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U.S. Department of Labor

Mine Safety and Health Administration
201 12th Street South, Suite 401
Arlington, VA 22202-5450

ISSUE DATE: June 16, 2006
LAST VALIDATED: 03/31/2021


                     Administrator for
                     Coal Mine Safety and Health

SUBJECT:   Common Air Courses and Examinations

Who needs this information?
Mine Safety and Health Administration (MSHA) enforcement personnel, coal mine operators, and miners’ representatives need this information.

Why is MSHA issuing this bulletin?
This PIB reminds the mining community of MSHA’s characterization of common air courses and the need to examine each separate intake and return air course in the mine on a weekly basis [30 CFR § 75.364(b) (1) & (2)].

What is the background for this PIB?
An air course is defined in 30 CFR § 75.301 as:

An entry or a set of entries separated from other entries by stoppings, overcasts, other ventilation control devices, or by solid blocks of coal or rock so that any mixing of air currents between each is limited to leakage.

In the 1992 revision of the ventilation regulations, the preamble discusses air courses
(57 Fed Reg at 20870).  This preamble states that “MSHA believes that air courses that are not common should be examined separately and has defined an air course to achieve this purpose.  The Agency does not consider air courses that are common only at each end to be the same air course if the separation between the common openings is more than 600 feet.  Weekly examination of all such separate air courses is necessary to ensure that the ventilation system of the mine is functioning properly.”

What are the main points of this PIB?
Common air courses are functionally equivalent to a single air course; therefore, weekly examination on only one side of common air courses satisfies the requirements of 30 CFR § 75.364(b) (1) & (2).  Air courses are considered common if they are connected through openings or cross-overs every 600 feet or less.  Each portion of air courses that are not connected at intervals of 600 feet or less with non-restrictive openings have to be separately traveled during the weekly examination.  The connections between common air courses should be of sufficient size to provide free air exchange through non-restrictive openings.  Non-restrictive openings provide at least 30% of the cross-sectional area of the non-examined side of the common air courses.  Non-restrictive openings are necessary to minimize potential changes to the mine ventilation system if roof falls, water impoundments, or other blockages were to occur in the unexamined side of the common air courses. 

What is MSHA's authority for this PIB?
30 CFR § 75.301, 30 CFR § 75.364(b) (1) & (2), Preamble to 1992 Ventilation Rule [Fed Register, Vol. 57, No. 95, p 20870].

Who is the contact person for this PIB?
Mine Safety and Health Enforcement, Safety Division
Don Vickers, (202) 693-9760

Is this PIB on the Internet?
This Program Information Bulletin may be viewed on the World Wide Web by accessing the MSHA Home Page  and then choosing “Compliance Info” under the “Compliance Assistance” menu, then choosing “Program Information Bulletins.”

Who will receive this PIB?
Program Policy Manual Holders
Miners’ Representatives
Underground Mine Operators
Special Interest Groups