Occupational Audiometric Testing in South Africa Explained (Part 1: The Baseline)

Everything you need to know about occupational audiometric testing, and how it determines the success of hearing-conservation programmes.

As an occupational healthcare practitioner, you play a crucial role in the protection of worker rights and livelihoods. Without you, noise-induced hearing loss would go undetected, and employees might use inadequate personal protective equipment (PPE). Untreated workers suffering hearing loss usually slide into poor health, without recognition or compensation. The hearing-impaired often have shorter lifespans too. As a healthcare worker, you are a vital node in a large network with improving lives as its goal. And it all starts with occupational audiometric testing.

This article is the first of a three-part series on occupational audiometric testing and hearing-conservation programme markers in South Africa, such as PLH (percentage loss of hearing) and STS (standard threshold shift). Read part 2 here.

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

Audiometric Testing at the Workplace

Occupational audiometric testing is important for the success of hearing-conservation programmes. It helps to determine if the current noise-control measures prevent hearing loss.

Occupational hearing loss often occurs over time. Therefore, workers often fail to notice changes in their hearing ability until significant deterioration occurs. It is your responsibility to compare audiometric tests results from past years. As soon as you detect any change, you have to implement protective measures. This will prevent further damage.

If an employee presents with hearing loss due to work conditions, the historical screening test results will support the compensation process. Therefore, it is essential to perform audiometric testing. It is the practitioner’s responsibility to enforce the correct procedures to collect the baseline test data. This ensures neither the employee nor the employer is exploited.

Kuduwave product testing
Audiometric Testing at the Workplace with the Kuduwave Prime.

Types of Audiograms Conducted in Different Industries

1. The South African Occupational Health and Safety Act (Act85 of 1993)

  • Baseline (Instruction 171)
  • Entry / Pre-placement / Pre-employment
  • Screening / Periodic
  • Exit
  • Diagnostic

2. The South African Mines Health and Safety Act (Act 29 of 1996)

[Guidance note for implementation of standard threshold shift in medical surveillance of noise-induced hearing loss]

  • Milestone Baseline / Initial
  • Monitoring
  • Exit
  • Diagnostic

Criteria for an Instruction 171 Baseline Audiogram (BL)

The baseline can establish possible future grounds for a claim in accordance with the Compensation for Occupational Injuries and Diseases Act (COIDA). The criteria below provide guidance regarding the most appropriate time window for conducting the required baseline examinations. Adhere to these criteria to avoid non-compliance or dismissal of the results.

  • A ‘competent person’, as defined in the NIHL regulation of 2003, must conduct the audiometry testing of a patient.
  • The audiometry test is conducted for the first time before an employee starts work, or when an employee is changing from a quiet zone to one more prone to noise.
  • Perform the test before or within 30 days of starting work in a noise zone, with a preceding  period of 16 hours without exposure to noise and no hearing-protective devices worn.
  • Conduct two audiograms on on the same day in the same setting. The two audiograms will secure the same hearing threshold level (HTL) in each ear. Should they differ, then it should not be ≥10 dB at any of the following frequencies: 0.5, 1, 2, 3 and 4 kHz. Retake both tests if the differences exceed 10 dB.
  • Ethical practice dictates that there must be no avoidable otopathology. Learn more about otoscopic examinations and identifying otopathologies that you should address before conducting audiometric tests.

Step-by-Step Guide to Audiometric Testing Procedures

  1. Conduct two tests on the same person on the same day. Although PLH calculations only require the results of five frequencies, the audiogram must include all seven frequencies (0.5, 1, 2, 3, 4, 6, 8 kHz).
  2. Conduct the second test shortly after the first, but not directly afterwards, to prevent a lack of concentration.
  3. Conduct both tests in the same setting or environment.
  4. Compare the two audiograms, and choose the one with the better PLH result. Mark the best result as the baseline, and the second as the baseline comparison.
  5. Repeat both tests if they differ by more than 10 dB in the frequencies 0.5, 1, 2, 3 or 4 kHz, from one test to the next. If you suspect the patient to be dishonest or malingering, read the following two articles:

    How to catch a malingering patient
    Stenger test and patient-response monitoring with KUDUwave

Note: If the patient suffered exposure to noise levels ≥85 dB (A) prior to the baseline, conduct a baseline audiogram within 16 hours of the noise exposure event. Furthermore, if a patient discloses that he will be working in a noisy environment with levels above 85 dB (A), the baseline audiogram is non-negotiable. However, if the noise level will be less than 85 dB (A), there’s no need for a baseline.

The baseline audiogram should always be available to the employee, should he or she leave the company.

When to Conduct a Baseline Audiogram

A baseline audiogram is only performed once in a worker’s lifetime, and usually before noise exposure. This is to determine what loss of hearing already exists prior to possible exposure. The baseline audiogram should always be available to the employee. Should he leave the company, the audiogram goes to the next employer, who will file it for record purposes. It serves as proof of his hearing level before noise exposure.

Should any new employee start work without an existing baseline audiogram on record, it is the medical professional’s responsibility to trace it. If it does not exist, or fails to meet the criteria below, perform an entry audiogram. In these cases, the baseline audiogram PLH will automatically become 1.1%.

A baseline audiogram is invalid if:

  • 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

Purpose of the baseline audiogram

The baseline audiogram is a point of comparison for all other audiograms, hence its importance in providing accurate hearing-threshold level shifts (HTLS) and PLH. All following tests, including entry, pre-placement / pre-employment, screening / periodic, exit and diagnostic, will be compared to the baseline audiogram’s PLH. This is to obtain the percentage loss of hearing shift (PLHS), for claims 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 (PLHS)

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%:

  1. Find 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.
  5. Keep a record of the related documentation of the procedures followed.

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. (An audiologist or ENT specialist is to conduct diagnostic tests. This is 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:

  1. Should the same results appear after a retest, remove the patient from the environment and refer him to an audiologist for a diagnostic audiogram.
  2. Should the findings of the diagnostic audiogram have the same PLHS result, the operating technician or nurse must regard the date of the test as the onset of disease.
  3. Furthermore, if the PLHS is related to the workplace, it becomes a reportable incident as stated in the legislation, with possible grounds for compensation claims.
  4. The HPD must conduct an inspection.
  5. Take steps to prevent any further hearing loss.
  6. Should the loss of hearing continue, permanently remove the patient from the noise zone.
  7. Report your findings to the relevant authority and employer.

Milestone Baseline

Mine Health and Safety Act (MHSA) 26 of 1996
This regulation is applicable to South Africa’s mining industry and serves as a guidance note for the implementation of Standard Threshold Shift (STS) in the medical surveillance of noise-induced hearing loss. The Department of Mineral Resources published Regulation 839 in the Government Gazette of 15 July 2016. (Visit 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 possibly be expressed simply as an ‘audiometric zero’, from which practitioners can identify a deterioration in hearing, and take measures to prevent a 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 three frequencies to be monitored, South African legislation still requires all seven 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.
Audio gram

The milestone baseline result, the initial audiometric value determined at the first STS testing, is a reference for all following audiograms. Determine the milestone baseline result 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.

STS Calculation

Standard Threshold Shift (STS) Intervention Methods

  1. Investigate any STS that exceeds 5 dB.
  2. An STS of 25 dB or more is reportable.
  3. Determine if the 25 dB or greater STS is work-related, and report the incident to the relevant authorities. Document all findings.

What Is the Difference Between Instruction 171 Baselines and Milestone Baselines?

Why do we conduct these tests?

  • Instruction 171: to claim from COIDA.
  • Milestone baseline: 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 2 000, 3 000 and 4 000 Hz and later on the shift in these frequencies (STS).

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


  • 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

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