Occupational Health Audiometric Testing in South Africa Explained (Part 1)

Part 1: The Baseline

As an occupational healthcare practitioner,  you can take comfort in knowing that you play a vital role in the protection of workers’ rights. Without you, noise induced hearing loss would not be detected, and workers would continue to use inadequate PPE*. Would PPE even exist? Ultimately, untreated workers would continuously slide into poor health without recognition or compensation. Can we go so far as to say you are saving their lives? You may not be an ER surgeon miraculously bringing people back from the pearly gates, but most people agree that prevention is better than a cure. People with hearing loss have been found to have shorter lifespan, so technically you are saving lives. It is undeniable that you are an important engine in a large network driving to improve the lives of people and the environment they work in.  Where does all of this start?

Audiometric testing in occupational settings is important for the success of a hearing conservation program. It helps to determine if occupational hearing loss is actually being prevented by the current noise control measures. Due to occupational hearing loss occurring  gradually over time, workers often fail to notice changes in their hearing ability until significant  deterioration occurs. This can be avoided by simply comparing audiometric tests from past years and acting as soon as a change is detected, implementing protective measures to prevent further damage. In the event that an employee presents with a hearing loss due to occupational conditions, the historical screening  test results will be used to support the compensation process. This is why it is of utmost importance to perform a baseline hearing test on a patient. It is the practitioner’s responsibility to enforce the correct procedures to collect the baseline test to ensure that neither the employee nor the employer is taken advantage of.

This article is the first of a three part series that will be published over the next few weeks focusing on audiometry tests and hearing conservation program markers in South Africa, such as PLH (Percentage Loss of Hearing) and STS (Standard Threshold Shift). We will discuss the types of audiograms and how to compare and interpret test results, thus distinguishing the patient’s right to claim compensation according to the relevant legislation.

What types of audiograms are conducted in the different industries:

1. South African Occupational Health and Safety Act  (Act No. 85 of 1993)

    1. Baseline (Instruction 171)
    2. Entry/Pre-placement/Pre-employment
    3. Screening/Periodic
    4. Exit
    5. Diagnostic

2. South African Mines Health and Safety Act No 29 of 1996 [Guidance note for implementation of standard threshold shift in medical surveillance of noise induced hearing loss]

    1. Milestone Baseline/Initial
    2. Monitoring
    3. Exit
    4. Diagnostic


Criteria for an Instruction 171 Baseline Audiogram (BL)

The Baseline is conducted in order to establish possible future grounds to make a claim as according to the Compensation for Occupational Injuries and Diseases Act (COIDA) . The below criteria provides guidance  with regards to  the most appropriate time frame to conduct the required baseline examinations. It is important to adhere to the criteria to avoid non-compliance or dismissal of the results.

  • Audiometry testing of a patient must be conducted by a competent person as set out and defined in the NIHL regulation 2003.
  • Audiometry test is conducted for the first time (before an employee commences employment), or when an employee is changing from a non-noise zone to a zone more prone to noise.
  • The test must be performed prior to, or within 30 days of commencement of work in a noise zone, with a  preceding  period of 16 hours during which there’s been no exposure to noise levels and no hearing protective devices were worn.
  • Two audiograms must be conducted, on the same day, in the same setting. The two audiograms are to secure the same Hearing Threshold Level (HTL) in each ear. Should they differ, then it should not be ≥10dB at any of the following frequencies: 0.5, 1, 2, 3 and 4 kHz. Differences larger than 10dB require both tests to be retaken.
  • Ethical practice dictates that there must be no avoidable otopathology. Learn more about Otoscopic examinations and identifying otopathologies which should be addressed before conducting audiometric tests.

Procedure to Follow

  1. Conduct two tests on the same person on the same day. Although PLH calculations only require the results of 5 frequencies, the audiogram is still required to include all 7 frequencies on the audiogram (0.5, 1, 2, 3, 4, 6, 8 kHz)
  2. Conduct the second test a short while after the first test and not directly afterwards to prevent lack of concentration. 
  3. Both tests must be conducted in the same setting / environment.
  4. Compare the two audiograms, and select the best test on the principle of the better PLH result. Mark the best test result as the Baseline, and the second test as the Baseline Comparison.
  5. Both tests must be repeated should they differ more than 10 dB in the frequencies 0.5, 1, 2, 3 or 4 kHz from one test to another. If you are struggling to get a true result from the patient and suspect faking or malingering, these articles below may be helpful: 
    1. How To Catch A Malingering Patient. 
    2. Stenger Test and Patient response monitoring with KUDUwave.

Note: Should the patient have been exposed to noise levels ≥85 dB(A) prior to the Baseline, then Baseline Audiogram should not be conducted within 16 hours from when the employee has been exposed to noise.. Furthermore, if a patient discloses that he will be working in a noisy environment and be exposed to levels higher than 85 dB(A), the Baseline Audiogram is non-negotiable. However, if the noise level will be less than 85dB(A), the Baseline is not needed. 

It is important to remember that a Baseline Audiogram  is only performed once in an employee’s lifetime and usually conducted before he/she is exposed to noise. This is to determine what loss of hearing already exists prior to possible exposure. The Baseline Audiogram should always be available for the employee should he/she leave the company and in turn that Baseline Audiogram is then presented to the next employer for record purposes and contributes as proof of his/her hearing level before he/she had been exposed to noise.

Should any new employee commence duties without an existing Baseline Audiogram on record – it is the responsibility of the medical professional to trace it.  Should no Baseline Audiogram have been done or should it not fulfill the criteria mentioned below, then an Entry Audiogram must be done. The Baseline Audiogram  PLH will automatically become 1.1% in these cases.

A Baseline Audiogram is considered invalid for the following three reasons:

  • There was a difference of 10 dB or more between the two tests at any of the following frequencies: 0.5 kHz, 1 kHz, 2 kHz, 3 kHz or 4 kHz
  • Only one test was performed
  • The Baseline was performed on a longstanding employee after November 2003

Your Baseline Audiogram is used as a reference for all other audiograms to be compared with hence the significant importance to provide accurate Hearing Threshold Level Shifts (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 Percentage Loss of Hearing Shift (PLHS) for claiming purposes. 


Baseline PLH: 1.5%

Follow-test PLH: 4.3%

PLHS is: 4.3% – 1.5% = 2.8%

Percentage Loss of Hearing Shift Intervention Methods:

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

  1. PLHS of 3.2% 
    1. Investigate the reason for the shift (otoscopic investigation or retest)
    2. Investigate the effectiveness of the provided Hearing Protection Devices (HPD) (i.e. attenuation values and adequacy)
    3. Investigate the usage (frequency) and fitting of the HPD
    4. Educate the patient on the proper use of HPD for them to have a clearer understanding
    5. Keep a record of the related documentation of the procedures followed etc.
  2. 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 client for a Diagnostic Audiogram (Diagnostic tests to be conducted by an Audiologist or ENT specialist. 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)
  3. PLHS of 10% or more 
    1. Should the same results appear after a retest has been concluded then remove the patient from the environment and refer them to an Audiologist for a Diagnostic Audiogram 
    2. Should 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.
    3. Should the PLHS be related to the workplace, then it becomes a reportable incident as stated in the legislation, with possible grounds for compensation claims
    4. An inspection needs to be conducted on the HPD.
    5. Steps need to be taken to prevent any further loss.
    6. Should the loss of hearing continue then the patient needs to be permanently removed from the noise zone.
    7. Report findings to the relevant authority and employer.

Milestone Baseline

MHSA 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 Noise Induced Hearing Loss. Regulation 839  was published in the 15th July 2016 Government Gazette from the Department of Mineral Resources. www.gpwonline.co.za

A Milestone Baseline (or audiometric zero)  is done for hearing conservation purposes. Similarly to the Baseline PLH and PLHS, the Milestone Baseline means the initial audiometric value determined at the first Standard Threshold Shift audiometric testing. However, the STS principle  does not apply to compensation for Industrial Hearing Loss and is not meant to replace Instruction 171. It can perhaps be simply put as an “audiometric zero”, from which practitioners can identify a deterioration in hearing and take measures to prevent further decline in health. In South Africa, PLH and STS will most likely be monitored in conjunction with one another. Although legislation will work from the PLH results, STS monitoring may result in earlier detection of an issue. This is why the procedure to follow below will make reference to both indicators of hearing threshold shifts.

Procedure to follow and criteria for best result selection:

  • Conduct two full tests on the same person on the same day. Although STS only requires 3 frequencies to be monitored, the SA legislation still requires all 7 frequencies (tabulated below) to be included on the audiogram.
  • Choose the better test on the basis of the lowest PLH result
  • Confirm that it is the better result by inspecting the total average of the dB levels at frequencies 2 kHz, 3 kHz and 4 kHz for both ears
  • Select the best test value as your Audiometric Zero / Milestone Baseline.

Example: Using the criteria stipulated above, Audiogram 2 will be accepted as the Milestone Baseline.

table 1


Your Milestone Baseline result, the initial audiometric value determined at the first STS testing, is used as a reference for all following audiograms to be compared to. The Milestone Baseline result is determined as mentioned previously by averaging the dB values found at three frequencies: 2, 3 and 4 kHz. 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.


table 2


Standard Threshold Shift (STS) Intervention Methods:

  • Any STS that is more than 5 dB should be investigated.
  • An STS of 25 dB or more is reportable.
  • Determine if the 25dB or greater STS is work related and report the incident to the relevant authorities. All findings to be documented.

What is the difference between Instruction 171 Baselines and Milestone Baselines?

Why do we conduct these tests?

  • Instruction 171 is done in order to claim from COIDA
  • Milestone baseline is done for hearing conservation

What to compare?

  • Instruction 171 compares PLH results and later on the PLHS
  • Milestone baseline “audiometric zero” compares the average dB results  for frequencies 2000, 3000 and 4000Hz and later on the shift in these frequencies (STS).

For further reading  refer to the  PLH Contribution Tables (Government Gazette Staatskoerant, Vol 431, Pretoria, 16 May 2001,  No: 22296) 

Reference list

  • NIHL Regulation
    • Section 8: Baseline, Periodic, Exit
  • MHS Act 1996
    • Section 13: Medical Surveillance
    • Section 14: Service Records
    • Section 17: Exit Certificates
  • Supplement Instruction 171
  • SASOHN Guidelines (SASOHN, 2005)
  • Circular Instruction 171
  • Momentum OCSA  Audiometric Techniques Manual 6th Edition
  • Industrial Audiometry Short Course – Dr. E de Koker & H de Clercq