Which quantity explicitly uses sample time in its calculation?

• A. Field area
• B. Fiber density
• C. Filter area
• D. Volume

Answer: (B)

Fiber density is a concentration measure expressed as fibers per unit volume of air. To turn a counted number of fibers on a filter into a density, you divide by the volume of air that was drawn through the sampler. That volume is obtained by multiplying the sampling flow rate by the sampling duration, so the sampling time appears explicitly in the calculation. Field area and filter area are fixed geometric quantities and don’t depend on how long you sampled. Volume itself comes from flow and time, but the density calculation inherently relies on that time to express the result as fibers per volume.