I was in a similar situation when I joined, I was an ex soldier who used to be in my battalion shooting team. Even though I always wore ear protection, my right ear has suffered quite a lot. When I joined the fire service, I was a borderline pass, although I don't know what the unit of measurement that was used.
Last year I changed brigades, but during my transfer medical, I failed the hearing test. I was given a vocational hearing test which meant that I did certain tasks which were normal firefighting operations in order to check that I was safe operationally and passed the test with flying colours.
I was informed that prior to the Disability Discrimination Act, I could have been medically discharged for my hearing definciency, but as I had passed the initial hearing test and my hearing has deteriorated as part of my aging process, this is no longer the case as long as I can continue to pass the vocational hearing test.
I don't know if this test is possible for new entrants to the service but I would make enquiries about it if you fail the hearing test, you never know, it may all work out.
If you are asked which brigade the vocational hearing test was done by, direct them to the occupational health unit at Nottinghamshire Fire & Rescue Service, Bestwood Lodge, Arnold, Nottingham. Tel 0115 967 0880 and ask for the Occupational Health Department.
Good Luck
Kaiser