No person shall use or cause to be used any steam boiler operating at a pressure in excess of 15 pounds per square inch, or operating at a pressure less than 15 pounds per square inch unless provided with an unassisted gravity return, or any unfired pressure vessel operating at a pressure in excess of 60 pounds per square inch and having a capacity in excess of 15 gallons, except such vessels as may be exempted by the Council of the District of Columbia, without having first obtained a certificate of inspection from the Boiler Inspector.
