The KI (potassium iodide) discus test is defined in the European Standard for microbiological safety cabinets, EN12469:2000 as a test method for validating the operator/aperture protection performance of the cabinet. The KI Discus test has been designed to enable operator/aperture protection factors to be measured for class I and Class II open-fronted biological safety cabinets. Unlike test methods employing a micro-biological aerosol challenge this technique enables cabinets to be evaluated without the risk of microbial contamination of either the biological safety cabinet or the laboratory and results are available almost immediately.


The Potassium Iodide Test

A fine mist of potassium iodide droplets, produced by a spinning disk, is used as a challenge aerosol to measure the containment of a cabinet or fume cupboard. Centripetal collectors sample the air outside or inside the cabinet - depending on the nature of the test. The collectors deposit any potassium iodide particles that are in the sampled air on to filter membranes. At the end of the sampling period the filter membranes are placed into a solution of palladium chloride whereupon the potassium iodide "develops" to form clearly visible and easily identified grey/brown dots.

A knowledge of the number of droplets in the challenge produced by the mist generator and the number collected in the air samplers enables the protection factor for the cabinet to be calculated. All open-fronted microbiological safety cabinets are assessed on this protection factor. The test method enabled through KI-DISCUS is fully described in British Standard BS5726-1992 and now BS:EN12469:2000.