No details yet but the news story said there was a small fire with high CO readings. Perhaps there was a smoldering fire that touched off a gas leak. Philly is famous for a lot of things and gas leaks is one of them. FYI, the chimneys and combustion venting in South Philly are a nightmare. There isn't a house I've inspected down there that shouldn't have the chimney rebuilt or at min. relined and the venting/ vent connections and equipment practices are always Wall of Shame material. Very few CO alarms down there and those only alert when the CO is at deadly levels and that's if the POS alarm is working at all or the kids didn't steal the battery. If you went down one block you would wonder why thousands don't die every night down there. As the efficiency rises, the destruction of chimneys and vents is escalating so this sort of thing will become much more commonplace. Inspect before you replace equipment! It's the law!
For what it might be worth, I have a good friend who is a really experienced firefighter (Captain). He told me that when they hop up on the roof of a burning structure and cut a hole in the roof the ventilate the structure, when the hole is made, there is almost always a huge tongue of flame shooting out of the hole. It is the trapped CO burning off.
Always made sense to me.