OHS Code Explanation Guide

Published Date: July 01, 2009
Bookmark this page

Part 16 Noise

Section 222 Hearing protection

The following factors must be considered when selecting hearing protectors:

(a) who will be wearing the equipment;
(b) compatibility with other safety equipment;
(c) workplace conditions such as temperature, humidity and pressure;
(d) comfort – protectors that are not comfortable will not be worn;
(e) ease of use and handling; and
(f) impact on the wearer’s ability to communicate.

The hearing protectors selected must meet the requirements of CSA Standard Z94.2-02, Hearing Protection Devices – Performance, Selection, Care and Use. This Standard provides performance requirements for personal hearing protection devices. The Standard classifies muffs and earplugs as Class A, B or C depending on the level of protection they provide. Class C provides the least degree of protection while Class A provides the greatest. Table 2 of Schedule 3, indicates the class of hearing protection to be used at various noise levels.

The classification of hearing protectors is based on how much they attenuate or reduce sound levels at nine different frequencies: 125 Hz, 250 Hz, 500 Hz, 1000 Hz, 2000 Hz, 3150 Hz, 4000 Hz, 6300 Hz and 8000 Hz. The manufacturer must provide this information to the equipment user.

The CSA Standard has introduced a 0 to 4 grading system for hearing protection devices. A device with a “0” grading provides the least protection, a device with a “4” grading provides the most. Grades are assigned to hearing protection devices based on laboratory attenuation measurements. The purpose of using a grade system is to be able to make a “go” or “no-go” determination i.e. either the hearing protection is right for the noisy situation or it is not. Such absolute decisions require the actual hazard to be known i.e. both sound pressure levels and duration of exposure must be assessed.

Equipment manufactured in the United States may bear a Noise Reduction Rating (NRR) – a class will not be specified. The NRR is not comparable to the attenuation data required by CSA. However, the manufacturer must still provide the attenuation data required by the Standard and a comparison of this data with the information provided in Table 3 of the Standard, shown as Table 16.4 will allow the user to determine the class of the hearing protector. The equipment must, in addition, comply with other requirements specified in the CSA standard.

Table 16.4 Sound Attenuation Requirements for Hearing Protectors

Frequency, Hz

Minimum attenuation, dB

Class A

Class B

Class C

125

10

5

None

250

18

12

None

500

26

16

None

1000

31

21

11

2000

33

23

13

3150

33

23

13

4000

31

21

11

6300

33

23

13

8000

33

23

13

Source: CSA Standard Z94.2-02

The noise reduction rating (NRR) of a hearing protector cannot be used reliably to determine its classification. Because NRR values are calculated differently than the class definitions given in Table 16.4, there is considerable overlap of NRR values between Classes A and B. Generally however, a hearing protector with an NRR value of at least 24 and with mean attenuation values of at least 26, 31, and 33 dB at 500, 1000 and 2000 Hz, respectively, meets the Class A requirements. A protector that does not meet the Class A mean attenuation requirements at 500, 1000 and 2000 Hz, but has an NRR value of at least 17, generally falls into Class B. Likewise, a protector with an NRR value of less than 17 generally falls into Class C.

Note that the attenuation values shown in Table 16.4 are determined in a laboratory by the manufacturer. When hearing protectors are worn, they generally provide much less protection. An often used rule of thumb is to reduce the manufacturer’s attention value by half to estimate the actual noise reduction achieved in the field.

Use of dual hearing protection

If hearing protection has been chosen according to Table 2 of Schedule 3 to control worker exposure to noise, once a worker is exposed to noise greater than 105 dBA Lex the worker must wear both a plug and a muff (dual hearing protection). At noise levels greater than 110 dBA Lex, dual hearing protection must be worn and time of exposure reduced.

When dual hearing protection is worn, the noise reduction (attenuation) at each frequency is not the sum of the individual hearing protector’s attenuations, it is usually much less. This is due to the fit of the hearing protectors and the volume of air trapped between them as well as limitations created by bone conduction. Bone conduction allows sound energy to be transmitted through the bones and tissues of the skull to the inner ear, bypassing the hearing protector. It poses a limitation on the protection that any hearing protector can provide, regardless of how well it seals to the ear canal and prevents sound from entering the ear.

Hearing protectors do not work well at noise levels greater than 110 dBA Lex. For this reason a worker’s exposure time must also be reduced, even while dual hearing protection is worn. The time reduction should be based on a 3 dBA exchange rate, as shown in Table 16.5.

Table 16.5 Exposure time reduction with dual hearing protection

Exposure Level (dBA Lex1)

Exposure Time2 (hours)

110

8

113

4

116

2

119

1

122

0.5

125

0.25

  1. Worker exposure must be measured in accordance with CSA Standard Z107.56-06, Procedures for the Measurement of Occupational Noise Exposure.
  2. This is the total noise exposure that the worker may have over the work shift. For the remainder of the work shift the worker cannot be exposed to noise greater than 85 dBA.

Proper use of hearing protection

To be of value, hearing protection must be used properly and whenever the worker is in a noisy area. For this reason, workers must be trained in the selection, maintenance and proper use of the equipment. To ensure that noise-exposed workers are motivated to use and care for the equipment properly, they must understand the hazards associated with noise exposure.

It is critical that workers know how the equipment is to be worn. For maximum protection, a hearing protector must make a tight seal within the ear canal or against the side of the head. Earplugs or muffs that do not fit properly can lose 5 to 15 dB of their noise protection capacity. Modifying hearing protectors to reduce wearer discomfort by drilling holes in earcups or reducing earmuff headband tension can seriously compromise their effectiveness and is not permitted. More comfortable but equally effective protectors should be found.

While it is important to have manufacturer instructions describing the use and maintenance of the equipment, workers cannot be relied upon to receive effective instruction on fit, care and use by reading the instructions alone. Proper fitting techniques should be demonstrated and practiced by the worker under supervision.

Once hearing protectors are issued to workers, the employer must ensure they are worn. In turn, workers must use the equipment according to the training provided by the employer.

Figure 16.1 Examples of hearing protectors