Page 24 - Advanced Mine Ventilation

Underground Coal Mine Atmosphere 7

Table 1.3 Permissible Exposure Limits for Coal Mine Air Contaminants

8-hr Time Weighted Limit Ceiling Limit
Contaminant (ppm) (ppm)
Methane (fresh air) e 1%e1.25%
Methane (return air) e 2%
Carbon dioxide e 0.5%
Carbon monoxide 50 77
Nitrogen oxide 25 37.5
Nitrogen dioxide 3 5
Sulfur Dioxide 5 10
Radon (uranium mines) 1.0 working level e
Respirable coal dust (United 1.5 mg/m 3 e
States)
Respirable silica dust (United 0.1 mg/m 3a e
States)
Diesel particulate matter (coal) 120 mg/m 3b e
Diesel particulate matter (metal 160 mg/m 3 e
mines)

a
Coal dust concentration is limited by silica concentration in the respirable dust by the following formula: respirable coal
dust ¼ 10/silica concentration in %, mg/m . 3
b
Applicable only in Pennsylvania and West Virginia in the United States. It is the most stringent standard in the world for
diesel particulate matter.

Table 1.4 Properties of Air
Molecular Weight 28.97
Specific gravity 1.00
a
Density (at STP ) 0.075 lb/ft 3
Atmospheric air pressure 14.7 psi

Specific heat at constant pressure 0.240 Btu/lb F
Specific heat at constant volume 0.171 Btu/lb F

Critical temperature and pressure Nitrogen: 147.1 C at 492.5 psi

Oxygen: 118.8 C at 730.6 psi
a
STP Standard temperature of 70 F and pressure 29.92 inches of Hg.