The following boilers and unfired pressure vessels shall be exempt from the requirements of RCW 70.79.220 and 70.79.240 through70.79.330 :

     (1) Boilers or unfired pressure vessels located on farms and used solely for agricultural purposes;

     (2) Unfired pressure vessels that are part of fertilizer applicator rigs designed and used exclusively for fertilization in the conduct of agricultural operations;

     (3) Steam boilers used exclusively for heating purposes carrying a pressure of not more than fifteen pounds per square inch gauge and which are located in private residences or in apartment houses of less than six families;

     (4) Hot water heating boilers carrying a pressure of not more than thirty pounds per square inch and which are located in private residences or in apartment houses of less than six families;

     (5) Approved pressure vessels (hot water heaters, hot water storage tanks, hot water supply boilers, and hot water heating boilers listed by a nationally recognized testing agency), with approved safety devices including a pressure relief valve, with a nominal water containing capacity of one hundred twenty gallons or less having a heat input of two hundred thousand b.t.u.'s per hour or less, used for hot water supply at pressure of one hundred sixty pounds per square inch or less, and at temperatures of two hundred ten degrees Fahrenheit or less: PROVIDED, HOWEVER, That such pressure vessels are not installed in schools, child care centers, public and private hospitals, nursing and boarding homes, churches, public buildings owned or leased and maintained by the state or any political subdivision thereof, and assembly halls;

     (6) Unfired pressure vessels containing only water under pressure for domestic supply purposes, including those containing air, the compression of which serves only as a cushion or airlift pumping systems, when located in private residences or in apartment houses of less than six families, or in public water systems as defined in RCW 70.119.020;

     (7) Unfired pressure vessels containing liquified petroleum gases.

[2005 c 22 § 2; 1999 c 183 § 4; 1988 c 254 § 20; 1983 c 3 § 174; 1972 ex.s. c 86 § 2; 1951 c 32 § 9.]