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Local exhaust ventilation for biological safety cabinets

posted on: November 9th, 2012
In any laboratory situation involving hazardous biological substances, a class 1 or class 2 laminar air flow cabinet should be used. We at Contained Air Solutions Ltd (CAS) manufacture a wide range of recirculating and exhaust-type biological safety cabinets, with our unique TriPass Onboard bypass exhaust system offering a unique solution for negative containment laboratories.

When working with biological agents, a COSHH assessment should be carried out to determine what level of biocontainment is required, including any LEV (local exhaust ventilation) issues. LEV involves maintaining a clean air environment by filtering airborne contaminants, not necessarily biological ones. Chemical vapours, dust from industrial machinery and even water vapour also come into this category, although the method of ventilation will vary. A biohazard cabinet, such as our BioMAT 2 Class 2 safety cabinet, is a specialised type of LEV device, specific to biomedical laboratories and similar environments.

How a COSHH evaluation affects the type of cabinet you use

Microbiological laminar air flow cabinet models vary according to whether the air is recirculated, exhausted or a mixture of the two. The UK does not have a classification system for type 2 biohazard cabinets, but broadly follows the American A2 model in which 70% of the air is recirculated back into the cabinet and 30% ducted to the outside via a thimble connection, or else exhausted into the room via a common plenum. Total exhaust cabinets are also available.

A COSHH LEV assessment considers all the hazards involved, not just those associated with biological agents. Generally, Hazard Group 1 (HG1) agents do not require a biological safety booth, but if volatile chemicals are involved then a suitable form of local exhaust ventilation, such as a fume cupboard must be employed. Where the work involves radioisotopes, the cabinet should be ducted direct to the roof, without the use of in-line isotope filters.

HG2 and HG3 experiments must never be carried out in a fume cupboard or laminar flow hood; instead, a class 2 or class 1 cabinet should be used. Hoods containing hazardous chemicals or radioisotopes must be ducted direct to roof level, although in the case of small volumes of volatile chemicals a cabinet ducted through a wall or window is permissible.

COSHH regulations and cabinet fumigation

COSHH regulation 7, which requires that exposure to hazardous substances must be controlled or prevented at all times, is as relevant to the fumigation of biological safety cabinets as it is to everyday use, especially as formalin - a volatile and hazardous chemical - is widely used in cabinet decontamination.

The rules for exhausting formalin vapour are the same as for any other chemical hazard. To prevent the re-entry of dangerous chemical fumes, exhausts should be sited at least three metres from:

• windows with opening latches
• air intakes
• the ground, if near pedestrian walkways
• nearby flat roofs
• nearby buildings

Ideally, a BioMAT 2 Class 2 safety cabinet should be exhausted to the roof at a minimum height of 2.5m, or to a wall with no opening windows but, where this is not possible, these tips will help minimise the contamination risks.
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Contained Air Solutions Ltd, Unit 4, Greengate, Middleton Junction, Manchester, M24 1RU. Tel +44(0)161 655 8860 Fax: +44(0)161 655 8865 Email: info@containedairsolutions.co.uk