The filters used in the fume cupboards are manufactured from high grade coconut shell charcoal. All types of activated charcoal used in these filters are of amorphous structure obtained from the heat controlled oxidation of coconut shells. The cellulose structure of the coconuts provides the highest adsorption efficiency through a large surface area of up to 1050 m2/gm.
High performance pre- filters are designed to remove particulates from the air stream. The filter material is based on electrets, which are permanently charged di-electrics. They remove particulates from polluted air by strong electrostatic forces generated by the fibres from which they are made.
The combination of strong electric charges and open structure provides a filter with high efficiency, low air flow resistance and high loading capacity. Pre-filter efficiency is equal to 75-85% dust weight arrestance (ASHRAE).
b) MAIN FILTERS
Eight types of filter media are available. Most of these are impregnated activated carbon, to provide a higher filter capacity for lower molecular weight organic compounds and inorganic gases and vapours. A number of filter efficiency studies have been carried out, and all results using single bed filters show efficiencies very close to 100%.
1. A/C FILTER
The A/C filter is the most widely used filter in the range, and is used primarily for solvent fume removal. It is manufactured from coconut-shell based activated carbon of 4 x 8 USS mesh size and surface area up to 1050 m2/gm. Filtration is achieved by the physical adsorption of molecules in the pores of the activated carbon by Van der Waals forces.
2. ACR FILTER
This filter is impregnated with halide salts and is used for the high efficiency removal of iodine and methyl iodine. It is frequently used for iodination reactions with low-level radioactive iodine and efficiencies in excess of 99,99% have been measured.
3. FORM FILTER
This filter is impregnated with an oxiding agent to oxidise formaldehyde to form salts. It is widely used in hospital pathology and cytology laboratories.
4. SUL FILTER
5. ODOUR FILTER
6. CYN FILTER
7. MERC FILTER
8. AMM FILTER
9. HEPA/ULPA FILTER
HEPA stands for High Efficiency Particulate Air, this type of filter traps particulates and organisims such as dust and microbiological material.
Most HEPA filters are constructed by extensively pleating filter material, contained within a rigid filter housing. Sealant is used to bond the filter and a gasket is attached to the filter body to provide an air tight seal around the filter once fitted.
There are many applications for a HEPA filter, those commonly found within laboratory environments are H14 rated (penetrating particle size of >99.995%). They are usually housed within clean air devices such as safety cabinets and laminar flow clean benches to ensure the particulate free cleanliness of a specific environment.
For HEPA filter change, it is important the equipment such as safety cabinets to be fumigated prior to opening. It is possible for material contained within the HEPA filter to become dislodged and contaminate the environment and personnel if handled. We strongly advise an engineer is used to fumigate your HEPA filter equipment and perform the HEPA filter change on your behalf.