I suddenly recalled my father's case. You might say that his was a one-time exposure to noise, though rather extreme.
He was having a fairly good war by all accounts. Somewhere up north. He didn't get hit by a bomb, but a shed. The said building, - that he was in or near - blew up. He got tinnitus at that moment.
They sent him off to Edinburgh to see a 'Brain Specialist', so one of his letters said. What a waste of time. Even then, they would have known what was going on - and that there was no treatment for tinnitus.