Mass. Gen. Laws ch. 146 § 46
No person shall have charge of or operate a steam boiler or engine or its appurtenances, except boilers and engines upon locomotives, turbines on test stands being operated solely for the purpose of testing such turbines by qualified testing personnel approved by the turbine designer and manufacturer, motor vehicles, boilers and engines in private residences, boilers in apartment houses of less than five apartments, boilers and engines under the jurisdiction of the United States, boilers and engines used for agricultural, horticultural and floricultural purposes exclusively, boilers and engines of less than nine horsepower and boilers which are provided with a device approved by the state fire marshal limiting the pressure carried to 15 pounds to the square inch, unless he holds a license referred to in section 49. Boilers and engines, not exempt under this section, of nine to 250 horsepower, in the aggregate, shall require periodic attendance, boilers and engines of 251 horsepower to 500 horsepower, in the aggregate, shall require noncontinuous attendance and boilers of 501 horsepower or more, in the aggregate, shall require continuous attendance. The owner or user of a steam boiler or engine, other than boilers or engines above excepted, shall not operate or cause to be operated a steam boiler or engine or its appurtenances for a period of more than one week, unless the person in charge of and operating it is duly licensed; provided, that in manufacturing plants an unlicensed person may operate, under a licensed person on duty, a simple non-condensing engine of not more than one hundred and fifty horse power, and in any plant one unlicensed person may be employed under the personal direction of each licensed person in the plant to operate the appurtenances of a boiler or engine.
As used in this section the following words shall, unless the context clearly requires otherwise, have the following meanings:
"Continuous attendance", manned attendance by a licensed operator during all times of operation.
"Noncontinuous attendance", in addition to the requirements of periodic attendance, a remote monitoring station shall be in place that has the ability to shut down the boiler and the boiler shall be inspected by the operator between four and six times per shift.
"Periodic attendance", a licensed engineer shall perform daily maintenance as required by the department's maintenance log book, the engineer shall remain in the same building as the operating boiler, the boiler shall be equipped with automatic shut-down devices as required by law; provided, however, that the safe operation of the boiler shall be the primary duty of the operator and such operator shall retain full discretion to return to the boiler room for monitoring purposes and all such visits shall be required to be recorded in the department's log book.
Mass. Gen. Laws ch. 146, § 46