Surface Environment, Mine Ventilation and Underground Hazards · Underground Hazards · 2 marks · Numerical answer
The Coward diagram shows sealed-area gas composition A(CH₄7%, O₂17%). Sealed volume is 10000 m³. Find the minimum inert gas volume, at the same pressure, needed to reach the lower explosive boundary shown, in m³ to one decimal.
Mixing with oxygen-free, methane-free inert gas scales both percentages by the same factor f, so the dilution path has O₂=(17/7)CH₄. The lower explosive edge joins approximately(5, 20) and(6, 12), giving O₂=60−8CH₄. Intersection gives f=60/(17+8×7)=60/73. With additive gas volumes, f=10000/(10000+Vi); hence Vi=10000(73/60−1)=2166.7 m³. An arbitrarily greater volume moves below the boundary.
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