A Washington County jail guard who said he was assaulted behind the facility in October has resigned prior to a scheduled termination hearing before the county commissioners. Troy Lyons of Lubec resigned Thursday. He had worked at the Machias jail for 12 years. Sheriff Donnie Smith suspended Lyons after an internal investigation concluded that the multiple injuries for which Lyons was treated the night of Oct. 29 were self-inflicted. Smith told the Bangor Daily News that he concluded the assault was a hoax because of ‘‘improprieties and inconsistencies’’ in Lyons’s story.