That is a compact burn area, and the only area to supply air is from underneath. You must have good coal, an adequate draft and the perfect situation to support combustion. Lots of us have been saying for years that the fires will burn for several days with the controls turned off. If you need it to go out, either burn the hopper down and remove any extra coal, or wait a couple weeks for the burn to slowly quit. You know I am kidding, but if the fire is that low, you can ventilate and dismantle the blower assembly and have it out, on the floor in about 15 minutes. When we do service work, seldom do we have the luxury of the boiler being dead cold. Only do what you are comfortable with, no dead hero's needed.