THERE is general agreement that hearing conservation programs are essential in industry in spite of the fact that there is a paucity of acceptable data relating to the long-term effectiveness of such hearing conservation programs.
The data to be presented in succeeding portions of this paper should constitute at least a start in the direction of evaluation of the long-term effectiveness of an industrial hearing conservation program.
The program to be described began in 1956 prior to the start of plant production. The plant in which it was conducted was one connected with the ore extraction industry. Preplacement audiograms were done on all prospective employees, with a work force of approximately 2,200 people. The reference audiograms were obtained using a portable audiometer in a testing booth. A biological (real ear) calibration was accomplished before each daily use of the audiometer, monthly on normals, with an annual return of the