Except as otherwise provided in this subtitle, this subtitle applies to all boilers and pressure vessels. This subtitle does not apply to: a boiler or pressure vessel that is under federal control or regulation; a pressure vessel that: is used to transport or store compressed gases; is constructed in compliance with specifications of the U.S. Department of Transportation; and when charged with gas, is marked, maintained, and periodically requalified for use, as required by the regulations of the U.S. Department of Transportation; an air tank that is located on a vehicle that is operating under the rules of other State authorities and is used for carrying passengers or freight; an air tank that is installed on the right–of–way of a railroad and is used directly in the operation of trains; a pressure vessel that does not exceed: 5 cubic feet in volume and 250 psig pressure; 1 1/2 cubic feet in volume and 600 psig pressure; or an inside diameter of 6 inches with no limitation on pressure; a pressure vessel that operates at a working pressure not exceeding 15 psig; subject to subsection (c) of this section, a vessel that contains water under pressure, including a vessel that contains air, the compression of which serves only as a cushion, if neither of the following limitations is exceeded: a design pressure of 300 psig; and a design temperature of 210 degrees Fahrenheit; a hot water supply boiler that is equipped with a safety relief valve and is directly fired with oil, gas, or electricity if none of the following limitations is exceeded: heat input of 200,000 BTU/hour; water temperature of 210 degrees Fahrenheit; and nominal water capacity of 120 gallons; a mechanical device of any of the following types: a pump; a compressor; a turbine; a generator; or a hydraulic or pneumatic cylinder; or the water–containing part of an air–conditioning or refrigeration system condenser or evaporator: that uses halocarbon refrigerant; that is constructed in accordance with the requirements of ANSI/ASHRAE Standard 15 (the Safety Code for Mechanical Refrigeration) in effect at the time of construction; and if neither of the following limitations is exceeded: a design pressure of 300 psig; and a design temperature of 210 degrees Fahrenheit. For purposes of subsection (b)(7) of this section, water may contain additives if the ASTM flash point of the aqueous solution at atmospheric pressure is 185 degrees Fahrenheit or higher.