Which statement best describes the Walton-Beckett Graticule criterion?

• A. It sets a detection limit of 100 f/mm^2
• B. It requires exactly 7 fibers per cubic centimeter
• C. It allows either 7 f/cc or 5 fibers in 100 fields
• D. It uses 855 mm^2 as the operating area

Answer: (C)

The Walton-Beckett Graticule criterion is a practical rule for deciding when an air sample analyzed by graticule counting indicates a detectable fiber level. It gives two acceptable paths to a positive result: either the estimated concentration reaches seven fibers per cubic centimeter, or, when counting fibers on the graticule across fields, five or more fibers are found in 100 fields. This dual approach accounts for how fibers may be distributed on a filter and how counts translate to concentration, making the rule reliable and repeatable across technicians and samples. The other options don’t fit because the criterion isn’t defined by a single fixed detection limit like 100 f/mm^2, nor does it require exactly seven fibers per cubic centimeter in all cases, and it doesn’t depend on a specific operating area like 855 mm^2.