Methods
This experimental study was performed in the blast furnace plant of a steel industry located at the west of Iran. The basic information about the BF unit and its workers exposure were collected. Then, noise emission around the BF unit and personal noise exposure of workers were measured. In next step, noise control interventions were planned and its performances were estimated.
Study of noise levels around the blast furnace.
The sound pressure levels (SPL) around the BF were measured at each defined station characterized on designed grid map using sound level meter CEL.450 calibrated with CEL-110/2 based on ISO-9612 and ISO-11200 methods.
The furnace unit with 31 m in length, 15.8 m in width was divided into grid pattern squares of 4 x 4 m and finally, 32 measurement stations were considered. The noise map was designed by Surfer software. This software can display the buffers and isometric map of noise propagation in the measured domain.
Evaluation of the efficacy of interventions employed in the furnace unit was performed based on actual personal noise exposure. Then, the received noise dose was measured during 8 h before and after interventions using noise dosimeter TES-1345 calibrated with CEL-282. In this way, dosimeter was attached to the worker’s lumbar region and its microphone was attached to the worker’s collar from the back region. The rate of the dose received by three workers during the three work shifts of morning, evening, and night was measured.
Acoustic analysis of rooms based on noise transmission loss.
Acoustic characteristics of rooms and the walls separating those rooms around the BF were reviewed based on noise transmission loss. For determining of actual transmission loss, sound pressure levels were also measured in tow points besides the window and wall in the external and internal side of the rooms.
Design and implement of noise control solutions.
Based on the results of acoustic analysis, appropriate noise controls were designed for control room and rest room with considering the three criteria including interventions cost, efficiency and effectiveness.
In the control room, a UPVC window with vacuumed double-layered glass 80x80 cm and double wall for entrance by 90° rotate plus a 2.0×1.2 m steel door without glass were applied.
For the rest room, noise control solutions were including change the locations of the door and window towards the external side of the furnace and installation of two cameras to monitor furnace operation at rest times. For reduce exposure to direct noise, a wall facing to the furnace was made from the armed concrete with a thickness of 20 cm, length of 9 m, and height of 3 m and was located in the entrance by 90° rotate. For providing natural lighting, a window with ordinary 1.0×1.2 m glass panel was installed on the external side of the furnace behind the room.
For evaluation the results of noise control methods, data were analyzed using Excel software. For drawing the noise maps, Auto CAD and Surfer software for GIS calculation were used.