Massachusetts General Laws Part I. Administration of the Government (Ch. 1-182) Ch. 160, § 165

A passenger, mail or baggage car shall not be heated by a stove or furnace kept in the car or suspended therefrom unless it is temporarily necessary by reason of an accident or other emergency, and no method of heating such cars nor heater shall be used until it shall have been approved in writing by the department; but the department may from time to time grant such exemptions from the requirements of this section as may seem to it necessary or reasonable, and may grant permission to any railroad corporation to make such experiments in heating its passenger cars as the department determines is proper. A corporation which violates this section shall forfeit not more than five hundred dollars.