This chapter provides detailed information of National Institute for Science and Technology standards for calibrating various air-sampling devices. Optical particle-counting instruments hold great promise for use in identifying and measuring releases of high-potency compounds. Optical particle counting based on discrete particle counts lends itself to observing the ambient versus incident experiences at very low levels of fugitive airborne releases. The chapter presents features of the different sampling devices. Typical dust monitoring is performed by counting particles down to either 0.5 µm diameter or 0.3 µm diameter in size, depending on the standard, to show the performance of the entrance air High Efficiency Particulate Air filter filtration efficacy and the gowning, robing, and cleanup procedures. Monitoring devics in a clean room are used effectively to measure a “go/no go” situation. The aerodynamic particle size is based on many years of experience in the environmental field using impaction collection devices, which have been calibrated by the American Society of Mechanical Engineers procedures.