Control comes after measurement
Once a workplace has found where it is loud, the next question is what to do about it. The usual answer is to work through controls in order of effectiveness: remove or reduce the noise at its source first, interrupt its path second, manage how long people are exposed third, and use hearing protection as the final layer. Measuring and mapping noise is the subject of noise level monitoring. This article covers the control options in general terms.
It is general information, not acoustic engineering advice. Noise control can be technically involved, and the right fix for a given machine depends on how it makes noise. Involve qualified professionals for significant projects, and follow local rules.
Principle: source, path, receiver
A helpful way to think about noise is as a chain: a source (a machine or process) produces sound, a path carries it (through air, floors and structures) and a receiver (a person) hears it. Controls can be applied at each link, and the earlier in the chain they are applied, the more broadly they help.
At the source
Quieting the source is typically the most effective approach, and it benefits everyone nearby.
- Choose quieter equipment. When buying or replacing equipment, noise information from the manufacturer can be a selection factor. Different designs of the same type of machine can differ noticeably.
- Change the process. Some operations can be altered to reduce impact or turbulence, such as using smoother material transfer, lower fall heights or different fastening methods.
- Reduce speed or force where the process allows. Many machines get louder as speed increases.
- Fix air leaks and exhausts. Compressed air discharges can be loud, and mufflers or properly designed nozzles can help in some cases.
Maintenance as noise control
Worn machines are often noisy machines. Maintenance can reduce noise and has other benefits too:
- Replacing worn or damaged bearings, an issue discussed in bearing wear patterns.
- Rebalancing or realigning rotating parts, since imbalance and misalignment can cause vibration and noise. See shaft alignment.
- Tightening loose panels, guards and fasteners that rattle.
- Lubricating moving parts according to the manual.
- Cleaning and servicing fans, such as through fan bearing care.
A sudden change in a machine’s sound is also worth investigating, as it can indicate a developing fault.
Damping and isolating vibration
Vibrating surfaces radiate sound like a drum. Controls include:
- Damping materials applied to panels, chutes and hoppers that ring when struck by material.
- Vibration isolators or mounts between machines and their supports so vibration does not travel into floors and structures.
- Flexible connections in ducts and pipes, which reduce the transmission of vibration along them.
- Proper pipe supports, since unsupported pipework can vibrate and amplify noise.
Enclosures, barriers and absorption
When the source cannot be made much quieter, the path can be interrupted.
- Enclosures surround a noisy machine. For good results they need to be well sealed, with access doors and openings carefully designed. Ventilation for heat and for dust or fumes must be considered, so the enclosure does not create new hazards. Enclosures also must not defeat guarding or emergency access, so coordinate them with safety staff.
- Barriers and screens block direct sound between a source and workers. They work best when close to the source or receiver and when they have no gaps.
- Sound-absorbing materials on walls and ceilings can reduce reverberation in a room, which helps in large hard-surfaced spaces. They are usually less effective at cutting noise for someone standing right next to a machine.
- Quiet rooms or control booths let operators work away from the loudest areas where the process allows.
Layout and administrative controls
Layout can also help. Grouping noisy machines together, placing them away from quiet work, and keeping a sensible distance between sources and people reduce exposure. Administrative measures include rotating tasks to limit time in loud areas, scheduling noisy work when fewer people are present, and posting signs at entrances to hearing protection zones. These measures reduce exposure but do not reduce the noise itself, so they are usually considered after engineering controls.
Hearing protection as the last layer
Earplugs and earmuffs can reduce the sound reaching the ear, but their real-world effect depends on correct fit, proper use and comfort. If workers find them uncomfortable or hard to use with other equipment, they may not wear them consistently. Good programs usually include a choice of suitable types, training on fitting and care, and checks that they are actually used. Communication and awareness of warnings also need consideration. Treat hearing protection as a backup that complements other controls and not a replacement.
Check that it worked
After any change, measure again. Results can differ from expectations, and sometimes fixing one source makes another noticeable. Record what was done and the new measurements so later changes can be compared.
Limits
No control is guaranteed to bring levels below any particular value, and the effect of each measure depends on the machine and building. Workplace noise exposure can affect health over time, so take it seriously, follow the applicable regulations and rely on qualified people for assessments and design.