2 Test dust description Test dusts according to this part of ISO 12103 are manufactured from Arizona desert sand. Arizona desert sand is a naturally occurring contaminant consisting primarily of silicon dioxide with smaller amounts of other compounds. It is collected from a select area of Arizona desert, jet-milled and classified to specific particle size. 4 Particle size distribution Particle size distribution is determined using a Coulter1) Multisizer IIeTM particle size analyser. Table 2 specifies cumulative volume particle size limits for ISO-specified test dusts made from Arizona desert sand.