|Decibel (dB(A)), Noise Induced Hearing Loss (NIHL), Temporary Threshold Shift (TTS), Permanent Threshold Shift (PTS), Corti, Cochlea
|The Noise Induced Hearing Loss (NIHL) is likely to happen in the Long Product Mill area because of high noise level. The findings suggest that more specific intervention is required to protect workers exposed to such hazards at the work places employed in this study.
|Like home and school, workplace is also an important part of man’s environment. The protection of the health and safety of the workforce from hazards related to work activities is an imperative that underpins health and vibrant economy of any country. Exposure to loud distracting and possibly hazardous noise is a common experience for everyone, but whether to allow such exposure to be hazardous to one’s hearing is often a personal not really a choice.
|The noise level measured at long products indicates that it is likely cause the Noise Induced Hearing Loss (NIHL). The NIHL is irreversible subtle change in the sensory cells and other structures in the organ of Corti (Sensory Hair Cells) in the Cochlea.
|As a result of which, the hair cells and supporting cells disintegrate and ultimately the nerve fibers’ that weaken the hair cells disappear resulting in permanent threshold shift and hence irreversible hearing loss at the higher frequencies. The adverse effects of Noise on hearing may be classified into three categories namely, temporary threshold shift (TTS), Permanent threshold shift (PTS) and a caustic Trauma source of the information. No study has been focused on workers who are working in Long Product Mills in Integrated Steel Industry. There is the need to conduct such investigation since several workers work in such areas where noise generated from the Stand Mills which are being used for rolling the steel ingots and producing the final products of different sizes of steel rods. Thus in this paper, results are presented of a study conducted to determine noise and post set noise levels after the engineering management change. Thus, there is reduction of noise level which meets the National and international standards might be more appropriate in summary section.
|The experimental apparatus used in recording the Noise Level at Long Product Mill is Quest Technologies Sound Level Meter (SLM), Model – NOISEPRO DLX Dosimeter, Serial Number: NX FO70051, CE 0539. The desired response of the SLM was set at Slow why?. When the measurement was made, the microphone was located in such way as not to be in the acoustic shadow of any obstacle in appreciable field of reflected waves. Noise levels were measured at the position of employees head while they kept their work posture. Five reading were taken for each stand and average one is recorded in the Table. The preliminary noise survey was made with the help of Quest Sound Level Meter and the readings were recorded. Time frame of study and locations along with hours or time of day, operation areas etc. were included.
|Works Environment at Wire Rod Mill and Bar Mill
|The Wire Rod Mill and Bear Rod Mill have installed the Rolling Stands for rolling the higher size ingot to desired size steel rods. The rolling stands produces the noise during mill running time. The predominant noise has been observed at the initial stage.
|- The rolling stands have cylindrical roller bearing.
|- These bearings are lubricated by AIR-OIL system.
|- Air carries oil at a design pressure of 3 to3.5 bar in the form of “mist”.
|- From the mist, the oil particles lubricate the bearing and the air was creating
|- High pitch noise is generating from the Roller Bearing Housing during discharge time. What we are talking about here is highly unclear.
|The main contributory factor for high noise level is due to air-mist was not getting discharged after the lubrication of roll bearings. This was prompted the Research to be carried out through the engineering control method.
THE ROLL STAND AND BEARING ASSEMBLY ARE SHOWN BELOW
|Roll Stand and Roller Bearings
|After commissioning the Mill, the noise level was beyond Threshold Limit Value. Workers are experiencing dissatisfaction due to high noise level. During noise survey, it was observed that the noise level was found to be more at Roll Bearing Housing Assembly of the Mill Stand. It was decided to change the oil seal material from metallic to non metallic.
|Engineering Control Method ( Change Management)
|The modification of existing cooling system so as to achieve the desired and acceptable results of noise level.
Replacement of Oil Seal from Metallic to Non Metallic
|After surveying the works environment, the technical discussion was done with the concerned technology supplier and user department. It was decided to carry out the necessary modification to bring down the noise level. Initially, it was decided to change the Metallic Oil Seal of the Bearing Housing Assembly to Non Metallic Oil Seal. After the specification change of the oil seal, there was slight reduction in noise level but it was not appreciable change in the works environment.
|Changing the height of slots in spigot
|After modifying the height of the slot in the Spigot of the Inner Retainer Ring, there was substantial reduction of level by 10 dB(A). But, there was mild gushing noise was observed from Bearing Housing Assembly.
|The height of the slots in the spigot of inner retainer ring has been increased from 3.5 mm to 7 mm which helped in discharging the air from inside to outside without causing much noise.
|Step – 3
|Providing Additional Holes on Ring
|Further technical study was carried out to eliminate the gushing noise. It was given thought that drilling hole of size of 1.5 mm to 2 mm on ring at three equal angles so as to let out the cooled air from the housing. After drilling the holes, the noise level was substantially reduced to acceptable levels.
|Further, 1.5 mm to 2mm size holes are drilled on Labyrinth Ring spaced at equal angles so as to discharge adequate cooling air after the cooling the bearing assembly. At this stage, it was observed that the noise was brought down substantially.
|No more modification was possible to carry out on Bearing Housing as it may affect the cooling system. Hence, the Noise Survey was carried out at this Stage and Noise Level was measured and recorded at both Bar Rod Mill and Wire Rod Mill.
|The observation of noise level have been shown in the Table 1 and 2 and the graphical representation was shown in Graph 1 & 2 respectively.
|After achieving noise reduction level through the change management, it was given thought to enforce the preventive control measures so as to achieve the maximum comfort for workforce.
|The various methods for reducing exposure to noise in place of work can be summarized under three headings:
|A. R eduction at Sources
|The noise reduction at source is moderately achieved through the
|a. Replacement of Oil Seal from Metallic to Non Metallic
|b. Changing the height of slots in spigot
|c. Providing Additional Holes on Ring:
|The above three steps has been achieved through the Change Management.
|B. R educing the noise energy by preventing its propagation
|The vibrating machinery parts and structures are prevented with the help of padding. Equipment maintenance practices have been followed from time to time so as to ensure smooth running of machineries. Proper upkeep and repair of machinery and equipment will do much to reduce noise. Regular inspections are being carried out to ensure healthiness of the equipment.
|C. H earing protection
|The workers should be well educated about the hazards out of the work noise. The Training Program on Noise Induced Hearing Loss (NIHL) is to be conducted and the importance of Ear plug and its attenuation level should be briefed. The ear plug reduces the noise level by 29 dBA and further reduction of noise level is possible if they use the Ear muff which reduces noise level by 20 dBA. Further, the employees are to be trained in proper use of Ear Protection Equipment so as to feel comfort from noise hazard. The quality of Ear muff and its material used absorbing the sound plays a vital role in noise attenuation level.
|Meaning of Decibel (Symbol dB)
|B means Bell the sound Pressure and Deci means One Tenth (1/10).
|Sound Pressure Level (dB(A))=10.Log( pA / p0)2
|Where: pA = A-Weighted Sound Pressure in Pascal (Pa). p0 = Reference Sound Pressure of 20 Micro Pascal (20μPa)
The letter (A) in dB(A) stands for A-Filter to compensate for the Subjective Loudness Level (Sensitivity) of the average ear, when presenting objectively measured in the Frequency Domain
|There are different Filters used dB(A), dB(B), dB(C) and dB(D). The following graph shows dB Vs. Sound Frequency in Hz. For different Filters and the most commonly used Filter is dB(A) shown in Blue line is a smooth curve.
|OSHA has put new emphasis on protecting workers from hearing loss. Most workers subject to noise should have an annual audiogram. If there is a shift in their hearing threshold relative to their baseline audiogram of an average of 10 dB or more in the 2000, 3000 and 4000 hertz (hz) frequency levels, in either ear, the worker must be rested within 30 days and the person must be logged as injury on the company’s OSHA 300 report. If the standard threshold shift in hearing still exists after the reset, the hearing loss is permanently logged on that year’s OSHA 300 report and the employer must take several steps. Here are some of the most important ones.
|• Hearing protection or other means must reduce the noise levels to 85 dBA on an eight hour time weighted basis.
|• Fit or retrofit the worker to a clinical audio logical evaluation that includes evaluation as to whether hearing protection is aggravating a medical pathology of the ear. OSHA has established permissible noise exposure limits to help avoid the standard threshold shifts in working. If the noise level exceeds 85 dBA on a time-weighted average, a hearing program is required.
|Source : http://ohsonline.com/articles/2007/09/ industrial-noise-control.as
|Very high noise levels exceeding the Threshold Limit Value were observed in the Long Products that is Bar Rod Mill and Wire Rod Mill which was posing serious threats of Noise Induced Hearing Loss (NIHL) were effectively reduced to acceptable Levels as per OSHA-Standards after carrying out the Engineering Management Change and Administrative Controls.
|The Noise Levels were measured at Long Products that is Bar Rod Mill and Wire Rod Mill using Quest Sound Level Meter (SLM), Type -2 Model 2700. Tables 1 & 2 and Graphs 1 & 2, clearly shows that there is reduction of 15% of Noise Level by Engineering Management Change. Further, impact of noise level on the hearing capabilities upon the workers can be achieved by enforcing the administrative control measures such as use of personal protective equipThe Noise Levels were measured at Long Products that is Bar Rod Mill and Wire Rod Mill using Quest Sound Level Meter (SLM), Type -2 Model 2700. Tables 1 & 2 and Graphs 1 & 2, clearly shows that there is reduction of 15% of Noise Level by Engineering Management Change. Further, impact of noise level on the hearing capabilities upon the workers can be achieved by enforcing the administrative control measures such as use of personal protective equipment namely ear plugs and ear muffs which in turn reduces the noise level by 39 dBA
|Noise Reduction Ratings (NRR) is the measurement, in decibels, of how well a hearing protector reduces noise as specified by the Environmental Protection Agency. The higher the NRR numeral the greater the noise reduction. While wearing hearing protection your exposure to noise is equal to the total noise level minus the NRR of the hearing protectors in use. For example, if you were exposed to 80 dB of noise but were wearing earplugs with a NRR of 29, your actual noise exposure would only be 51dB.
|Noise Reduction Rating : http://www. coopersafety. com/NoiseReduction.aspx
|When dual Protectors are used, the combined NRR provides approximately 5-10 decibels more than the higher rated of the two devices. For example using disposal ear plugs (NRR 29 dB) with ear muffs (NRR 27 dB) would provide a Noise Reduction of approximately 39 decibels.
|Ear Plugs + Ear Muff = Noise Reduction of 39 dB appx.
|NRR 29 dB + NRR 27 dB
|The engineering control method – change management includes Change of metallic oil seal to non-metallic and Modification of slots in the spigot and providing the holes on ring resulting the reduction of noise level.
|This change management is recommended for air-oil cooling system of high speed rotating machine- ries.
Tables at a glance
Figures at a glance
- Permanent hearing Loss:
- Noise reduction
- Noise Reduction Rating : http://www. coopersafety.