This is the view of the GPMTCP from in front of Battery Ash. The underground rooms were behind the visible Observation Booths, the east (near) side was gas proof, the west (far) side was not. The gas proof side had 2 12 inch cast iron pipe ceiling vents with valves that could be used to close them in case of an attack. The other side had 2 8 inch vents with no valves. The boiler room at the far rear corner had it's own 8 inch vent plus a chimney flue.

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