Sampling low concentrations of particles can be costly and time-consuming. A technique called sequential sampling can help minimize the number of samples needed by testing probabilities of events. This technique can be extended to different sampling intervals like time or volume. By setting upper and lower limits on counts, it is possible to accept specified concentrations with desired probabilities. Sequential sampling can make decisions with very few samples at extremely low or high probabilities of finding particles. Taking multiple samples with evaluation after each sample can also lead to quick decisions. These approaches could be useful for cleanroom certification.