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7 The Role of Ventilation in Fires and Explosions
As examples, the Graham and the Jones and Trickett formulae will be considered.
Graham’s Ratio (1920)
This ratio works with the relationship between the carbon monoxide generated and
the oxygen consumed. It is calculated by Eq. 7.35:
GR =
100 CO(%)
0.265(N 2 + Ar)(%) − O 2 (%)
(7.35)
Each mine must establish its own characteristic ranges, although the normal values
for this ratio are below 0.5%. If the ratio is exceeded, it usually indicates heating of
the coal. Values above 3% reliably reveal the presence of a fire.
The following is the set of average values normally used in European mines:
• 0.4%: Normal,
• 0.5%: Check,
• 1%: Coal heating,
• 2%: Severe heating, and
• 3%: Active fire.
This index is generally not considered to be very reliable if O 2 < 0.3%.
Question 7.4 The following gas concentrations have been measured in a mine: N 2
= 77.23%, O 2 = 20.15% and CO = 18 ppm. Estimate the state of the coal seam.
Answer
O 2 =
20.93
79.04
· 77.23(%) − 20.15(%) = 0.3
Very little oxygen has been consumed, so the use of the Graham index does not
seem advisable, and no further opinions can be offered.
Jones-Trickett Ratio (1954)
Is the ratio between the oxygen required for combustion and the amount consumed
by burning. Its expression is the following (Eq. 7.36):
TR =
CO 2 (%) + 0.75 CO(%) − 0.25 H 2 (%)
0.265(N 2 + Ar)(%) − O 2 (%)
(7.36)
As in the previous case, in accordance with the values recorded some conclusions
can be reached. Among the commonest are the following:
• 0.5: CH 4 is burning,
• 0.7–0.9: Coal, lubricants or even a conveyor belt are burning,
• 1–1.6: Wood is burning, and
• Greater than 1.6: Such figures are not possible values for the ratio.
7 The Role of Ventilation in Fires and Explosions
As examples, the Graham and the Jones and Trickett formulae will be considered.
Graham’s Ratio (1920)
This ratio works with the relationship between the carbon monoxide generated and
the oxygen consumed. It is calculated by Eq. 7.35:
GR =
100 CO(%)
0.265(N 2 + Ar)(%) − O 2 (%)
(7.35)
Each mine must establish its own characteristic ranges, although the normal values
for this ratio are below 0.5%. If the ratio is exceeded, it usually indicates heating of
the coal. Values above 3% reliably reveal the presence of a fire.
The following is the set of average values normally used in European mines:
• 0.4%: Normal,
• 0.5%: Check,
• 1%: Coal heating,
• 2%: Severe heating, and
• 3%: Active fire.
This index is generally not considered to be very reliable if O 2 < 0.3%.
Question 7.4 The following gas concentrations have been measured in a mine: N 2
= 77.23%, O 2 = 20.15% and CO = 18 ppm. Estimate the state of the coal seam.
Answer
O 2 =
20.93
79.04
· 77.23(%) − 20.15(%) = 0.3
Very little oxygen has been consumed, so the use of the Graham index does not
seem advisable, and no further opinions can be offered.
Jones-Trickett Ratio (1954)
Is the ratio between the oxygen required for combustion and the amount consumed
by burning. Its expression is the following (Eq. 7.36):
TR =
CO 2 (%) + 0.75 CO(%) − 0.25 H 2 (%)
0.265(N 2 + Ar)(%) − O 2 (%)
(7.36)
As in the previous case, in accordance with the values recorded some conclusions
can be reached. Among the commonest are the following:
• 0.5: CH 4 is burning,
• 0.7–0.9: Coal, lubricants or even a conveyor belt are burning,
• 1–1.6: Wood is burning, and
• Greater than 1.6: Such figures are not possible values for the ratio.