A hearing conservation program should (and in some states must) be initiated any time workers are exposed to an average noise level of 85 dBA over an 8 hour day. An effective hearing conservation program includes:

• Noise level measurement
• Worker training
• Using engineering and administrative control to lower noise levels
• Providing a variety of appropriate hearing protectors
• Regular hearing test
• Program documentation

Whenever it becomes difficult to have a conversation at a few feet the noise level is probably at or above 85 dBA.  This may occur, for example, when compressors or vehicles are running, power tools are being used or hammering is being done. Long-term exposure to noise above about 80 dBA can damage hearing.  The louder the noise, the less time it takes to cause damage.  When the noise level at a job-site averages 85 dBA a hearing conservation program is required.

Exposures above 85 dBA (averaged over a full day) call for a hearing conservation program that includes noise monitoring. A written program is not required by Federal OSHA rules but is required by some states.  All noise sources, even those created by other contractors or from the environment must be included in the determination of exposure level. If it is often difficult to hold a conversation without greatly raising your voice, noise monitoring is likely required.  Assistance in monitoring may be obtained from OSHA consultation services or through your trade association.

When noise levels exceed a 90 dBA average OSHA requires that engineering or administrative controls be used to reduce the noise.  The most cost effective way to reduce noise is to control it as close to the source as possible by:

• Buying or renting equipment that is muffled or silenced.  Silenced compressors and generators usually run at about 75 dBA while unmuffled versions of the the same output may run at more than 90 dBA. Ask your equpiment supplier about low-noise equipment.
• Locating noisy equipment or operations as far away from the majority of workers as feasible. Noise levels drop sharply with distance - about 6 dBA for every doubling of distance.  Moving a noisy generator a few yards can make a big difference in your worker(s) noise exposure.  When equipment is inside an enclosed work area echoing makes distance a less effective control.
• Isolating noisy equipment and operations by erecting barriers or by placing them behind existing barriers such as walls.  The barrier should be higher and wider than the line of sight between workers and the noise source.  A simple plywood barrier can reduce noise levels 10-12 dBA. Barriers do not protect workers inside the barrier.
• Keeping cutting tools sharp reduces both the noise level and the cutting time.
• Maintaining and lubricating mechanical equipment to reduce operating noise.

If engineering controls are not feasible or not sufficient, work practices can help reduce worker noise exposure.  Good work practices include:

• Run noisy equipment only when necessary.
• Notify nearby workers before beginning noisy task so that they can move or use hearing protectors.
• Establish, mark and enforce restricted access zone around very noisy equipment or operations.  Put a barrier around this area if feasible and and prohibit unprotected persons from entering.
• Mark tools that generate more than 90 dBAs of noise.  Require hearing protection when using those tools. Red tape can be used to distinguish loud tools.

Effective use of engineering and work practice controls can reduce or even eliminate the need for hearing protectors. However, feasible engineering and work practice controls should be used even if hearing protectors will still be needed.  Hearing protectors are the least effective and least reliable means of noise reduction.

If hearing protectors (muffs and plugs) are required (figure 1), a variety of protectors should be made available to ensure that workers can select ones that provide the right protective level and that are comfortable for them to wear.

Figure 1. Earplugs (Photo courtesy of 3M)

Hearing protector packaging is required to carry noise reduction ratio (NRR) labeling.  The NRR was meant to be a simple guide to the amount of protection provided. In reality the NRR must be modified for the workplace.  First, since hearing protectors have been shown to provide far less protection in the field than in the lab, NIOSH recommends that the NRR for muffs be reduced by 25%, for foam plugs by 50% and for all other protectors by 70%.  After this reduction (or derating) 7 dB must be subtracted because the NRR is based on dBC measurements that are about 7 dB off from dBA reading. 

According to NIOSH a foam plug with an NRR of 29 only reliably provides a noise reduction of  8 dB. Muffs with an NRR of 32 would provide 17 dBA of reliable reduction.  Other types of protectors may provide little if any reliably effective noise reduction in the field. Combining muffs and plugs only adds about 5 dBA of protection to the highest rated component.  Combining foam plugs and muffs might provide 22 dBA of reduction, allowing them to reduce full shift noise level of 107 dBA to the desired 85 dBA. Higher noise levels would require a reduction in exposure time, for example to 4 hours for a noise level of 110 dBA or to 2 hour for a noise level of 113 dBA (a true reduction of 3 dB results from cutting a noise level or exposure time in half).  OSHA compliance guidelines are less stringent, they call for first subtracting the 7 dB correction factor from the NRR of any hearing protector and then dividing the resulting number by 2.  Any hearing protector with an NRR of 25 would be considered to provide 9 dB of noise reduction at the ear under the OSHA guidline.

These derating schemes are conservative estimates.  A well conducted hearing conservation training and fit testing program should result in workers achieving significantly better levels of protection. To achieve greater and more reliable protection, fit testing should be included in the contractors hearing conservation program.

Audiometric Testing

In some jurisdictions, such as Washington, Oregon and California, baseline and annual hearing test are required for construction workers exposed above 85 dBA.  Audiograms can be provided by a local occupational medical clinic, mobile audiomentric test facility, and sometimes through a union or trade organization. 

Training

Workers exposed above 85 dBA must be trained on the effect of noise on hearing, how to wear and maintain hearing protectors, and how to understand their hearing test results.  Well trained workers are likely to get more protection from hearing protections than untrained workers.

Records

All records of training and audiometric testing, where required,  must be retained by the contractor. Monitoring records should be maintained for two years. 

Hearing protectors may reduce a worker's ability to hear warning signals and directions, especially when more protection is used than is needed.

Hearing protectors, especially those that are inserted into the ear canal, must be kept clean to prevent the spread of infection.

In many cases, use of hearing protection has been shown to actually increase workers ability to hear speech and critical sounds.  The earmuffs or plugs muffle the drone of background noises and improve perception of speech.  The determining factor seems to be whether the worker already has a hearing loss, as well as the tonal qualities of the desired sounds in question.  Workers with existing hearing loss may have more trouble hearing speech and sounds UNLESS provided with hearing protectors that enhance speech with special amplification circuitry that are readily available even sold in stores for hunters as "sportsmen earmuffs".  Most normal hearing people who are not grossly overprotected will hear speech from a person standing next to them BETTER with the hearing protectors while in a drone of background noise.  The hearing conservation manager should work with people individually to be sure that they are adequately protected, but not overprotected. 

• Sheet Metal & HVAC
  • Assemble fittings and fasten seams and joints using hand and power tools
    • Noise
  • Cut, file, grind, deburr, buff and smooth assembled parts
    • Noise
  • Install heating and air conditioning duct hangers and ductwork
    • Noise
  • Layout, shear, drill and punch holes in metal
    • Noise
  • Operate laser cutter and metal shearing machine
    • Noise
  • Operate metal press, hand brake and forming machines
    • Noise
  • Rig and set HVAC equipment with cranes, helicopters, hoists and lifts
    • Noise
  • Shape metal material over anvils, blocks or other forms
    • Noise
  • Weld, braze and solder seams and joints
    • Noise