Levels of Sound - Canada Occupational Health and Safety Regulations, Part VII - IPG-074

3.1

What is the relationship between A-weighted Sound Pressure Levels and Noise Exposure Levels?

3.2

How are measurements made and exposure calculated?

3.3

What is involved in a Hazard Investigation?

3.4

What needs to be considered regarding hearing protection?

4.1 Sound Pressure Level and Noise Exposure Section 7.1

Most sound-measuring instruments respond to sound pressure. When all the sound frequencies are treated uniformly (i.e., no particular emphasis is placed on some frequencies over others) we measure sound pressure level, and the unit of measurement is the decibel (abbreviated as dB). If an electronic network known as the "A" weighting network is included in the measurement, we are said to measure A-weighted sound pressure level, and the unit of measurement is called "decibel, A-weighted" (abbreviated as dBA). A-weighted sound pressure level is also commonly referred to as sound level.

Noise exposure level (abbreviated as L_{ex, 8}) refers to the exposure of an employee to sound. It is a measurement which combines the A-weighted sound pressure level to which an employee is exposed with the duration of exposure to that sound level. The mathematical definition of noise exposure level is given in this section. The main points to be noted are: (a) all work place exposure to sound during a continuous 24-hour period is taken into consideration when measuring or calculating the noise exposure level, and (b), the exposure is averaged over 8 hours regardless of the number of hours worked during a 24-hour period. Noise exposure level is usually measured with a noise dosimeter, whereas A-weighted sound pressure level is measured with a sound level meter.

4.2 Measurement and Calculation of Exposure

Subsection 7.2(1) deals with the type of instruments (and their specification) which shall be used to measure the exposure to sound of an employee. It references the appropriate clauses in the Canadian National Standard CAN/CSA Z107.56-M86, Procedures for the Measurement of Occupational Noise Exposure, as amended from time to time.

Subsection 7.2(2) specifies the procedures to be followed for measuring the exposure to sound of an employee. It references the appropriate clauses in the CSA standard cited in 7.2(1).

Subsections 7.2(3) and (4) specify what is known as the "Threshold Level" for noise exposure measurement. This is the lowest sound level which shall be included in the measurement (or calculation) of the noise exposure level of an employee. Subsection 7.2(3) requires that sound levels down to at least 74 dBA shall be included ^[1] . While it may be possible to program some noise dosimeters for this threshold, it is not a feature common to all dosimeters.

This is recognized in the regulation. The employer is permitted to use a dosimeter even if it cannot be programmed for 74 dBA, as long as it is capable of measuring (and including in the calculation of noise exposure level) sound levels below 74 dBA.

4.3 Hazard Investigation

Section 7.3 requires the employer, under certain conditions, to carry out an investigation in the work place for the purpose of assessing the exposure of employees to sound.

Subsection 7.3(1) provides that where an employee may be exposed to A-weighted sound pressure levels of 84 dBA, or greater, for a period of time likely to damage the employee's hearing, the employer shall initiate an investigation to be made for assessing the exposure. In the interest of health and safety, it is suggested that employers should carry out hazard investigations where there are identifiable sources of noise which produce sound levels of at least 80 to 90 dBA on a regular basis, and to which employees might be exposed.

Paragraphs 7.3(1)(a) and (b) require the employer to appoint a qualified person to conduct an investigation for the purpose of determining the degree of employee exposure to sound in the work place and to notify the work place committee or the health and safety representative of the name of the investigator.

It should be noted that paragraph 135(7)(e) of Part II of the Code stipulates that a work place committee shall participate in all inquiries and investigations pertaining to occupational health and safety. Similar powers are granted to the health and safety representative under paragraph 136(5)(g).

Subsection 7.3(3) prescribes that the measurement of the A-weighted sound pressure level referred to in 7.3(1) shall be performed instantaneously using the slow response setting of a sound level meter. These measurements are required to be made under normal working conditions.

Paragraphs 7.3(4)(a), (b), (c), (d) and (e) specify certain elements which the qualified person must consider when conducting the hazard investigation.

Subsection 7.3(5) states that, on completion of the investigation, and after the qualified person has consulted with the work place committee or the health and safety representative the qualified person shall make a written report, date it and sign it. The intent of this subsection is that the qualified person is made fully aware of the concern of the work place committee or the health and safety representative, and that he or she has taken into consideration any recommendations or suggestions made by the committee/representative. It is not incumbent upon the qualified person to adopt such recommendations or suggestions.

Paragraphs 7.3(5)(a), (b) and (c) require the qualified person to include in the investigation report, observations with respect to paragraphs 7.3(4)(a), (b), (c), (d) and (e). The report must also include recommendations for the purpose of complying with the prescribed sound level limits, the posting of warning signs and the use of hearing protectors. The qualified person may recommend the use of hearing protectors if the noise exposure level is more than 84 dBA and less than 87 dBA. For example, if the employee is exposed to a L_{ex, 8} of 84 or 85 dBA on an intermittent basis (say one day a week), the qualified person may well decide that hearing protection is not needed. On the other hand, if the exposure persists for 3 or 4 days a week, the qualified person might recommend the use of hearing protection.

Subsection 7.3(6) requires the employer to keep the hazard investigation report at the work place where the investigation was conducted for a period of ten years after the date of the report.

Paragraphs 7.3(7)(a) and (b) prescribe that where the investigation reveals that employees are likely to be exposed to a noise exposure level (L_{ex, 8}) of 84 dBA or greater, the employer shall post, and keep posted, a copy of the report in the work place where the investigation took place, and also provide employees, so exposed, with written information describing the hazards associated with exposure to high sound levels.

The employer may obtain this material from such sources as the Labour Program, the Canadian Centre for Occupational Health and Safety (CCOHS) in Hamilton, or prepare an information package in consultation with the work place committee or the health and safety representative.

4.4 Hearing Protection

Paragraphs 7.7(1)(a) and (b) prescribe that when an employer is required to make a report to a regional health and safety officer as referred to in section 7.6, the employer shall provide a hearing protector to every employee whose exposure is likely to exceed the maximum permitted levels prescribed in subsection 7.4(1).

It should be noted that the use of hearing protection is considered the last line of defence to protect the hearing of workers. If an employee's exposure to noise is in excess of 87 dBA ( L_{ex, 8} ), or exceeds the limits in the Schedule, and cannot be reduced by administrative or engineering controls or other physical means, in a reasonably practicable manner, the use of hearing protection is mandatory.

Paragraphs 7.7(2)(a) and (b) require the employer to consult with the work place committee or the health and safety representative to formulate a program to train employees in the fit, care and use of hearing protectors, and for the employer to implement a training program.

CSA Standard Z94.2-M1984, Hearing Protectors, as amended from time to time, which is referenced in the regulations, outlines the proper selection, fit, care and use of hearing protectors. If qualified personnel are available on site (e.g., occupational health nurse, hygienists, etc.), a hearing conservation program may be provided by them, or outside consultants may be hired, but the work place committee or the health and safety representative must be consulted in formulating the program. The approach is left up to the discretion of the employer, as long as each employee who is required to use hearing protection is adequately trained in the fit, care and use of hearing protection.

Subsection 7.7(3) requires that every person, other than an employee granted access to a work place where the exposure to sound is likely to exceed the prescribed limits shall use a hearing protector that meets the prescribed standards. It should be noted that the regulation does not require the employer to provide the hearing protection, only that the person granted access shall use one.