Abstract:
The French research institute, INERIS, requested the assistance of
the CSIR’s Division of Mining Technology in developing further
precautionary measures against explosions in their collieries. In
response to this approach, an on-board active suppression system
was adapted to meet their mining requirements.
This system is used on tunnelling machines in Germany where
the machine is positioned in the middle of the tunnel, which is
therefore not much wider than the machine itself. With this configuration,
the machine is never away from the tunnel face during the
cutting cycle. As a result, the possible volume in front of the
machine of combustible gas requiring suppression is less than
50 m3.
In South Africa this technology has been adapted to suit a twocut
mining method which entails greater distances from the face
and thus much larger volumes of methane mixtures requiring
suppression. The particular configuration of the Explo-Stop®
system being investigated required the suppression of possible
methane ignition volumes of up to 180 m3 of a 9% per volume
methane/air mixture. The volume is a consequence of the large
cross-sectional area of French underground workings and of the
two-cut mining method used in France. In order to take the second
cut in the coal seam, the machine is pulled back a maximum
distance of 4 m, leaving an air pocket in which gas can accumulate.
The machine-mounted system is required to effectively suppress
any flame ignited by such a large accumulated volume of methane.
The results of the protocol tests done at Kloppersbos showed
that the system was capable of suppressing all simulated methane ignitions for the prescribed conditions. This was achieved with a
temperature increase of less than a 100°C at the operator’s position
and without any flame being detected at this position.
