Site visits

The purpose of a site visit

Whilst a site visit may be helpful, it is not always essential because the description of the scene given by the investigating inspector or other witnesses will usually be supported by photographs which can be used in court. The expert can base his/her report on this evidence.

A site visit by an expert may be appropriate in order to examine the scene of an incident (where the condition of the site, or something at the site, is in issue), remove samples, take photographs or assess whether any further tests need to be undertaken. This should be agreed with the person managing the investigation. The expert should bear in mind that if s/he carries out a site inspection, s/he may be called upon at trial to give evidence of fact as well as his/her expert opinion. This might affect the procedure in court.

A list of matters to be dealt with on the site visit should be made in advance, all necessary equipment obtained and any required procedures agreed. At the workplace, all relevant matters should be noted, such as weather conditions, position of plant and equipment, measurements etc.

Where a complex, technical investigation on site could recover evidence that would provide the basis of an expert's report (in the event that one is required), a specialist could form part of the investigation team. However, whether s/he should then give evidence as the expert in any subsequent prosecution would need is for the procurator fiscal to decide. Experts should generally maintain a professional distance from the investigation so as to preserve (and be able to demonstrate) their objectivity, but the ultimate decision as to the role of those attending site remains with the person managing the investigation.

Similar considerations will apply to the examination of a machine or other product on site for the purpose of a section 6 HSWA investigation. In gathering evidence from a supplier, it is permissible for an expert to visit the supplier on site, look at the machinery, see it in operation and ask questions about its operation and the guidance that is given. Having obtained that information, it is desirable that someone else gathers any further information and takes any statements, so as to avoid the expert becoming involved too closely in the ongoing investigation.


Section 20(2)(i) HSWA empowers an inspector to take possession of any article or substance found in any premises which appears to have caused, or to be likely to cause, danger to health or safety. Section 20(2)(g) enables an inspector to take samples of articles or substances and to take atmospheric samples.

Specialist equipment should, where necessary, have a certificate of calibration. Each item must be uniquely identified by a label and recorded. Suitable containers, packing, labels and seals should be used. The labels should state the premises of origin, a description of the sample, a number if there is more than one sample, the date, and your name and title.

When the sample has been taken, the suspect should, where practicable, be given part of the sample or otherwise informed that a prosecution may follow and invited to take their own sample. NB this is legally incorrect, the sample should be given to a responsible person on site who may not be the suspect, or connected to them – s.20 (6) HSWA.

If an item has to be irreversibly altered to obtain a sample or to allow a test to be made, both the person in charge of the investigation and the person who took possession of the article should be informed before the sampling or testing is undertaken.

If prosecution is a possibility, the investigating inspector should contact any potential defendants before the item is tested or irreversibly altered to give them an opportunity to be present at such tests. This ensures fairness in this element of the investigation and will also assist in preserving the continuity of evidence (see The chain of evidence below). Furthermore, persons who have any responsibility in relation to premises being investigated also have the right - at their request - to be present when any relevant article or substance is being examined, tested or analysed.

However, where an item is to be tested, the investigating inspector should, in each case, balance the need for fairness and continuity of evidence with the need to ensure that the presence of observers will not impede or inhibit the test. It may be appropriate, for example, to:

  • Limit the numbers of those attending;
  • Inform those attending how the test will be conducted and clarify their role as observers only to avoid confusion or dispute on the day;
  • Seek agreement in advance to appropriate rules of attendance, such as restrictions on photography/video, or safety rules.

So far as possible, enough of the item should be retained to allow further independent tests if necessary. If this is not possible, all practicable steps should be taken to ensure that the results can be proved in court; for example, by videoing or photographing the test and retaining all notes and records of results. These matters should be noted in the expert/specialist's notebook and included in his/her statement and/or report.

The chain of evidence

It is vital in all cases that real evidence (ie material objects) is preserved and the defence allowed to inspect it. If a test may destroy the evidence, the defence should be given an opportunity to attend the test (see above).

There should be an unbroken chain of evidence accounting for the safe-keeping and treatment of each piece of real evidence (including samples) from the moment it is collected or created, through all inspections and tests, to trial. See Operational Guidance: Material and evidence management (collection, retention and disposal). A laboratory statement should indicate the labelling on samples as received, which must be sufficiently detailed to identify the sample uniquely. The statement from the laboratory can then tie in with a corresponding statement from the person who packed, labelled and dispatched the sample.

Whether any real evidence should be produced in court should be agreed with the procurator fiscal prior to trial . It may will still be possible to give evidence if it is not, provided there is admissible evidence to show that it has been properly attended to. The defence may seek production of the evidence at court by issuing a witness summons to require a person to attend and produce it. The defence may also apply to the court for an order permitting tests to be carried out. See also the section Preparing evidence for court for guidance on the continuity of evidence.

Analysis and tests

In general, where tests are carried out in a laboratory (eg HSL) or by other scientific means, an expert may give evidence of such work carried out by persons under his/her control or supervision. It is always open to the courts to be dissatisfied as to the arrangements in any particular case.

If an expert attends court, s/he should be able to understand and carry out those parts of the analysis that were performed by every person under his/her supervision. S/he should be in a position to vouch for the propriety of the procedure and to support the results which follow from it. If s/he is not in a position to do so, any person who actually carried out a test or analysis should also be called to give evidence. The expert may not tell the court what that second person told him/her simply because they are both experts (if, indeed, that second person is an expert rather than only a witness of fact).

Evidence of results which are dictated to an expert may usually only be given by him/her if s/he observed the result. S/he should therefore see the note of results and sign it in order to refresh his/her memory from it in court if necessary.

A defendant may request in writing a copy of, or an opportunity to inspect, the record of any "observation, test, calculation or other procedure" on which an expert's finding or opinion is based.


In Scotland evidence does not have to be corroborated to be admissible. However, in criminal cases the essential, or crucial, facts that constitute the alleged offence require "full" or "legal" proof from two separate sources. Therefore evidence of sampling and analysis does not need to be corroborated to be admissible but, if the result of the sampling/analysis process is the only evidence of an essential fact, then the entire process of taking and analysing the sample must be corroborated by two witnesses.

Similarly expert opinion does not need to be corroborated to be admissible but if that opinion relates to an essential fact then a corroborating expert witness may be required.

Regulatory and discipline specialist inspectors should be aware of the standards of evidence required in Scottish criminal cases however, it is the responsibility of the investigating, or coordinating inspector, to ensure proper management of the investigation and that all evidence is identified, secured, gathered, examined, kept and presented for use in court in an appropriate manner, and that the requirements for corroboration are met.

The opinion evidence of an expert, when lead to establish an essential fact, must be corroborated by a second expert.  Therefore, if the result of a sampling / analysis process is the only evidence of an essential fact, then the entire process of taking and analysing the sample must be corroborated, though only those aspects requiring expertise require to be corroborated by an expert – taking or corroborating sampling  can be done by anyone provided expertise is not required.  However, in many cases the opinion of an expert is only an element in the proof of an essential fact. In such a case the testimony of a corroborating second expert is not necessary, since the evidence of the first expert is merely corroborative of the other non-expert evidence.

In prosecutions under section 2 and 3 of HSWA, the following test is applied (see R v Chargot – House of Lords):

  1. It is for the Crown to prove that the results in section 2 / section 3 HSWA had not been achieved or prevented, but the Crown does not have to prove the acts and omissions by which it was alleged that there was a breach of statutory duty by the employer.
  2. That once the Crown have proved the result set out in section 2 / section 3 HSWA had not been achieved, the onus passed to the accused to establish, on a balance of probabilities, that it was not reasonably practicable for the employer to do more than he did do to achieve the required objective of health and safety.

The above test requires to be applied to each individual case however, the following can be used as a general guide:

Cases where only one expert will usually be required - accident cases

  1. Usually the facts speak for themselves and will be sufficient to satisfy the above test without any further evidence - the facts of the accident should be corroborated from at least two sources.
  2. The recovery of any evidence at the scene or elsewhere should be corroborated.
  3. The connection between the work the employee was doing (or the conduct of the undertaking) and the risk to which they were exposed should be corroborated.
  4. The identity of the accused should corroborated.
  5. Given that the facts usually speak for themselves and that it is not essential to prove that they caused the accident, it may not be necessary to call an expert witness.  However, proof of the cause of accident / precise failure of system is likely to strengthen the Crown's case.  If necessary, a single expert can then consider the corroborated facts of the accident and provide: (a) additional evidence regarding failure of systems / cause of accident etc which supports the factual evidence that the results in section 2 / section 3 HSWA had not been achieved; and (b) evidence to rebut a not reasonably practicable argument by the employer.

Cases where two experts will usually be required – risk of harm cases

  • The facts of the state of affairs constituting a risk of harm should corroborated.  The particular risks to which the employees were exposed must be identified and corroborated.
  • The recovery of any evidence at the scene or elsewhere should be corroborated.
  • The connection between the work the employee was doing (or the conduct of the undertaking) and the risk of harm should be corroborated.
  • The identity of the accused should corroborated
  • How the particular risk(s) of harm was liable to affect persons exposed to the risk and why this resulted in a breach of duty should be corroborated.  For some risks the court can draw its own conclusions, eg where a guard rail is missing and someone can fall a distance then the risk of harm is something the court can draw its own conclusion on without an expert; but for other risks specialist knowledge is required so two experts are likely to be needed because the risk of harm is an essential fact – electrical cases would usually fit into these cases because few lay people, including  sheriffs/juries, would be able to draw their own conclusions.

Each expert must consider all the facts independently. If their opinion results from testing and analysis, they may need to be present when the testing and analysis is conducted and form their own independent conclusion.

There is a duty to disclose all information that could help exculpate the accused.  Any disagreement between experts MUST be revealed to the procurator fiscal so that it can be disclosed to the defence.  Disagreements between experts retained by the different parties are for the court to resolve.

At least one expert should also be available give evidence to rebut a not reasonably practicable argument by the employer. For every prosecution HSE should provide evidence of reasonably practicable precautions that could/should have been taken.  For some cases this can be a general inspector but for many it will involve a specialist providing a report based on the investigation findings/witness statements/photographs etc.  They will then be a witness to speak to their report

Although it is not essential for the proof of breaches of health and safety law there may be cases where the Crown consider it important, in the public interest, to prove the cause of the accident / injury (ie complicated cases where there could be a number of different causes of the accident / injury).  In such cases HSE investigators should, wherever possible, secure and gather evidence to prove the cause.  

  1. There may be complicated cases where the Crown consider that it is essential to prove the cause of the accident / injury.
  2. The facts of the accident  / injury should corroborated.
  3. The recovery of any evidence at the scene or elsewhere should be corroborated ie by the investigator and one other person.  The specialist may secure/corroborate and indeed their specialism may be needed to obtain/record the evidence in its context, Though such direct involvement may compromise their independence and hence their ability to provide expert evidence in court, in which case the Crown may need to instruct a further expert.
  4. The connection between the work the employee was doing (or the conduct of the undertaking) and the accident should be corroborated.
  5. The identity of the accused should be corroborated.
  6. The cause of the accident /injury and why this resulted in a breach of duty – should be corroborated by two experts if the experts are the only persons able to speak to this.  NOTE each expert must consider all the facts independently. If their opinion results from testing and analysis, they must be present when the testing and analysis is conducted and form their own independent conclusion.
  7. At least one expert to also give evidence to rebut a not reasonably practicable argument by the employer.

Example: A specialist inspector examines an electrical system following a fire and identifies that an electric conductor, connected to a plug, is too small, that it does not meet the relevant British Standard, and could overheat the assembly to the extent that it acts as an ignition source.  Consequently the specialist concludes this a potential source of ignition and, given the conclusions of the fire investigators, is likely to be the source of ignition in this case.

  • There could be a number of causes of the fire (ie dropped cigarette, chip pan, electrical fault etc).  In this instance the Crown is likely to consider it essential to prove the cause of the fire and that the cause of the fire resulted from a breach of duty.
  • The investigation team, advised by a specialist(s) ( who may subsequently be compromised from giving opinion evidence, so further experts may need to be instructed following consultation with the fiscal) should advise on lines of enquiry to ensure all potential causes of the incident are investigated.  
  • The facts observed at the scene as part of the physical examination, such as the condition of the electrical assembly, the conductor and the plug must be corroborated). Corroboration should be by at least one specialist.  If the fact(s) being evidenced are matters a non specialist can corroborate eg simply by observing and recording in their note book and then narrating in their statement. If the fact needs a specialist to observe/interpret then two specialists are needed.
  • The recovery from the scene of the electrical assembly, the conductor, plug and any other evidence relevant to subsequent expert analysis should be corroborated (this is know as best evidence and the conductor, plug etc should be produced in court  – with label attached and identified by two persons).
  • The size and capacity of the conductor will be crucial to expert analysis and should be corroborated by two expert witnesses.
  • The expert opinion that the cause of the fire was that the electrical assembly was unsafe, did not comply with the relevant British Standard, should be corroborated by two expert witnesses as they are the only witnesses able to speak to the likely cause of the fire.  The two experts may make the observations together but must draw their opinions independently.  There must be two reports.
  • At least one expert to also give evidence to rebut a not reasonably practicable argument by the employer.

If the facts on which the expert's opinion is based are themselves not sufficiently proved, the expert's testimony will be valueless.  Therefore all the facts used by an expert to develop their opinion must be corroborated by two witnesses who observed and can identify the evidence.

The procurator fiscal may give guidance on this issue and indeed may retain an independent expert directly.

Is this page useful?

Updated 2020-11-16