This chapter explores a progressive learning curve that has occurred over the years with regard to particle monitoring, in several of its various forms. Primarily, a photo-ionization detector was used to monitor for hydrocarbons, and an RDM 101 OPC and a Piezo balance were used to monitor for particles. Rapid empirical measurement of smoke leakage, made possible by real-time air-monitoring techniques, was used to identify problems before extensive quantitative testing was conducted. The chapter provides case studies demonstrating how particle monitoring has been used in real-world applications. A particle counter was used intermittently to measure the decay rate of smoke levels inside the glove box. Transient excursions were seen at the mannequin breathing zone by the particle counters whenever the hood was approached to observe the performance of the effuser and whenever a hand and arm entered the hood space to adjust the source cassette located behind the dust effuser.