printer-friendly version

Does Hearing Conservation Work?
Christine Harrison, MSc, Aud(C)

WorkSafeBC (WC or the Workers’ Compensation Board of British Columbia, also known as “the board”) is charged by law with providing workplace insurance coverage to the workers of the province and with developing and implementing occupational health and safety regulations (OSHR) to safeguard workers.

Background
Occupational noise-induced hearing loss (ONIHL) became a compensable disease in British Columbia (BC) in 1975, while the OSHR designed to prevent it followed in 1978 (WCB, 1978). As of 1978, a “noise control and hearing conservation program” with wording around engineered noise control, hearing protection devices, warning signs, annual hearing tests, and record keeping provided by employers became mandatory. The trigger level for inclusion in the program was noise exposure in excess of 85dBA timeweighted average, with a 3dB exchange rate. Training of hearing testers, known as “industrial audiometric technicians” (IATs), was conducted by audiologists in the Occupational Health & Safety Division of the board.

In a forward thinking move, the board developed a centralized data base in 1978. The cornerstone of this database was the data entry method: a paper based, “mark sense” form which was printed and supplied by the board to all IATs and used to record all industrial hearing tests. IATs sent the forms to the board where they were scanned by an optical scan reader and then stored in a mainframe data base. The objective of this process was to ensure that the same information was collected and stored for each test conducted.

Each audiogram included, and still includes, the following information:

• hearing threshold measurements, to 0dB HL, at 500, 1000, 2000, 3000, 4000, 6000, and 8000 Hz
• age
• gender
• hours away from noise prior to test
• occupation
• years at occupation
• hearing protection use (consistency, type of device)
• medical history questions (which are optional)
• type of audiometer
• category of test

Currently the database contains well over three (3) million audiograms.

Protocol
Requirements for both IATs and physical plant (audiometric facility) have been unchanged since 1978, save for complying with any amendments to the relevant ANSI Standards.

For example, every IAT who conducts industrial hearing tests in BC must successfully complete a four-day training course that is based on the CAOHC curriculum. There is no transferability of any credential from any jurisdiction or certification/licensing body anywhere in the world. In addition, a one day recertification course must be completed every two years. Manual hearing tests must be conducted in accordance with the current ANSI S3.21 Standard (ANSI, 2004b).

The board has strict requirements for physical plant (audiometric facilities):

1. Minimum of 50 square feet devoted to the hearing test area
2. Audiometer that meets the specifications of the current ANSI 3.6, at least a Type 4 (ANSI, 2004a)
3. Audiometric room (booth) that meets the current maximum permissible ambient sound levels in ANSI 3.1, Table 1 (ANSI, 2003)
4. Display of hearing protection samples
5. IAT certificate displayed
6. Confidential record keeping system

Both manual and automated audiometry (microprocessor or Bekesy type) are permitted. Personal, face-to-face counseling takes place immediately after each hearing test and includes an explanation of the audiogram and the significance of any non-normal results, recommended follow-up for significant hearing loss, and an evaluation of the worker’s hearing protection. The hearing protection evaluation includes examination of the protector’s fit and a discussion of the worker’s use, care, maintenance, and replacement of the device. Off-the-job use of hearing protection is also discussed.

The watchword of this program is consistency; consistency so that reasonably rigorous research can be conducted using the data collected. Assessing the success of an occupational health or safety program is always on the mind of those who fund the programs. “Are we getting our money’s worth” is a common question.

With over three million audiograms on file, spanning a 30 year period, there should be a robust enough data base to reveal important hearing conservation results and trends, and to be able to answer this question.

This Study
In this longitudinal study, the workers considered were all male, in the wood products manufacturing (sawmills, pulp mills, etc.) and construction industries. These workers were tested in 1988, when they were 16-24 years of age, and again in 2007, when they were 35-43 years of age. In 1988, both groups had a mean age of 22 years, with a mean of two years of occupational noise exposure; in 2007, they had a mean age of 41 years, with 21 years of occupational noise exposure. The number of workers tested in the wood products manufacturing industry was 1255, while in construction it was 427. All 1682 workers reported wearing hearing protection consistently over the 19 year period. In fact, it was impossible to get a group of workers of any size, in either industry, who did not report consistent use of hearing protection (good news!).

Why these two industries? On the surface, they differ in several important ways which might lead to different hearing conservation outcomes.

1. Wood Products Manufacturing:
   1. stable workforce
   2. physically captive workforce, i.e., in ‘mills’ or ‘plants’
   3. engineered noise control used, to varying degrees
   4. formal hearing conservation education & training conducted fairly consistently
   5. good occupational health and safety buy-in from employers
2. Construction:
   1. highly transient workforce
   2. physically mobile workforce, i.e., “work outside all over the place”
   3. very little engineered noise control, except in some mobile equipment
   4. very little formal hearing conservation education & training, beyond what can occur during the counseling portion of the annual hearing test
   5. general health and safety buy-in from employers may be good, but not necessarily around hearing conservation

The hearing conservation outcomes examined were:

1. 0,5 fractile (median) hearing levels, better ear, at 500, 1000, 2000, 3000, 4000, 6000, 8000 Hz; comparison between industries in 1988 and 2007, and then compared to
2. 0,5 fractile hearing levels per the International Standards Organization ISO-1999 standard
   1. Total predicted hearing levels, which comprise predicted noise, induced permanent threshold shift, or NIPTS (ONIHL) + Annex B (unscreened population) thresholds. We have assigned the noise exposure level 90 dBA for both industries, for 20 years duration.
   2. Annex B thresholds (= median age related hearing). We have used the 4th decade, i.e., 40 years of age.

So, two null hypotheses for this research would be

1. there is no difference in hearing conservation outcomes between workers in the wood products manufacturing and construction industries
2. there is no difference between hearing levels in these two industries compared to the same-age total predicted hearing levels from ISO-1999

Results

Null hypothesis 1
Figure 1 shows the two industries’ median hearing levels for 1988 and 2007.

It is clear no statistically significant differences in hearing levels exist between the two industries, both in 1988 and then again in 2007. Thus the null hypothesis is proven.

There are obvious differences between hearing levels between the two sample years, as the workers have aged 19 years between the two tests.

Null hypothesis 2
Figure 2 shows two additional graphs from the ISO-1999—median hearing levels for 40 year old males with 20 years of noise exposure at 90 dBA and median hearing levels for 40 year old males with no noise exposure (ISO, 1990).

Not only are the median hearing levels of the BC workers better than the predicted median hearing levels based on age plus noise exposure, but the hearing levels are better than the predicted hearing levels based on age alone!

The null hypothesis has been resoundingly disproven. This means that workers in these two industries demonstrate the success of their hearing conservation programs. To have hearing levels better than non-noise exposed men of the same age is truly amazing.

Another interesting set of numbers reveals the pattern of hearing protection use in the two industries, and in the two test years. Table 1 shows this. Note: the system of hearing protection classification used in BC is called the “Class” system. Basically, Class A protectors have NRRs of 24 dB or higher and Class B protectors have NRRs between 17-24 dB.

Table 1. Hearing Protection Use (Percentage)

	1988 WPM	1988 C	2007 WPM	2007 C
A Class EP	61	57	62	73
A Class EM	31	18	20	13
B Class EP	3	10	12	7
B Class EM	2	8	1	1
Combination	3	7	5	6

WPM = Wood Products Manufacturing
C = Construction
EP = earplug
EM = earmuff

Highlights:

1. Both industries show increased use of earplugs from 1988 to 2007.
2. Wood products manufacturing shows increased use of Class B earplugs, which are likely the vented, custom molded type.
3. Wood products manufacturing shows increased use in both protectors worn simultaneously (“combination”).

Conclusions:
It is apparent that this hearing conservation program has been a success and for two very different industries. Workers show median hearing levels better than predicted, even based solely on their age alone, let alone age plus occupational noise exposure. This may not be a surprise to anyone familiar with the wood products industry, but construction? For those who think that the second group is too transient, difficult to find, and difficult to monitor, think again. This is evidence that any industry is able to experience success in hearing conservation.

References:

1. ANSI (2003). American National Standard—Maximum Permissible Ambient Noise Levels for Audiometric Test Rooms S3.1-1999 (reaffirmed 2003). Acoustical Society of America: New York.
2. ANSI (2004a). American National Standard—Specification for Audiometers S3.6-2004. Acoustical Society of America: New York.
3. ANSI (2004b). American National Standard—Methods for Manual Pure-Tone Threshold Audiometry S3.21-2004. Acoustical Society of America: New York.
4. ISO (1990). Acoustics - Determination of occupational noise exposure and estimation of noise-induced hearing impairment ISO-1999:1990(E). International Organization for Standardization. Geneva, Switzerland.
5. WCB (1978). Industrial Health & Safety Regulations. Workers’ Compensation Board of British Columbia: Vancouver, pp 13-4 to 13-8.

Christine Harrison is the sole occupational audiologist for the province of British Columbia, Canada, and works for WorkSafeBC (formerly the Workers’ Compensation Board). She oversees hearing conservation programs for over 10,000 employers and 250,000 workers. Her particular areas of professional interest include speech and communication challenges in noisy industry, hearing conservation in the construction industry, use of hearing protection in different industries and age groups, as well as adult education.