4.

Commonly used in microbiology, toxicology, diagnostic, and cancer research labs, class II cabinets protect bacteria, viruses, and carcinogens being manipulated inside the cabinet while shielding them from outside contamination.

There are four types of class II cabinets, A1, A2, B1 and B2, based on the amount of air vented outside of the building. Details about differences between the four categories is beyond the scope of this article but contacting a specialist supplier would be the best option.

Class III: Also known as glove boxes or isolation glove boxes, class III are totally enclosed cabinets providing maximum protection for the operator. Users can manipulate materials inside by using rubber gloves that are attached to the cabinet. These type of MSCs are mostly used for HG4 biological agents.

Anaerobic chambers are also available. These units allow researchers to easily process, culture and examine samples without exposure to atmospheric oxygen.

MSC Classes Collage

Source - Slideshare

Performance criteria for MSCs are given in British Standard BS EN 12469:2000.

To help decide which class of microbiological safety cabinet is right for your laboratory, a combination of factors such as the type of material to be handled, size, cost of running and maintenance, and available space will all need to be considered.

In the current situation for handling Coronavirus (SARS-CoV-2) and the disease it causes (COVID-19) samples, Class II microbiological safety cabinets should provide sufficient protection (subject to individual sample risk assessment).

References:

1. GOV.UK: COVID-19: safe handling and processing for samples in laboratories
2. HSE: The Control of Substances Hazardous to Health Regulations 2002. Approved Code of Practice and guidance

Dr Manisha Kulkarni
Head of Science & Technology
Bulb Laboratories

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