They were only hosing down the outside because most of the water didn't reach the top;)
Seems there was some confusion when the chimney passed from NCB to the council. Either someone forgot to explain the set up or it wasn't fully taken in by them. As when it fired a couple of times previously the simple solution was just to close the valve under the plate on the cap until the flames died off, wait a few hours then reopen it.
I don't know what will happen when, or even if, it fires again as, according to someone " in the know" the valve is reputedly seized. Against this he says the emissions here and at the other associated vents are much lower nowadays.