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

GENERAL COAL MINE INSPECTION PROCEDURES AND
INSPECTION TRACKING SYSTEM HANDBOOK CHAPTER 5
The average velocity obtained by the timed smoke cloud technique is about 10 percent
higher than the true velocity when readings are taken at the centerline of four quadrants.
Therefore, a correction called “method factor” should be applied. The method factor for
smoke cloud measurements in four quadrants is equal to 0.9. This factor, when multiplied
by the calculated velocity, yields the true velocity.
True Velocity = Calculated Velocity x Method Factor
True Velocity = 90.0 fpm x 0.9 = 81.0 fpm
STEP 3: CALCULATING AVERAGE AREA
The next step in determining air quantity is to calculate the average (Avg) of the airway
over the measured distance.
Example:
Release 1 (February 2013) 5-9