7.8 Explosiveness of Mine Gases
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7.8.2 Explosiveness Determinations with the USBM Method
Of all the existing explosiveness diagrams, the graphic produced by the USBM
(Zabetakis et al. 1959) is illustrated here.
In using this diagram, a point must first be represented on the x and y axes of
Fig. 7.8.
The x-axis constitutes the percentage of inert gases, in accordance with Eq. 7.22:
X (%) = N ex (%) + 1.5 CO 2 (%)
(7.22)
Excess nitrogen (N ex ) is calculated as:
N ex (%) = N 2 (%) − O 2 (%)
79.04
20.93
Hence Eq. 7.23
N ex (%) = N 2 (%) − 3.8 O 2 (%)
(7.23)
Equation 7.24 ensues:
X (%) = N 2 (%) − 3.8 O 2 (%) + 1.5 CO 2 (%)
(7.24)
Explosive
mixtures
Explosive when
mixed with air
Impossible mixture
in air
Non-explosive mixtures
Effective inert [Excess N2 (%) + 1.5 CO2 (%)] % Vol.
Effect. Comb. [CH4 (%) + 0.4 CO (%) + 1.25 H2(%)] % Vol.
Fig. 7.8 Explosiveness diagram for mixtures of N 2 , CO 2 , CH 4 , H 2 and CO at 26.67 °C and
atmospheric pressure. Modified from Zabetakis et al. (1959)