As used in this article, the following terms shall have the meanings indicated:
A steam boiler or battery of steam boilers having a single or combined rating of 75 or more horsepower at all times when the furnace or furnaces attached to said boiler or boilers contain fire or other generating elements.
A steam boiler or battery of steam boilers containing, singly or combined, 825 or more square feet of heating surface at all times when the furnace or furnaces attached to said boiler or boilers contain fire or other generating elements.
A steam boiler or battery of steam boilers on which or on any part of which the safety valve or valves are set to open at a pressure of 15 pounds or more per square inch at all times when the furnace or furnaces attached to said boiler or boilers contain fire or other generating elements.
A steam boiler or battery of steam boilers having a single or combined evaporative capacity of 2,585 pounds of water per hour from and at 212° F. at all times when the furnace or furnaces attached to said boiler or boilers contain fire or other generating elements.
Any device, apparatus, motor machine or combination thereof used to operate refrigerating, water-cooling or air-conditioning plants having a single or combined capacity of 30 tons or over.
Any person operating a stationary boiler for the generation of steam under 50 horsepower or 75 pounds' steam pressure, except that this article shall not apply to any person so operating a boiler under the direction and supervision of a person licensed either under this article or under the provisions of the municipal ordinance of this City relating to the licensing of engineers for the operation of steam boilers and engines.
Any person who operates a portable power-produced or power-controlled equipment, including but not limited to the operation of derricks, pile drivers, hoisting equipment, road rollers, excavating equipment and cableways, whenever such equipment is operated by a unit producing 50 horsepower or more.
Any person who operates a stationary boiler or power-producing unit for the generation of power of more than 50 horsepower. Stationary engineers licensed hereunder shall be classified as of First Class or Second Class. There shall be no limitations as to the capacity of the power-producing unit which a First Class stationary engineer may operate. A Second Class stationary engineer, however, shall not operate any unit or units for the generation of power, the aggregate of which is in excess of 150 horsepower, unless under the direct supervision of a First Class stationary engineer.