Fire Investigation

The knowledge required to conduct a fire investigation is considerable and is outside the remit of this guidance. There are many books on the subject; an excellent example is The Principles of Fire Investigation by Roy A. Cooke and Rodger H. Ide. You can amass a large amount of information on the theory of fire investigation by studying the books available and by other means. However, very rarely does anybody discuss the practical side of fire investigation and it is quite often overlooked so I shall concentrate on this aspect of fire investigation.

Reasons for Fire Investigations

  • Once a fire is extinguished the officer in charge of the incident initiates a fire investigation to ascertain the cause of a fire. On occasions a specialist fire safety officer will take over when more time and expertise is required. The resulting information is forwarded to the appropriate government department who compiles national statistics. When these statistics are analysed they can identify areas where fire prevention measures can be introduced to reduce fire losses.
  • Fire consultants on behalf of owners/occupiers may conduct an additional fire investigation. There are many reasons for this but ultimately it will help to ensure a similar situation does not repeat itself.
  • Specialist fire safety officers investigate fires that have resulted in the death of a person and the subsequent report is submitted to the coroner office for the inquest.
  • Arson or malicious firing has to be investigated to assist the police in apprehending the perpetrators. It is essential a properly conducted formal fire investigation is undertaken to identify the cause. A specialist officer will be involved and he must work in partnership with the police, which may involve police forensic scientists.

Note: In English law malicious firing is only considered arson if a person’s life is put in danger as the result of the fire. In Scottish law they do not have malicious firing as it is considered a degree of arson.

A Practical view to Fire Investigation

All I can hope to achieve here is to give you a basic understanding of the practicalities of conducting a fire investigation. This guidance is for dedicated fire investigation officers and is not designed for the officer in charge of the initial attendance but parts will be of interest to them. I would divide a fire investigation into various stages:

  • Interviewing eye witnesses
  • Locating the seat of the fire
  • Excavating the seat
  • Evaluation of evidence
  • Review all your findings
  • Report

Although I consider it ideal to follow the above sequence occasionally you may have to conduct your investigation out of sequence.

Interviewing eye witnesses

Having a full understanding of interview techniques is essential when conducting fact-finding interviews. The officer in charge of the initial attendance should be first to be interviewed because he can provide very useful information. He will have carried out his own investigation and be able to provide names of relevant people who may be able to assist in your investigation. He will have interviewed the person who discovered the fire, maybe the owners, occupiers, bystanders, and crews of other appliances. The information that can be gathered by interviewing eyewitnesses are, how the fire behaved in the early stages, the rate of growth of the fire and what part of the building was first involved. Colour of the smoke and flames will give indications of the materials involved in the fire. Firefighters will be able to establish if the premises had been subjected to an illegal entry, if doors were wedged open and if the fire spread faster that one would expect.

You now can move onto the next stage but this does not preclude you from interviewing witnesses again to clarify points. Liaison between other agencies such as the Police, Forensic Service Laboratories and insurance investigators is very important in maintaining good co-operation and ensuring that all skills from each authority are used to their best advantage. The Police are the experts and they use a system called investigative interviewing which is fully explained in a document produced by the New Zealand Police called Review of Investigative Interviewing. There are also many books and training courses on this subject depending on how deep you wish to study this aspect.

Locating the seat of the fire

Establishing the area where the fire started is essential in determining how the fire started. It is known as the seat of the fire and is usually, but not necessarily, the area of severest burning. For example a small fire in the basement with a low fire loading could spread up a vertical shaft to a roof space with a high fire loading and consequently the severest burning could be the roof space. In determining the location of the seat of the fire it is necessary to understand the behaviour of fire in an uncontrolled situation, smoke, flame and burning patterns, and how materials usually behave in fire. An example is the arrow theory, which works on the principle, as a fire spreads its front widens thus creating an arrow shape, consequently locating the point of the arrow will indicate the seat of the fire. At all times you must be aware of the possibility of arson and multiple seats of fire will indicate possible deliberate ignition.

Excavating the seat of the Fire

Once you have located the seat of the fire you need to find the source of ignition and any anomalies that may be present. This is achieved by excavation, which can be likened to how archaeologists work and many tools used by archaeologists are used by fire investigators – small trowels, small paintbrushes, dustpan and riddles. You are looking for possible sources of ignition at the seat of the fire and you may find more than one possible cause. These may include electrical or gas appliances, electric wiring, sockets, gas pipes, smoking and many more. You should also study the layers, which can indicate if the fire developed naturally. For example a fire starting at floor level may spread to the curtains and then to the ceiling. This would show burnt floor covering on the bottom layer, next the remains of the curtains and top layer should show the ceiling plaster. That would be considered normal. However, other than that you would be required to explain why. Again you must always be aware of the possibility of arson and floor coverings or material showing liquid burn patterns will indicate possible deliberate ignition.

Evaluate the evidence

At any stage, if evidence indicates malicious ignition, then the Police should be involved because they are primary responsible authority. This does not exempt you from the investigation as you could be called as an expert witness, but you must liaise with the Police and the Forensic Service Laboratories. They are the experts in the collection of exhibits because a prosecution could fail if the correct procedures were not followed. Evaluation of evidence in an accidental fire investigation is similar to a malicious fire investigation but the methods of collection of the exhibits are not as strict. The purpose of an accidental fire investigation is statistics, which are used for many purposes including the reduction of fire losses. You automatically evaluate the situation at the scene of the fire but you need to re-evaluate later, requiring you to take notes and photographs during the course of the investigation to assist you. You may have more than one possible source of ignition; you should examine each one in turn and eliminate those that could not have started the fire. You may eventually have more than one possible source of ignition and in accidental fire investigation you can give percentages based on the likelihood of each cause. Experimentation can be used to prove a theory but the results should be fully documented for future reference.

Review all your findings

You must now review all the evidence and the conclusions that you have formed. It is useful to discuss your findings with your colleagues who may identify some aspect that you could have missed. Once you are totally convinced of your findings you are then ready to move to the next stage.

Write the Report

Most fire investigations use form FDR1 to complete the fire report and these are used to create the national fire statistics. Fires requiring the intervention of a specialists officer require him to write a report which will be attached to the FDR1. The report should be clear, concise and with no ambiguities, because the reader should understand your conclusions fully, and in the future you may have to refer to it to defend your findings at an inquiry. Technical report writing is a complicated subject and is outside the scope of this page. However there are many web sites on this subject; try our own pages on report writing.

Further Reading and Information

The Institute of Fire Engineers publish The Principles of Fire Investigation by Roy A. Cooke & Rodger H. Ide and is considered the bible for British fire services.


March 24, 2011[Last updated: February 9, 2022]

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