Occupational Audiometric Testing Explained (Part 2)

Here we explain audiometric testing in occupational healthcare. We want you to worry less about administration and focus on the patient instead.

Unlike superheroes who fly in and out to save the day, occupational health practitioners are the true heroes, returning for follow-ups year after year after year. Monitoring the status of workers’ hearing is the responsibility of each occupational health practitioner.

But sometimes regulations and red tape make this difficult, and keep you from attending to your patients. Here we will shed some light on audiometric testing in occupational healthcare, so that you can worry less about administration and focus on the patient instead.

This article is the second of a three-part series on audiometric testing and hearing conservation program markers, such as percentage loss of hearing (PLH) and standard threshold shift (STS). (Read part-1 here.)

We will discuss the types of audiograms and how to interpret the differences between compared test results. This is to distinguish the patient’s right to claim compensation according to the relevant legislation.

Types of audiograms conducted in the industries:

  1. South African Occupational Health and Safety Act No 85 of 1993
  2. Baseline (Instruction 171)
  3. South African Mines Health and Safety Act No 29 of 1996
  4. Milestone Baseline / Initial

What Is an Entry/Pre-Placement/Pre-Employment Audiogram?

An entry audiogram consists of a single completed audiogram that the occupational health practitioner conducts on:

  • All employees new to a company or site.
  • Employees who could have been exposed to harmful noise before.
  • New employees who present an invalid baseline audiogram. The practitioner cannot repeat a baseline audiogram if the former site or employment has lost the (previous) results. The previous employer will be held liable in these cases. For more on criteria for dismissal of a baseline, read our first article in this series: Part 1: The Baseline.
  • An employee who transfers from one department to another where the possible exposure to noise will be different. Conduct a single pre-placement audiogram in this scenario.

An entry audiogram must comply with the same criteria as that of a baseline audiogram (see previous article). The only difference is that it consists of one audiogram and that the patient possibly suffered exposure to excessive noise before.

What is a Periodic or Screening Audiogram?

The periodic audiogram is mandatory. This kind of audiometric testing is either performed annually or every six months, depending on the noise level the patient is exposed to.

Occupational health practitioners perform these to determine a possible hearing threshold level shift (HLTS) from the baseline audiogram, which is indicated by a change in PLH.

Prepare the patient for the periodic audiogram. They cannot be exposed to excessive noise for at least 16 hours prior to the test, with no exceptions or use of hearing protection devices allowed.

Identifying Percentage Loss of Hearing Shifts (PLHS)

The Baseline Audiogram is used as a reference for all other audiograms, hence the importance in providing accurate HTLS and PLH. All tests following, including  Entry, Pre-placement/Pre-employment, Screening/Periodic, Exit and Diagnostic will be compared to the Baseline Audiogram’s PLH to obtain the PLHS for interventional purposes (i.e. claiming purposes).


Baseline PLH: 1.5%
Follow-test PLH: 4.3%
PLHS is: 4.3% – 1.5% = 2.8%

Noise Induced Hearing Loss (NIHL) guidelines stipulate that should there be no percentage loss of hearing shift (PLHS = 0%) from the baseline audiogram after three  years of annual follow-ups, then the employer can reduce the frequency of testing  to once every two years.

However, should a change be visible in the PLH, then the surveillance frequency changes back to every six months, until the PLH has been stabilised. Once the PLH is stable, surveillance testing can continue on an annual basis.

Intervention Methods

Where a decrease has been detected in the hearing threshold level between the baseline audiogram and the periodic/screening audiogram of 15 dB or more, at 3 kHz, 4 kHz or 6 kHz, the audiometric testing must be repeated to confirm the results.

Once confirmed, follow these steps:

1. Explain the findings on the audiogram to the patient.

2. Refer the patient for a retraining and re-instruction course, in accordance with the Mine Health and Safety Act, Act 29 of 1996 which stipulates:

  • Education to be provided on the potential source of exposure to noise.
  • Education to be provided on the potential health effects associated with noise exposure.
  • Training to be provided on adhering to standard precautions such as protecting oneself from noise exposure and the importance of the use of proper personal protective equipment.
  • Education to be provided  on the importance of audiometric testing and medical surveillance.

3. Reassess the provided hearing protection devices for suitability.

4. Inform the employer and the health and safety practitioner of the case findings.

According to the latest amendments as published in SANS 10083:2013 Edition 5.2, focusing on hearing conservation and not just NIHL reporting.

PLHS of 3.2%

  • Investigate the reason for the shift (otoscopic investigation or retest).
  • Examine the effectiveness of the provided hearing protection devices (HPD) (i.e. attenuation values and adequacy).
  • Investigate the usage (frequency) and fitting of the HPD
  • Educate the patient on the proper use of HPD.
  • Keep a record of the related documentation of the procedures followed etc.

PLHS of 6.4%

  1. Investigate the reason for the shift.
  2. Investigate the effectiveness of the provided HPD.
  3. Retrain the patient on the importance of the HPD.
  4. Refer the patient for a diagnostic audiogram. This is a diagnostic test that an audiologist or ENT specialist will perform. This test is for the purpose to investigate possible ear pathologies, where there is an inconsistent baseline result or for the potential of a compensation claim.

PLHS of 10% or more

  • Should the same results appear after a retest, remove the patient from the environment and refer him to an audiologist for a diagnostic audiogram.
  • If the findings of the diagnostic audiogram conclude the same PLHS result, then it is the responsibility of the operating technician or nurse to regard the date of the test as the onset of disease.
  • Should the PLHS be related to the workplace, then it becomes a reportable incident as stated in the legislation, with possible grounds for a compensation claim.
  • Conduct an inspection on the HPD.
  • Take steps to prevent any further loss.
  • Should the loss of hearing continue, permanently remove the patient from the noise zone.
  • Report findings to the relevant authority and employer.


  • Conduct only one audiogram.


  • Should the person be exposed to noise levels greater than 85 dB, conduct follow-up screening tests annually.
  • Should the person be exposed to noise levels greater than 105 dB, or should there be signs of any abnormalities indicated by PLHS, be sure to conduct the follow-up screening test every six months (bi-anually).

Noise free preparation:

  • The patient must not be exposed to noise for at least 16 hours prior to testing. No hearing-protection devices (HPD) may be used to sidestep this requirement.


  • The purpose of the follow up screening test is to identify the possibility of a hearing threshold shift (PLHS) early enough for intervention or surveillance to take place.
  • It forms part of Medical Surveillance (MS)

Intervention Methods:

  • Good practice and preventative guidelines would recommend interventional procedures and re-training to occur in the event of any kind of increase in PLH from the baseline audiogram. Note that some legislation stipulates waiting for a 10% increase. However, waiting on the possibility of permanent disability to occur at a 10% increase in PLH is too late.

What Is a Monitoring Audiogram?

Mine Health and Safety Act 26 of 1996

This regulation is applicable  to the Mining Industry of South Africa and serves as a guidance note for the implementation of standard threshold shift (STS) in the medical surveillance of NIHL. The Department of Mineral Resources published regulation 839 in the Government Gazette of 15 July 2016. www.gpwonline.co.za

It requires audiometric testing on all employees exposed to 105 dB or more, for a monitoring audiogram. The employees are to be monitored and tested every six months with the aim of focusing on the prevention of permanent hearing loss and to assess the effectiveness of the Hearing Protection Devices (HPD). Monitoring audiograms are conducted at the same frequencies as that of a Milestone or Initial Audiogram (0.5, 1, 2, 3, 4, 6 and 8 kHz). This is required even though STS calculations only require three of those frequencies.

Conduct monitoring audiograms directly after employees are exposed to noise in high noise risk workplaces or occupations for the prevention of permanent hearing loss by testing for temporary threshold shifts (TTS, a reversible condition where the hearing threshold level (HTL) changes which is attributed to recent noise exposure). In an instance where audiometric testing detects, conduct a monitoring audiometry test to determine if the shift is transient or not. Should it be the latter, determine the extent of the shift in the HTL.

Identifying Standard Threshold Shifts (STS)

The milestone baseline result, the initial audiometric value determined at the first STS testing, is used as a reference for all following audiograms. The milestone baseline result is determined, as mentioned previously, by averaging the dB values found at three frequencies: 2, 3 and 4 kHz. The standard threshold shift (STS) is the average change in the hearing levels at these frequencies, and it is the monitoring of these changes which initiates conservation efforts to prevent further hearing loss.

  • Milestone baseline: The initial audiometric value determined at the first STS testing.
  • Standard threshold shift (STS) is the average change in hearing levels of ≥10 dB at the following frequencies, 2 kHz, 3 kHz and 4 kHz in one or both ears when compared to the milestone baseline.  An STS of ≥25 dB hearing loss at the same frequencies is reportable.
    Investigate any STS that is >5 dB.
  • Determine if the STS is ≥25 dB, determine if it is work related and report the incident to the relevant authorities. Document all findings.


left and right ear Hz

Intervention Methods:

For a monitoring audiogram, adhere to the following :

  • When compared to the milestone audiogram and an increase of 15 dB or more in the HTL is identified in either one, or both ears at any of the frequencies; 500 Hz, 1 000 kHz, 2 000 kHz, 3 000 kHz, 4 000 kHz, 6 000 kHz or 8 000 kHz, repeat the test to confirm the results. (Note: a repeat test can only be done after the provision of a re-instruction of the audiometric testing procedure was given to the employee and the earphones were refitted by the medical professional).
  • After confirmation of a 15 dB shift or more, follow these steps:
    Inform the employee of their hearing-status findings.
    Refer the employee for retraining and re-instruction.
    Reassess the provided hearing protection devices for suitability.
    Inform the employer and the health-and-safety professional of the findings.
    Record the indicated increase of HTL on the monitoring audiogram in the employee’s records.

Standard threshold shift (STS) intervention methods:

  • Investigate any STS that exceeds 5 dB.
  • Report an STS of 25 dB or more.
  • Determine if the 25 dB or greater STS is work related and report the incident to the relevant authorities. Document all findings.


  • Conduct only one audiogram.


  • Only in accordance with the Mine Health and Safety Act, Act  29 of 1996.
  • Should an employee be exposed to noise levels that are ≥105 dB.
  • Conduct annually or every six months.

Noise free preparation:

  • No noise-free preparation required


  • The purpose is to determine noise-induced hearing loss (NIHL) in time.
  • For the testing of temporary threshold shifts (TTS)
  • To identify and educate on the correct use of hearing protection devices (HPD).

Intervention Methods:

  • Hearing threshold level shifts (HTLS) greater than 15 dB at any of the frequencies tested in your monitoring audiogram, compared to your baseline audiogram, must be retaken to confirm the threshold shift. Thereafter, follow the steps stipulated to process the patient through the conservation program.
  • Investigate STS shifts greater than 5 dB. This early identification marker is a great benefit to proactive work in bettering working environments.

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