7.10 Coefficients of Gases Indicating the Evolution of Fires
277
Exercise 7.7 Let there be a mine gas sample with the following characteristics
10 :
• O 2 : 16,000 ppm,
• CO: 1.47%,
• CH 4 : 2.3%,
• CO 2 : 17%,
• H 2 : 0, and
• N 2 : 77.63%.
Calculate Graham’s and Trickett’s ratios and offer possible conclusions about the
potential status of fires in the mine.
Solution
Calculation of the key figures:
First, it is determined whether Graham’s expression is applicable:
O 2 =
20.93
79.04
N 2 (%) − O 2 (%) =
20.93
79.04
· 77.63 − 1.6 = 18.9 > 0.3
This expression might thus give rise to errors. Nevertheless, it can be computed:
GR =
100CO(%)
0.265(N 2 + Ar)(%) − O 2 (%)
=
100 · 1.47
0.265 · 77.63 − 1.6
= 7.75
Thus suggesting the presence of an active fire.
The Jones-Trickett ratio is now calculated:
TR =
CO 2 (%) + 0.75 CO(%) − 0.25 H 2 (%)
0.265(N 2 + Ar)(%) − O 2 (%)
=
17 + 0.75 · 1.47 − 0
0.265 · 77.63 − 1.6
= 0.95
This suggests a fire in the coal, in fuel or in a conveyor belt. Since the ranges are not
precise, it may even indicate the possibility of wood burning inside the mine.
7.11 Fire-Fighting Techniques
Fire-fighting methodologies include the displacement of O 2 and the reduction of
heat. These can be achieved by isolating the affected portion of the mine by means of
an adequate ventilation system, by creating inert atmospheres, by using foams and
sludge, or even by controlled flooding. As they are directly related to ventilation, the
10 Note that in the gas data the sum is 100%, without any account being taken of the concentration
of argon, probably because of difficulties in obtaining a detector for this gas.
277
Exercise 7.7 Let there be a mine gas sample with the following characteristics
10 :
• O 2 : 16,000 ppm,
• CO: 1.47%,
• CH 4 : 2.3%,
• CO 2 : 17%,
• H 2 : 0, and
• N 2 : 77.63%.
Calculate Graham’s and Trickett’s ratios and offer possible conclusions about the
potential status of fires in the mine.
Solution
Calculation of the key figures:
First, it is determined whether Graham’s expression is applicable:
O 2 =
20.93
79.04
N 2 (%) − O 2 (%) =
20.93
79.04
· 77.63 − 1.6 = 18.9 > 0.3
This expression might thus give rise to errors. Nevertheless, it can be computed:
GR =
100CO(%)
0.265(N 2 + Ar)(%) − O 2 (%)
=
100 · 1.47
0.265 · 77.63 − 1.6
= 7.75
Thus suggesting the presence of an active fire.
The Jones-Trickett ratio is now calculated:
TR =
CO 2 (%) + 0.75 CO(%) − 0.25 H 2 (%)
0.265(N 2 + Ar)(%) − O 2 (%)
=
17 + 0.75 · 1.47 − 0
0.265 · 77.63 − 1.6
= 0.95
This suggests a fire in the coal, in fuel or in a conveyor belt. Since the ranges are not
precise, it may even indicate the possibility of wood burning inside the mine.
7.11 Fire-Fighting Techniques
Fire-fighting methodologies include the displacement of O 2 and the reduction of
heat. These can be achieved by isolating the affected portion of the mine by means of
an adequate ventilation system, by creating inert atmospheres, by using foams and
sludge, or even by controlled flooding. As they are directly related to ventilation, the
10 Note that in the gas data the sum is 100%, without any account being taken of the concentration
of argon, probably because of difficulties in obtaining a detector for this gas.