High sound levels are present in many different manufacturing processes and sound is easily and quite seamlessly turned into noise. The noise may not be directly harmful to the hearing but it can create a feeling of stress and fatigue. There are multiple noise sources and it’s easy to feel that you don’t know where to start when you want to reduce the overall noise levels.
Sound vs. noise
Exposure to high sound levels results in reduced hearing ability.
Noise is unwanted sound.
Exposure to relatively low noise levels can be distracting but not necessarily lead to hearing loss.
Continued exposure to high sound levels destroys the sound sensitive hair cells in the inner ear, which reduces hearing ability. Since hearing is one of the brain’s main senses, even relatively low levels of noise can be distracting. This can lead to loss of concentration and fatigue.
Occupational hearing loss (or deafness) is one of the most common work-related disorders in the industry. Only in the US it’s estimated that about 22 million workers are exposed to potentially damaging noise every year.
Noise exposure doesn’t only affect the person using the equipment but also people in the surrounding areas may also be affected. The risk of hearing losses to other persons not directly using the equipment is a concern that has to be taken into account. It’s therefore important that everyone working in areas with high sound levels uses ear protection.
Health and safety regulations
Laws and regulations to protect workers from excessive sound exposure levels are common in many countries. The regulations are expressed as exposure levels over an 8-hour workday.
| Country/Region | Exposure limits |
| The European directive states three exposure limits | 80, 85 and 87 dB(A) |
| In the United States, the exposure limits are regulated by OSHA standard 1910.95 Occupational Noise Exposure. | 90 dB(A) |
| China | 85 dB(A) |
Two main noise sources linked to the use of power tools
The noise from the tool itself
All direct driven tightening tools, pneumatic or electric, are louder than the actual process (with only a few exceptions, e.g. screaming joints). Large pneumatic tightening tools are loud and will add noise to the manufacturing process. Small pneumatic and electric tools will have a small impact on the overall sound level as they are declared to well below 70 dB(A).
The noise from low speed sanders and drills often comes from the tools, while the source from the high speed versions is harder to separate.
The noise generated by the process
The noise from e.g. grinding, chipping and riveting and some other material removal processes is process dominated. Even though the tools themselves can be loud, the process is often louder. When grinding, the contact between the abrasive and the workpiece generates a lot of noise. The noise from the percussive tools is a consequence of the vibrations induced in the workpiece by the tool, causing the workpiece to vibrate. The vibrating workpiece acts as a loudspeaker, thus generating what is known as vibration induced noise.
Vibration induced noise from the workpiece is also common when tightening bolts with impact wrenches and pulse tools on weak structures such as large beams and metal plates.