(1) pressure vessels meeting the requirements of the United States department of transportation for the shipment of liquids or gases under pressure;

(2) air tanks used on vehicles used for carrying passengers or freight or used directly in the operation of trains;

(3) pressure vessels having a volume of five cubic feet or less or having an inside diameter not exceeding six inches;

(4) pressure vessels designed for pressures of less than fifteen pounds per square inch;

(5) hot water supply storage tanks, provided none of the following limitations is exceeded: (i) a heat input of two hundred thousand BTU's per hour; (ii) a water temperature of two hundred ten degrees fahrenheit; (iii) a nominal water containing capacity of one hundred twenty gallons;

(6) pressure vessels under federal control or regulation;

(7) pressure vessels containing water under pressure, including those containing air, the compression of which serves only as a cushion, when none of the following limitations are exceeded: (i) a design pressure of thirty pounds per square inch; (ii) a design temperature of two hundred ten degrees fahrenheit; and

(8) pressure vessels used for agricultural purposes. 7. Cities. a. A city which qualifies under the provisions of this subdivision shall enforce the provisions of this section and the rules of the board promulgated hereunder and for such purpose shall have the powers of the commissioner prescribed in subdivision two of this section. In order to so qualify, a city shall have enacted a local law or ordinance requiring an inspection of all boilers required to be inspected by the provisions of this section located in such city, which inspection shall be conducted with at least the same frequency as is required by this section, but in no case more often than once a year. Such boilers shall be inspected by competent inspectors employed by the city except boilers inspected and insured by a duly authorized insurance company in accordance with the provisions of subdivision eight of this section and with the rules of the commissioner. b. The fee schedule contained in subdivision three of this section shall not apply within a city which qualifies under the provisions of this subdivision. Such a city may, by local law or ordinance, impose reasonable fees for the inspection of boilers by the inspecting agency of such city. 8. Inspection by insurance companies. a. All boilers which are inspected by a duly authorized insurance company shall be exempt from inspection by the commissioner and by cities which qualify under the provisions of subdivision seven of this section, under the following conditions: (1) that inspections by the insurance company are made with the same frequency as is required by this section except that, for all such boilers located within a city which qualifies under the provisions of subdivision seven of this section, inspections are made with the same frequency as is required by such city; (2) that the insurance company complies with the rules of the commissioner; (3) that the inspectors of the insurance company hold certificates of competency; (4) that the insurance company gives notice to the owner or lessee of each boiler inspected listing all violations of any provision of the rules of the commissioner; (5) that a certified copy of the report of each inspection is filed with the commissioner or the inspecting agency of such city, as the case may be, within twenty-one days of the inspection, on such forms and in such manner as required by the commissioner or the inspecting agency of such city, as the case may be. A copy filed with the commissioner shall be accompanied by a non-refundable fee of one hundred dollars paid for each boiler inspected. If insurance is refused, cancelled or discontinued for the boiler inspected the report shall so state, together with the reasons therefor; the report shall also list any instances of the failure of an owner or lessee of the boiler to comply with the rules of the commissioner. b. In order to satisfy the inspection requirements of this section, all inspections which are made by duly authorized insurance companies shall be made by inspectors whose competency has been certified by the commissioner in accordance with the rules of the board. The commissioner may, after a hearing upon notice, suspend or revoke a certificate of competency in accordance with the rules of the board. The commissioner may require reasonable cooperation from a city which qualifies under the provisions of subdivision seven of this section in the course of his or her investigation into the competency of a certified inspector. 9. Members of boards. Any member of a boiler inspection examining board or other board created pursuant to rules and regulations of the commissioner to implement this section shall serve without salary or other compensation.