An investigation into different aspects of importance in the understanding of explosibility of hybrid mixtures of coal dust,
air and gases potentially found within mine workings through a comprehensive laboratory program of explosibility tests
was conducted. Plotting of test results revealed that conditions of potential explosibility could be described using two
dimensional flammability limit surfaces- for coal dust/oxygen; methane/oxygen; and coal dust/methane mixtures. From
these plots, the three dimensional flammability envelopes defining the explosibility of the coal dust/methane/oxygen
mixtures can be defined and illustrated for a coal sample. The surfaces of the three dimensional envelope describe limits
which separate inert mixtures of coal dust and methane at varying oxygen levels from those concentrations which are
ignitable under defined conditions. It is considered appropriate to generalise that the geometric shapes of these limit
regions are applicable to all type classifications of coal dust. There are practical applications of these results to the
underground environment.
The action of free radical initiators in the propagation of a methane gas explosion was examined for its applicability to the
flammability of coal dust/gas/air mixtures. The oxides of nitrogen or NO x radicals have influence upon the lean limits of
flammability of hybrid mixtures and this is illustrated by use of three dimensional coordinate geometry. Gases can be
introduced to the underground environment through the exhaust gases of diesel equipment. It is concluded that radical
species can substantially increase the flammability of gas and dust flames and as a consequence raise risk of mine
atmosphere explosibility.