30 CFR § 75.361
Supplemental examination.
(a) Except for certified persons conducting examinations required by this
subpart, within 3 hours before anyone enters an area in which a preshift
examination has not been made for that shift, a certified person shall
examine the area for hazardous conditions, determine whether the air is
traveling in its proper direction and at its normal volume, and test for
methane and oxygen deficiency.
(b) Certification. At each working place examined, the person
making the supplemental examination shall certify by initials, date, and the
time, that the examination was made. In areas required to be examined outby a
working section, the certified person shall certify by initials, date, and
the time at enough locations to show that the entire area has been
examined.