MSHA HANDBOOK SERIES - PH13-V-1 - Mine Safety and Health ...

GENERAL COAL MINE INSPECTION PROCEDURES AND
INSPECTION TRACKING SYSTEM HANDBOOK CHAPTER 5
report. If the analysis of an air sample discloses a violation not determined with
testing instruments during the inspection, the inspector shall issue the appropriate
enforcement action.
B. Air Measurements.
Anemometer - Use a properly calibrated anemometer to measure the velocity when
calculating the volume of air for compliance with the Act and for calculating the
liberation of methane in, but not limited to, a return aircourse. When determining air
velocities, take a traverse reading of the cross section that is measured. Use correction
factors for the individual anemometers to determine the actual air velocity.
When measuring air velocities less than 100 feet-per-minute, the use of chemical
smoke may be necessary. However, if the instrument is calibrated for a lower
velocity, it is acceptable.
Pitot Tube - The pitot tube is a primary standard instrument for determining
velocities of 750 to 10,000 fpm. Velocities in excess of 2,000 fpm may crack the
bearings of ordinary vane anemometers and thus prohibit their use in high velocities.
High airflow velocity measurements are often required in auxiliary fan tubing or
main fan ducts. For such measurements the pitot tube is often the most practical
instrument. Commercial-type pitot tubes generally are accurate to within 1.0 percent
and specially made types can be accurate to within .01 percent.
Use the pitot tube in conjunction with a differential pressure gauge, such as a
manometer or water gauge, to determine the velocity pressure of the airflow. The
pressure gauge most commonly used by MSHA is the “Magnehelic”, which provides
a reading in inches of water (in. wg.). Using the inches of water reading, determine
the velocity and air quantity by calculation or by using conversion tables. Further
information about the techniques for using anemometers/chemical smoke and pitot
tubes is available in the 1960 Bureau of Mines Bulletin 589, “Introduction to Mine
Ventilation Principles and Practices.”
To convert inches of water to velocity, use the following formula:
V = 4005 √VP
Where V = velocity in feet-per-minute (fpm)
VP = velocity pressure in inches of water (in wg.)
NOTE: To correct centerline measurements, multiply velocity (V) by a method factor
of 0.9. The true velocity is then multiplied by area (A) to obtain air quantity (Q).
Release 1 (February 2013) 5-3