A steam boiler that operates at pressures that exceed 50 psig (gauge pressure of 345 kPa) or an industrial appliance larger than 100 ft3 (2. 8 m3) in size, excluding blower compartment, fan compartment, and burner equipment, such as an annealing furnace (glass or metal), a charcoal furnace, a galvanizing furnace, a gas producer, or a commercial or industrial incinerator.