In this title the following words have the meanings indicated. “Board” means the State Board of Stationary Engineers. “Boiler” means: a closed vessel in which water is heated, steam is generated, steam is superheated, or a combination of these functions is accomplished, under pressure or vacuum for use externally to the vessel by the direct application of heat from the combustion of fuels or from electricity or nuclear energy; or a fired unit for heating or vaporizing liquids other than water if the unit is separate from a processing system and is complete within itself. “Heating boiler” means: a steam boiler that operates at pressures not exceeding 15 psig; or a hot water boiler that operates at pressures not exceeding 160 psig or temperatures not exceeding 250 degrees Fahrenheit. “License” means, unless the context requires otherwise, a license issued by the Board to perform the functions of a stationary engineer. “License” includes, unless the context requires otherwise: a Grade 5 license; a Grade 4 license; a Grade 3 license; a Grade 2 license; and a Grade 1 license. “Provide stationary engineer services” means to oversee the operation of a power plant, plant of machinery, or boiler, each generating pressure of more than 15 psi and operating at 30 or more horsepower. “Provide stationary engineer services” does not include overseeing the operation of a heating boiler. “Stationary engineer” means an individual who is licensed by the Board to provide stationary engineer services in accordance with the license grades described in § 6.5–302 of this title.