A driving-under-the-influence prosecution under section 65 of the National Road Traffic Act 93 of 1996 rarely turns on whether the accused had been drinking. It turns on whether the State can prove, beyond reasonable doubt, that the concentration of alcohol in the accused’s blood or breath exceeded the prescribed limit at the time of driving. That proof depends almost entirely on a specimen, a breath reading, or a blood sample, and on the unbroken record of everyone who collected, labelled, stored, transported, and analysed it.
That unbroken record is the chain of evidence, also called the chain of custody. Where it is broken or incomplete, the specimen’s integrity is called into question, and a court may be forced to treat the analytical result as unreliable or even inadmissible. For an accused person, the chain of evidence is often the single most important battleground in a section 65 trial.
What the chain of evidence actually means
The chain of evidence is the chronological, documented history of a piece of evidence from the moment it is taken from the accused to the moment it is produced in court. Every person who handled the specimen, and every place it was kept, must be accounted for. The object is to exclude any reasonable possibility that the specimen was tampered with, contaminated, mislabelled, swapped, or allowed to deteriorate in a way that would affect the result.
In a South African criminal trial the State bears the burden of proving the chain, together with all the other elements of the offence, beyond reasonable doubt. The accused does not have to prove that the chain was broken. The accused only has to raise, through cross-examination or argument, a reasonable doubt about whether the specimen analysed in the laboratory is the same specimen taken from the accused, in the condition it was in when taken.
The statutory framework: section 65 of the National Road Traffic Act
Section 65 of the National Road Traffic Act 93 of 1996 prohibits driving, or occupying the driver’s seat of, a vehicle while the concentration of alcohol in the blood or breath exceeds the prescribed limit. For ordinary drivers, the prescribed blood alcohol limit is 0,05 grams of alcohol per 100 millilitres of blood, or 0,24 milligrams of alcohol per 1 000 millilitres of breath. For professional and novice drivers the limit is lower.
Because the offence is committed by exceeding a measured concentration, the specimen and its analysis are not peripheral evidence. They are the central evidence. The regulations made under the Act, together with the Criminal Procedure Act 51 of 1977, set out how breath and blood specimens are to be collected, handled, and analysed. Departure from those procedures goes directly to the weight the court will attach to the result.
Collection of the specimen
Collection is the first link in the chain. A breath specimen is typically taken by a traffic officer using an evidential breath testing apparatus operated by someone certified to use it. A blood specimen is taken by a registered nurse or a medical practitioner at a police station or a clinic. The arrested person is entitled to certain information at this stage, including the identity of the person taking the sample and the apparatus used.
- Identification of the taker. The officer or nurse who draws the specimen must be identifiable and available to give evidence at trial.
- Time of collection. The exact time is recorded, because the concentration of alcohol in the blood rises and falls over time and a back-calculation may be required.
- Equipment and reagents. For a breath test, the apparatus must be on the official type-approval list and must have been calibrated in accordance with the regulations.
- Consent and rights. The arrested person must be informed of the right to have a further blood sample taken by a medical practitioner of their own choice, within a reasonable time.
Labelling, sealing, and storage
Immediately after collection, the specimen container must be sealed, labelled, and identified. The label typically carries the date, the time, the arrested person’s name, a unique reference number, and the signature or mark of the person who took the sample. The seal is intended to ensure that any later opening of the container is obvious.
Storage conditions matter because biological specimens degrade. A blood specimen must be kept in conditions that inhibit fermentation and bacterial action, which can otherwise produce alcohol within the container and falsely inflate the reading. Where a specimen is left unrefrigerated, or stored in a vehicle for hours, the analytical result becomes open to challenge on the basis that the measured alcohol was not all present at the time of driving.
Transport to the forensic laboratory
The sealed specimen must be transported to the relevant forensic chemistry laboratory. The Act and regulations expect this to happen promptly, and the persons who take possession of the specimen during transport must be recorded. Each transfer, from the nurse to the investigating officer, from the officer to the police station exhibit store, and from the store to the courier or laboratory, must be capable of being traced to a named individual.
Gaps at this stage are common. A specimen may sit in a fridge with no entry in the exhibit register, or may be carried in a vehicle for several hours before it reaches the station. Where the State cannot account for the specimen during those periods, the defence can argue that the court cannot be satisfied the specimen reached the laboratory in the condition in which it was collected.
Analysis at the laboratory
At the forensic chemistry laboratory the seal is broken in controlled conditions, the specimen is analysed, and a certificate of result is issued. The analyst must be competent and must be called as a State witness, or the certificate must be admissible under the relevant statutory provisions. The analytical method, the calibration of the instrument, and the reagents used must all be defensible.
The defence is entitled, through discovery and cross-examination, to scrutinise the laboratory’s records. These include the chain-of-custody form that accompanied the specimen, the internal transfer of the specimen between analysts, and the quality-control results for the batch in which the specimen was analysed. Inconsistencies between the collector’s documentation and the laboratory’s receipt records are precisely the kind of detail that can undermine a reading.
How a break in the chain undermines the State’s case
A break in the chain of evidence does not automatically result in acquittal, but it raises a reasonable doubt that the State must overcome. The consequences depend on the nature and severity of the gap.
- An unaccounted period in transit. If the specimen cannot be traced for hours or days, the court may accept that tampering or deterioration cannot be excluded.
- A broken or unverified seal. A seal that is broken on arrival at the laboratory, without explanation, goes directly to the integrity of the specimen.
- An unqualified operator. Where the breath operator’s certification had lapsed, or the nurse was not registered, the validity of the collection itself is in question.
- An uncalibrated apparatus. A breath testing instrument used outside its calibration interval produces a reading the court may decline to act upon.
- Missing documentation. Absent or contradictory entries in the exhibit register and the laboratory receipt make it impossible to confirm continuity.
Where one or more of these defects is present, the court must consider whether the State has discharged the burden of proof beyond reasonable doubt. South African judgments reported on the Southern African Legal Information Institute database repeatedly confirm that a reasonable doubt about the integrity of a specimen entitles the accused to an acquittal, even where a high reading was recorded.
The evidential burden in practice
The State leads its evidence through the arresting officer, the person who took the specimen, the investigating officer, and the analyst. Each must be able to identify the specimen, explain how it came into their hands, and account for the period during which it was in their possession. Cross-examination is directed at the gaps between their evidence: the times that do not line up, the signatures that are absent, the seals that were not checked, and the records that were not kept.
A defence attorney who understands the National Road Traffic Act and the Criminal Procedure Act does not need to prove the specimen was tampered with. The attorney needs only to demonstrate, on the State’s own evidence, that tampering or deterioration cannot reasonably be excluded. That is the difference between a reading and a conviction.
Why the chain matters as much as the reading
It is common for accused persons to focus on the blood or breath reading and to assume that a high reading makes a conviction inevitable. It does not. A reading is only as reliable as the chain that brought it into court. A specimen handled in breach of the regulations, analysed after an unexplained delay, or recorded against an incomplete exhibit register may be excluded from evidence, and without that specimen the State usually has no reading to rely on at all.
This is why the chain of evidence is examined in detail in every section 65 defence. The prescribed limit, the apparatus, and the laboratory are fixed and verifiable. The human handling of the specimen is variable, and it is in that variability that reasonable doubt most often arises.
Frequently Asked Questions
What is the chain of evidence in a drunk driving case?
The chain of evidence is the documented, unbroken record of everyone who collected, labelled, sealed, stored, transported, and analysed a breath or blood specimen, from the moment it is taken from the accused to the moment it is produced in court. Its purpose is to show that the specimen analysed in the laboratory is the same specimen taken from the accused, in an unaltered condition.
What happens if the chain of custody is broken in a section 65 case?
A break does not automatically result in acquittal, but it raises a reasonable doubt that the State must overcome beyond reasonable doubt. Where the State cannot account for the specimen during a material period, the court may treat the analytical result as unreliable and may even exclude it, which usually leaves the State without its central evidence.
How long after a drunk driving arrest must a blood sample be taken?
A blood specimen must be taken within a reasonable time of the alleged offence, and the exact time is recorded because blood alcohol concentration changes over time. The arrested person must also be informed of the right to have a further sample taken by a medical practitioner of their own choice within a reasonable period.
Can a breathalyzer result be challenged in a South African court?
Yes. A breath result can be challenged on the basis that the apparatus was not type-approved, that it was used outside its calibration interval, that the operator was not properly certified, or that the chain of custody for the breath reading was not established. Each of these goes to the weight the court will attach to the result.
Who must prove the chain of custody in a drunk driving trial?
The State bears the burden of proving the chain of custody, together with every other element of the offence, beyond reasonable doubt. The accused does not have to prove the chain was broken. The accused only has to raise, through cross-examination or argument, a reasonable doubt about the integrity of the specimen.
What is the prescribed blood alcohol limit under section 65 of the National Road Traffic Act?
For ordinary drivers the prescribed limit is 0,05 grams of alcohol per 100 millilitres of blood, or 0,24 milligrams per 1 000 millilitres of breath. For professional and novice drivers a lower limit applies. Exceeding the limit is only an offence if the State proves the reading beyond reasonable doubt, which in turn depends on a proper chain of custody.
Get help with a criminal law matter. Otrebski Attorneys’ Criminal Law department, based at the firm’s single Sandton office, defends clients facing section 65 driving-under-the-influence charges across Johannesburg and the wider Gauteng area. The firm is 100% women-led, holds a Level 4 B-BBEE rating, carries a 5-star Google rating across 12 reviews, and is led by Director Nastasja Otrebski.
Disclaimer. This article is general information about the chain of evidence in South African drunk driving cases and is not legal advice. For guidance on a specific charge, confirm current requirements with the Legal Practice Council, the relevant Regional Court, or a qualified criminal law attorney. The applicable law includes the National Road Traffic Act 93 of 1996 and the Criminal Procedure Act 51 of 1977, both of which may be amended.