The biosafety cabinet, or BSC is an effective method of primary containment when working with infectious or hazardous biological substances at biosafety level 2 and above. A BSC is not required for level 1 work, although a laminar flow hood may still be useful to protect the experimental area from contamination from airborne particles, which can exist even in a clean room cleansed by a laminar flow of HEPA-filtered air at negative pressure.
We at Contained Air Solutions Ltd (CAS) realise there can be a lot of confusion over which laminar flow products to choose for particular biological situations, especially given the COSHH definition of a biological agent extends to cell cultures, allergens and endoparasites as well as micro-organisms.
Biohazard classification
In the UK, biological agents are classified into four hazard groups (HGs) according to:
• their pathogenicity to humans
• the risk posed to employees
• the risk posed to the community
• measures available to treat or prevent the disease
Each category has an assigned level of biocontainment, reflecting the risks involved. The categorisation of biological agents has legal status under the Health and Safety at Work Act, and while an approved list is available it is by no means exhaustive. A product deemed as low risk, for example, may change its status if it is genetically modified, and may no longer be suitable for handling in a BSL-1 (biosafety level 1) zone. It may have to be handled in a biosafety cabinet under BSL-2 or 3, instead. In addition, the HSE categorisation does not take into account the type of procedures and quantities involved, or factors such as compromised immunity among lab personnel, so risk assessments must always be done and a higher biosafety level allocated if necessary.
Laminar flow solutions for group 3 and 4 pathogens
Agents in biohazard group 3 and 4 have the ability to cause severe or fatal human disease, which can be transmitted to the wider community by inhalation. The main difference between the groups is that there is no known treatment or prophylaxis available for HG-4 pathogens, whereas there are for HG-3. However, it must be remembered that genetic modification may make previously treatable HG-3 microbes unsafe.
In a BSL-3 laboratory, all procedures involving infectious tissues or animals, where aerosols may be produced, must be performed using a BioMAT 2 Class 2 safety cabinet or similar primary containment device. Other criteria include isolating the room from the rest of the building, keeping it under negative pressure and HEPA-filtration of exhaust air.
The level 4 laboratory – two models for primary containment
In a level 4 laboratory, a biohazard cabinet must be used at all times, in addition to other criteria such as secure entry via an air-lock key, and double HEPA-filtration of both inflow and exhaust air.
Owing to the high level of barrier protection required, level 4 facilities are generally associated with Class III, or ‘glove’ cabinets. However, while the cabinet model is popular, there is an alternative: the suit laboratory. In this model, a positive pressure personnel suit, or PPPS, is used. While a biosafety cabinet must still be employed, the protection offered by the suit means a Class II laminar flow hood is sufficient.
