The following steam boilers are not subject to this part:
(a) Boilers under the jurisdiction or inspection of the United States Government, and all other boilers operated by employers not subject to Division 4 of this code.
(b) Boilers on which the pressure does not exceed 15 pounds per square inch.
(c) Automobile boilers and boilers on road motor vehicles.
(Added by Stats. 1945, Ch. 1142.)