Interviewing witnesses after an incident involving hazardous chemicals

Apr 2, 2019 Posted by Walter Ingles

Interviewing witnesses can be the most challenging part of an HAZCHEM incident investigation. Incidents involving hazardous chemicals can be fatal, cause debilitating injuries, and lead to destruction of property or the environment. Workers directly involved in the incident (as well as any witnesses) will likely be suffering emotional stress and may be hesitant to talk about what happened. This blog is about interviewing witness: we look at everything from post-incident reporting, organising the interview, and techniques for questioning a witness.

Deciding who to interview

Anyone involved in a workplace incident (or near-miss) that involved hazardous chemicals should complete and submit an incident report as soon as possible after the incident. This includes injured workers, witnesses and anyone else involved in the event. Your workplace should already have an official procedure (and form) for incident reporting which requests the following information (as a minimum):

  • Date, time, and location of the incident.

  • Description of what happened.

  • Tasks being completed before and during the incident.

  • Names of people involved or present at the time.

  • Where everyone (including witness) was standing/located during the incident.

  • Details of chemicals and substances.

  • Details of injuries, first aid treatment and medical care.

These incident reports play an essential part in your investigation and will help you determine who needs to be interviewed. Incident reports may uncover people like supplier deliver drivers or customers who were present at the time and have never been given an opportunity to talk about what happened.

Organising the interview

It’s always best to interview witnesses as soon as possible after an incident, but if the investigation has been triggered from a review of incident reports, sometimes many months may have passed since the incident occurred.

Arrange to interview each person alone and in a neutral environment. As much as possible separate workers during the interview process so they don’t start to create a collaborated story. This isn’t always a deliberate effort to hide the truth, sometimes when there are gaps in a person’s understanding of an incident their recollection may be influenced by someone else (especially a supervisor).

For example: a worker is sprayed with caustic chemicals and later dies from their injuries. Three workers were present in the work area at the time of the incident and you want to establish if the worker performed their pre-operational safety checks. Two of the workers definitely saw the safety checks performed but the other worker was not in a position to verify if the actions took place. If these workers begin to talk among themselves the third worker may begin to adopt their story into their own testimony.

Conducting the interview

When conducting the interview remember that some workers may be suffering from PTSD (post-traumatic stress disorder) if someone was seriously harmed or killed in the incident. Be compassionate and respectful, reassure the witness that their testimony will help determine the cause of the incident and assist in the implementation of additional safety measures.

Before beginning the questioning you should inform the witness how the interview will be recorded and who will have access to their responses. Introduce the interview panel and briefly explain their roles, assuring them their confidentiality will be maintained. This is also the time to remind them of their legal responsibility to give accurate testimony.

Questioning witnesses

When interviewing witnesses use questions that allow people to give detailed responses, and especially avoid narrow questions that trigger ‘yes’ or ‘no’ responses. For example, a question like: Was your co-worker wearing chemical resistant goggles before using the acid? is too narrow, ask instead What PPE was your co-worker wearing before using the acid?

Once you have asked a question give the witness time to answer each question in full. Listen carefully, and allow silences — sometimes that silence actually triggers the witness to add more details. Frame your questions so you can find out:

  • What systems of work were being carried out and what instructions had been given.

  • If there was any variation from standard procedures, and if so why.

  • What chemicals were being used or handled.

  • Details about PPE: was it used, what condition was it in, did it fail.

  • Location of relevant people (co-workers, supervisors, bystanders) and their involvement in the incident.

  • Workplace conditions (lighting, warning signs, weather, floor surfaces, housekeeping, noise, presence of fumes/vapours).

  • First aid and emergency responses (were safety showers used, was emergency equipment available and operational, who reported the incident).

At the end of the interview you can ask the witness for their opinion on what may have caused the incident. Remain impartial during their response, you want to record their testimony to establish facts not jump to conclusions.

IMPORTANT: During the interview you might take the witness back to the scene of the incident to re-enact what happened in slow motion. If you do, make sure you aren’t creating another safety hazard when you ask a worker to replicate a task.



Any questions, comments or queries? Feel free to contact one of our friendly team here.  Alternatively, you can call us on our support line: 1300 134 223


Walter Ingles

Walter Ingles Compliance Specialist

Walter is STOREMASTA’s Dangerous Goods Adviser. He loves helping businesses reduce the risk that Dangerous Goods pose upon their employees, property and the environment through safe and compliant dangerous goods storage solutions.

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