Published : PROCEEDINGS OF THE 7TH INTERNATIONAL MINE
VENTILATION CONGRESS, June 17-22, Crakow, Poland
PREVENTION OF SPONTANEOUS FIRES BY DIRECTED NITROGEN SUPPLY
A.S. Chumak
RESPIRATOR Research-andManufacturing Association on
Mine Rescue Work
Donetsk, Ukraine
P.S. Pashkovsky, M.A. Yaremchuk
RESPIRATOR Research-andManufacturing Association on
Mine Rescue Work
Donetsk, Ukraine
ABSTRACT
The most widespread means of localization and fighting the spontaneous fires are inert gases, water-air and inert
foams. In spite of this tactics of their use is developed insufficiently in the mines of Ukraine. In the first place it
concerns the directed inertization of the goaf. Analysis of cases shows that following mining-and-geological and
mining factors influence on the endogenic fire hazard most strongly. Air losses into the goaf exert the decisive
influence on development of the process of spontaneous ignition of coal. The zone of caved rocks is constantly
ventilated at their expense. It creates places of spontaneous combustion of coal. The performed investigations of air
losses through the goaf of the panels allowed to construct graphs of the dependence of air losses along the whole
length of the zone of active ventilation of the goaf for the most typical ventilation schemes. Determination of bounds
of the zone of fire-hazardous air losses, points of appearance of spontaneous heating places permits purposeful
nitrogen supply only there where places of spontaneous heating are formed. The point of the matter of the method of
prevention of the spontaneous fires consists in lowering the oxygen volume fraction up to 14% in the places of
spontaneous heating being predicted, which excepts spontaneous ignition.
KEYWORDS
Prevention, spontaneous fire, fighting, endogenic fire hazard, liability of coal to spontaneous ignition, coal oxidation,
air losses.
The most widespread means for localization and
fighting the spontaneous fires are inert gases, water-air
and inert foams. Tactics of the use is developed
insufficiently by their wide introduction in mines of
Ukraine. In the first place it concerns the directed
inertization of the goaf in the immediate proximity to a
place of spontaneous coal heating.
Analysis of cases of appearance of the spontaneous
fires shows that following mining-and-geological and
mining factors influence on the endogenic fire hazard
most strongly, viz.:
natural liability of coal to spontaneous ignition being
determined by its chemical activity with respect to air
oxygen (rate constant of oxygen sorption) and by
reaction heat of coal oxidation;
thickness and dip angle of a seam being mined;
tectonic disturbances;
strength properties of enclosing rocks, their
consolidation, permeability;
method of opening and preparation of the seam;
mining method and its parameters (especially such as
rate of face advance, seam thickness being mined, coal
losses in the goaf);
method and plan of ventilation, ventilating pressure
drop of mine and area.
Air losses into the goaf exert the decisive influence on
development of the process of spontaneous ignition of
coal. The zone of caved rocks being adjacent to the face
is constantly ventilated at the expense of air losses. It
promotes emergence of places of spontaneous
combustion of coal.
It was determined on the basis of results of
investigations that nitrogen is the most suitable for
inertization of mine atmosphere in the zone of firehazardous losses. In contrast to carbon dioxide it isn’t
disposed to dividing into layers when moving in air. It is
stipulated by nitrogen and air density values that are
similar to each other.
Over 30 years the mine rescuers use nitrogen and inert
vapour-gas mixture for fighting the underground fires in
mines. An attempt of realization of the technology of
active fighting the fires with nitrogen and vapour-gas
mixture was made in the “Your-Shor” mine of the
“Vorkutaugol” coal society (Пашковский, 1984) for the
first time. This mine is supercategorical in respect of
methane content. Operative use of volume inertization
prevented fire propagation, eliminated explosion hazard
and allowed to cool burning places.
straight-through ventilation directed to the pillar with
sub-freshening (figure 1d).
Experience of use of nitrogen for fighting the
spontaneous fires in mines of the Donbas and other
regions of the CIS is described in the works
(Пашковский, et al., 1992; Каледин, et al., 1985).
Periodic nitrogen feed into the fire-hazardous zones of
the goaf allowed to mine the k8, l8' and m3 seams in
Technology of inertization of atmosphere of accident
areas and equipment for its realization are described in
the normative documents developed by the NIIGD
(Игишев, 1987; Руководство…, 1989).
Analysing the cases of the use of nitrogen for fighting
the spontaneous fires mentioned above one can
conclude about high effectiveness of the method of
inertization of fire-hazardous zones of the goaf and
localization of places of spontaneous ignition of coal.
But volume inertization of the fire districts was used
more often. In spite of the fact that the cases of the use
of nitrogen for directed feed to the burning places are
adduced, the data concerning investigations of the
process of directed nitrogen feed into the zones of firehazardous air losses are not cited for all this. Carryingout such investigations allows to raise effectiveness of
the method of localization and fighting the spontaneous
fires with nitrogen.
Proceeding from above-stated the purposes of the
present work are investigation of the processes of
inertization of mine atmosphere and cooling the heated
coal accumulations by directed feed of nitrogen into the
zone of fire-hazardous air losses in the goaf.
Conformably to the most widespread mining systems
and development plans of panels one can pick out four
ventilation schemes that are the most characteristic for
mines of the Donbas:
inverted ventilation directed to the goaf (figure 1a);
inverted ventilation directed to the pillar (figure 1b);
straight-through ventilation directed to the goaf with
sub-freshening (figure 1c);
Figure 1.The most widespread ventilation schemes of
the panels mining flat seams.
The performed investigations allowed to construct
graphs of air losses along the whole length of the zone
of active ventilation of the goaf for the most
characteristic
(typical)
ventilation
schemes
(figures 2, 3).
In this case a value of air losses by running length
of 1 m of the zone of active ventilation of the haulage
gate (belt road) as well of the air roadway makes up
(depending on the ventilation scheme and consolidation
quality of packs) from 0.1 up to 6 m3/min which is
commensurable with capacity of the nitrogen
gasification plants the units of the State Para-military
Mine Rescue Service of Ukraine are supplied with.
The constructed graphs (figures 2, 3) give a general
idea of the character of air losses through the goaf (roof
control with roof caving). But it is necessary to measure
air volume entering the panel, longwall face and further
along the whole longwall face at intervals of 10…15 m
including the longwall face output in each concrete case
before the feed of nitrogen for the purpose of prevention
of the spontaneous fires.
Air losses, m3/min
Toshkovka, Bazhanow, 9th five-year plan and Chaykina
mines successfully. The equipment developed by the
Scientific-and-Research Institute of Mine Rescue Work
(NIIGD) was used in all the cases. Analogous
investigations and development of technology and
equipment for inertization of mine atmosphere in
workings and goafs are carried out in Russia by the
Russian Scientific-and-Research Institute (RosNII), the
Eastern Department of the NIIGD formerly
(Судиловский, 1984; Голик, et al., 1986; Игишев, et
al., 1982).
Distance, m
Figure 2. Air losses in the zone of active ventilation of
the goaf depending on distance to the longwall face
and accepted ventilation scheme:
1 – for inverted ventilation directed to the goaf;
2 – for inverted ventilation directed to the pillar.
Air losses, m3/min
Qi – rate of air flow passing along the longwall face at
the i – measurement point, m3/sec;
V1 – maximum value of the interval of fire-hazardous
velocities of air losses through the goaf, m/sec
(V1 = 0.0150 m/sec);
V2 – minimum value of the interval of fire-hazardous
velocities of air losses through the goaf, m/sec
(V2 = 0.0017 m/sec);
Distance, m
S – cross-section area of the longwall face, m2;
Figure 3. Air losses in the zone of active ventilation of
the goaf depending on distance to the longwall face
and accepted ventilation scheme:
1 – for straight-through ventilation directed to the
pillar with sub-freshening (air roadway); 2 – for
straight-through ventilation directed to the pillar with
sub-freshening (haulage gate); 3 – for straightthrough ventilation directed to the goaf with subfreshening (air roadway); 4 – for straight-through
ventilation directed to the goaf with sub-freshening
(haulage gate).
Boundaries of the zone of active spontaneous heating
for the inverted ventilation scheme of the panel with
directing an air stream returning from the longwall face
to the rock mass which is widely practised in mines of
the Donbas are determined from the mathematical
dependences:
 Q n  Qут  V1  S
A1  kl 

Q n  Qут



 ;



 Q n  Qут  V 2  S 
 ,
A2  kl 


Q n  Qут


(1)
where A1 and A2 – distances from the face up to the
neighbouring and distant boundaries of the zone
of active spontaneous heating accordingly, m;
k – index characterizing roof stability (k=0.5 for the
unstable roof; k=0.7 for the average stable roof;
k=1.0 for highly stable roof);
l – distance from the face up to the caving zone of the
rock mass where the process of caving the roof
rock and its placing in the goaf brings to a stop
(for conditions of the Donbas l=100…150 m);
Qn – rate of air flow arriving into the longwall face,
m3/sec;

Qут  max Qn  Qi )i 1,2... - air loss into the goaf,
m3/sec;
d
kmlQ n  Q ут ( S  hlk ) - dimensionless parameter
Q ут  S
charakterizing intensity of reduction of air losses
through the goaf depending on distance from the
longwall face;
А - width of the zone of active spontaneous
heating, m
А  А2  А1 .
Fire-hazardous zones and places of origin of the fires
in the goaf of panels in mines of the Donbas (flat and
inclined seams) are shown in figures 4, 5, 6 for four
ventilation schemes named before and being the most
characteristic.
Determination of boundaries of the zone of firehazardous air losses, points of appearance of
spontaneous heating places permits purposeful nitrogen
feed only into that part of the goaf where places of
spontaneous heating are formed.
Figure 4. Fire-hazardous zones of the panel by inverted
ventilation directed to the pillar (flat and inclined
seams).
Figure 5. Places of origin of the fires by straightthrough ventilation of the panel (flat and inclined
seams):
1 – return air borders upon the goaf; 2 – return air
borders upon the unworked coal.
Figure 6. Places of origin of the spontaneous fires in the
panel by inverted ventilation directed to the goaf
(flat and inclined seams).
As migration of nitrogen takes place in direction of air
losses the point of the matter of the method of
prevention of the spontaneous fires by its directed feed
consists in lowering the volume fraction of oxygen up to
14% in the places of spontaneous heating being
predicted. In this case the oxidation processes slow
down so that heat accumulation and spontaneous
combustion, therefore, are impossible. Intensity of
nitrogen feed can be 40…50% from the value of air
losses in the zone of the spontaneous heating place
being forecasted in this case.
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