I hope I may be forgiven for going slightly off-topic here. I had an interesting conversation with the saxophonist Gerard McChrystal over the summer about musicians' hearing. He spoke of a crisis waiting to happen to a whole generation of performers, because not enough attention had been paid in the past to the high volumes to which individual musicians are subject.
I cannot find the link now, but I recall watching a video of Lorin Maazel's Ring Without Words (the main themes of Wagner's cycle compressed into a symphonic piece). The (literal) hammer blows in the percussion section seemed to cause distress to the players around.
I couldn't really say how the risk for organists compares to that for other musicians. I imagine organ tuners don't have it easy!