WAC 296-104-265
WAC 296-104-265. Installation—What are the requirements for unfired pressure vessels installed underground?
Unfired pressure vessels installed underground shall comply with the following requirements:
(1) A pit with concrete or masonry sides and floor shall enclose the underground portion of the unfired pressure vessel.
(2) Pit covers shall be removable.
(3) Clearances shall be as required by WAC 296-104-260 .