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My mother always seemed to be very concerned not to have our coal fire burning too fiercely. In fact she often panicked if she thought that the flames were getting too high in case the chimney might catch fire. I suppose her family's chimney must have caught light before she was married, or she would not have been so concerned.
As far as I know, no chimney in our house in Edgware ever did catch fire, but it did in my mother's nephew's house. He describes what happened below.
An occasion for excitement was when the chimney caught fire. When the coal was burned, soot (carbon) was deposited in the chimney. If the fire was too hot, and too much soot had built up, the soot itself could catch fire. This led to acrid grey smoke belching from the chimney, and such fires could be difficult to control, because the heat of the soot fire increased the draught in the chimney, drawing in more air from below, feeding the fire further. A roaring could be heard in the chimney breast, and the brickwork got hot. Meanwhile clumps of red hot soot could be falling down the chimney into the fireplace, and possibly falling out into the room.
Almost the worst part of a chimney catching fire was that all the neighbours could see what was going on. It was frowned upon to allow one's chimney to catch fire because it was considered to show a lack of proper management. Householders should, it was felt, have had the chimney swept before it got that bad.
It was difficult to put out chimney fires. Pouring water onto the fire didn't help, because the fire was in the chimney, not in the grate: pouring water on only succeeded in filling the room with smoke and ash. The best method was to starve the fire of oxygen, by blocking off the fireplace completely with an asbestos (or metal) sheet. If the fire could not be controlled, the fire brigade had to be called, which the neighbourhood enjoyed, but which was deeply embarrassing for the victim.