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?
Answer: (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).