Page 436 - Advanced Mine Ventilation

Mine Sealing and Recovery 405

1. Always make sure the sampling line is outgassing (not intaking) when an air sample is drawn.
2. Preferably sample each location at the same time every day at the same intervals (that is,
every 4 or 8 h and so on).
3. Track total emissions of CO, CH 4 , and other gases if the mine is not sealed yet.
4. Purge the sampling line by letting the air pump run for a while when it is used to collect a gas
sample.
5. Increase sampling frequency if there is sudden change in the barometric pressure.
6. Trained personnel should be used for sample collection/gas analysis.

24.3.3 Interpretation of Air Analysis Data

The CO Index and CO 2 Index usually confirm if there is fire still burning. CO Index
has been defined in Chapter 21, Spontaneous Combustion of Coal. CO 2 Index was also
developed by Graham [6] and is given by Eq. (24.2).

CO 2 0.03
CO 2 Index ¼ (24.2)
100 O 2
where CO 2 and O 2 are expressed as volume percents.
In a normal mine atmosphere, the CO 2 Index tends to be zero. Once ignition occurs,
CO 2 Index increases and continues to increase with rising temperature. A persistently
increasing CO 2 Index also confirms existence of an active fire just as the CO Index
does.
The JoneseTrickett Ratio discussed in Chapter 21 can also be used for sealed areas
to determine what is burning. Values above 0.5 indicate that coal is burning.
When the above indices go to their baseline value (prior to a fire), they indicate that
the fire may be dead. Litton Ratio and Hydrocarbon Ratio are also used to confirm if
the fire is dead.

24.3.3.1 Litton Ratio (R)
It was developed by Litton [7] to confirm if fire in a sealed area is dead and is safe to
open up the sealed area. In order to derive an equation for R, we need to find three
parameters.

1. Equivalent air
2. Methane plus other hydrocarbons
3. Residual gas; Rg
Equivalent air is the oxygen equivalent of air and is equal to 4.774 O 2 (% by vol-
ume). In coal mines besides methane, only ethane is present in measurable quantities.
Hence,

Rgð%Þ¼ 100 4:774O 2 ðCH 4 % þ C 2 H 6 %Þ (24.3)