sentences:  In addition to the inner opening to the fire passage, each room also has an outside door, through which recently fired brick is removed, and replaced with wet brick to be dried and then fired in the next firing cycle.In a classic Hoffmann kiln, the fire may burn continuously for years, even decades; in Iran, there are kilns that are still active and have been working continuously for 35 years.Any fuel may be used in a Hoffmann kiln, including gasoline, natural gas, heavy petroleum and wood fuel.