|
Different indices are use in different countries to
predict an outburst
Ettinger’s
Sorption/ Desorption index : This index was developed initially
by Ettinger
(1953) as the means of classifying coal in terms of proneness to
outburst. The gas emission index was based on the gas pressure build-up
( P) in millimeters
of Mercury (Hg) of coal enclosed in a pressure chamber of known dimensions.
This was also reported by Lama & Bodziony (ACARP
project C 4034, chapter 9, section 9.2.1) outburst scoping study.
Po-60
index: This index was developed as a follow up to P
0-30 index based on the work of Ettinger et
al (1953).This method was mainly used in Belgian coal mines (Vandeloise,
1964). P 0-60 Index
is used to estimate the liability of outburst in an advancing face. The
value has been found to depend upon the depth of the borehole and the
structure of coal ( ACARP C 4034
Chapter 9 Section 9.2.2).
Polish
Desorbometer: This instrument was mainly used in Poland for defining
outburst conditions in Anthracite mines with CO2 in the lower Silesian
coal field basin (Kozlowski and Polak, 1978 a, b). Its application in
Australian mines was also reported by Lama (ACARP
project no C3079, chapter 13, page 573).
KT
index: This index is a measure of the change in desorption
rate of coal sample ( ACARP C 4034
Chapter 9 Section 9.2.4). The index KT was determined by Janas and
Winter (1977) for Leichhardt Colliery, Gemini seam (Australia) as reported
in ACARP C 4034.
P
Express index: Developed by Paul,(1977), this method was used to
determine KT index when the automatic equipment for KT determination
was not developed ( ACARP
C 4034 Chapter 9 Section 9.2.5).
Gas
emission V index: The V index is the measure of the volume of gas
in the early stages of desorption of coal sample under atmospheric
pressure. This index was
used in France Somnier (1960) ( ACARP
C 4034 Chapter 9 Section 9.2.6).
Hargraves
emission rate: Hargraves
emission meter, measures gas emitted from the samples with virtually
no back pressure (± 25mm H2O) in a tube coiled flat on a plate.
This index has been widely used in several Australian coal mines, particularly
at Metropolitan and other mines in the southern coal fields of NSW,
and in some mines of Queensland ( ACARP
C 4034 Chapter 9 Section 9.2.7).
Gas
flow index G: This index has been used mainly in Russia, Ukraine,
Czech Republic and other Eastern European countries. The method is
based upon measurement
of gas flow from bore holes drilled in the face ( ACARP
C 4034 Chapter 9 Section 9.3).
Seam
thickness variation index Mm: Seam thickness variation index is
a measure of the tectonic stress which can cause local compression
of the coal seam. Seam thickness variation
index (Mm) was used in Bulgaria and Russia ( ACARP
C 4034 Chapter 9 Section 9.6).
V30 index :
This is an index of the initial desorption rate which defines the amount
of
gas liberated in the first 30 seconds after the coal face has been
blasted. It is a measure of the gas content of coal and the rate of gas
emission based on the assumption that the firing pattern and the amount
of explosive used remain the same. The underlying assumption is that
the outbursts manifest themselves when the gas content exceeds 9 m3/t
(Noak et al, 1983) ( ACARP C 4034
Chapter 9 Section 9.7).
|
