Engineering Controls
Workplace safety and health specialists agree that engineering controls are the best way to control noise. That's true if the engineering control is effective, practical, and affordable. When you replace a noisy machine with a quiet one, modify it to make it quieter, or change the sound path so that the noise never reaches the listener, you're using an engineering control.
Replacement
If you have an old, noisy electric hand drill, you can replace it with a newer, quieter one. But, if you have a large noisy chipper/shredder, replacing it may not be practical. Instead, you might enclose the shredder to isolate the noise.
Enclose the Offending Equipment
Creative solutions may also be effective ones. Construction workers were using a concrete mixer to de-grease metal parts by tumbling them in sawdust — effective but noisy. To reduce the noise level to below 85 decibels, the employer built an enclosure around the mixer with two-by-fours and acoustic sound board, sealing the access door with polyurethane foam. The cost was minimal and the design was effective; it lowered noise levels to 78 decibels.
Increase the Distance
When you double the distance between the worker and the sound source, you decrease the sound pressure level by six decibels. For example, a hazardous 96-decibel noise source at five feet is a safe 84 decibels at 20 feet.
Reduce the Impact
When you reduce the height that materials collected in bins and boxes will drop, you can quiet noisy processes. Consider lining containers with damping materials such as plastic or rubber to keep them quiet.
Applying practical engineering controls to a noise problem can be challenging because there may not be ready-to-order solutions. You're more likely to find a solution when you:
- Understand what's causing the noise.
- Determine how the noise is reaching the worker.
- Identify the most appropriate point, or points, at which to control the noise, either at the source, along the sound path, or at the worker.
Administrative and Work Practice Controls
Unlike engineering controls that prevent hazardous noise from reaching a worker, administrative controls manage workers' activities to reduce their exposure. Closely related to administrative controls are work practice controls, which emphasize safe practices.
Administrative and work-practice controls are usually less expensive than engineering controls because there are no significant capital costs involved in changing or modifying equipment. In some cases, administrative controls can reduce employee exposure to noise and increase productivity by rotating employees through a demanding, noisy task. Work practice controls can also improve performance by emphasizing safe work practices.
Administrative and work practice controls usually may not be as effective as engineering controls because they don't control the noise exposure. Noisy machines are still noisy and the exposure is still present. Some controls that can be used to reduce exposure include:
- Reduce the time employees spend working in noisy areas;
- Rotate two or more employees so that each is exposed to noise less than 85 decibels, averaged over an eight-hour day.
- Shut down noisy equipment when it's not needed for production.
- Ensure that employees maintain equipment so that it runs smoothly and quietly.
- Ensure that employees know how to perform their tasks and operate equipment at safe noise levels.
- Use warning signs to identify work areas where noise exceeds safe levels.
- Encourage employees to report noise hazards to supervisors.
If you can't eliminate or control noise with an engineering control, you may be able to control it with an administrative control. However, if an administrative control won't reduce employee exposures to safe levels, you'll need to consider a third noise-control tool — hearing protectors.
Personal Protective Equipment: Hearing Protectors
When workplace noise equals or exceeds 85 dBA, averaged over an eight-hour period, can't be reduced through engineering, administrative, or work practice controls, employees must be provided with hearing protection. Those who receive hearing protectors must have the opportunity to select them from a variety of types that are compatible with their work tasks. Employees must also be properly fitted and trained to use and care for their hearing protectors.
There are two types of hearing protectors: ear plugs and earmuffs. Both types reduce the pressure of sound that reaches the eardrum and are the next line of defense when noise levels can't be reduced to safe levels with engineering or administrative controls.
Expandable Foam Plugs
Expandable foam plugs are made of a formable material designed to expand and conform to the shape of each person's ear canal. Roll the expandable plugs into a thin, crease-free cylinder. Whether you roll plugs with thumb and fingers or across your palm doesn't matter. What's critical is the final result — a smooth tube thin enough so that about half the length will fit easily into your ear canal. Some individuals, especially women with small ear canals, have difficulty rolling typical plugs small enough to make them fit. A few manufacturers now offer a small size expandable plug.
Pre-Molded, Reusable Plugs
Pre-molded plugs are made from silicone, plastic or rubber and are manufactured as either "one-size-fitsmost" or are available in several sizes. Many pre-molded plugs are available in sizes for small, medium or large ear canals.
A critical tip about pre-molded plugs is that a person may need a different size plug for each ear. The plugs should seal the ear canal without being uncomfortable. This takes trial and error of the various sizes. Directions for fitting each model of pre-molded plug may differ slightly depending on how many flanges they have and how the tip is shaped. Insert this type of plug by reaching over your head with one hand to pull up on your ear. Then use your other hand to insert the plug with a gentle rocking motion until you have sealed the ear canal.
Advantages of pre-molded plugs are that they are relatively inexpensive, reusable, washable, convenient to carry, and come in a variety of sizes. Nearly everyone can find a plug that will be comfortable and effective. In dirty or dusty environments, you don't need to handle or roll the tips.
Canal Caps
Canal caps often resemble earplugs on a flexible plastic or metal band. The earplug tips of a canal cap may be a formable or pre-molded material. Some have headbands that can be worn over the head, behind the neck or under the chin. Newer models have jointed bands increasing the ability to properly seal the earplug.
The main advantage canal caps offer is convenience. When it's quiet, employees can leave the band hanging around their necks. They can quickly insert the plug tips when hazardous noise starts again. Some people find the pressure from the bands uncomfortable. Not all canal caps have tips that adequately block all types of noise. Generally, the canal caps tips that resemble stand-alone earplugs seem to block the most noise.
Earmuffs
Earmuffs come in many models designed to fit most people. They work to block out noise by completely covering the outer ear. Muffs can be "low profile" with small ear cups or large to hold extra materials for use in extreme noise. Some muffs also include electronic components to help users communicate or to block impulsive noises.
Workers who have heavy beards or sideburns or who wear glasses may find it difficult to get good protection from earmuffs. The hair and the temples of the glasses break the seal that the earmuff cushions make around the ear. For these workers, earplugs are best. Other potential drawbacks of earmuffs are that some people feel they can be hot and heavy in some environments.
Miscellaneous Devices
Manufacturers are receptive to comments from hearing protection users. This has led to the development of new devices that are hybrids of the traditional types of hearing protectors. Because many people like the comfort of foam plugs, but don't want to roll them in dirty environments, a plug is now available that is essentially a foam tip on a stem. You insert this plug much like a pre-molded plug without rolling the foam. Scientists are developing earmuffs using high-tech materials to reduce weight and bulk, but still effectively block noise. On the horizon may be earplugs with built in two-way communication capability.
Select the Right Protection
The best hearing protector is the one that is comfortable and convenient and that will be worn every time a person is in an environment with hazardous noise. Select hearing protectors based on comfort, convenience, and compatibility. Employees won't wear hearing protectors that are uncomfortable or difficult to use or that interfere with their work. To ensure they will wear the protectors, allow employees to choose, with the help of a person trained in fitting hearing protectors, from among a variety of appropriate types and sizes.
Most hearing protectors are labeled with a noise reduction rating (NRR) indicating a protection level in decibels. However, these ratings are not reliable outside of a testing laboratory, which is where they received the rating. The NRR rating tends to overestimate the protection a hearing protector will provide under realworld conditions.
One way to estimate the real-world effectiveness of a hearing protector is to subtract 7 dB from the manufacturer's NRR as shown below:
- Noise level to which the worker is exposed, averaged over an eight-hour period...95dBA
- NRR shown on the hearing protector label .......25 decibels
- Subtract 7 dB from the NRR .............25 - 7 = 18
- Subtract 18 dB from 95 dBA ........95dBA - 18dB = 77dBA
This hearing protector may be able to reduce the worker's exposure from 95 dBA to 77 dBA.
No comments:
Post a Comment