hey can someone help me out? specifically regarding the context of pics 39 and 41 which show these 2 beams:

were these beams cut by the workers? i see some acetane tanks, which might possibly be for blow-torches. But is that what was used to cut these beams?
the reason i ask is cuz of the gunpowder colored residue at the ends of the two beams. Can anyone verify how those beams came to be where they are?
thanks