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Fire Investigation - ‘Completing the Jigsaw’

Special Reports

by James Holder MSc, FIFireE, MCSFS, IAAI-CFI, CFEI.

While standing in the blackened remains of a burntout room, unsurprisingly, the most commonly asked question of a fire investigator is where did the fire start and what caused it? What usually follows, after I have provided my answer, is something on the lines of ‘how do you know that, everything is charred and black?'

The answer to where and how a fire started is crucial to determining the cause, origin and development of any fire. Reaching the correct cause and origin determination can sometimes be a relatively straightforward process at simple fire scenes, or it can be extremely protracted where the scene is complex, and the fire damage is more significant. My aim in writing this article, therefore, is to offer the reader an insight into the work of a fire investigator, and how we reach the conclusions that we do.

My route to becoming a fire investigator began in 1998 when I joined the Fire Service as a firefighter. Within a year I had unfortunately attended my first fatal fire, and it was while watching the fire investigator who came onto the scene to determine the cause, that the fire investigation spark (no pun intended) within me was struck. I was fascinated by how the charred remains of what remained could decipher the fire's origin and cause. After 13 years of fighting fires, I transferred into the fire investigation team, a small cohort of expertly trained and highly experienced fire investigators, where I have remained ever since.

So where to begin with a fire scene investigation? Although every fire scene is different, the process in determining the cause is the same, and chiefly involves collecting as much ‘data’ as possible, and interpreting that data to develop and test hypotheses, before a final hypothesis is selected. Data comes in many forms and includes the account of any witnesses to the fire, closed-circuit television (CCTV) images and the analysis and interpretation of fire patterns at the fire scene, to name but a few.

I like a fire investigation to collecting the pieces of a jigsaw puzzle. If all the pieces to the jigsaw can be found, then the picture becomes crystal clear. However, at the point that I am notified of my requirement to attend a fire scene, I have no pieces to the jigsaw, and my quest for those missing pieces begins. Obviously, the more pieces I can find then the clearer the picture becomes, and so, the investigation of a fire begins before I even leave my office. Any previous fires are clearly of interest to me, and any other intelligence relating to a particular address is recorded.

A point of note, however, worth emphasising at this juncture, is the issue of bias. It is imperative that investigators maintain an open mind and remain completely impartial. Establishing that a property had been subjected to three previous arson attacks does not preclude the fourth fire from being the result of an accident. Expectation bias can be a dangerous animal and fire investigators need to be acutely aware of the potential negative impact bias can have. Unwittingly trying to confirm what an investigator ‘expects' the fire cause to be, can be a dangerous road to go down. Instead, and by maintaining an open mind throughout, data collected that could potentially lead to bias is instead noted but assessed for its reliability and relevance.

Returning to the investigation in hand, further jigsaw pieces can be obtained before mobilising to the fire scene. These pieces (or data) might include confirmation of where an address is and the local topography, such as playing fields, railway lines etc.… that may provide unrestricted access to a site. Google can be a wonderful tool and a quick check of a company's website, if one exists, can be extremely useful in determining what processes occur at that site or its occupancy. Confirming the type of building or location that a fire has occurred also allows an investigator to gauge its construction and therefore begin to assess its likely reaction to the fire. The data collected before mobilising to the fire scene may have provided only one or two pieces of the jigsaw, but the picture is beginning to form nonetheless.

Once at the scene, however, the collection of data can really begin. It is worthy of mention that fire, particularly when used at a crime scene, presents arguably a unique set of circumstances when it comes to evidence. In most cases, when a crime occurs, the longer the crime is in progress, the more evidence is produced. Evidence at a fire scene, on the other hand, diminishes as time passes because the fire destroys more and more of what evidence there was.

The actions of the first responders to any fire scene are therefore vital to the preservation of any remaining evidence. As a fire investigator, it is imperative that I obtain the accounts of these first responders regarding their actions and observations. Typically, a severe fire in a two-storey house confined to a bedroom, for example, would attract two fire appliances carrying around nine firefighters; if people are reported trapped inside, then a third appliance is usually sent. This results in up to six firefighters donned in breathing apparatus entering the property to undertake search and rescue activities. They will undoubtedly be equipped with firefighting water hoses to extinguish the fire and could, therefore, apply approximately 500 litres or more of water onto the fire at high pressure. Modern-day firefighting can also involve positively pressurising the building to force the smoke out of windows and other openings. This effectively means placing a large industrial fan close to the property's front door and blowing air into the building at high speed. When these activities are considered and combined with the fact that firefighters entering burning buildings in zero visibility, tasked to locate and rescue any occupants, as well as extinguish the fire and who are extremely task focused, it is not surprising that the preservation of evidence at a fire scene is somewhat challenging.

It is imperative therefore that as a fire investigator, I identify those first responders and obtain their accounts in detail. What was the security of the building when you arrived? Where was the fire at its most severe? What extinguishing media and tactics did you employ? What doors and windows have you opened either during your search or to ventilate post-fire? Has any furniture been moved and if so, where to? What could you hear? Have you turned off any electrical appliances or isolated the services? The list of questions goes on, but ultimately the aim is clearly to elicit as much information as possible and thus collect more jigsaw pieces. Coming from an operational firefighting background certainly helps when questioning fire crews, having ‘been there and done it' so to speak.

Data collection from witnesses then extends to any occupants of the affected property, neighbours, passers-by and any other person that could potentially provide any useful information. What were the actions of the person who was the last to leave the property? Do any occupants smoke? Are candles used? What is the method of heating the property? What were the electrical appliances present in the room when the fire started and were they plugged in? Where are the electrical sockets? Again, the list goes on, but witness information should be gathered as soon as possible after the event, for obvious reasons. It could be that what somebody didn’t see be equally as important. For example, a witness who can confirm that at a particular time there was no sign of any fire, or that a building was locked securely can be equally helpful.

If we consider the fire on a timeline, the witness that takes us the furthest point back in time and closest to when the fire started is often the most useful. The difference between a reliable witness who recalls seeing flames issuing from multiple windows and one who confirms that flames were confined to just one window when they saw the fire is clear. By collating the information obtained from all available witnesses, interpreting its relevance and ensuring its reliability, hypotheses can begin to form having not yet even stepped foot into the building.

The checking of witness evidence for its reliability, however, cannot be over-emphasised. Witnesses can be deliberately untruthful, whether that be because they would implicate themselves in a crime or demonstrate that their negligence caused the fire, albeit accidentally. Further, people may inaccurately describe what they saw, whether that be because of excitement, upset or other emotions experienced by people who may well have not been exposed to such an incident before. The ‘ABC’ rule of thumb in fire investigation is to ‘assume nothing, believe nobody and check everything’, and remember that witnesses can be mistaken, or lie of course, and physical evidence does not.

Footage captured by CCTV cameras is an obvious source of reliable data, and time invested in checking for cameras in the local vicinity is time well spent. I recall one case where CCTV footage obtained, although scant and which did not record the fire itself because it faced the wrong direction, did capture a passing vehicle that was later traced. Although the sole occupant of the passing car couldn’t recall seeing anything to assist the investigation themselves, the onboard dashboard camera fitted to their vehicle did. A bonus jigsaw piece to say the least!

Having spent what can be many hours speaking to witnesses, retrieving alerts from both fire and intruder alarm systems and identifying possible sources of CCTV, and of course, having recorded everything contemporaneously on paper, attention turns to the fire scene itself. Top of the priority list at this point, by a long way I might add, is scene safety. No fire investigation is worth getting injured, or worse, for and an assessment of the buildings structural integrity must be undertaken. In addition to the obvious risk of a severely fire damaged building collapsing, there are many other nasties to consider. Exposed electrical cables, holes in floors, broken glass and other sharps, chemical and biological hazards and the exposure to asbestos, for example, present an often-unpleasant environment in which to work in. Ensuring adequate control measures are in place before entering a fire scene is therefore vitally important.

Having deemed the risk to my safety to be adequately controlled, a survey of the scene can begin. It is usual practice for a fire investigator, certainly at a crime or fatal fire scene, to be accompanied by a Police Forensic Scene Investigator (FSI), perhaps more commonly known as a Scenes of Crime Officer (SOCO). They are responsible for retrieving any physical evidence and will routinely record the scene by way of digital photographs. Because of this, a fire scene investigation is very much a team effort that utilises the skills of both the fire investigator and the FSI.

When assessing a fire scene, there is often as much useful information to be had from areas remote from the fire compartment, as there is within in it. A great deal of information can be obtained about the occupancy of a building by spending some time surveying the surroundings and away from the room of origin. Children’s toys in a rear garden, a wallmounted handrail by a front doorstep, littered cigarette ends on a driveway or a skip containing builders waste are just a few examples of the information on offer, if one takes the time to look and take note of it. Toys could mean that children were present at the time of the fire. The answer to where any children were and what they were doing when the fire occurred could be useful to know. A handrail could mean that the occupant is elderly. Are they in receipt of care and if so, when was the last visit from a carer before the fire? Littered cigarette ends not only indicate the presence of a smoker and a potential source of ignition, but also those cigarettes are disposed of carelessly. Finally, a skip containing builders waste could mean that a recent refurbishment of the property involved some sort of alteration to the electrical installation or a plumbing task that involved ‘hotworks’.

‘Lifestyle indicators’ allow the fire investigator to build a picture of how the building and its occupants ‘usually’ behave and without yet having reached the room where the fire occurred, many pieces of the jigsaw can be collected. It is sometimes easy to become focused on the ‘burned bits' at a fire scene and neglect the wealth of information on offer. Once inside, consideration to lifestyle indicators continues. Is the property secure? If not, is any damage to doors and windows consistent with the actions of the first responding fire crews or is there evidence of a break-in before the fire? Is the property in order or unkempt? Are electrical appliances and extension leads being used appropriately? By what means do any occupants heat the property? Is there evidence of candles being used? Is there further evidence of smoking materials? And the list goes on.

By the time the investigator reaches the room of the fire’s origin, it is likely that several working hypotheses have been developed based on the information gathered up until that point. It is then a case of continually testing those hypotheses against new information obtained as the investigation continues. Once in the fire compartment, a survey of the burn patterns and the way that the contents of the room have reacted to the fire will enable the fire investigator to narrow down their area of interest and focus in on the fire’s origin.

To do this, a variety of methods are employed. The way that fire inside a compartment, such as a bedroom, develops is controlled by just two things; the amount of fuel available and the availability of an oxidiser, which in almost every fire is the oxygen in the air. A bonfire in the open is an example of a ‘fuel controlled' fire because it is the amount of fuel present that determines how large the fire gets and not any restriction on the amount of available oxygen. Although a fire inside a well-insulated room with closed doors and windows will initially be fuel controlled in its very early stages, it requires more oxygen as it develops. When the point is reached that the fire is consuming more oxygen than the amount of air being drawn into the room, it becomes a ventilation-controlled fire and limits its ability to develop. If, however, there is an adequate supply of air to the fire, and enough fuel, of course, it will develop to involve the entire contents of the fire, and it is at this point the fire is said to have ‘flashed over'.

If a fire is prevented from spreading beyond the item that first ignited, such as an armchair, for example, it is a relatively straightforward task to identify the origin of the fire. If, however, the fire has spread to involve the entire room and its contents, it becomes more a challenge to identify where the fire may have started. Despite this, by surveying the fire, heat and smoke damage inside a room it is possible to identify where the fire’s origin lies. By possessing a degree of scientific knowledge, particularly an understanding of fire dynamics, and by conforming to some basic laws of physics, such as that heat rises and radiation travels in straight lines, fire, heat and smoke patterns can be interpreted.

Because fire consumes the fuel that is involved, the longer the fire is burning in a particular place then, the greater the degree of damage, generally speaking. So, by assessing and comparing the depth of charring on wood, the degree of melting to plastics or arc damage on electrical cables, for example, the investigator can begin to home in on where the fire may have originated. Burn patterns on walls and ceilings can be clues to where the fire was at its most severe and the way soot has been deposited onto surfaces can indicate the ventilation effects in play at the time. Gypsum plasterboard contains moisture, and during a fire a process known as calcination causes the moisture to evaporate. Fire investigators take advantage of this process and survey the extent of calcination to assist in determining where the fire was at its most intense.

By continuing the process of fire pattern analysis, and thus collecting more data, the information obtained from any witnesses can be compared to the physical evidence encountered for both its consistency and reliability. Having hopefully identified where the origin of the fire is, the next task is to determine what the source of ignition was. Three critical questions must be precisely answered by any fire investigator to identify the circumstances that led to a fire. What was the item that was first ignited, what was the source of ignition competent enough to ignite that fuel and how was it that both the first item to be ignited and the source of ignition came together?

Fire scene excavation is comparable to an archaeological dig. As a fire develops, debris collects on the floor and forms layers that constitute a timeline. Because the source of ignition is likely to be right at the heart of the point of origin, as the fire develops it becomes buried beneath a layer of fire debris. It is for this reason that a fire investigator will excavate comprehensively and systematically utilising small trowels, paint brushes, sieves and magnets, for example, to locate the sometimes-minute pieces of evidence that may be all that remains of the ignition source. It may be that all that’s left of a faulty electrical appliance are the metallic components that were originally within its plastic body. It may also be that the small metal disc at the base of a tea-light candle wick is all that survives an intense fire caused by the careless use of such a candle.

It may be however that the source of ignition cannot be found, despite a thorough and proper excavation. A match thrown into a waste paper bin that then develops into a significant fire is not going to be found. It is important to remember therefore that the job of a fire investigator is to consider all potential ignition sources and work towards eliminating as many as possible. Although a single match dropped into a bin is not likely to be found after a fire, a thorough excavation may confidently exclude other sources of ignition such as electrical wiring, a candle carcass or a cigarette lighter.

By then considering data previously obtained during the investigation, it may be that the other carelessly dropped matches in various places throughout the scene, remote from the bin, give real credence to a cause determination that a dropped match did indeed start the fire, although the actual match responsible was entirely consumed.

Hopefully, by this stage of an investigation, the investigator has collected many pieces of the jigsaw, and a clear picture is forming. Hypotheses will have been developed and tested, some then discarded and some maintained until hopefully enough data has been collected to select one final hypothesis. At this stage of the investigation, I will usually sit down, hopefully with a cup of tea, and retest my final hypothesis. Have I considered everything? Are there any sources of data that I have missed? Will my hypothesis withstand the test of scrutiny from my peers? Only when I am content that I have exhausted the fire scene of all available data will I leave and return to my office. Having then considered all of the information available to me, I will then produce my expert report in preparation for any court proceedings.

Further to this, however, is how fire investigation plays a pivotal role in fire prevention strategy, and why accurate fire cause determination is key to keeping our communities safer… after all, fires cannot be prevented, if how they start in the first place is not understood. And so, hopefully, this brief insight into the work of a fire investigator has achieved its aim, and given you, the reader, an awareness of how fire investigation is all about trying to, so to speak, complete the jigsaw!

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