Guide to Contamination Standards This guidebook is aimed at engineers, technicians and quality control personnel involved in contamination control. Its purpose is to make available accepted and widely-used cleanliness specification levels for liquid samples. The tables in this guide allow users of using automatic portable particle counters to see the relationship between raw particle counts at various sizes and the reporting code numbers of various contamination standards. A NOTE ON THE FIGURES USED Note that some of the table entries are defined as cumulative counts (e.g. “> 6µm”) and others are defined as differential counts (e.g. 6–14µm”). Instances of particle sizes given as “µm” refer to ACFTD (i.e. Air Cleaner Fine Test Dust) distributions. Instances of particle sizes given as “µm(c)” refer to MTD (i.e. ISO Medium Test Dust) distributions. All standards are in counts per volume, and provide easy methods for converting particle counts into limits that are simple to interpret. By noting the requirements of the standard, particle counts can be accurately converted to contamination levels.