Noise-induced hearing loss is permanent, painless and gradual, which is why it is easy to ignore until it is too late. Provincial rules set an occupational exposure limit for noise and require employers to measure exposure, reduce noise where they can, provide hearing protection, and in many cases run a hearing conservation program with hearing tests. The aim is to catch and stop damage before it becomes disabling.
How noise causes damage
Loud sound damages the sensory hair cells in the inner ear. Brief exposure can cause temporary dullness or ringing; repeated exposure over months and years causes permanent loss, often starting in the higher frequencies that matter for understanding speech. Very loud impulse noise, such as from explosive tools or impacts, can cause immediate damage. Hearing loss is often accompanied by tinnitus, a lasting ringing or buzzing.
Measuring exposure
Noise is measured in decibels, A-weighted (dBA) to reflect how the ear responds. Because the scale is logarithmic, a 3 dB increase roughly doubles the sound energy.
Occupational limits combine level and time. In Alberta, British Columbia and Ontario the limit is generally based on 85 dBA averaged over an eight-hour shift, with an exchange rate of 3 dB: for every 3 dB increase, the allowed time halves. Other jurisdictions may differ, and details such as how longer shifts are treated are set in each province's rules, so check the current requirements.
Exposure is assessed with sound level meters for spot measurements and noise dosimeters worn by workers over a full shift. CSA Z107.56 describes procedures for measuring occupational noise exposure. Measurements should be done by a competent person, and repeated when equipment, processes or schedules change.
A rough field check: if you have to raise your voice to talk to someone an arm's length away, the noise level is probably high enough to need assessment.
Controlling noise
Apply the hierarchy of controls:
- Eliminate or substitute: choose quieter equipment and processes when buying or replacing. Specify noise levels in purchasing.
- Engineering: enclose noisy machines, add silencers to exhausts and air outlets, isolate vibration, use sound-absorbing materials, maintain equipment so worn bearings and loose panels do not add noise. Compressed air leaks and open blow-offs are common, fixable noise sources; see compressed air leaks.
- Administrative: limit time in noisy areas, schedule noisy work when fewer people are present, provide quiet break areas, post signs at noisy area boundaries.
- Hearing protection: earplugs and earmuffs, selected and fitted properly.
Hearing protection
CSA Z94.2 covers hearing protection devices and their selection. Good selection considers:
- The noise level, so that protection brings exposure below the limit without over-protecting to the point where workers cannot hear alarms or each other.
- Comfort and fit, since protection only works when worn for the whole exposure.
- Compatibility with hard hats, safety eyewear and respirators.
- Hygiene in dirty environments, where reusable earplugs or muffs may be better than foam plugs inserted with dirty fingers.
- Communication needs, where electronic or level-dependent protectors may help.
Manufacturers' laboratory ratings overstate real-world protection. Training on proper insertion makes a large difference for earplugs, and individual fit testing systems can show how much protection a worker is actually getting.
Short gaps matter. Because the scale is logarithmic, removing hearing protection for even a small part of a noisy shift can greatly reduce the protection received over the day. Protection needs to be worn the whole time in noisy areas.
The hearing conservation program
When exposures exceed the limit, provincial rules generally require a program that includes:
- Noise exposure assessment and records
- Noise control measures and a plan to reduce exposure
- Selection, fitting and maintenance of hearing protection
- Worker training on the effects of noise and the use of protection
- Audiometric (hearing) testing at the intervals set by your provincial rules, typically a baseline near the start of employment and periodic tests after
- Review of test results by a qualified person, with follow-up for workers showing changes
- Annual review of the program's effectiveness
Hearing test results are confidential health information. Workers should be told their own results and what they mean.
How ehZee can help
ehZee helps employers build noise and hearing conservation programs into their safety program and review existing ones against provincial requirements. See safety program development and review.
Common questions
Do noise limits apply to office or retail workplaces?
The limits apply everywhere, but most office settings are well below them. Workplaces with loud music, kitchens, mechanical rooms and loading docks can be closer than people expect, so measure if in doubt.
Is double protection (plugs and muffs) ever needed?
In very high noise, combining earplugs and earmuffs can be required. The combined protection is less than the sum of the two ratings, so get advice on selection.