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Well. i think there are 8 or 9 vents, and the one leading to the marine Main Control area can be shut down from the other side (Data Processor #2) room. THe weldable place is marked with a crappy semitransparent texture.i do think the range of sieges is correct, as to siege a hive you gotta be very near it and ifaliens do let marines that far, they deserve it.