Skip Navigation

Course 751 - Hearing Conservation Program Management

Safety guides and audits to make your job as a safety professional easier

The Basics

manual lift
Sound generates pressure waves of compression and decompression.

Sound and Noise – What’s the difference?

Sound - consists of pressure changes in a medium (usually air), caused by vibration or turbulence. These pressure changes produce waves emanating away from the turbulent or vibrating source.

Noise - is nothing more than unwanted sound. Noise is one of the most widespread occupational health problems. It is a by-product of many industrial processes.

Check out this short audio clip by Dan Clark of the that gives a quick overview of nature of sound, noise, and ways to prevent hearing loss in the workplace.

How is sound measured?

Sound is measured in two ways: decibels and frequency.

Decibels measure the pressure of sound. Frequency is related to a sound’s pitch and is measured in units called hertz (Hz), or cycles per second. The pitch of a sound — how high or low it seems — is how you perceive its frequency; the higher the pitch, the higher the frequency. High-frequency sounds are generally more annoying than low-frequency sounds and can be more harmful to hearing.

Human hearing is most sensitive to frequencies between 3,000 and 4,000 Hz. That’s why people with damaged hearing have difficulty understanding higher-pitched voices and other sounds in the 3,000 to 4,000 Hz range.

Check out the CDC Noise Meter page to get a better idea how “loud” is loud.

How does the ear work?

When sound waves enter the outer ear, the vibrations impact the ear drum and are transmitted to the middle and inner ear.

In the middle ear three small bones called the malleus (or hammer), the incus (or anvil), and the stapes (or stirrup) amplify and transmit the vibrations generated by the sound to the inner ear.

The inner ear contains a snail-like structure called the cochlea which is filled with fluid and lined with cells with very fine hairs. These microscopic hairs move with the vibrations and convert the sound waves into nerve impulses–the result is the sound we hear. Exposure to loud noise can destroy these hair cells and cause hearing loss!

The Perils of Exposure

Exposure to noise is measured in units of sound pressure levels called decibels, named after Alexander Graham Bell, using A-weighted sound levels (dBA). The A-weighted sound levels closely match the perception of loudness by the human ear.

Exposure to high levels of noise causes hearing loss and may cause other harmful health effects as well. The extent of damage mostly depends on the intensity of the noise and the duration of the exposure. Hearing loss caused by noise can be temporary or permanent.

  • Temporary hearing loss results from short-term exposures to noise, with normal hearing returning after a period of rest.
  • Prolonged exposure to high noise levels over a period of time gradually causes permanent damage.

Loud noise can also create physical and psychological stress, reduce productivity, interfere with communication and concentration, and contribute to workplace accidents and injuries by making it difficult to hear warning signals.

Noise-induced hearing loss limits your ability to hear high frequency sounds, understand speech, and seriously impairs your ability to communicate.

The effects of hearing loss can be profound as hearing loss can interfere with your ability to enjoy socializing with friends, playing with your children or grandchildren, or participating in other social activities you enjoy, and can lead to psychological and social isolation.

Exposure to chemicals

No longer is noise considered to be the only source of hearing loss associated with work. Exposure to chemicals, such as aromatic solvents and metals such as lead, arsenic, and mercury can result in hearing loss.

Combined exposures to noise and chemicals can cause more hearing loss than exposure to either agent alone. Vibration and extreme heat are also potentially harmful to hearing when combined with noise.

How does sound damage hearing?

Damaged earhair cells.
Repeated exposures to loud noise can damage hair cells to the point that they won't recover.

Very loud sounds can damage the sensitive hair cells in your inner ear. Hair cells are the foot soldiers for your hearing. As the number of damaged hair cells increases, your brain receives fewer impulses to interpret as sound. When you damage hair cells, you damage hearing.

While a single exposure to loud noise can damage your hair cells, it probably won’t destroy them. You may experience ringing in your ears and some sounds may be muffled, but your hair cells will recover and so will your hearing. This is called a temporary threshold shift. But repeated exposures to loud noise can damage hair cells to the point that they won’t recover. Because the damage is permanent, the result is called a permanent threshold shift . No treatment will restore it. When you destroy hair cells, you destroy hearing.

How to know if your hearing is damaged

Hearing loss is painless and gradual. It usually develops over several years — you might not even notice the loss during those years.


Sometimes, overexposure to loud noise can trigger ringing or other sounds in your ears, called Tinnitus. While tinnitus may be a symptom of damaged hearing, it can also be caused by infections, medications, and earwax.

The only way to know for sure if noise has damaged your hearing is to have a hearing examination by a certified audiometric technician, audiologist, otolaryngologist, or physician.

If you answer "yes" to any of the following questions, your hearing may be at risk:

  • Do you frequently ask people to repeat sentences?
  • Do you feel your hearing is not as good as it was 10 years ago?
  • Have family members noticed a problem with your hearing?
  • Are you exposed to loud noise without hearing protection where you work?
  • Do you have to shout to a co-worker because of the noise around you?
  • Are you exposed to noise from firearms, motorcycles, snowmobiles, power tools, or loud music without hearing protection?

Congratulations! You’re finished with the first module. Don’t forget to review the quiz.

The Hearing Video

Produced in the style of a TV science show, The WorkSafeBC Hearing Video uses vintage films, computer animation, and noise-defying stunts to demonstrate how your ears work and the effects of hazardous noise on your hearing. The video also demonstrates the proper use and maintenance of hearing protection and how to chose the right protection for you.


Before beginning this quiz, we highly recommend you review the module material. This quiz is designed to allow you to self-check your comprehension of the module content, but only focuses on key concepts and ideas.

Read each question carefully. Select the best answer, even if more than one answer seems possible. When done, click on the "Get Quiz Answers" button. If you do not answer all the questions, you will receive an error message.

Good luck!

1. Sound - consists of pressure changes in a medium (usually air), caused by _____ or _____.

2. What is noise?

3. Between which frequencies is human hearing most sensitive to?

4. What are the two factors that determine the amount of hearing loss a person experiences when exposed to loud noises?

5. Sometimes, overexposure to loud noise can trigger ringing or other sounds in your ears, called _____.

Have a great day!

Important! You will receive an "error" message unless all questions are answered.