Quick Reference Guide to Cabinet types The following notes are designed as a guide to the different types of cabinets used in Laboratories, Pharmacies, Universities or Industry. They may be used as a guide, to help choose the type of cabinet best suited to the work being undertaken. It must be stressed however that advice as to the final choice of cabinet should be sought from your Health and Safety Office and a specialist supplier such as Vodex Ltd GLOSSARY OF TERMS IN GENERAL USE Pre-Filter These are fitted to remove large dust particles from the airflow to prevent the Main Filter blocking and to extend its life. HEPA This is a shortened version of High Efficiency Particulate Air Filter and refers to a type of filter used. HEPA Filters are tested using an average particle size of 0.3 micron and above. DOP Test This is a test carried out to check that a HEPA Filter is sound and undamaged. It is always carried out after installation of a new filter and should also be carried out each time the cabinet is serviced. The DOP Test aims to reproduce tests carried out on a HEPA Filter after manufacture in a more convenient form in the working environment (i.e. Laboratory etc). An oil is mixed with an inert gas to produce a smoke of a known particle size, this enters the cabinet via the Pre-filter. A probe on the clean-side of the filter looks for any trace of DOP smoke, which could have leaked through a hole in the filter or via a badly fitting seal on the filter. Any leak above the allowed maximum is indicated by an audible and visual alarm, the necessary remedial work must then be undertaken.
K.I. Discus Test This test applies to Microbiological Safety Cabinets only and is a test to prove the cabinet is working within the parameters laid down by BS5726. Newly designed Safety Cabinets are tested to prove compliance with BS5726 using a bacillus subtilis on plates which are then cultured. This method is time consuming and not suitable for use in the laboratory. The K.I. Test was developed using Potassium Iodide to give equivalent results in a shorter time. K.I. Test for Class I Microbiological Safety Cabinet The Class I Microbiological Safety Cabinet is designed to protect the operator at all times. Spray heads are therefore placed within the Cabinet facing out of the Cabinet directed to where the operator would normally sit. Filter papers, in holders, are placed outside the cabinet facing the spray heads. The Cabinet is switched on, giving an airflow into the Cabinet, the spray heads are then activated producing a fine mist of yellow droplets. Should any of the droplets escape from the Cabinet, they will be collected on the filter paper. The number of droplets trapped on the filter paper will determine a pass or fail for an individual cabinet. Positions of spray head and filter paper is laid down in Guidelines, full details can be supplied if required. The above test must be carried out five times consecutively; a pass must be recorded each time. K.I. Test for Class II Microbiological Safety Cabinet The Class II Microbiological Safety Cabinet is designed to offer protection for both the operator and the working environment. The K.I. Test is therefore primarily for a Class I Safety Cabinet, with an additional test to ensure a clean working environment. Control of Substances Hazardous to Health (COSHH) COSHH lays down guidelines on when protection against a chemical or particulate (dust) is required but not on which type of cupboard to use. Service Visit A service or more correctly check is required at least once per year on all types of cabinets mentioned in these notes as laid down in the COSHH regulations.
British & European Standards BS5726 & EN12469 covers the design and manufacture of Microbiological Safety Cabinets and Positioning. BS7258 & EN14175 covers the design and manufacture of Fume Cupboards and Positioning. EN18/22 European Standard for testing HEPA Filters. Laminar Laminar is a term used to describe the direction of the airflow within a cabinet, i.e. Vertical Laminar Flow or Horizontal Laminar Flow. These are described later. Advisory Committee on Dangerous Pathogens (A.C.D.P) Fourth Edition 1995, Published by HSE All hazardous material handled in a laboratory is categorised to give a hazard value, the A.C.D.P. has four hazard levels 1-4. Before choosing a Biological Safety Cabinet the material to be handled must be placed in a category (1-4) as this affects the type of cabinet used. See below. Definitions of Hazard Groups For the purpose of these definitions disease refers to disease caused by infection. Group 1 A biological agent unlikely to cause human disease. Group 2 A biological agent that can cause human disease and may be hazardous to employees; it is unlikely to spread to the community and there is usually effective prophylaxis or effective treatment available. Group 3 A biological agent that can cause severe human disease and presents a serious hazard to employees; it may present a risk of spreading to the community, but there is usually effective prophylaxis or treatment available. Group 4 A biological agent that causes severe human disease and is a serious hazard to employees; it is likely to spread to the community and there is usually no effective prophylaxis or treatment available.
CABINET TYPES Laminar Flow Cabinets - Laminar, this term means a straight uninterrupted airflow. Laminar flow cabinets are generally used where protection is required for the work or product i.e. in a pharmacy, or occasionally plate pouring. They come in two types:- Horizontal here the main HEPA Filter is placed immediately behind the working area, clean air is blown across the work surface towards the operator. Vertical here the main HEPA Filter is placed immediately above the working area, clean air is blown vertically down over the work surface. NB Laminar Flow Cabinets are primarily designed to protect the work or product and offer no operator protection. Some Vertical Laminar Flow Cabinets offer a degree of Operator Protection, these are not Biological Safety Cabinets and should be chosen with care and advice from your Safety Officer. Microbiological Safety Cabinets There are three types of Biological Safety Cabinets, choosing a cabinet should be done in conjunction with the A.C.D.P. Guidelines to assess the hazard levels of material being used, your Safety Officer and a recognised manufacturer. Class I A Class I Biological Safety Cabinet has an airflow into the cabinet in order to protect the operator from potential aerosols produced during normal work. A HEPA Filter is fitted immediately above the working area, air leaves the cabinet via this filter through a duct to atmosphere. This cabinet would be typically used in laboratories where patient specimens are handled prior to identification of any disease. Class I Safety Cabinets are normally vented to atmosphere (outside the building) via a duct using an exhaust fan mounted separately to the cabinets. (All exhaust ducting should be under negative pressure). Material in hazard categories in 1 3 as laid down in A.C.D.P. guidelines are normally used in a Class I Biological Safety Cabinet. See notes in Glossary for definitions of Hazard Categories.
Class II A Class II Biological Safety Cabinet is used primarily for research, e.g. using tissue culture techniques, as it offers a clean working environment combined with a balanced inward airflow at the working aperture giving a high degree of Operator Protection. A HEPA Filter mounted above the working area provides a vertical flow of clean air down over the work surface. This air is drawn under the work surface and up the rear of the cabinet, 70% is then recirculated back into the cabinet via the HEPA Filter mounted above the work surface. The remaining 30% of air exits the cabinet via a second (and sometimes third) HEPA Filter, the lost air is made up at the working aperture providing the Operator Protection. Class II Biological Safety Cabinets are normally used for hazard category 1 and 2 material as defined by the A.C.D.P. in Categorisation of biological agents according to hazard and categories of containment. See notes in Glossary for definitions of Hazard Categories. Category 3 material may be handled on occasion at the discretion of your Safety Officer. It is possible to duct Class II cabinets to the atmosphere if required. Class III This is a fully sealed Safety Cabinet accessed via sealed glove ports, material enters through a transfer hatch. Air is drawn into the cabinet via a HEPA Filter and exits to atmosphere via a HEPA Filter and exhaust duct with a separate exhaust fan. Class III Safety Cabinets are normally used for the Highest Hazard Category of material (4) under the A.C.D.P. guidelines and will normally be sited in a specially designed laboratory. Design details for the laboratory which houses the Class III cabinet can be found in the A.C.D.P. document. See notes in Glossary for definitions of Hazard Categories. Installation of Safety Cabinets Siting and Testing of Biological Safety Cabinets is very important, details can be found in BS5726. Advice is best sought from a recognised supplier or your Safety Officer as no two installations are the same. Class I and II Biological Safety Cabinets must be K.I. Tested to prove full compliance with BS5726 on completion of Commissioning. Further details are provided later. Fume Cupboards Fume Cupboards are designed to protect the operator usually from a chemical fume hazard, but can be used where dust is also a hazard.
Ducted Fume Cupboards Historically Fume Cupboards have drawn air through a front opening, the air then exhausted directly to atmosphere via an exhaust duct and fan. They are simple to use, straightforward, but can prove costly as exhaust ducts must run to a high level plus an exhaust stack. Pre-heated or cooled air is also lost so careful consideration is needed prior to installation. Filtration or Recirculating Fume Cupboards The Filtration Fume Cupboard operates in the same way as a ducted version and offers the same level of Operator Protection. Exhaust air is however filtered and returned to the laboratory via a charcoal filter and not exhausted to atmosphere as in a Ducted Fume Cupboard. Filtration or Recirculating Fume Cupboards offer more flexibility not being restricted by permanent ducting. However utmost care must be taken to select the correct type of charcoal, or mix of charcoal if a variety of Chemicals are being used. Regular testing must be carried out to enable carbon filter life to be estimated. It is therefore very important that advice be obtained from a specialist/safety advisor before a final decision is made on both type of filter used and testing. Installation of Fume Cupboards Ducted or Filtration Fume cupboards must comply to the positioning and installation requirements of BS7258. Your Safety Office should have a copy of this report. Down flow Bench A down flow bench is designed to draw air down away from the operators face without the need for an enclosure, as in a fume cupboard where an enclosure may be restrictive to the operation being carried out. Down flow benches can be ducted to the atmosphere or have filters to remove potentially hazardous material before exhaust air is returned to the working area. Care should be taken where a down flow bench is being considered for an application to ensure the correct levels of safety are achieved.
Summary Before choosing a cabinet you should assess the level of risk, decide the conditions you require from the cabinet, i.e. is the risk simply chemical or is there a biological hazard, are clean working conditions required? Siting within the workplace must also be considered carefully. If unsure on any points seek advice from your Safety Office or Vodex Ltd. You should then be in a position to approach a Company such as Vodex Ltd for costings and details on your chosen Cabinet. Airflow Characteristics Class I Microbiological Safety Cabinet - Air is drawn through a HEPA filter before allowing the clean air to the atmosphere via exhaust ducting Class II Microbiological Safety Cabinet (Recirculating) - Air travels under the work surface and behind the back panel of the cabinet where any particulate contamination is removed with the pre-filter. Air is then drawn into the plenum chamber where 70% of the air is recirculated back into the cabinet via the first HEPA filter. The remaining 30% is expelled through the exhaust HEPA filter before passing through a secondary exhaust HEPA filter (where fitted) before being safely returned to the laboratory. Class III Microbiological Safety Cabinet - With a sealed front panel (access via glove ports) clean air is drawn into the cabinet via an external HEPA filter. The air passes through another HEPA filter before being expelled to the atmosphere. Down flow Benches - Air is drawn through the perforated work surface into the large plenum chamber. The air will then be pulled through the pre-filter before passing through large capacity carbon filters. Clean air is then expelled through the ventilation grille on the right hand side. Filtration Fume Cupboards - Air is drawn through the aperture, collecting any fumes that may be present before passing through the pre-filter and then immediately through the main Carbon filter. Clean air is then vented out of the top of the cabinet and back into the room. If an optional outlet HEPA or Carbon Safety filter is fitted, the air will pass through this filter before being expelled. Horizontal Laminar Flow Cabinets Air is drawn in through the top of the cabinet passing through the pre-filter and then through the fan into the rear plenum chamber to ensure even distribution of air over the whole HEPA filter face. Vertical Laminar Flow Cabinets Air is drawn in through the pre-filter at the top of the cabinet. It then passes through the fan before entering the plenum chamber above the main filter. The air is distributed evenly before passing through the main filter.