Once a dust sample has been collected, it must be evaluated. Of principal concern is quantitation--determining how much dust or how many particles. Certain methods of quantitation are favored for the various sampling methods. The number basis is preferable for evaluating a pulmonary hazard, while the weight basis is preferred for toxic, radioactive, or explosive hazards. Number quantitation is usually employed for impinger, konimeter, molecular filter, and thermal precipitator samples. Weight quantitation is used for filter paper and electrostatic samples.