It is important machinery is operated in a manner that accounts for noise exposure.
By Alexandra Walsh
Occupational hearing loss is one of the most common work-related illnesses, and unlike the result of many accidents on a jobsite, it is permanent.
A total of 22 million workers are exposed to hazardous noise levels at work each year in the United States. According to the National Institute for Occupational Safety and Health (NIOSH), about 51% of all workers in construction have been exposed to hazardous noise and 52% of noise-exposed construction workers report not wearing hearing protection.
The NIOSH-recommended exposure limit for occupational noise exposure is 85 decibels over an eight-hour shift. If workers are repeatedly exposed to noise at or above the recommended exposure limit, employers must have in place a hearing loss prevention program.
Noise levels are likely hazardous if a person must raise their voice to speak with someone 3 feet away (about at arm’s length). Hearing loss from routine noise exposure is 100% preventable and is best addressed by creating a quieter workplace.
Measuring Noise Exposure
To properly control and reduce noise in the workplace, you should know:
- How loud an area is
- How much noise reaches a worker’s ear
- The frequency content of the noise
- Where the noise is coming from.
Occupational noise measurements are usually reported in the following ways:
- Sound level: the measured noise level at a given point in time
- Time-weighted average sound level: the noise level averaged over an eight-hour period
- Noise dose: the percentage of allowable noise exposure. A noise dose of 100% or more means that a worker has exceeded their daily limit.
The two basic instruments for characterizing noise are sound level meters and noise dosimeters.
You can use sound level meters to assess noise in an area, discover how much noise is coming from specific equipment, and get a general idea of the noise frequency. They are ideal when noise levels in an area are fairly constant as you can use them to estimate a worker’s average exposure to noise.
When noise levels vary quite a bit or when workers are mobile, use personal noise dosimeters to assess a worker’s noise exposure. Dosimeters average noise levels over time and calculate a noise dose.
Addressing Noise Sources
Retrofitting noisy equipment and tools costs much more than designing them to operate quietly. Companies are encouraged to purchase or rent quieter machinery and tools to reduce worker exposure to noise when possible.
Reducing or eliminating noisy processes with quieter equipment is also more effective than depending on personal protective equipment.
When ordering made-to-order PPE, make clear provisions in the contract that the equipment noise levels will not exceed maximum desirable noise levels. Use noise levels as a deciding factor when buying new equipment and tools.
Be sure to keep up preventive maintenance of your new equipment. Poorly serviced equipment often becomes noisier over time.
Comparing Noise Levels of Tools
Comparing the noise levels of equipment and tool options doesn’t take long and can save money over time. There are several ways to obtain noise data when purchasing new equipment.
- Check equipment specifications for information on noise levels.
- Ask the manufacturer for noise data if it is not already provided.
- Measure noise levels prior to purchase when possible.
Make sure you take noise measurements the same way for each piece of equipment. For each measurement, keep the microphone on the sound level meter the same distance from the tool and record for the same amount of time.
Noise controls involve modifying equipment or making physical changes to the surrounding environment that reduce the noise level at the worker’s ear.
Noise controls are not always complicated or expensive, and frequently they may be the most cost-effective option. The cost of implementing noise controls can be offset by savings on the costs of a hearing loss prevention program, workers’ compensation premiums, and claims for hearing loss.
Before you undertake noise controls, make sure machinery is in good repair and all maintenance procedures have been conducted. Sometimes proper maintenance is all that is needed to reduce noise to a safe level.
If further sound reduction is needed, some of the following simple noise controls may work. If a more sophisticated solution is necessary, an experienced noise professional should be able to help.
Reduce speed of moving parts
Parts of machinery that are in motion produce less sound energy at slower speeds. For example, slower fans with larger blades are quieter than smaller, faster fans that move the same volume of air.
The same principle applies to noise created by falling parts. The farther they fall, the more speed they pick up on the way, and the louder they land. Decrease the impact noise of falling parts by decreasing the falling distance.
Using softer materials at the point of impact can also create less noise. For example, replace metal parts with quieter plastic parts or line impact areas with cushioning materials such as rubber.
Eliminate restricted flow in pipes and ducts
Air or fluid flowing in ducts and pipes can create extra turbulence that will increase noise. Eliminating obstructions such as flanges and valves can reduce this noise.
A pipe or valve with small, smooth transitions is quieter than one with sharp edges and large volume changes. Turbulence can increase the noise produced by flow in pipes and ducts. A pipe or valve with smooth transitions will be quieter than one with sudden changes or obstructions.
Isolate machinery vibration
Machines that vibrate can cause excessive noise. Isolating machines can reduce the amount of noise. Vibrating machinery can be placed on vibration isolators, preventing noise from travelling through the floor to workers. Consult the manufacturer or an expert to select the correct vibration isolation, as the wrong mounts can actually increase vibration.
Reduce vibrating parts and surfaces
Panels connected rigidly to vibrating machinery can radiate more sound than the machine alone. Moving instrument or control panels off the vibrating machinery can reduce the total noise from the machine. Securing loose parts can also reduce the noise level.
Use anti-vibration connectors
Rigid connections can transfer vibrations to walls and ceilings. Isolating these connectors will decrease noise. Mounting pipes with anti-vibration connectors will reduce the vibration that is transferred to the wall or ceiling.
Keep noisy machines away from hard surfaces
Sound reflects from walls, floors, and ceilings—all hard surfaces. These sound reflections increase the overall noise levels in a space. The closer you place the noise source to a hard surface, the louder the reflected noise will be.
Usually, the best placement for a noise source is away from the walls and suspended between the floor and ceiling. The worst placement is in corners where sound will reflect from three surfaces.
Build enclosures around equipment
Enclosures can block transmitting mid- and high-frequency sounds. Workplace tasks that can generate these levels of noise include drilling, riveting, grinding, and cutting.
Enclosing noisy equipment in a box with a sound-absorbing lining can reduce the noise level at the worker’s ear. Block high-frequency noise by using a barrier, a sound shield. A barrier is more effective the taller it is and the closer it is placed to the source. Indoor barriers are more effective if the ceiling is sound-absorbent.
The Benefits of Prevention
Noise is part of everyday life, but at certain levels it can become hazardous. Repeated exposures to sounds that are 85 decibels or higher can cause permanent hearing loss and are associated with other problems including:
- Ringing in the ears (tinnitus)
- High blood pressure (hypertension)
- Cardiovascular disease.
High noise levels can also contribute to serious workplace accidents and injuries. Noise can reduce workers’ awareness of what is happening around them such like signals, alarms, and verbal warnings.
Reducing workplace noise below 85 decibels is the best way to prevent occupational hearing loss and other effects from hazardous noise. Additional benefits of reducing worker noise exposure include:
- Less stress and fatigue
- Increased productivity and better morale
- Improved relations with management
- Lower workers’ compensation costs.
Until you reduce workplace noise levels to under 85 decibels, workers should be protected by establishing an effective hearing loss prevention program.