In the hallway, there's a vent just large enough for a small person to crawl through. It doesn't look like a heating unit, but rather and unused gas pipe. Given its size, it was probably used to carry gas to something like a smelter - maybe for metallic toy parts? It seems like there's enough ventilation to last a human a few hours, considering its size. That is, if anyone is willing to crawl through a dark, old vent.