30 CFR §57.22229

1. (a)The mine atmosphere shall be tested for methane and carbon monoxide at least once every seven days by a competent person or an atmospheric monitoring system, or a combination of the two. Such testing shall be done at the following locations:
   1. (1)The return of each split where it enters the main return;
   2. (2)Adjacent to retreat areas, if accessible;
   3. (3)At least one seal of each sealed area, if accessible;
   4. (4)Main returns;
   5. (5)At least one entry of each intake and return;
   6. (6)Idle workings; and
   7. (7)Return air from unsealed abandoned workings.
2. (b)The volume of air (velocity in Subcategory I-A mines) shall be measured at least once every seven days by a competent person. Such measurement shall be done at the following locations:
   1. (1)Entering main intakes;
   2. (2)Leaving main returns;
   3. (3)Entering each main split;
   4. (4)Returning from each main split; and
   5. (5)In the last open crosscuts or other ventilation openings nearest the active faces where the air enters the return.
3. (c)Where such examinations disclose hazardous conditions, affected persons shall be informed and corrective action shall be taken.
4. (d)Certification of examinations shall be made by signature and date. Certifications shall be retained for at least one year and made available to authorized representatives of the Secretary.