Hammer forges generate loud noise due to the multiple impacts required to form each part from preheated metal stock. Employees are required to handle the parts with tongs and continuously insert the parts into multiple dies where there is metal-to-metal contact as the parts are struck repeatedly by the hammer forge. The operators are thus exposed to frequent loud impact noise. The operators for the manual forging presses are within 3 to 15 feet of the source of very high noise levels. Over a typical 10-hour shift workers were routinely exposed to Time Weighted Average (TWA) exposures of 110-115 dBA, which far exceeded the OSHA 8-hour TWA permissible exposure limit (PEL) for noise of 90 dBA.
The company had long recognized the potential risk of the loud noise exposure to employees. A hearing conservation program was in place and employees wore hearing protection of their choice. Audiometric testing was conducted to screen for audiometric threshold shifts, and several shifts were noted during each annual testing program. However, follow-up testing and medical evaluation demonstrated that only one permanent threshold shift had occurred. In 2005, the company was inspected by the Tennessee Division of Occupational Safety and Health (TOSHA) and was issued a citation for failure to provide hearing protection that attenuates employees’ exposure to below the OSHA PEL. After the inspection, the company began requiring exposed employees to wear double hearing protection (ear plugs covered by ear muffs) when the forging operation was in progress. However, using the published criteria for estimating actual Noise Reduction Ratings (NRR), the double hearing protection could only reduce the noise exposure to the employees’ ears to an equivalent 8-hour TWA of 92 dBA and thus still exceeded the OSHA PEL.
The company had already implemented a series of engineering controls which provided some noise reduction. However, given the inherent loud noise levels associated with the hammer forging process it was felt that the incremental progress made was not sufficient to provide employee protection in the short run. Administrative controls were also considered but the maximum employee exposure to levels of 92 dBA would only be 6 hours per day which would cause serious problems with the facility’s 10-hour schedule and the incentive pay structure for hammer mill operators. Replacement of the hammer mills with mechanical screw presses was evaluated, but the capital cost of the presses would be prohibitively expensive to the point of making the facility non-competitive in the marketplace.
The company contracted with a speech and hearing center to test subjects in a controlled setting to determine the maximum effectiveness using the combined hearing protection. The center found that an attenuation of 41.5 dBA was possible which meant that an effective noise exposure to the employees’ ears could be less than a TWA of 80dBA. However, it has long been known that laboratory testing does not equate to real world experience, therefore the company retained a consulting firm that had developed technology to measure the noise dose to the ear during actual workplace operations. By embarking on a detailed sampling and monitoring program using the contractor’s technology, the company was able to demonstrate that, with proper training and supervision in the use of the dual hearing protectors, employees were protected to an average TWA of 79.6 dBA, thus reducing employee exposures to below both the OSHA action and compliance levels.
Impacts of the Intervention
As a result of the intervention the company was able to demonstrate to TOSHA that its employees were receiving an adequate level of hearing protection despite the published NRR calculation formulas. TOSHA accepted the intervention as proof that employees were not overexposed to damaging noise levels, in violation of the OSHA PEL. The intervention also provided additional assurance to both management and employees that the dual hearing protection was protecting their hearing. The intervention also demonstrated that the employee who had been removed from high noise exposure due to a permanent threshold shift could return to his former (and higher paying job) as a hammer forge operator.
No formal value proposition associated with the intervention was initially developed, as it was determined that other options would likely make the facility non-viable. Therefore, as part of the IH Value Study, a retrospective analysis was conducted of three possible strategies to achieve compliance: 1) use administrative controls, 2) purchase a mechanical screw press, and 3) use the hearing dose measuring technology to demonstrate an effective level of protection for employees. The following net present values (NPVs) for each of the projects was calculated for a project length of 5 years:
|Intervention Evaluated||Net Present Value ( ) = negative|
|1. Administrative Controls||($1,799,801)|
|2. Purchase Mechanical Screw Press||($563,108)|
|3. Demonstrate PPE Effectiveness||($49,467)|
Thus, the formal retrospective analysis confirmed management’s judgment that demonstrating PPE effectiveness provided the most cost-effective and rapid solution to achieving regulatory compliance and ensuring the protection of their employees’ hearing. Management also realized that their efforts to reduce employee noise exposures via engineering controls needed to continue on an ongoing basis. However, due to the loud metal-to-metal contact associated with hammer forging processes, it is likely that employees will need hearing protection against hazardous noise exposures as long as this technology is in use.
- The case study demonstrated that an industrial hygienist working with business partners can help protect the overall viability of a business. In this case, management estimated that without the selected intervention it would not have been possible to maintain operational continuity given the nature of a commodity product and the highly competitive global marketplace.
- The use of PPE can be an effective measure to protect employees in high noise areas.
- Relying on PPE as the primary means of protection requires extraordinary measures to ensure that expected levels of protection are validated in actual field operations.
- Where PPE is a primary means of protection, employees must be properly trained and understand the level of hazard so that they can utilize the PPE in the most effective manner.
- Sound IH investigations and measurement can be a key to reducing employee exposures, ensuring regulatory compliance, and contributing to business profitability.