U.S. Nuclear Regulatory Commission
Question 405: Regulatory Guide 8.25 (Section C.1.7) states that "to determine whether the concentration exceeds the DAC over the short term, the sample collection time should not exceed one hour. Shorter sample collection times may be used if desired, but they are not required."
(a) Does this section mean to imply that the duration of a work zone air sample should not exceed one hour if it may be used to determine whether an area needs to be posted or otherwise controlled?
(b) Under what circumstances does this one hour rule apply?
(a) No. The one-hour criterion applies only for sampling used "to determine whether the concentration exceeds the DAC over the short term" (emphasis added).
(b) The one-hour criterion is guidance; it is not a "rule." See answer to (a) regarding the circumstances of application.
(References: Regulatory Guide 8.25, 10 CFR 20.1902).