Describe a scenario where both engineering controls and hearing protection must be used to achieve the desired noise reduction levels.
In many industrial scenarios, relying solely on either engineering controls or hearing protection devices (HPDs) is not sufficient to achieve the desired noise reduction levels. A combination of both is often necessary to protect workers effectively. Here's a detailed scenario illustrating this:
Scenario: A large metal fabrication facility with multiple noisy operations including cutting, grinding, welding, and heavy machinery.
The Problem: Noise levels throughout the facility are consistently measured above the Permissible Exposure Limit (PEL) of 90 dBA as an 8-hour Time Weighted Average (TWA), and in some areas peak sound pressures are also very high. Several machines and processes contribute to the overall noise: a large hydraulic press, several metal grinders, multiple welding stations, and an area for cutting steel with powered saws. Despite some initial noise reduction efforts, the overall noise remains too high and has resulted in some employees developing standard threshold shifts on their annual audiograms. In this situation, a combination of engineering and administrative controls and hearing protection devices are required.
Engineering Controls Implemented:
1. Source Modification and Isolation: The first step taken to reduce the noise is to modify the machines, and isolate noisy equipment, by:
Hydraulic Press Enclosure: The large hydraulic press, which was identified as one of the major noise sources, has been enclosed with sound-absorbing panels and has access via self-closing sealed doors. This significantly reduces the direct noise emitted by the machine and contains a lot of the sound energy. The enclosure was fitted with seals to prevent any gaps. The press was also placed on vibration isolators to reduce any noise transmitted into the floor.
Grinder and Cutting Machine Guards: Individual grinders and metal saws have been fitted with partial enclosures to reduce the direct noise reaching workers. The cutting blades were also modified to a lower-noise design, which reduced some of the whine when cutting. Where possible, quieter methods of cutting were considered.
Welding Station Sound Barriers: Welding stations were separated with partial sound barriers made of absorptive panels. This reduced the propagation of noise from multiple welding areas.
Damping Materials: Some of the metal panels on the machines were treated with damping materials to reduce vibration and any resonant ringing noises.
2. Path Modification and Absorption: Engineering controls were also used to reduce the path of noise, and to absorb excess noise:
Acoustic Panels: Sound-absorbing acoustic panels were installed on the walls and ceilings of the fabrication floor, especially in the areas with many machines and operations. This reduced reverberation, and the build-up of noise in the factory. The ceiling panels were suspended to maximize the area of absorptive material.
Layout Changes: Where possible, noisy areas were moved further away from quieter areas of the factory.
The Remaining Noise Issue:
Even with these significant engineering controls in place, the noise levels throughout the facility, particularly close to the cutting and grinding areas, were still above the action level (85 dBA TWA) and peak sound pressures were still very high in some areas. Even though these engineering controls have achieved substantial noise reduction, it is still not enough to meet the required targets. Several factors contributed to this: the multiple sources of noise, the difficulty in achieving complete sound barriers in a large open space, and the variability in how machines are used. The sheer number of noisy processes and operations meant that it was difficult to achieve complete noise reduction, as some machines would need to be accessible and not completely enclosed.
The Need for Hearing Protection Devices:
In this situation, HPDs are essential to reduce the risk of NIHL. Engineering controls alone cannot guarantee that all workers are exposed to safe noise levels in all work areas. Even with good engineering controls, it is still possible to be exposed to high noise levels when working close to some machines, or during some operational periods. The noise levels were now lower but still high enough to require a comprehensive hearing protection program. HPDs are now required for all workers within defined high-noise areas.
Hearing Protection Devices Implementation:
1. Selection and Availability of HPDs: Employees in the fabrication facility have been provided with a selection of well-fitted earplugs and earmuffs. They are also given training and have been shown how to correctly fit the devices, and are provided with fit tests. In some cases, employees may require custom-fitted earplugs. All workers in the high noise areas have been given a choice of earplugs and earmuffs, and they have been given ongoing support and training in the use of HPDs.
2. Mandatory Use Policy: A mandatory policy is in effect stating that HPDs must be worn when in areas where noise levels are measured above the action level. Signage is used to indicate these areas. Workers have also been trained in the importance of consistent use of HPDs. Regular observation by supervisors ensures that the rules are being followed.
3. Double Hearing Protection: Workers performing tasks in the very loudest areas, particularly close to the cutting saws, are required to use both earplugs and earmuffs for double hearing protection. This is important because the high peak noise levels in this area pose a significant risk of hearing damage.
4. Regular Fit Checks and Maintenance: All employees are trained to regularly check the fit of their HPDs, and to replace any damaged or worn devices. A regular supply of HPDs is made available, and cleaning of earmuffs is regularly done. All reusable HPDs are carefully cleaned before each use.
Why both Engineering Controls and HPDs are Necessary:
The scenario above demonstrates that while engineering controls can significantly reduce noise levels at the source and along the path, they may not eliminate noise completely. In many situations the remaining noise levels are still potentially hazardous, and they need to be addressed using other methods. HPDs are needed as the final layer of protection to safeguard individual workers, in a situation where noise levels still present some risk. Engineering controls address the overall noise environment, whereas HPDs provide individual worker protection. Together they form a comprehensive strategy for managing the risk of NIHL.
This case highlights that an effective hearing conservation program requires both proactive engineering controls to reduce noise levels to as low as possible and the correct use of appropriate HPDs to minimize the risk of NIHL, when engineering controls have not achieved the required levels of noise reduction.