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.