Noise Alert  

By: Simon Fridlyand
Unwanted sounds in the workplace can cause all kinds of hazards. Here are tips for determining if you have a problem and what you should do about it if you do.

Noise -- any kind of unwanted sound -- is one of the most common health problems in workplaces. Exposure to high levels of noise may cause hearing loss, create physical and psychological stress, reduce productivity, interfere with communication or contribute to accidents and injuries by making it difficult to hear warning signals.

Noise is usually defined simply as unwanted sound. Sound is the physical phenomenon that stimulates our sense of hearing. It is an acoustic wave that results when a vibrating source, such as machinery, disturbs an elastic medium, such as air.

Noise doesn't just have to be an irritating screech. High-frequency sound (ultrasound) cannot be heard by the human ear; however, it may still affect hearing and produce other health effects.

The upper frequency of audibility of the human ear is approximately 15,000-20,000 Hertz (15-20 kHz). This is not a set limit and some individuals may have higher or lower (usually lower) limits. The frequency limit normally declines with age.

Most of the audible noise associated with ultrasonic sources, such as ultrasonic welders or ultrasonic cleaners, consists of subharmonics of the machine's major ultrasonic frequencies. For example, many ultrasonic welders have a fundamental operating frequency of 20 kHz, a sound that is at the upper frequency of audibility of the human ear. However, a good deal of noise may be present at 10 kHz, the first subharmonic frequency of the 20 kHz operating frequency, and is therefore audible to most persons.

Standards that limit and control noise exposure

In Ontario the Occupational Health and Safety Act limits and controls noise exposure in the workplace. Regulation 851, Section 139 states:

"Where a worker is exposed to a sound level of 90 decibels (dB) or greater, measures shall be taken to reduce the sound level below 90 dB; and where such measures are not practicable, the duration of exposure set out in Column 2 of the Table [see Table 1] shall not exceed the duration shown for the particular sound level set opposite thereto in Column 1 of the Table, or the person shall wear hearing protection.

"A worker exposed to a sound level of 115 decibels or greater shall wear hearing protection.

"Clearly visible warning signs shall be posted at the approaches to an area where the sound level is more than 90 decibels.

"The warning signs referred to shall state, (a) the daily exposure for the particular sound level permitted by the following Table [see Table 1]; and (b) that hearing protection must be worn when the daily exposure is more than that permitted for the particular sound level.

"Where hearing protection is required by this section, the protection shall be sufficient to reduce the sound level below the sound level in Column 1 of the Table for the exposure corresponding to that sound level in Column 2 of the Table."

Evaluating noise exposure

The first step toward solving any noise problem is to define it. To understand what requirements must be implemented, it is necessary to determine exposure levels.

There are various factors that may indicate that noise is a problem in the workplace. While people react differently to noise, subjective responses should not be ignored because they may provide warnings that noise may be at unacceptable levels.

Noisy conditions can make normal conversation difficult. For example:

* When noise levels are above 80 dB, people have to speak very loudly.

* When noise levels are between 85 and 90 dB, people have to shout.

* When noise levels are greater than 95 dB, people have to move close together to hear each other at all.

A sound level meter is the basic instrument for investigating noise levels. Sound level meters can be used to:

* Spot-check noise dosimeter performance.

* Determine an employee's noise dose whenever use of a noise dosimeter is unavailable or inappropriate.

* Identify and evaluate individual noise sources for abatement purposes.

* Aid in determining the feasibility of engineering controls for individual noise sources.

* Evaluate hearing protectors.

Sound level meters must conform to the requirements of the Canadian Standards Association standard Z107.1.

Ontario's Occupational Health & Safety Act requires employers to determine if workers are exposed to excessive noise in the workplace. If they are, employers must implement feasible engineering or administrative controls to eliminate or reduce hazardous levels of noise. Where controls are not sufficient, the employers must implement an effective hearing conservation program.

Simon Fridlyand, P.Eng., is president of S.A.F.E. Engineering, a Toronto-based company specializing in industrial health and safety issues and compliance. He can be reached at 416-447-9757 or simonf@safeengineering.ca.

Back to ARCHIVE >>