Hearing loss as a result of working in or around aircraft is something that the RAF has been aware of since at least the early 1960's. Some time back whilst working on Human Factors at Cranfield Uni. I came across a medic who had worked on a project at Farnborough looking into this problem. As far as he could remember this was either 1961/2. The project concluded that whilst most jets of the period were capable of damaging hearing the worst by far was the Gloster Javelin. This was apparently something to do with the harmonics created by the Sapphire engines mounted side by side.