Page 30 - Advanced Mine Ventilation

Underground Coal Mine Atmosphere 13

Thus if silica concentration is 10%, the respirable dust standard is reduced to
3
1 mg/m . Additional details on dust measurement will be provided later in the book.
Both the mechanized mining units and the designated areas are sampled for an
effective control of respirable coal dust. Respiratory equipment, either a filter type
respirator or a supplied-air type device, is provided to a miner required to inspect dusty
3
areas with more than 1.5 mg/m of dust concentration.
1.5.3.2 Methane Measurements
30 CFR 75 requires frequent checks on methane levels. Each working area is examined
within 3 h of start of work for methane concentrations. A certified person uses an
approved device to measure and record all methane readings in a working area.
The second examination is on-shift measurement of both methane and oxygen. At
the working face, a reading should be taken every 20 minutes. In addition, each mining
machine is fitted with a methane detector. At 1.5% the machine gives a visible (yellow
light) and audible alarm. At 2% a red light comes on and electric power to the machine
is cut. The machine is not restarted until excess methane is cleared and safe levels of
methane are obtained.

1.5.3.3 Minimum Air Requirements

Minimum air quantities, often at specified velocities, are required to make sure all con-
taminants are adequately diluted.
Federal government requires a minimum of 6000 CFM for the development sec-
tions and 9000 CFM for longwall sections. These air quantities may be grossly inad-
equate if the coal seam is moderately or highly gassy [8]. State regulations of West
Virginia require larger air quantities because mines are gassier.

1.5.3.4 Permissible Electrical/Diesel Equipment
To further secure the safety of coal mines, all electrical or diesel equipment working
inbye of last open cross-cut must be permissible. Such equipment will not ignite an
explosive mixture of methane and air. This is verified in laboratory before a ‘permis-
sible’ certificate is issued. The 30 CFR is a large document and goes in detail to secure
mine safety. Reference can be made to it for additional information.

1.6 Definition of Air (Gas) Properties [9]

For a clear understanding, various properties of air and gases are defined in the
following section.

1.6.1 Atomic Weight

Atomic weight is the relative weight of the atom on the basis of oxygen as 16. For a
pure isotope, the atomic weight rounded off to the nearest integer gives the total