A polygraph test, more commonly known as a “lie detector test”, is a procedure commonly used to verify whether the person being tested is being truthful in their responses to a set of questions posed to them by the conductor of the test. The test seeks to record the relevant person’s bodily responses to the questions posed which include, amongst others, increased heart-rate, blood-pressure and respiration rate which will indicate to the examiner whether the person tested is being honest or deceitful.

Consequently, the question then arises as to whether the results of a “failed” polygraph test constitutes admissible evidence, and therefore compelling grounds justifying an employer’s dismissal of an employee charged with misconduct in the workplace.

It is worth noting that the general position in criminal proceedings, the evidentiary rules of which are mirrored, albeit to a lesser extent, in employment matters, is that the results of polygraph testing are generally inadmissible and cannot be relied upon by the prosecution in proving their case against an accused, unless supported by corroborating evidence.

The Labour Relations Act, No. 66 of 1995, affords every employee the right not to be unfairly dismissed. In order for an employer to show that its dismissal of an employee was fair, it has to prove, firstly, that the dismissal was affected on the basis of a fair reason and, secondly, that the dismissal was affected in accordance with fair procedure giving effect to the employee’s rights to, inter alia, a fair hearing, to state his or her case  (audi alterem partem) and to be provided with sufficient time to consider and prepare his or her defence to the charges raised.

The use of polygraph testing, and an employee’s consent thereto, may be included in employment contracts which would entitle employers the right to use the test as part of the disciplinary hearing process and / or the employer’s investigations into the employee’s alleged misconduct prior to conducting a disciplinary hearing. Currently, there is no specific legislation controlling the use of polygraph testing and / or regulating the protection of the rights of employees against the potential abuse of the test and its results. Generally, it remains unlawful and in contravention of the prescripts of the Constitution of South Africa for an employer to compel an employee to undergo a polygraph test without the employee’s express consent. It is thus imperative for an employer to ensure that such consent is reduced to writing and specifically acknowledged by the employee.

In the case of Goldplat Recovery (Pty) Ltd v Commission for Conciliation Mediation and Arbitration & Others[1], the Labour Court was faced with a matter in which an employer dismissed an employee on the strength of the results of a polygraph test.

In dealing with the reliability of polygraph tests generally, the Labour Court made reference to the case of DHL Supply chain (Pty) Ltd v De beer No and Others where the Labour Appeal Court held that:

the mere fact that an employee fails a polygraph test is not in itself sufficient to find an employee guilty of dishonesty. The onus rests on the employer to lead expert evidence to prove the cogency and accuracy of the polygraph test[2]. [emphasis added]

Accordingly, and relying on the dicta of the Labour Appeal Court in the DHL matter, the Labour Court ruled in the Goldplat case that there was no direct evidence implicating the employee in the wrongdoing alleged and that the assumption made by the employer that the employee was guilty by virtue of him failing the polygraph test amounted to no more than speculation. Thus, the Labour Court ruled that the employer could not rely on the results of the polygraph test in dismissing the employee as a result of, inter alia, the employer’s failure to lead expert and / or corroborating evidence on the reliability of the polygraph test results.

In conclusion, it follows that the results of a polygraph test, without any supporting expert and / or corroborating evidence as to its reliability, will not constitute valid grounds for dismissal. An employer’s reliance on a failed polygraph test is accordingly insufficient to prove that an employee is guilty of the misconduct alleged or that the employee has been economical with the truth when tested.

Employers are cautioned against using the results of polygraph tests as the sole basis for disciplining an employee. The probative value of polygraph testing remains open ended, and its reliability, if any, is to be determined by the courts on a case-by-case basis and in conjunction with expert and / or further corroborating evidence.

[1] Goldplat Recovery (Pty) Ltd v Commission for Conciliation Mediation and Arbitration & Others (JR 488/2019) [2021] ZALCJHB 48 (3 February 2021)

[2] DHL Supply chain (Pty) Ltd v De beer No and Others (DA4/2013)[2014] ZALAC 15;[2014] 9 BLCR 860 (LAC), (2014) 35 ILJ 2379 (LAC) (13 May 2014)