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.

a) PRE-FILTERS

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. Primary use: organic odours, hydrocarbons, aromatic solvents, animal odours, excrements, urines, acid odours, cadaverine, putrescine. Secondary use: oxygenated nitrogen compounds.

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. Primary use: radioactive iodine. Secondary use: hydrocarbons.

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. Primary use: formaldehyde. Secondary use: organic emissions, hydrocarbons, aromatic solvents, acid gases.

4. SUL FILTER

Primary use: acid odours, putrescine, cadaverine, acid gases, hydrogen sulphide, methyl mercaptan, sulphur compounds, sulphur dioxide, R.H.>85%.

5. ODOUR FILTER

Primary use: acid odours, putrescine, cadaverine, acid gases, hydrogen sulphide, methyl mercaptan, sulphur compounds, sulphur dioxide, nitrogen oxygenated compounds. Secondary use: organic emissions, hydrocarbons, aromatic solvents, hydrocyanic acid, R.H. <85%.

6. CYN FILTER

Primary use: hydrocyanic acid. Secondary use: organic emissions, hydrocarbons, aromatic solvents.

7. MERC FILTER

Primary use: mercury vapours Secondary use: organic emissions, hydrocarbons.

8. AMM FILTER

Primary use: ammonia and its derivatives Secondary use: organic emissions, hydrocarbons, aromatic solvents, alkaline odours, excrement, urines animal odour.

9. HEPA/ULPA FILTER

Primary use: powder and particulate.